Metal oxide film formation method

Abstract

Provided is a novel method for forming a metal oxide film. This method has: a first step for supplying a first precursor to a chamber; a second step for supplying a second precursor to the chamber; a third step for supplying a third precursor to the chamber; and a fourth step for introducing an oxidant to the chamber after each of the first step, the second step, and the third step. The first to third precursors are of different types from each other. In the first to fourth steps, a substrate disposed in the chamber is heated to a temperature that is not lower than 300 degrees and not higher than the decomposition temperatures of the first to third precursors.

Description

[Technical field]

[0001] One embodiment of the present invention relates to a method for forming a metal oxide film and a metal oxide film formation apparatus. Another embodiment of the present invention relates to a semiconductor device using the metal oxide film and a method for manufacturing the semiconductor device. Another embodiment of the present invention relates to a semiconductor wafer, a module, and an electronic device.

[0002] In this specification and the like, a semiconductor device refers to any device that can function by utilizing semiconductor characteristics. Semiconductor elements such as transistors, semiconductor circuits, arithmetic devices, and memory devices are all embodiments of semiconductor devices. Display devices (such as liquid crystal display devices and light-emitting display devices), projection devices, lighting devices, electro-optical devices, power storage devices, memory devices, semiconductor circuits, imaging devices, electronic devices, and the like may be considered to include semiconductor devices.

[0003] Note that one aspect of the present invention is not limited to the above technical field. One aspect of the invention disclosed in the present specification etc. relates to an object, a method, or a manufacturing method. Alternatively, one aspect of the present invention relates to a process, a machine, a manufacture, or a composition of matter. [Background technology]

[0004] Technology that constructs transistors using semiconductor thin films formed on substrates with insulating surfaces is attracting attention. Such transistors are widely used in electronic devices such as integrated circuits (ICs) and image display devices (also simply referred to as display devices). Silicon-based semiconductor materials are widely known as semiconductor thin films that can be used in transistors, but oxide semiconductors are also attracting attention as other materials.

[0005] In oxide semiconductors, c-axis aligned crystalline (CAAC) structures and nanocrystalline (nc) structures, which are neither single crystal nor amorphous, have been found (see Non-Patent Documents 1 and 2).

[0006] Non-Patent Documents 1 and 2 disclose techniques for manufacturing a transistor using an oxide semiconductor having a CAAC structure. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] S. Yamazaki et al., “SID Symposium Digest of Technical Papers”, 2012, volume 43, issue 1, p.183-186 [Non-Patent Document 2] S. Yamazaki et al., “Japanese Journal of Applied Physics”, 2014, volume 53, Number 4S, p.04ED18-1-04ED18-10 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of one embodiment of the present invention is to provide a novel metal oxide and a method for forming the same. Another object of one embodiment of the present invention is to provide a novel metal oxide film formation apparatus. Another object of one embodiment of the present invention is to provide a semiconductor device having high on-state current. Another object of one embodiment of the present invention is to provide a semiconductor device having high field-effect mobility. Another object of one embodiment of the present invention is to provide a semiconductor device with high reliability. Another object of one embodiment of the present invention is to provide a semiconductor device having good electrical characteristics. Another object of one embodiment of the present invention is to provide a semiconductor device that can be miniaturized or highly integrated. Another object of one embodiment of the present invention is to provide a method for manufacturing the semiconductor device.

[0009] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that problems other than these will become apparent from the description of the specification, drawings, claims, etc., and it is possible to extract problems other than these from the description of the specification, drawings, claims, etc. [Means for solving the problem]

[0010] One embodiment of the present invention is a method for forming a metal oxide film, comprising: a first step of supplying a first precursor to a chamber; a second step of supplying a second precursor to the chamber; a third step of supplying a third precursor to the chamber; and a fourth step of introducing an oxidizing agent into the chamber after the first step, after the second step, and after each of the third steps, wherein the first to third precursors are different types of precursors; and in the first to fourth steps, a substrate placed in the chamber is heated to a temperature of 300° C. or higher and lower than the lowest temperature among the decomposition temperatures of the first to third precursors.

[0011] Another embodiment of the present invention is a method for forming a metal oxide film, comprising: a first step of supplying a first precursor to the chamber; a second step of supplying a second precursor to the chamber; a third step of supplying a third precursor to the chamber; and a fourth step of plasmatizing an oxidant and introducing the plasma into the chamber after the first step, the second step, and the third step, respectively; the first to third precursors are different types of precursors; and in the first to fourth steps, a substrate placed in the chamber is heated to a temperature of 300° C. or higher and lower than the lowest temperature among the decomposition temperatures of the first to third precursors.

[0012] In the above, it is preferable that the first precursor contains indium, the second precursor contains an element M (M is one or more of gallium, aluminum, yttrium, and tin), and the third precursor contains zinc.

[0013] In the above, it is preferable that the first to third precursors are free of carbon and hydrogen. Also, in the above, the first to third precursors may contain chlorine.

[0014] In the above, it is preferable that each of the first to fourth steps is performed at least once to form one cycle, and that one cycle is repeated a number of times.

[0015] In the above, in the method for forming a film of a metal oxide containing indium, an element M (M is one or more of gallium, aluminum, yttrium, and tin), and zinc, it is preferable that the first precursor contains indium, the second precursor contains the element M (M is one or more of gallium, aluminum, yttrium, and tin), and the third precursor contains zinc, and the ratio of the number of the first step to the number of the second step to the number of the third step in one cycle is the same as the ratio of indium to the element M to gallium in the metal oxide.

[0016] In the above, it is preferable to carry out a heat treatment after repeating one cycle multiple times.

[0017] Another embodiment of the present invention is a metal oxide film formation apparatus including a chamber, first to fourth raw material supply units, and a heater, where the first to fourth raw material supply units are each connected to the chamber via a valve, the first to third raw material supply units each have a means for supplying a different type of precursor, the fourth raw material supply unit has a means for supplying an oxidizing agent, and the heater has a means for heating a substrate placed in the chamber to a temperature of 300° C. or higher and not exceeding the lowest temperature among decomposition temperatures of the precursors.

[0018] Another embodiment of the present invention is a metal oxide film formation apparatus including a chamber, first to fourth raw material supply units, a heater, and a plasma generator, wherein the first to third raw material supply units are each connected to the chamber via a valve, the fourth raw material supply unit is connected to the chamber via the plasma generator, the first to third raw material supply units each have a means for supplying a different type of precursor, the fourth raw material supply unit has a means for supplying an oxidizing agent, and the heater has a means for heating a substrate placed in the chamber to a temperature of 300° C. or higher and not exceeding the lowest temperature among the decomposition temperatures of the precursors.

[0019] In the above, it is preferable that the plasma generating device has a coil connected to a high frequency power source.

[0020] In the above, it is preferable that the first raw material supply unit has a means for supplying a precursor having indium, the second raw material supply unit has a means for supplying a precursor having an element M (M is one or more of gallium, aluminum, yttrium, and tin), and the third raw material supply unit has a means for supplying a precursor having zinc.

[0021] In the above, the precursor containing indium, the precursor containing element M, and the precursor containing zinc preferably do not contain carbon and hydrogen. In addition, in the above, the precursor containing indium, the precursor containing element M, and the precursor containing zinc may contain chlorine.

[0022] In the above, it is preferable to have a pipe heater covering pipes provided between the first to fourth raw material supply parts and the chamber.

[0023] In the above, it is preferable that the system has a transfer chamber and a processing chamber, the chamber is connected to the processing chamber via the transfer chamber, the transfer chamber has a means for transferring the substrate from the chamber to the processing chamber, and the processing chamber has a heating device. Effect of the Invention

[0024] According to one embodiment of the present invention, a novel metal oxide and a method for forming the same can be provided. According to one embodiment of the present invention, a novel metal oxide film formation apparatus can be provided. According to one embodiment of the present invention, a semiconductor device having high on-state current can be provided. According to one embodiment of the present invention, a semiconductor device having high field-effect mobility can be provided. According to one embodiment of the present invention, a semiconductor device with high reliability can be provided. According to one embodiment of the present invention, a semiconductor device having good electrical characteristics can be provided. According to one embodiment of the present invention, a semiconductor device that can be miniaturized or highly integrated can be provided. According to one embodiment of the present invention, a method for manufacturing the above semiconductor device can be provided.

[0025] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not need to have all of these effects. Note that effects other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract effects other than these from the description in the specification, drawings, claims, etc. [Brief description of the drawings]

[0026] 1A to 1E are cross-sectional views illustrating a method for forming a metal oxide film according to one embodiment of the present invention. 2A to 2D are cross-sectional views of a metal oxide according to one embodiment of the present invention. 3A to 3D are cross-sectional views of a metal oxide according to one embodiment of the present invention. 4A to 4C are diagrams illustrating the range of the atomic ratio of a metal oxide according to one embodiment of the present invention. 5A to 5D are cross-sectional views illustrating a method for forming a metal oxide film according to one embodiment of the present invention. 6A to 6C are cross-sectional views illustrating a method for forming a metal oxide film according to one embodiment of the present invention. FIG. 7 is a top view and a cross-sectional view illustrating a film forming apparatus. 8A and 8B are cross-sectional views illustrating a film forming apparatus. 9A to 9C are cross-sectional views illustrating a film forming apparatus. 10A and 10B are diagrams illustrating a method for forming a metal oxide film according to one embodiment of the present invention. 11A and 11B are diagrams illustrating a method for forming a metal oxide film according to one embodiment of the present invention. FIG. 12 illustrates a method for forming a metal oxide film according to one embodiment of the present invention. Fig. 13A is a diagram for explaining the classification of IGZO crystal structures, Fig. 13B is a diagram for explaining the XRD spectrum of a CAAC-IGZO film, and Fig. 13C is a diagram for explaining the ultrafine electron beam diffraction pattern of a CAAC-IGZO film. 14A is a top view of a semiconductor device according to one embodiment of the present invention, and FIGS. 14B to 14D are cross-sectional views of the semiconductor device according to one embodiment of the present invention. 15A and 15B are cross-sectional views of a semiconductor device according to one embodiment of the present invention. 16A is a top view illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention, and FIGS. 16B to 16D are cross-sectional views illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention. 17A is a top view illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention, and FIGS. 17B to 17D are cross-sectional views illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention. 18A is a top view illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention, and FIGS. 18B to 18D are cross-sectional views illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention. 19A is a top view illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention, and FIGS. 19B to 19D are cross-sectional views illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention. 20A is a top view illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention, and FIGS. 20B to 20D are cross-sectional views illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention. 21A is a top view illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention, and FIGS. 21B to 21D are cross-sectional views illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention. 22A is a top view illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention, and FIGS. 22B to 22D are cross-sectional views illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention. 23A is a top view illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention, and FIGS. 23B to 23D are cross-sectional views illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention. 24A is a top view illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention, and FIGS. 24B to 24D are cross-sectional views illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention. 25A is a top view illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention, and FIGS. 25B to 25D are cross-sectional views illustrating a method for manufacturing a semiconductor device according to one embodiment of the present invention. FIG. 26 is a top view illustrating a microwave processing apparatus according to one embodiment of the present invention. FIG. 27 is a cross-sectional view illustrating a microwave processing apparatus according to one embodiment of the present invention. FIG. 28 is a cross-sectional view illustrating a microwave processing apparatus according to one embodiment of the present invention. FIG. 29 is a cross-sectional view illustrating a microwave processing apparatus according to one embodiment of the present invention. Fig. 30A is a top view of a semiconductor device according to one embodiment of the present invention, and Fig. 30B and Fig. 30C are cross-sectional views of the semiconductor device according to one embodiment of the present invention. FIG. 31 is a cross-sectional view showing a configuration of a memory device according to one embodiment of the present invention. FIG. 32 is a cross-sectional view showing a configuration of a memory device according to one embodiment of the present invention. FIG. 33 is a cross-sectional view of a semiconductor device according to one embodiment of the present invention. 34A and 34B are cross-sectional views of a semiconductor device according to one embodiment of the present invention. FIG. 35 is a cross-sectional view of a semiconductor device according to one embodiment of the present invention. 36A and 36B are block diagrams illustrating configuration examples of a memory device according to one embodiment of the present invention. 37A to 37H are circuit diagrams illustrating configuration examples of a memory device according to one embodiment of the present invention. 38A and 38B are schematic diagrams of a semiconductor device according to one embodiment of the present invention. 39A and 39B are diagrams illustrating an example of an electronic component. 40A to 40E are schematic diagrams of a memory device which is one embodiment of the present invention. 41A to 41H are diagrams illustrating electronic devices according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, the embodiments will be described with reference to the drawings. However, it will be easily understood by those skilled in the art that the embodiments can be implemented in many different ways, and that the modes and details can be changed in various ways without departing from the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited to the description of the following embodiments.

[0028] In addition, in the drawings, the size, thickness of the layer, or the area may be exaggerated for clarity. Therefore, it is not necessarily limited to the scale. In addition, the drawings are schematic illustrations of ideal examples, and are not limited to the shapes or values ​​shown in the drawings. For example, in the actual manufacturing process, layers or resist masks may be unintentionally thinned by etching or other processes, but this may not be reflected in the drawings to facilitate understanding. In addition, in the drawings, the same reference numerals are used in common between different drawings for the same parts or parts having similar functions, and repeated explanations may be omitted. In addition, when referring to similar functions, the same hatch pattern may be used and no particular reference numeral may be attached.

[0029] In order to facilitate understanding of the invention, particularly in top views (also called "plan views") or perspective views, some components may be omitted from the drawings. Also, some hidden lines may be omitted from the drawings.

[0030] In addition, in this specification, ordinal numbers such as first, second, etc. are used for convenience and do not indicate the order of steps or stacking. Therefore, for example, "first" can be appropriately replaced with "second" or "third" for explanation. In addition, the ordinal numbers described in this specification and the like may not match the ordinal numbers used to specify one embodiment of the present invention.

[0031] In addition, in this specification, the terms "above" and "below" indicating the arrangement are used for convenience in order to explain the positional relationship between the components with reference to the drawings. In addition, the positional relationship between the components changes as appropriate depending on the direction in which each component is depicted. Therefore, the terms are not limited to those described in the specification, and can be rephrased appropriately depending on the situation.

[0032] For example, when it is explicitly stated in this specification that X and Y are connected, the case where X and Y are electrically connected, the case where X and Y are functionally connected, and the case where X and Y are directly connected are considered to be disclosed in this specification. Therefore, it is not limited to a specific connection relationship, for example, a connection relationship shown in a figure or text, and a connection relationship other than that shown in a figure or text is also considered to be disclosed in the figure or text. Here, X and Y are objects (for example, a device, an element, a circuit, wiring, an electrode, a terminal, a conductive film, a layer, etc.).

[0033] In this specification, a transistor is an element having at least three terminals including a gate, a drain, and a source. A region where a channel is formed between the drain (drain terminal, drain region, or drain electrode) and the source (source terminal, source region, or source electrode) (hereinafter, also referred to as a channel formation region) is provided, and a current can flow between the source and the drain through the channel formation region. In this specification, a channel formation region refers to a region through which a current mainly flows.

[0034] In addition, the functions of the source and drain may be interchanged when transistors of different polarities are used, or when the direction of current changes during circuit operation, etc. For this reason, in this specification and the like, the terms source and drain may be used interchangeably.

[0035] The channel length refers to, for example, a region where the semiconductor (or a portion in the semiconductor through which current flows when the transistor is on) and the gate electrode overlap in a top view of a transistor, or a distance between the source (source region or source electrode) and the drain (drain region or drain electrode) in a channel formation region. Note that the channel length of one transistor does not necessarily have the same value in all regions. That is, the channel length of one transistor may not be fixed to one value. Therefore, in this specification, the channel length is defined as any one value, maximum value, minimum value, or average value in the channel formation region.

[0036] The channel width refers to, for example, the length of a channel formation region in a vertical direction based on the channel length direction in a region where a semiconductor (or a portion in the semiconductor through which current flows when the transistor is on) and a gate electrode overlap in a top view of a transistor, or in a channel formation region. Note that the channel width does not necessarily have the same value in all regions in one transistor. In other words, the channel width of one transistor may not be determined to a single value. Therefore, in this specification, the channel width is defined as any one value, maximum value, minimum value, or average value in the channel formation region.

[0037] In this specification and the like, depending on the structure of a transistor, the channel width in a region where a channel is actually formed (hereinafter also referred to as an "effective channel width") may differ from the channel width shown in a top view of the transistor (hereinafter also referred to as an "apparent channel width"). For example, when a gate electrode covers a side surface of a semiconductor, the effective channel width may be larger than the apparent channel width, and the influence of this may not be negligible. For example, in a fine transistor in which a gate electrode covers a side surface of a semiconductor, the proportion of a channel formation region formed on the side surface of the semiconductor may be large. In that case, the effective channel width is larger than the apparent channel width.

[0038] In such a case, it may be difficult to estimate the effective channel width by actual measurement. For example, in order to estimate the effective channel width from the design value, it is necessary to assume that the shape of the semiconductor is known. Therefore, if the shape of the semiconductor is not precisely known, it is difficult to accurately measure the effective channel width.

[0039] In this specification, when simply described as a channel width, it may refer to an apparent channel width. Alternatively, when simply described as a channel width, it may refer to an effective channel width. Note that the values ​​of the channel length, channel width, effective channel width, apparent channel width, etc. can be determined by analyzing a cross-sectional TEM image, etc.

[0040] Note that impurities in a semiconductor refer to, for example, anything other than the main components constituting the semiconductor. For example, an element with a concentration of less than 0.1 atomic % can be said to be an impurity. The inclusion of impurities can, for example, increase the density of defect states in the semiconductor or reduce the crystallinity. When the semiconductor is an oxide semiconductor, impurities that change the characteristics of the semiconductor include, for example, Group 1 elements, Group 2 elements, Group 13 elements, Group 14 elements, Group 15 elements, and transition metals other than the main components of the oxide semiconductor, such as hydrogen, lithium, sodium, silicon, boron, phosphorus, carbon, and nitrogen. Note that water can also function as an impurity. For example, the inclusion of impurities can cause oxygen deficiencies (V O Sometimes it is written as ". ) may be formed.

[0041] In this specification and the like, an oxynitride is a material whose composition contains more oxygen than nitrogen. For example, a silicon oxynitride is a material whose composition contains more oxygen than nitrogen. A nitride oxide is a material whose composition contains more nitrogen than oxygen. For example, a silicon nitride oxide is a material whose composition contains more nitrogen than oxygen.

[0042] In this specification and the like, the term "insulator" can be replaced with an insulating film or an insulating layer, the term "conductor" can be replaced with a conductive film or a conductive layer, and the term "semiconductor" can be replaced with a semiconductor film or a semiconductor layer.

[0043] In addition, in this specification, "parallel" refers to a state in which two straight lines are arranged at an angle of -10 degrees or more and 10 degrees or less. Therefore, it also includes the case of -5 degrees or more and 5 degrees or less. "Approximately parallel" refers to a state in which two straight lines are arranged at an angle of -30 degrees or more and 30 degrees or less. "Perpendicular" refers to a state in which two straight lines are arranged at an angle of 80 degrees or more and 100 degrees or less. Therefore, it also includes the case of 85 degrees or more and 95 degrees or less. "Approximately perpendicular" refers to a state in which two straight lines are arranged at an angle of 60 degrees or more and 120 degrees or less.

[0044] In this specification and the like, the term "metal oxide" refers to an oxide of a metal in a broad sense. Metal oxides are classified into oxide insulators, oxide conductors (including transparent oxide conductors), oxide semiconductors (also referred to as oxide semiconductors or simply OS), and the like. For example, when a metal oxide is used for a semiconductor layer of a transistor, the metal oxide may be referred to as an oxide semiconductor. In other words, an OS transistor can be rephrased as a transistor having a metal oxide or an oxide semiconductor.

[0045] In this specification and the like, metal oxides containing nitrogen may also be collectively referred to as metal oxides. Furthermore, metal oxides containing nitrogen may also be referred to as metal oxynitrides.

[0046] In this specification and the like, normally off means that when no potential is applied to the gate or when a ground potential is applied to the gate, the drain current flowing through the transistor per 1 μm of channel width is 1×10 -20 A or less, 1×10 at 85℃ -18 A or less, or 1×10 at 125°C -16 This means that it is A or lower.

[0047] In addition, in the present specification, when upper and lower limit values ​​are specified, it is understood that any combination of these values ​​is also disclosed.

[0048] (Embodiment 1) 1 to 12, a metal oxide (hereinafter also referred to as an oxide semiconductor or oxide) that can be used for a semiconductor layer of a transistor and a method for forming the same will be described. Note that the metal oxide according to one embodiment of the present invention is not limited to being used for the semiconductor layer of a transistor and may be used as an insulating material or a conductive material depending on the type, combination, composition, or the like of elements constituting the metal oxide.

[0049] Metal oxides may have lattice defects. Lattice defects include point defects such as atomic vacancies and heteroatoms, line defects such as dislocations, surface defects such as grain boundaries, and volume defects such as voids. Factors that cause lattice defects include deviations in the ratio of the number of atoms of the constituent elements (excess or shortage of constituent atoms) and impurities.

[0050] When a metal oxide is used for the semiconductor layer of a transistor, lattice defects in the metal oxide can cause carrier generation or capture. Therefore, when a metal oxide with many lattice defects is used for the semiconductor layer of a transistor, the electrical characteristics of the transistor may become unstable. Therefore, it is preferable that the metal oxide used for the semiconductor layer of a transistor has few lattice defects.

[0051] In particular, transistors using metal oxides have oxygen vacancies (V O ) and impurities may cause electrical characteristics to fluctuate and reliability to deteriorate. In addition, hydrogen near the oxygen vacancy may enter the oxygen vacancy (hereinafter referred to as V O H defects) may be formed, generating electrons that serve as carriers. For this reason, if oxygen vacancies are present in the channel formation region in the metal oxide, the transistor is likely to have normally-on characteristics (characteristics in which a channel exists and a current flows through the transistor even when no voltage is applied to the gate electrode). Therefore, it is preferable that oxygen vacancies and impurities are reduced as much as possible in the channel formation region in the metal oxide. In other words, it is preferable that the carrier concentration of the channel formation region in the metal oxide is reduced and the region is made i-type (intrinsic) or substantially i-type.

[0052] The type of lattice defects likely to exist in a metal oxide and the amount of lattice defects vary depending on the structure of the metal oxide or the method for forming the metal oxide film.

[0053] Metal oxide structures are divided into single crystal structures and other structures (non-single crystal structures). Non-single crystal structures include, for example, CAAC structures, polycrystalline structures, nc structures, pseudo-amorphous (a-like: amorphous-like) structures, and amorphous structures. The a-like structures are intermediate between the nc structures and the amorphous structures. The classification of crystal structures will be described later.

[0054] In addition, metal oxides having an a-like structure and metal oxides having an amorphous structure have voids or low density regions. That is, metal oxides having an a-like structure and metal oxides having an amorphous structure have lower crystallinity than metal oxides having an nc structure and metal oxides having a CAAC structure. In addition, metal oxides having an a-like structure have a higher hydrogen concentration than metal oxides having an nc structure and metal oxides having a CAAC structure. Therefore, lattice defects are easily generated in metal oxides having an a-like structure and metal oxides having an amorphous structure.

[0055] Therefore, it is preferable to use a metal oxide with high crystallinity for the semiconductor layer of a transistor. For example, it is preferable to use a metal oxide having a CAAC structure or a metal oxide having a single crystal structure. By using such a metal oxide for a transistor, a transistor with good electrical characteristics can be realized. In addition, a highly reliable transistor can be realized.

[0056] The metal oxides with high crystallinity do not include metal oxides with a polycrystalline structure. A polycrystalline structure is a crystal structure in which clear crystal grain boundaries are observed. When a metal oxide with a polycrystalline structure is used in a semiconductor layer of a transistor, the crystal grain boundaries are likely to become recombination centers and capture carriers, resulting in a decrease in the on-current of the transistor and a decrease in the field effect mobility.

[0057] In addition, a metal oxide that increases the on-state current of a transistor is preferably used for the channel formation region of the transistor. In order to increase the on-state current of the transistor, it is preferable to increase the mobility of the metal oxide used in the transistor. In order to increase the mobility of the metal oxide, it is necessary to improve the transmission of carriers (electrons in the case of an n-channel transistor) or reduce scattering factors that contribute to the transmission of carriers. Note that carriers flow from the source to the drain through the channel formation region. Therefore, by providing a channel formation region in which carriers can easily flow in the channel length direction, the on-state current of a transistor can be increased.

[0058] Here, it is preferable to use a metal oxide having high crystallinity for the metal oxide including the channel formation region. Furthermore, it is preferable for the crystal to have a crystal structure in which multiple layers (for example, a first layer, a second layer, and a third layer) are stacked. That is, the crystal has a layered crystal structure (also called a layered crystal or layered structure). In this case, the c-axis of the crystal is oriented in the direction in which the multiple layers are stacked. Examples of metal oxides having such crystals include single crystal oxide semiconductors and CAAC-OS described later.

[0059] It is also preferable that the c-axis of the crystal is oriented in the normal direction to the surface on which the metal oxide is formed or the film surface. This allows the layers to be arranged approximately parallel to the surface on which the metal oxide is formed or the film surface. In other words, the layers extend in the channel length direction.

[0060] For example, the above three-layered crystal structure has the following structure. The first layer has an octahedral atomic coordination structure of oxygen with the metal of the first layer at the center. The second layer has a trigonal bipyramidal or tetrahedral atomic coordination structure of oxygen with the metal of the second layer at the center. The third layer has a trigonal bipyramidal or tetrahedral atomic coordination structure of oxygen with the metal of the third layer at the center.

[0061] The crystal structure of the above crystal is, for example, YbFe 2 O 4 Type structure, Yb 2 Fe 3 O 7 There are various types of structures, including modified types of these.

[0062] Furthermore, each of the first to third layers is preferably composed of one metal element or multiple metal elements having the same valence and oxygen. The valence of the one or multiple metal elements constituting the first layer is preferably the same as the valence of the one or multiple metal elements constituting the second layer. The first layer and the second layer may have the same metal element. The valence of the one or multiple metal elements constituting the first layer is preferably different from the valence of the one or multiple metal elements constituting the third layer.

[0063] The above structure can improve the crystallinity of the metal oxide and increase the mobility of the metal oxide, and therefore, by using the metal oxide in a channel formation region of a transistor, the on-state current of the transistor can be increased and the electrical characteristics of the transistor can be improved.

[0064] The metal oxide preferably contains at least indium or zinc. In particular, it is preferable that the metal oxide contains indium and zinc. In addition to the above, it is preferable that the metal oxide contains a metal element having the same valence as that of indium or zinc. Examples of the metal element include aluminum, gallium, and yttrium. The metal oxide may contain one or more elements selected from iron, cobalt, nickel, lanthanum, cerium, neodymium, magnesium, calcium, and the like.

[0065] Here, the case where the oxide semiconductor is an In-M-Zn oxide having indium (In), an element M, and zinc (Zn) is considered. The element M is aluminum, gallium, yttrium, etc. Other elements that can be used as the element M include iron, cobalt, nickel, lanthanum, cerium, neodymium, magnesium, calcium, etc. However, there are cases where a combination of a plurality of the above elements may be used as the element M.

[0066] In order to form the metal oxide having the layered crystal structure, it is preferable to deposit atoms one layer at a time, for example, ALD (Atomic Layer Deposition) can be used as a method for forming the metal oxide.

[0067] The ALD method utilizes the self-regulating nature of precursor molecules or atoms contained in the precursors to deposit atoms one layer at a time, and thus has the following advantages: extremely thin films can be formed; films can be formed on structures with high aspect ratios; films can be formed with fewer defects such as pinholes; films can be formed with excellent coverage; and films can be formed at low temperatures. The ALD method also includes the plasma enhanced ALD method, which is a film formation method that uses plasma. By using plasma, films can be formed at lower temperatures, which may be preferable. Note that some precursors used in the ALD method contain elements such as carbon or chlorine. For this reason, films formed by the ALD method may contain more elements such as carbon or chlorine than films formed by other film formation methods. The amount of these elements can be quantified using X-ray photoelectron spectroscopy (XPS).

[0068] Unlike the film formation method in which particles emitted from a target or the like are deposited, the ALD method is a film formation method in which a film is formed by a reaction on the surface of the object to be processed. Therefore, it is hardly affected by the shape of the object to be processed and has good step coverage. In particular, since the ALD method has excellent step coverage and excellent thickness uniformity, it is suitable for covering the surface of an opening with a high aspect ratio. However, since the ALD method has a relatively slow film formation rate, it may be preferable to use it in combination with other film formation methods such as the CVD method with a high film formation rate.

[0069] The composition of the obtained film can be controlled by the introduction amount of the source gas in the ALD method. For example, in the ALD method, a film with an arbitrary composition can be formed by adjusting the introduction amount of the source gas, the number of introductions (also referred to as the number of pulses), the time required for one pulse (also referred to as the pulse time), etc. Further, for example, in the ALD method, a film with a continuously changing composition can be formed by changing the source gas while forming the film. When forming a film while changing the source gas, the time required for film formation can be shortened because the time required for transfer and pressure adjustment is not required compared to the case of forming a film using a plurality of film formation chambers. Therefore, the productivity of semiconductor devices may be improved.

[0070] <Film Formation Apparatus Using ALD Apparatus and ALD Method> Here, a film formation apparatus using the ALD method (hereinafter also referred to as an ALD apparatus) that can be used for forming a metal oxide according to an aspect of the present invention, and a film formation method using the ALD method will be described.

[0071] The film formation apparatus using the ALD method alternately introduces a first source gas (sometimes referred to as a precursor, a precursory agent, a metal precursor) and a second source gas (sometimes referred to as a reactant, a reactant, an oxidizing agent, a non-metal precursor) for the reaction into the chamber, and film formation is performed by repeating the introduction of these source gases. The switching of the introduction of the source gas can be performed by switching each switching valve (sometimes referred to as a high-speed valve), for example. Further, when introducing the source gas, nitrogen (N2 An inert gas such as argon (Ar), argon (Ar), or helium (He) may be introduced into the chamber together with the source gas as a carrier gas. By using a carrier gas, even if the source gas has low volatility or low vapor pressure, it is possible to suppress the source gas from being adsorbed inside the piping and the valve, and to introduce the source gas into the chamber. In addition, the uniformity of the film formed is improved, which is preferable.

[0072] An example of a method for forming a film of a metal oxide having the above-mentioned three-layered crystal structure by the ALD method will be described with reference to FIGS. 1A to 1E. First, a precursor 11a is introduced into a chamber, and the precursor 11a is adsorbed onto the surface of a substrate 10 (see FIG. 1A. Hereinafter, this process may be referred to as the first step). Here, as shown in FIG. 1A, the precursor 11a is adsorbed onto the surface of the substrate 10, and a self-termination mechanism of the surface chemical reaction is activated, so that the precursor 11a is not further adsorbed onto the layer of the precursor 11a on the substrate 10. The appropriate range of the substrate temperature in which the self-termination mechanism of the surface chemical reaction is activated is also called the ALD window. The ALD window is determined by the temperature characteristics, vapor pressure, decomposition temperature, etc. of the precursor, and may be, for example, 100° C. to 600° C., preferably 200° C. to 400° C.

[0073] Next, an inert gas (such as argon, helium, or nitrogen) is introduced into the chamber to discharge excess precursor 11a and reaction products from the chamber (hereinafter, this step may be referred to as the second step). Instead of introducing an inert gas into the chamber, excess precursor and reaction products may be discharged from the chamber by vacuum evacuation. The second step is also called purging.

[0074] Next, reactant 12a (e.g., oxidant (ozone (O 3 ), oxygen (O 2 ), water (H 2O) and their plasma, radicals, ions, etc.) are introduced into the chamber and reacted with the precursor 11a adsorbed on the surface of the substrate 10, causing some of the components contained in the precursor 11a to be released while leaving the constituent molecules of the precursor 11a adsorbed on the substrate 10 (see FIG. 1B. Hereinafter, this step may be referred to as the third step). As a result, a layer of oxide 13a formed by oxidizing a portion of the precursor 11a is formed on the surface of the substrate 10.

[0075] In addition, when performing the plasma ALD method, oxygen may be constantly supplied as an oxidizing agent and plasma may be generated in the third step. As a result, oxygen plasma is formed in the third step and functions as the reactant 12a. In this case, a precursor 11a that does not react with oxygen heated to the above temperature may be used in any step other than the third step.

[0076] Next, the excess reactant 12a and reaction products are discharged from the chamber by introducing an inert gas or by evacuation (hereinafter, this step may be referred to as a fourth step).

[0077] Next, precursor 11b having a metal element different from precursor 11a is introduced, and the same process as the first step is performed to cause precursor 11b to be adsorbed on the surface of the layer of oxide 13a (see FIG. 1C). Here, as shown in FIG. 1C, as precursor 11b is adsorbed on the layer of oxide 13a, a self-terminating mechanism of the surface chemical reaction is activated, and precursor 11b is not further adsorbed on the layer of precursor 11b on substrate 10.

[0078] Next, as in the second step, excess precursor 11b and reaction products are discharged from the chamber by introducing an inert gas or by vacuum evacuation.

[0079] Next, as in the third step, reactant 12b is introduced into the chamber. Here, reactant 12b may be the same as reactant 12a or may be different from reactant 12a (see FIG. 1D). As a result, a layer of oxide 13b formed by oxidizing a part of precursor 11b is formed on the layer of oxide 13a.

[0080] Next, as in the fourth step, excess reactant 12b and reaction products are discharged from the chamber by introducing an inert gas or by evacuation.

[0081] Further, the first to fourth steps can be performed in a similar manner to form a layer of oxide 13c on the layer of oxide 13b. In this manner, by repeatedly performing the steps of forming oxides 13a to 13c, a metal oxide having a layered crystal structure in which the stacked structures of oxides 13a to 13c are repeated can be formed (see FIG. 1E). In other words, an oxide layer can be formed by performing the first to fourth steps as one set, and by repeating this set, a layered crystal structure in which multiple oxide layers are stacked can be formed.

[0082] In forming a metal oxide having a layered crystal structure, particularly a metal oxide having the above-mentioned CAAC structure, it is preferable to perform the steps shown in FIG. 1 while heating the substrate. For example, the substrate temperature may be set to 200° C. or higher and 600° C. or lower, preferably 300° C. or higher and lower than the decomposition temperature of the precursor. When forming a film by the ALD method using a plurality of different precursors, it is preferable to set the substrate temperature to the decomposition temperature of the lowest precursor among the plurality of precursors. This allows the plurality of precursors used to be adsorbed to the target (e.g., substrate) without being decomposed during film formation by the ALD method.

[0083] By performing the above-mentioned film formation while heating the substrate in such a temperature range, impurities such as hydrogen or carbon contained in the precursor or reactant can be removed from the metal oxide in each process from step 1 to step 4. For example, carbon in the metal oxide can be removed by CO 2 and CO, and hydrogen in the metal oxide is released as H 2 O. Furthermore, at the same time as the removal of the impurities, the metal atoms and oxygen atoms are rearranged, and each oxide layer can be arranged with high order. Therefore, a metal oxide with a highly crystalline layered crystal structure, particularly a metal oxide with the CAAC structure, can be formed. Note that, in FIG. 1A, a configuration in which the precursor 11a is formed on the substrate 10 is illustrated, but is not limited thereto. For example, an insulating film (insulating film having oxygen, nitrogen, silicon, aluminum, hafnium, etc.) or a conductive film (conductive film having tungsten, tantalum, molybdenum, zirconium, aluminum, titanium, etc.) may be provided on the substrate 10, and the precursor 11a may be formed thereon. Alternatively, the precursor 11a may be formed on a structure formed on the substrate 10 by an insulating film, a conductive film, etc.

[0084] In order to perform film formation while heating the substrate in the above temperature range, it is preferable that the precursor used in the film formation has a high decomposition temperature. For example, the decomposition temperature of the precursor is preferably 200° C. or more and 700° C. or less, and more preferably 300° C. or more and 600° C. or less. As a precursor having such a high decomposition temperature, it is preferable to use a precursor formed of an inorganic substance (hereinafter referred to as an inorganic precursor). Inorganic precursors generally tend to have a higher decomposition temperature than precursors formed of an organic substance (hereinafter referred to as an organic precursor), and some of them have an ALD window in the above temperature range. In addition, since inorganic precursors do not contain impurities such as hydrogen or carbon, it is possible to prevent an increase in the concentration of impurities such as hydrogen or carbon in the metal oxide film formed.

[0085] Furthermore, it is preferable to perform a heat treatment after the formation of the metal oxide film. In particular, it is preferable to perform a heat treatment continuously without exposing the film to the outside air after the formation of the film by the ALD method. The heat treatment may be performed at 100°C to 1200°C, preferably 200°C to 1000°C, more preferably 250°C to 650°C, even more preferably 300°C to 600°C, even more preferably 400°C to 550°C, and even more preferably 420°C to 480°C. The heat treatment is performed in an atmosphere of nitrogen gas or an inert gas, or an atmosphere containing 10 ppm or more, 1% or more, or 10% or more of an oxidizing gas. The heat treatment may be performed under reduced pressure. Alternatively, the heat treatment may be performed in an atmosphere of nitrogen gas or an inert gas, and then in an atmosphere containing 10 ppm or more, 1% or more, or 10% or more of an oxidizing gas to compensate for the desorbed oxygen. Furthermore, when the heat treatment temperature is increased, the metal oxide may become polycrystalline. Therefore, the heat treatment temperature should be appropriately set within a range in which the metal oxide does not become polycrystalline.

[0086] By carrying out the heat treatment in this way, impurities such as hydrogen and carbon contained in the metal oxide can be removed. For example, carbon in the metal oxide can be converted to CO 2 and CO, and hydrogen in the metal oxide is released as H 2 O. Furthermore, at the same time as removing the above impurities, rearrangement of metal atoms and oxygen atoms occurs, improving crystallinity. Therefore, it is possible to form a metal oxide with a highly crystalline layered crystal structure, particularly a metal oxide with the above CAAC structure.

[0087] Although the structure in which the oxides 13a to 13c are repeatedly stacked has been described with reference to FIG. 1, the present invention is not limited thereto. For example, a metal oxide in which a single layer, two layers, or four or more oxide layers are repeatedly stacked may be used. In addition, in FIG. 1, the oxides 13a, 13b, and 13c are repeatedly stacked without changing the order, but the present invention is not limited thereto. For example, the order of the oxides 13a, 13b, and 13c may be changed. Furthermore, the compositions of the oxides 13a, 13b, and 13c may be changed in the middle of the film. In addition, in FIG. 1, different oxide layers are provided adjacent to each other, such as the oxides 13a, 13b, and 13c, but the present invention is not limited thereto. For example, a structure in which layers of the same oxide are continuously provided, such as the oxides 13a, 13a, 13b, 13b, 13c, and 13c, may be used.

[0088] In the following description of this specification, unless otherwise specified, when ozone, oxygen, or water is used as a reactant or an oxidant, these are not limited to gaseous or molecular states, but also include plasma, radical, and ionic states. When forming a film using an oxidant in a plasma, radical, or ionic state, a radical ALD apparatus or plasma ALD apparatus described below may be used.

[0089] In order to remove impurities such as carbon or hydrogen contained in the precursor, it is preferable to react the precursor with the oxidizing agent sufficiently. For example, the pulse time for introducing the oxidizing agent may be lengthened. Alternatively, the oxidizing agent may be introduced multiple times. When the oxidizing agent is introduced multiple times, the same type of oxidizing agent may be introduced, or different types of oxidizing agents may be introduced. For example, water may be introduced into the chamber as a first oxidizing agent, and then the chamber may be evacuated, and ozone or oxygen not containing hydrogen may be introduced into the chamber as a second oxidizing agent, and then the chamber may be evacuated.

[0090] In the above description, an example in which the first raw material gas is introduced into the chamber and then the second raw material gas is introduced into the chamber is shown, but the present invention is not limited to this. The second raw material gas may be introduced into the chamber and then the first raw material gas may be introduced into the chamber. That is, the third step and the fourth step may be performed first, followed by the first step, the second step, the third step, and the fourth step, and then the first step to the fourth step may be repeatedly performed to form a film. Furthermore, the third step and the fourth step may be repeated a number of times, and then the first step to the fourth step may be repeatedly performed to form a film.

[0091] In this way, it is preferable to perform the third step and the fourth step once or multiple times before the first step, since the deposition atmosphere in the chamber can be controlled. For example, in the third step, O 3 , and O 2 By introducing oxygen into the chamber, the chamber can be made into an oxygen atmosphere. By forming a film in an oxygen atmosphere in the chamber, the oxygen concentration in the film can be increased, which is preferable. Furthermore, oxygen can be supplied to the insulator and oxide that are the base of the film. A semiconductor device formed using such a method has good characteristics and can obtain high reliability. Also, for example, by introducing water as an oxidizing agent in the third step, a hydrophilic group can be formed on the surface to be formed. This can further improve the adsorption of the precursor.

[0092] In addition, after the first and second steps, the introduction of the second raw material gas in the third step and the evacuation or introduction of the inert gas in the fourth step may be repeated multiple times. That is, the first and second steps may be performed after the first, second, third, fourth, third, fourth steps, third, fourth steps, and the third and fourth steps are repeated.

[0093] For example, in the third step, O is used as the oxidizing agent. 3 , and O 2In the third step, an inert gas is introduced, and in the fourth step, this process may be repeated several times. When the third and fourth steps are repeated, it is not necessary to repeat the introduction of the same type of raw material gas. For example, in the first third step, H 2 O was used as the oxidizing agent in the third step from the second time onwards. 3 may also be used.

[0094] In this way, by repeating the introduction of the oxidizing agent and the introduction of the inert gas (or evacuation) multiple times in a short period of time within the chamber, it is possible to more reliably remove excess hydrogen atoms, carbon atoms, chlorine atoms, etc. from the precursor adsorbed on the substrate surface and expel them from the chamber. Also, by increasing the number of types of oxidizing agents to two, it is possible to remove more excess hydrogen atoms, etc. from the precursor adsorbed on the substrate surface. In this way, by preventing hydrogen atoms from being incorporated into the film during film formation, it is possible to reduce the amount of water, hydrogen, etc. contained in the formed film.

[0095] By using this method, the amount of water molecules desorbed was 1.0×10 in the surface temperature range of 100°C to 700°C or 100°C to 500°C. 13 molecule / cm 2 Above 1.0×10 16 molecule / cm 2 Less than or equal to 1.0×10 13 molecule / cm 2 Above 3.0×10 15 molecule / cm 2 It is possible to form a film having the following properties:

[0096] The ALD method is a film formation method in which precursors and reactants are reacted with each other using thermal energy. The temperature required for the reaction of the precursors and reactants is determined by their temperature characteristics, vapor pressure, decomposition temperature, etc., and is 100°C to 600°C, preferably 200°C to 600°C, and more preferably 300°C to 600°C.

[0097] Furthermore, in addition to the above-mentioned precursor and reactant reactions, the ALD method in which a plasma-excited reactant is introduced into the chamber as a third raw material gas is sometimes called the plasma ALD method. In this case, a plasma generating device is provided at the introduction part of the third raw material gas. Inductively Coupled Plasma (ICP) can be used to generate plasma. In contrast, the ALD method in which the precursor and reactant react with thermal energy is sometimes called the thermal ALD method.

[0098] In the plasma ALD method, a plasma-excited reactant is introduced in the third step to form a film. Alternatively, the first to fourth steps are repeated while a plasma-excited reactant (second reactant) is introduced to form a film. In this case, the reactant introduced in the third step is called the first reactant. In the plasma ALD method, the second reactant used in the third raw material gas can be the same material as the oxidizing agent. That is, plasma-excited ozone, oxygen, and water can be used as the second reactant. In addition to the oxidizing agent, a nitriding agent may be used as the second reactant. Nitrogen (N 2 ) or ammonia (NH 3 ) can be used. Nitrogen (N 2 ) and hydrogen (H 2 ) can be used as a nitriding agent. 2 ) 5%, hydrogen (H 2 ) 95% mixed gas can be used as the nitriding agent. By depositing the film while introducing plasma-excited nitrogen or ammonia, a nitride film such as a metal nitride film can be formed.

[0099] In addition, argon (Ar), helium (He) or nitrogen (N 2) may be used. The use of a carrier gas such as argon, helium, or nitrogen is preferable because it facilitates plasma discharge and facilitates the generation of a plasma-excited second reactant. When forming an oxide film such as a metal oxide film using the plasma ALD method, if nitrogen is used as the carrier gas, the nitrogen may be mixed into the film, making it difficult to obtain the desired film quality. In this case, it is preferable to use argon or helium as the carrier gas.

[0100] The ALD method can deposit extremely thin films with uniform thickness and has a high surface coverage even on uneven surfaces.

[0101] In addition, deposition by the plasma ALD method allows deposition at lower temperatures than thermal ALD. For example, plasma ALD may be able to deposit a film at temperatures below 100°C without reducing the deposition rate. In addition, plasma ALD can use many reactants, such as nitriding agents as well as oxidizing agents, so it is possible to deposit many types of films, such as nitrides, fluorides, and metals, in addition to oxides.

[0102] Furthermore, when performing a plasma ALD method, plasma damage can be suppressed by generating plasma from a plasma source such as an inductively coupled plasma (ICP) or an electron cyclotron resonance plasma (ECR) away from the substrate.

[0103] Here, the atomic arrangement in the crystal when the metal oxide with a layered crystal structure is In-M-Zn oxide will be described with reference to Figs. 2A to 3D. In Figs. 2B, 2D, 3B, and 3D, atoms are represented by spheres (circles), and bonds between metal atoms and oxygen atoms are represented by lines. In Figs. 2B, 2D, 3B, and 3D, the c-axis direction in the crystal structure of In-M-Zn oxide is represented by an arrow in the figure. In addition, the ab-plane direction in the crystal structure of In-M-Zn oxide is perpendicular to the c-axis direction represented by the arrow in Figs. 2B, 2D, 3B, and 3D.

[0104] 2A is a diagram showing an oxide 60 having an In-M-Zn oxide formed on a structure 50. Here, the structure refers to an element constituting a semiconductor device such as a transistor. The structure 50 includes conductors such as a substrate, a gate electrode, a source electrode, and a drain electrode, insulators such as a gate insulating film, an interlayer insulating film, and a base insulating film, and semiconductors such as metal oxides or silicon. FIG. 2A shows a case where the surface of the structure 50 on which a film is to be formed is arranged parallel to the substrate (or base body, not shown).

[0105] 2B is an enlarged view showing the atomic arrangement in a crystal in a region 53 which is a part of the oxide 60 in FIG. 2A. The composition of the oxide 60 shown in FIG. 2A and FIG. 2B is In:M:Zn=1:1:1 [atomic ratio], and the crystal structure is YbFe 2 O 4 The element M is a metal element having a valence of +3.

[0106] 2B, the crystals of the oxide 60 are formed by repeatedly stacking a layer 21 having indium (In) and oxygen, a layer 31 having an element M and oxygen, and a layer 41 having zinc (Zn) and oxygen in this order. The layer 21, the layer 31, and the layer 41 are arranged approximately parallel to the deposition surface of the structure 50. That is, the ab-plane of the oxide 60 is approximately parallel to the deposition surface of the structure 50, and the c-axis of the oxide 60 is approximately parallel to the normal direction of the deposition surface of the structure 50.

[0107] As shown in FIG. 2B, each of layers 21, 31, and 41 of the crystal is composed of one metal element and oxygen, and is arranged with good crystallinity, thereby increasing the mobility of the metal oxide.

[0108] It should be noted that the In-M-Zn oxide with an atomic ratio of In:M:Zn=1:1:1 is not limited to the structure shown in FIG. 2B. The order of stacking the layers 21, 31, and 41 may be changed. For example, the layers 21, 41, and 31 may be repeatedly stacked in this order. Alternatively, the layers 21, 31, 41, 21, 41, and 31 may be repeatedly stacked in this order. Furthermore, part of the element M in the layer 31 may be substituted with zinc, and part of the zinc in the layer 41 may be substituted with the element M.

[0109] In the above, an example was shown in which an In-M-Zn oxide having a composition of In:M:Zn=1:1:1 [atomic ratio] was formed. (1+α) M (1-α) O 3 (ZnO) m Crystalline In-M-Zn oxide, represented by the formula (α is a real number greater than 0 and less than 1, and m is a positive number), can similarly have a layered crystal structure. As an example, In-M-Zn oxide with a composition of In:M:Zn=1:3:4 [atomic ratio] is shown in Figures 2C and 2D.

[0110] Fig. 2C is a diagram showing an oxide 62 having an In-M-Zn oxide formed on the structure 50. Fig. 2D is an enlarged view showing the atomic arrangement in the crystal in a region 54 that is part of the oxide 62 in Fig. 2C.

[0111] 2D, the crystal of the oxide 62 includes a layer 22 having indium (In), an element M, and oxygen, a layer 41 having zinc (Zn) and oxygen, and a layer 31 having an element M and oxygen. In the oxide 62, a plurality of layers are repeatedly stacked in the order of the layer 22, the layer 41, the layer 31, and the layer 41. The layer 22, the layer 31, and the layer 41 are arranged approximately parallel to the deposition surface of the structure 50. That is, the ab plane of the oxide 62 is approximately parallel to the deposition surface of the structure 50, and the c axis of the oxide 62 is approximately parallel to the normal direction of the deposition surface of the structure 50.

[0112] 2D, the In-M-Zn oxide with an atomic ratio of In:M:Zn=1:3:4 may have a structure that is different from that shown in FIG. 2D. For example, the stacking order of the layers 22, 31, and 41 may be changed. A part of the element M in the layer 31 may be substituted with zinc, and a part of the zinc in the layer 41 may be substituted with the element M. The layer 21 or the layer 31 may be formed instead of the layer 22.

[0113] 3A, a laminated structure may be formed in which an oxide 62 is formed on the structure 50, and an oxide 60 is formed thereon. Here, FIG. 3B is an enlarged view showing the atomic arrangement in the crystal in a region 56 which is a part of the oxide 62 and the oxide 60 in FIG. 3A.

[0114] As described above, the oxide 62 is an In-M-Zn oxide with an atomic ratio of In:M:Zn=1:3:4, and the oxide 60 is an In-M-Zn oxide with an atomic ratio of In:M:Zn=1:1:1. That is, the oxide shown in FIG. 3A is an oxide film in which the atomic ratio changes midway through the film. In addition, as shown in FIG. 3B, by forming the oxide 62 into a layered crystal structure, the crystallinity of the oxide 60 on the oxide 62 can be improved.

[0115] The oxide 62 and the oxide 60 are not limited to the structure shown in FIG. 3B, and as described above, the structures of the oxide 62 and the oxide 60 may be changed. In addition, although the layer 21 is disposed at the boundary between the oxide 62 and the oxide 60 in FIG. 3B, the present invention is not limited to this. For example, the layer 22 may be formed at the boundary between the oxide 62 and the oxide 60.

[0116] As described above, the ALD method allows deposition on a structure with a high aspect ratio, and allows deposition with excellent coverage on the side surface of the structure. By using the ALD method, a crystalline metal oxide such as a CAAC structure can be easily formed regardless of the orientation of the surface to be deposited. For example, even if the structure has a convex or concave shape, a metal oxide can be formed with good coverage on the top surface, bottom surface, side surface, and inclined surface of the structure. That is, a metal oxide having an approximately constant film thickness in the normal direction can be formed on each surface to be deposited. In the metal oxide formed on each of the top surface, bottom surface, side surface, and inclined surface of the structure, the ratio of the minimum film thickness to the maximum film thickness can be 0.5 to 1, preferably 0.7 to 1, and more preferably 0.9 to 1. In this case, when the metal oxide has a crystalline structure, its c-axis is oriented in a direction approximately parallel to the normal direction of each surface to be deposited. That is, the c-axis is oriented perpendicular to each surface to be deposited.

[0117] Here, FIG. 3C shows a case where the surface of the structure 50 to be deposited is arranged perpendicular to the substrate (or base, not shown), and an oxide 64 is formed on the surface of the structure 50. FIG. 3D is an enlarged view of a region 58 which is a part of the oxide 64 in FIG. 3C. FIG. 3D shows a state where a layer 21 containing indium (In), a layer 31 containing element M, and a layer 41 containing zinc (Zn) are laminated on the side surface of the structure 50 to be deposited. The layer 21 containing indium is arranged parallel to the surface to be deposited of the structure 50, the layer 31 containing element M is arranged thereon parallel to the surface to be deposited of the structure 50, and the layer 41 containing zinc is arranged thereon parallel to the surface to be deposited of the structure 50. That is, the ab plane of the oxide 60 is approximately parallel to the surface to be deposited of the structure 50, and the c axis of the oxide 60 is approximately parallel to the normal direction of the surface to be deposited of the structure 50. Although an example of In-M-Zn oxide with an atomic ratio of In:M:Zn=1:1:1 is shown in Figures 3C and 3D, oxides with different atomic ratios can also be formed on the surface of structure 50 whose deposition surface is arranged perpendicular to the substrate.

[0118] In addition, in the above, examples of metal oxides having an atomic ratio of In:M:Zn=1:1:1 and an atomic ratio of In:M:Zn=1:3:4 are shown, but the present invention is not limited to this.

[0119] A preferred range of the atomic ratio of indium, element M, and zinc in a metal oxide that can be used in the oxide shown in one embodiment of the present invention will be described below with reference to Figures 4A, 4B, and 4C. The atomic ratio of oxygen is not shown in Figures 4A, 4B, and 4C. The terms of the atomic ratio of indium, element M, and zinc in a metal oxide are [In], [M], and [Zn], respectively.

[0120] In Figures 4A, 4B, and 4C, the dashed lines represent the line where the atomic ratio of [In]:[M]:[Zn] = (1+α):(1-α):1 (-1≦α≦1), the line where the atomic ratio of [In]:[M]:[Zn] = (1+α):(1-α):2, the line where the atomic ratio of [In]:[M]:[Zn] = (1+α):(1-α):3, the line where the atomic ratio of [In]:[M]:[Zn] = (1+α):(1-α):4, and the line where the atomic ratio of [In]:[M]:[Zn] = (1+α):(1-α):5.

[0121] In addition, the dotted lines represent the line where the atomic ratio of [In]:[M]:[Zn] = 5:1:β (β≧0), the line where the atomic ratio of [In]:[M]:[Zn] = 2:1:β, the line where the atomic ratio of [In]:[M]:[Zn] = 1:1:β, the line where the atomic ratio of [In]:[M]:[Zn] = 1:2:β, the line where the atomic ratio of [In]:[M]:[Zn] = 1:3:β, and the line where the atomic ratio of [In]:[M]:[Zn] = 1:4:β.

[0122] Moreover, metal oxides having an atomic ratio of [In]:[M]:[Zn]=0:2:1, or values ​​close to this ratio, shown in FIGS. 4A, 4B, and 4C, tend to have a spinel-type crystal structure.

[0123] In addition, multiple phases may coexist in a metal oxide (two-phase coexistence, three-phase coexistence, etc.). For example, when the atomic ratio is close to [In]:[M]:[Zn]=0:2:1, two phases, a spinel-type crystal structure and a layered crystal structure, tend to coexist. In addition, when the atomic ratio is close to [In]:[M]:[Zn]=1:0:0, two phases, a bixbyite-type crystal structure and a layered crystal structure, tend to coexist. When multiple phases coexist in a metal oxide, grain boundaries may be formed between different crystal structures.

[0124] Region A shown in FIG. 4A shows an example of a preferable range of the atomic ratio of indium, element M, and zinc contained in the metal oxide.

[0125] The carrier mobility (electron mobility) of a metal oxide can be increased by increasing the indium content of the metal oxide. Therefore, a metal oxide with a high indium content has a higher carrier mobility than a metal oxide with a low indium content.

[0126] On the other hand, as the content of indium and zinc in the metal oxide decreases, the carrier mobility decreases. Therefore, when the atomic ratio is [In]:[M]:[Zn]=0:1:0 or a value close to that (for example, region C shown in FIG. 4C), the insulating property becomes high. Note that region C includes the above-mentioned region that is likely to have a spinel crystal structure, so it is preferable to have a composition that avoids the region that is likely to have a spinel crystal structure.

[0127] For example, the metal oxide used in the channel formation region and the low resistance region preferably has an atomic ratio shown in region A of FIG. 4A, which has high carrier mobility. The metal oxide used in the channel formation region and the low resistance region may have, for example, In:Ga:Zn=4:2:3 to 4.1, or a value close thereto. Also, for example, In:Ga:Zn=1:1:1, or a value close thereto. On the other hand, when the metal oxide is provided so as to surround the channel formation region and the low resistance region, it is preferable that the metal oxide has an atomic ratio shown in region C of FIG. 4C, which has relatively high insulation. The metal oxide provided so as to surround the channel formation region and the low resistance region may have, for example, In:Ga:Zn=1:3:4, or a value close thereto, or In:Ga:Zn=1:3:2, or a value close thereto. Alternatively, the metal oxide provided so as to surround the channel formation region and the low resistance region may be the same as the metal oxide used in the channel formation region and the low resistance region.

[0128] In particular, in region B shown in FIG. 4B, among the regions A, an excellent metal oxide having high carrier mobility and high reliability can be obtained.

[0129] Region B includes [In]:[M]:[Zn]=4:2:3 to 4.1 and their neighboring values. Neighboring values ​​include, for example, [In]:[M]:[Zn]=5:3:4. Region B also includes [In]:[M]:[Zn]=5:1:6 and their neighboring values, and [In]:[M]:[Zn]=5:1:7 and their neighboring values. Region B also includes [In]:[M]:[Zn]=1:1:1 and their neighboring values.

[0130] As described above, the electrical conductivity characteristics of the metal oxide vary greatly depending on the atomic ratio. By forming a metal oxide film using the ALD method as described above, it is possible to form a metal oxide film having a layered crystal structure according to each atomic ratio. Therefore, by using the ALD method, it is possible to form a metal oxide film according to the required characteristics.

[0131] Next, a method for forming the oxide 60 having the In-M-Zn oxide shown in FIGS. 2A and 2B will be described in detail with reference to FIGS. 5A to 6C.

[0132] First, a source gas containing a precursor having indium is introduced into the chamber, and the precursor is adsorbed on the surface of the structure 50 (see FIG. 5A). Here, the source gas contains a carrier gas such as argon, helium, or nitrogen in addition to the precursor. As the precursor having indium, trimethylindium, triethylindium, tris(2,2,6,6-tetramethyl-3,5-heptanedionate)indium, cyclopentadienylindium, indium(III) acetylacetonate, (3-(dimethylamino)propyl)dimethylindium, and the like can be used.

[0133] In addition, an inorganic precursor not containing a hydrocarbon may be used as the precursor containing indium. A halogen-based indium compound such as indium trichloride, indium tribromide, or indium triiodide may be used as the inorganic precursor containing indium. Indium trichloride has a decomposition temperature of about 500° C. or more and 700° C. or less. Therefore, by using indium trichloride, a film can be formed by the ALD method while heating the substrate at about 400° C. or more and 600° C. or less, for example, at 500° C.

[0134] Next, the introduction of the source gases is stopped, and the chamber is purged to discharge excess precursors, reaction products, and the like from the chamber.

[0135] Next, an oxidizing agent is introduced into the chamber as a reactant and reacted with the adsorbed precursor, and components other than indium are released while indium is still adsorbed on the substrate, forming a layer 21 in which indium and oxygen are combined (see FIG. 5B). As the oxidizing agent, ozone, oxygen, water, etc. can be used. Next, the introduction of the oxidizing agent is stopped, and the chamber is purged to discharge excess reactants and reaction products from the chamber.

[0136] Next, a source gas containing a precursor having element M is introduced into the chamber, and the precursor is adsorbed onto layer 21 (see FIG. 5C). In addition to the precursor, the source gas contains a carrier gas such as argon, helium, or nitrogen. When gallium is used as element M, trimethylgallium, triethylgallium, tris(dimethylamido)gallium, gallium(III) acetylacetonate, tris(2,2,6,6-tetramethyl-3,5-heptanedionate)gallium, dimethylchlorogallium, diethylchlorogallium, dimethylgallium isopropoxide, and the like can be used as a precursor having gallium.

[0137] In addition, an inorganic precursor not containing a hydrocarbon may be used as the precursor containing gallium. A halogen-based gallium compound such as gallium trichloride, gallium tribromide, or gallium triiodide may be used as the inorganic precursor containing gallium. Gallium trichloride has a decomposition temperature of about 550° C. or more and 700° C. or less. Therefore, by using gallium trichloride, a film can be formed by the ALD method while heating the substrate at about 450° C. or more and 650° C. or less, for example, at 550° C.

[0138] Next, the introduction of the source gas is stopped, and the chamber is purged to discharge excess precursors and reaction products from the chamber.

[0139] Next, an oxidizing agent is introduced into the chamber as a reactant and reacted with the adsorbed precursor to remove components other than element M while leaving element M adsorbed on the substrate, thereby forming layer 31 in which element M is combined with oxygen (see FIG. 5D). At this time, some of the oxygen adsorbed on layer 31 may constitute layer 41, which will be described later. Next, the introduction of the oxidizing agent is stopped, and the chamber is purged to discharge excess reactant and reaction products from the chamber.

[0140] Next, a source gas containing a zinc-containing precursor is introduced into the chamber, and the precursor is adsorbed onto the layer 31 (see FIG. 6A). At this time, a part of the layer 41 in which zinc and oxygen are combined may be formed. The source gas contains a carrier gas such as argon, helium, or nitrogen in addition to the precursor. As the precursor containing zinc, dimethyl zinc, diethyl zinc, zinc bis(2,2,6,6-tetramethyl-3,5-heptanedionate), zinc acetate, etc. can be used.

[0141] In addition, an inorganic precursor not containing a hydrocarbon may be used as the zinc-containing precursor. A halogen-based zinc compound such as zinc dichloride, zinc dibromide, or zinc diiodide may be used as the zinc-containing inorganic precursor. The decomposition temperature of zinc dichloride is about 450° C. or more and 700° C. or less. Therefore, by using zinc dichloride, a film can be formed by the ALD method while heating the substrate at about 350° C. or more and 550° C. or less, for example, at 450° C.

[0142] Next, the introduction of the source gas is stopped, and the chamber is purged to discharge excess precursors and reaction products from the chamber.

[0143] Next, an oxidizing agent is introduced into the chamber as a reactant and reacted with the adsorbed precursor, leaving zinc adsorbed on the substrate while components other than zinc are released, forming a layer 41 in which zinc and oxygen are combined (see FIG. 6B). Next, the introduction of the oxidizing agent is stopped, and the chamber is purged to discharge excess reactant and reaction products from the chamber.

[0144] Next, the layer 21 is formed again on the layer 41 by the above-mentioned method (see FIG. 6C). By repeating the above-mentioned method, an oxide 60 can be formed on the substrate or the structure.

[0145] The precursors may contain one or both of carbon and chlorine in addition to the metal element. A film formed using a precursor containing carbon may contain carbon. A film formed using a precursor containing a halogen such as chlorine may contain a halogen such as chlorine.

[0146] As described above, by forming the oxide 60 using the ALD method, it is possible to form a metal oxide having a CAAC structure in which the c-axis is oriented approximately parallel to the normal direction of the deposition surface.

[0147] It is preferable to perform the steps shown in Figures 5A to 6C while heating the substrate. For example, the substrate temperature may be set to 200°C to 600°C, preferably 300°C to the decomposition temperature of the precursor. By performing the above film formation while heating the substrate within such a temperature range, impurities such as hydrogen or carbon contained in the precursor or reactant can be removed from the metal oxide in each step of Figures 5A to 6C. For example, carbon in the metal oxide can be converted to CO 2 and CO, and hydrogen in the metal oxide is released as H 2 O. Furthermore, at the same time as removing the above impurities, rearrangement of metal atoms and oxygen atoms occurs, and each oxide layer can be arranged in a highly ordered manner. Therefore, a metal oxide with a highly crystalline layered crystal structure, for example, a metal oxide with a CAAC structure, can be formed.

[0148] In order to form a film while heating the substrate in the above temperature range, it is preferable that the precursor used in the film formation has a high decomposition temperature. For example, the decomposition temperature of the precursor is preferably 200° C. or more and 700° C. or less, and more preferably 300° C. or more and 600° C. or less. As a precursor having such a high decomposition temperature, it is preferable to use an inorganic precursor. In general, inorganic precursors tend to have a higher decomposition temperature than organic precursors, so that the precursor is less likely to decompose even if the film is formed while heating the substrate as described above.

[0149] As the inorganic precursor, for example, the above-mentioned indium trichloride, gallium trichloride, and zinc dichloride can be used. As described above, the decomposition temperature of these precursors is about 350° C. or more and 700° C. or less, which is considerably higher than the decomposition temperature of general organic precursors. However, as described above, the decomposition temperatures of indium trichloride, gallium trichloride, and zinc dichloride are different from each other. In this way, when performing film formation by the ALD method using multiple different types of precursors, it is preferable to set the substrate temperature to the decomposition temperature of the lowest precursor among the multiple precursors. In the above example, the substrate temperature may be set within a range in which zinc dichloride, which has the lowest decomposition temperature of the precursor, does not decompose. This allows other indium trichloride and gallium trichloride to be adsorbed to the target (for example, a substrate, etc.) without being decomposed.

[0150] In the above, the non-phase precursor is exemplified, but the present invention is not limited thereto. For example, the present invention can be applied to the ALD method using an organic precursor. For example, when forming a metal oxide (e.g., In-M-Zn metal oxide, etc.) using an organic precursor, it is preferable to set the substrate temperature to the decomposition temperature of the lowest precursor among the plurality of organic precursors or lower. This allows the plurality of precursors used to be adsorbed on the target (e.g., substrate, etc.) during the ALD film formation without being decomposed. In this case, the substrate temperature can be applied to a range of 100°C or higher and lower than the lowest temperature among the decomposition temperatures of the precursors (typically, 200°C or higher and 300°C or lower).

[0151] Furthermore, it is preferable to perform a heat treatment after the formation of the metal oxide film. In particular, it is preferable to perform a heat treatment continuously without exposing the film to the outside air after the formation of the film by the ALD method. The heat treatment is preferably performed at 250°C to 650°C, more preferably 300°C to 600°C, even more preferably 400°C to 550°C, and even more preferably 420°C to 480°C. By performing the heat treatment in this manner, impurities such as hydrogen or carbon contained in the metal oxide can be removed. For example, carbon in the metal oxide can be converted to CO 2and CO, and hydrogen in the metal oxide is released as H 2 O. Furthermore, at the same time as removing the above impurities, rearrangement of metal atoms and oxygen atoms occurs, improving crystallinity. Therefore, it is possible to form a metal oxide with a highly crystalline layered crystal structure, particularly a metal oxide with the above CAAC structure.

[0152] 5A to 6C show an example in which layer 21 is formed as a layer containing indium, layer 31 is formed thereon as a layer containing element M, and layer 41 is further formed thereon as a layer containing zinc, but the present embodiment is not limited to this. One of layer 31 and layer 41 may be formed, layer 21 may be formed thereon, and the other of layer 31 and layer 41 may be formed thereon. Alternatively, one of layer 31 and layer 41 may be formed, the other of layer 31 and layer 41 may be formed thereon, and layer 21 may be formed thereon.

[0153] When forming a metal oxide having an atomic ratio different from In:M:Zn=1:1:1 [atomic ratio], the above-mentioned layers 21, 31, and 41 may be formed appropriately according to the atomic ratio. For example, as shown in FIG. 6A, the formation of layer 41 may be repeated multiple times before and after the formation of layer 31, thereby forming a laminate of layers 31 and 41 having the desired number of atoms, number of layers, and thickness between two layers 21.

[0154] <Example of film formation equipment configuration> As an example of an apparatus capable of forming a film by the ALD method, the configuration of a film forming apparatus 4000 will be described with reference to Figures 7, 8A, and 8B. Figure 7 is a schematic diagram of a multi-chamber type film forming apparatus 4000, and Figures 8A and 8B are cross-sectional views of an ALD apparatus that can be used for the film forming apparatus 4000.

[0155] The film forming apparatus 4000 has a loading / unloading chamber 4002, a loading / unloading chamber 4004, a transfer chamber 4006, a film forming chamber 4008, a film forming chamber 4009, a processing chamber 4011, and a transfer arm 4014. Here, the loading / unloading chamber 4002, the loading / unloading chamber 4004, the film forming chamber 4008, the film forming chamber 4009, and the processing chamber 4011 are independently connected to the transfer chamber 4006 via gate valves. This allows continuous processing to be performed in the film forming chamber 4008, the film forming chamber 4009, and the processing chamber 4011 without exposure to the atmosphere, and prevents impurities from being mixed into the film. In addition, contamination of the interface between the substrate and the film and the interface between each film is reduced, and clean interfaces are obtained.

[0156] In addition, in order to prevent moisture from adhering to the loading / unloading chamber 4002, the loading / unloading chamber 4004, the transfer chamber 4006, the film forming chamber 4008, the film forming chamber 4009, and the processing chamber 4011, it is preferable to fill them with an inert gas (such as nitrogen gas) with a controlled dew point in order to prevent moisture from adhering to the chamber, and it is desirable to maintain a reduced pressure.

[0157] An ALD apparatus can be used in the film formation chamber 4008 and the film formation chamber 4009. A film formation apparatus other than an ALD apparatus may be used in either the film formation chamber 4008 or the film formation chamber 4009. Examples of film formation apparatuses that can be used in the film formation chamber 4008 and the film formation chamber 4009 include a sputtering apparatus, a plasma CVD (PECVD: Plasma Enhanced CVD) apparatus, a thermal CVD (TCVD: Thermal CVD) apparatus, a photo CVD (Photo CVD) apparatus, a metal CVD (MCVD: Metal CVD) apparatus, and a metal organic CVD (MOCVD: Metal Organic CVD) apparatus.

[0158] The processing chamber 4011 may be provided with a device having a function other than that of a film formation device, such as a heating device (typically, a vacuum heating device) and a plasma generating device (typically, a microwave processing device).

[0159] For example, when the deposition chamber 4008 is an ALD apparatus, the deposition chamber 4009 is a sputtering apparatus, and the treatment chamber 4011 is a heating apparatus, a base insulating film can be formed in the deposition chamber 4009, an oxide semiconductor film that functions as an active layer can be formed in the deposition chamber 4008, and heat treatment can be performed after the formation of the oxide semiconductor film in the treatment chamber 4011. At this time, the formation of the base insulating film, the formation of the oxide semiconductor film, and the heat treatment can be performed successively without exposure to air.

[0160] Further, the film forming apparatus 4000 is configured to have the loading / unloading chamber 4002, the loading / unloading chamber 4004, the film forming chamber 4008, the film forming chamber 4009, and the processing chamber 4011, but the present invention is not limited to this. The film forming apparatus 4000 may be configured to have one film forming chamber, or three or more processing chambers. The film forming apparatus 4000 may be configured to have two or more processing chambers. The film forming apparatus 4000 may be of a single wafer type, or may be of a batch type in which films are formed on multiple substrates at once.

[0161] <Heating device> Next, a heating device that can be used in the processing chamber 4011 will be described. The heating mechanism used in the heating device may be, for example, a mechanism that uses a resistance heating element for heating. Alternatively, it may be a mechanism that uses heat conduction or heat radiation from a medium such as a heated gas for heating. For example, an RTA (Rapid Thermal Anneal) such as a GRTA (Gas Rapid Thermal Anneal) or an LRTA (Lamp Rapid Thermal Anneal) can be used. The LRTA heats the workpiece by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressure sodium lamp, or a high-pressure mercury lamp. The GRTA performs heat processing using high-temperature gas.

[0162] The heat treatment by the above heating device may be performed at 100°C to 1200°C, preferably 200°C to 1000°C, more preferably 250°C to 650°C, even more preferably 300°C to 600°C, even more preferably 400°C to 550°C, and even more preferably 420°C to 480°C. The heat treatment is performed in an atmosphere of nitrogen gas or inert gas, or an atmosphere containing 10 ppm or more, 1% or more, or 10% or more of an oxidizing gas. For example, when the heat treatment is performed in a mixed atmosphere of nitrogen gas and oxygen gas, the oxygen gas may be about 20%. The heat treatment may be performed under reduced pressure. Alternatively, the heat treatment may be performed in an atmosphere of nitrogen gas or inert gas, and then in an atmosphere containing 10 ppm or more, 1% or more, or 10% or more of an oxidizing gas to compensate for the desorbed oxygen. In addition, since the metal oxide may have a polycrystalline structure when the heat treatment temperature is high, the heat treatment temperature may be appropriately set within a range in which the metal oxide does not have a polycrystalline structure. However, in one embodiment of the present invention, the metal oxide may have a polycrystalline structure.

[0163] In addition, the gas used in the heat treatment is preferably highly purified. For example, the amount of moisture contained in the gas used in the heat treatment may be 1 ppb or less, preferably 0.1 ppb or less, and more preferably 0.05 ppb or less. By using a highly purified gas for the heat treatment, it is possible to prevent moisture and the like from being incorporated into the metal oxide as much as possible.

[0164] For example, in the heat treatment, after forming a metal oxide film, a nitrogen gas to oxygen gas flow ratio is set to 4 slm:1 slm, and treatment is performed for 1 hour at a temperature of 400° C. to 550° C., preferably 420° C. to 480° C. This heat treatment can reduce impurities such as water and hydrogen contained in the metal oxide.

[0165] By carrying out the heat treatment in this way, impurities such as hydrogen and carbon contained in the metal oxide can be removed. For example, carbon in the metal oxide can be converted to CO 2and release it as CO, and the hydrogen in the metal oxide can be released as H 2 O. As described above, since the processing chamber 4011 is connected to the film forming chambers 4008 and 4009 via the transfer chamber 4006, the film formation of the metal oxide to the heat treatment can be continuously performed without being exposed to the outside air. Therefore, after the film formation of the metal oxide, the heat treatment can be performed without increasing impurities such as hydrogen or carbon in the film. Further, simultaneously with the removal of the above impurities, the rearrangement of metal atoms and oxygen atoms can be performed, and the crystallinity can be improved. Therefore, a metal oxide having a high crystallinity and a layered crystal structure, particularly the metal oxide having the above CAAC structure, can be formed.

[0166] In the above, an example in which a heat treatment apparatus is used in the processing chamber 4011 has been described, but the present invention is not limited thereto. For example, a configuration in which a microwave processing apparatus is used in the processing chamber 4011 may be employed. By performing microwave processing, impurities such as hydrogen or carbon contained in the metal oxide can be removed. For details of the microwave processing and the microwave processing apparatus, reference can be made to the description of the following embodiments.

[0167] <ALD apparatus> Next, the configuration of a thermal ALD apparatus that can be used in the film forming apparatus 4000 will be described with reference to FIG. 8A. The thermal ALD apparatus includes a film forming chamber (chamber 4520), a raw material supply unit 4521 (raw material supply units 4521a to 4521c), a raw material supply unit 4531, high-speed valves 4522a to 4522d that are introduction amount controllers, a gas supply unit 4532, a raw material introduction port 4523, a raw material discharge port 4524, and an exhaust device 4525. The raw material introduction port 4523 installed in the chamber 4520 is connected to the raw material supply unit 4521a, the raw material supply unit 4521b, the raw material supply unit 4521c, the raw material supply unit 4531, and the gas supply unit 4532 via supply pipes and valves, respectively, and the raw material discharge port 4524 is connected to the exhaust device 4525 via a discharge pipe, a valve, and a pressure regulator.

[0168] The chamber 4520 has a substrate holder 4526 inside, and the substrate 4530 is placed on the substrate holder 4526. The substrate holder 4526 may have a rotation mechanism. The chamber 4520 has an outer wall provided with a heater 4527, which can control the temperature inside the chamber 4520, the substrate holder 4526, the surface of the substrate 4530, and the like. The heater 4527 can control the temperature of the surface of the substrate 4530 to 100°C or more and 600°C or less, preferably 200°C or more and 600°C or less, more preferably 300°C or more and less than the decomposition temperature of the precursor, and the temperature of the heater 4527 itself can be set to 100°C or more and 600°C or less. By forming a film while heating the substrate in such a temperature range, impurities such as hydrogen or carbon contained in the precursor or reactant can be suitably reduced from the metal oxide. Furthermore, at the same time as the removal of the above impurities, rearrangement of metal atoms and oxygen atoms is performed, and each oxide layer can be arranged in a highly orderly manner. Therefore, a metal oxide film having a layered crystal structure with high crystallinity can be formed. Heat treatment may be performed using the heater 4527 after the metal oxide film is formed.

[0169] In raw material supplying unit 4521a, raw material supplying unit 4521b, raw material supplying unit 4521c, and raw material supplying unit 4531, a raw material gas is formed from a solid raw material or a liquid raw material by a vaporizer or a heating means, etc. Alternatively, raw material supplying unit 4521a, raw material supplying unit 4521b, raw material supplying unit 4521c, and raw material supplying unit 4531 may be configured to supply a gaseous raw material gas.

[0170] 8A, a metal oxide can be formed by appropriately selecting raw materials (such as a volatile organometallic compound) used in raw material supply unit 4521 and raw material supply unit 4531 and introducing them into chamber 4520. As described above, when forming In-Ga-Zn oxide containing indium, gallium, and zinc as a metal oxide, it is preferable to use a film formation apparatus provided with at least three raw material supply units 4521a to 4521c and at least one raw material supply unit 4531 as shown in FIG.

[0171] For example, a precursor containing indium may be supplied from the raw material supply unit 4521a, a precursor containing gallium may be supplied from the raw material supply unit 4521b, and a precursor containing zinc may be supplied from the raw material supply unit 4521c. The precursor containing indium, the precursor containing gallium, and the precursor containing zinc may be the precursors described above. The precursor containing indium, the precursor containing gallium, and the precursor containing zinc preferably have a high decomposition temperature, and for example, an inorganic precursor is preferably used. Note that when a halogen-based compound or the like is used as an inorganic precursor, the gas may be highly corrosive. Therefore, it is preferable to use a material with high corrosion resistance, such as titanium, for members that come into contact with gas, such as chambers, piping, and various gas supply units.

[0172] In addition, a reactant is supplied from the raw material supply unit 4531. As the reactant, an oxidizing agent containing at least one of ozone, oxygen, and water can be used.

[0173] A carrier gas is supplied from the gas supply unit 4532. The carrier gas may be argon (Ar), helium (He), or nitrogen (N 2 The precursor from the raw material supply unit 4521 and the reactant from the raw material supply unit 4531 are mixed with the carrier gas and introduced into the chamber 4520.

[0174] In addition, a piping heater 4534a is provided to cover the piping or valves between the raw material supply unit 4521a, the raw material supply unit 4521b, the raw material supply unit 4521c, the raw material supply unit 4531, and the gas supply unit 4532 and the chamber 4520. In addition, a piping heater 4534b is provided to cover the piping or valves between the exhaust device 4525 and the chamber 4520. The temperature of the piping heater 4534a and the piping heater 4534b may be appropriately set within a range of, for example, room temperature or 300° C. or less. By providing such a piping heater, it is possible to prevent the precursors supplied from the raw material supply unit 4521 from solidifying on the inner walls of the piping of the gas introduction system and the gas exhaust system. In particular, precursors with high decomposition temperatures such as inorganic precursors tend to solidify easily, so when such precursors are used, it is preferable to provide a piping heater to cover the piping of the gas introduction system and the gas exhaust system. Furthermore, the temperature control of piping heater 4534a, piping heater 4534b, and heater 4527 may be configured to be controlled independently. By controlling piping heater 4534a, piping heater 4534b, and heater 4527 independently, the temperature of each heater can be controlled individually. However, without being limited to this, the temperature control of piping heater 4534a, piping heater 4534b, and heater 4527 may be configured to be linked with each other. In this case, the temperature control can be adjusted collectively, so that the device components can be made cheaper.

[0175] The high-speed valves 4522a to 4522d can be precisely controlled in time, so that the source gases supplied from the source supply units 4521a, 4521b, 4521c, and 4531 can be controlled and introduced into the chamber 4520.

[0176] For example, when supplying precursors contained in the raw material supply unit 4521a, the raw material supply unit 4521b, and the raw material supply unit 4521c, the corresponding high-speed valves among the high-speed valves 4522a to 4522c may be opened. When supplying a reactant contained in the raw material supply unit 4531, the high-speed valve 4522d may be opened. When purging the chamber 4520, the high-speed valves 4522a to 4522d may be closed, and only the carrier gas contained in the gas supply unit 4532 may be introduced into the chamber 4520.

[0177] 8A shows an example in which three raw material supply units 4521 and one raw material supply unit 4531 are provided, but this embodiment is not limited to this. One, two, or four or more raw material supply units 4521 may be provided. Two or more raw material supply units 4531 may be provided.

[0178] 8A, heater 4527, raw material inlet 4523, and raw material outlet 4524 are arranged at the bottom of chamber 4520, but the arrangement can be appropriately set. In addition, in Fig. 8A, the inlets of raw material supply unit 4521a, raw material supply unit 4521b, raw material supply unit 4521c, raw material supply unit 4531, and gas supply unit 4532 are integrated into raw material inlet 4523, but the arrangement can be different and each inlet can be provided.

[0179] 8B, the configuration of a plasma ALD apparatus that can be used for the film formation apparatus 4000 will be described. The plasma ALD apparatus includes a film formation chamber (chamber 4020), a raw material supply unit 4021 (raw material supply units 4021a to 4021c), a raw material supply unit 4031, high-speed valves 4022a to 4022d that are introduction amount controllers, a gas supply unit 4032, a raw material inlet 4023, a raw material inlet 4033, a raw material outlet 4024, and an exhaust unit 4025. Raw material inlet 4023 and raw material inlet 4033 installed in chamber 4020 are connected to raw material supply unit 4021a, raw material supply unit 4021b, raw material supply unit 4021c, raw material supply unit 4031, and gas supply unit 4032 via supply pipes and valves, respectively, and raw material outlet 4024 is connected to exhaust device 4025 via an exhaust pipe, a valve, and a pressure regulator. Also, substrate holder 4026 is provided inside chamber 4020, and substrate 4030 is placed on substrate holder 4026. Also, heater 4027 is provided on the outer wall of the chamber, and piping heater 4034a and piping heater 4034b are provided to cover piping and the like connected to the chamber.

[0180] Here, the chamber 4020 corresponds to the chamber 4520, the raw material supply unit 4021 corresponds to the raw material supply unit 4521, the raw material supply unit 4031 corresponds to the raw material supply unit 4531, the high-speed valves 4022a to 4022d correspond to the high-speed valves 4522a to 4522d, the gas supply unit 4032 corresponds to the gas supply unit 4532, the raw material inlet 4023 corresponds to the raw material inlet 4523, the raw material outlet 4024 corresponds to the raw material outlet 4524, the exhaust device 4025 corresponds to the exhaust device 4525, the substrate holder 4026 corresponds to the substrate holder 4526, the substrate 4030 corresponds to the substrate 4530, the heater 4027 corresponds to the heater 4527, the piping heater 4034a corresponds to the piping heater 4534a, and the piping heater 4034b corresponds to the piping heater 4534b, and the detailed configuration can be referred to the above description.

[0181] As shown in FIG. 8B, the plasma ALD apparatus can perform film formation by the plasma ALD method in addition to the thermal ALD method by connecting a plasma generator 4028 to the chamber 4020. The plasma generator 4028 is preferably an ICP type plasma generator using a coil 4029 connected to a high-frequency power source. The high-frequency power source can output power having a frequency of 10 kHz to 100 MHz, preferably 1 MHz to 60 MHz, more preferably 2 MHz to 60 MHz. For example, it can output power having a frequency of 13.56 MHz. In the plasma ALD method, film formation can be performed without reducing the film formation rate even at low temperatures, so it is suitable for use in a single-wafer type film formation apparatus with low film formation efficiency.

[0182] The reactant discharged from the raw material supply unit 4031 passes through the plasma generator 4028 and becomes a plasma state. The reactant in a plasma state is introduced into the chamber 4020 from the raw material inlet 4033. Although not shown in FIG. 8B, the reactant discharged from the raw material supply unit 4031 may be mixed with a carrier gas.

[0183] Furthermore, a mechanism for applying a constant potential or high frequency may be provided to the substrate holder 4526. Alternatively, the substrate holder 4526 may be floating or grounded.

[0184] In FIG. 8B, raw material inlet 4033 is disposed at the top of chamber 4520, heater 4027 and raw material inlet 4023 are disposed at the side of chamber 4520, and raw material outlet 4524 is disposed at the bottom of chamber 4520; however, the present invention is not limited to this arrangement and these arrangements can be appropriately set.

[0185] 9A to 9C explain different configurations of an ALD apparatus that can be used for the film formation apparatus 4000. Note that detailed description of the same configuration and functions as those of the ALD apparatus shown in FIG. 8B may be omitted.

[0186] FIG. 9A is a schematic diagram showing one embodiment of a plasma ALD apparatus. The plasma ALD apparatus 4100 includes a reaction chamber 4120 and a plasma generation chamber 4111 above the reaction chamber 4120. The reaction chamber 4120 can be called a chamber. Alternatively, the reaction chamber 4120 and the plasma generation chamber 4111 can be collectively called a chamber. The reaction chamber 4120 has a raw material inlet 4123 and a raw material outlet 4124, and the plasma generation chamber 4111 has a raw material inlet 4133. In addition, a plasma generation device 4128 can apply high frequency such as RF or microwaves to a gas introduced into the plasma generation chamber 4111 to generate plasma 4131 in the plasma generation chamber 4111. When the plasma 4131 is generated using microwaves, microwaves with a frequency of 2.45 GHz are typically used. In addition, the plasma generated by applying such microwaves and a magnetic field may be called ECR (Electron Cyclotron Resonance) plasma.

[0187] The reaction chamber 4120 has a substrate holder 4126 on which a substrate 4130 is placed. The source gas introduced from the source inlet 4123 is decomposed by heat from a heater provided in the reaction chamber 4120 and deposited on the substrate 4130. The source gas introduced from the source inlet 4133 is turned into a plasma state by the plasma generating device 4128. The source gas in the plasma state recombines with electrons or other molecules before reaching the surface of the substrate 4130, and reaches the substrate 4130 in a radical state. An ALD device that uses radicals to form a film in this way may be called a radical ALD (radical-enhanced ALD) device. In addition, the plasma ALD device 4100 shows a configuration in which the plasma generation chamber 4111 is provided at the top of the reaction chamber 4120, but this embodiment is not limited to this. The plasma generation chamber 4111 may be provided adjacent to the side of the reaction chamber 4120.

[0188] FIG. 9B is a schematic diagram showing one embodiment of a plasma ALD apparatus. The plasma ALD apparatus 4200 has a chamber 4220. The chamber 4220 has an electrode 4213, a raw material outlet 4224, and a substrate holder 4226, and a substrate 4230 is placed on the substrate holder 4226. The electrode 4213 has a raw material inlet 4223 and a shower head 4214 that supplies the introduced raw material gas into the chamber 4220. In addition, a power source 4215 that can apply high frequency power via a capacitor 4217 is connected to the electrode 4213. A mechanism for applying a constant potential or high frequency power may be provided to the substrate holder 4226. Alternatively, the substrate holder 4226 may be floating or grounded. The electrode 4213 and the substrate holder 4226 function as an upper electrode and a lower electrode for generating a plasma 4231, respectively. The raw material gas introduced from the raw material inlet 4223 is decomposed by heat from a heater provided in the chamber 4220 and deposited on the substrate 4230. Alternatively, the raw material gas introduced from the raw material inlet 4223 becomes a plasma state between the electrode 4213 and the substrate holder 4226. The raw material gas in the plasma state is incident on the substrate 4230 due to a potential difference (also called an ion sheath) generated between the plasma 4231 and the substrate 4230.

[0189] FIG. 9C is a schematic diagram showing an embodiment of a plasma ALD apparatus different from that shown in FIG. 9B. The plasma ALD apparatus 4300 has a chamber 4320. The chamber 4320 has an electrode 4313, a raw material outlet 4324, and a substrate holder 4326, and a substrate 4330 is placed on the substrate holder 4326. The electrode 4313 has a raw material inlet 4323 and a shower head 4314 that supplies the introduced raw material gas into the chamber 4320. In addition, a power source 4315 that can apply high frequency power via a capacitor 4317 is connected to the electrode 4313. The substrate holder 4326 may be provided with a mechanism for applying a constant potential or high frequency power. Alternatively, the substrate holder 4326 may be floating or grounded. The electrode 4313 and the substrate holder 4326 function as an upper electrode and a lower electrode for generating a plasma 4331, respectively. The plasma ALD apparatus 4300 is different from the plasma ALD apparatus 4200 in that it has a mesh 4319 connected to a power source 4321 capable of applying high frequency through a capacitor 4322 between the electrode 4313 and the substrate holder 4326. By providing the mesh 4319, the plasma 4231 can be separated from the substrate 4130. The source gas introduced from the source inlet 4323 is decomposed by heat from a heater provided in the chamber 4320 and deposited on the substrate 4330. Alternatively, the source gas introduced from the source inlet 4323 becomes a plasma state between the electrode 4313 and the substrate holder 4326. The charge of the source gas in the plasma state is removed by the mesh 4319, and the source gas reaches the substrate 4130 in an electrically neutral state such as radicals. This allows film formation to be performed with reduced incidence of ions and damage caused by plasma.

[0190] Note that a plasma ALD apparatus shown in FIG. 8B and FIGS. 9A to 9C may be used to perform microwave treatment after forming a metal oxide film.

[0191] <Deposition sequence> Next, a metal oxide film formation sequence using the ALD apparatus shown in Fig. 8A will be described with reference to Fig. 10A to Fig. 12. In Fig. 10A to Fig. 12, the introduction of the first to fourth source gases is indicated by ON, and a period in which the source gases are not introduced is indicated by OFF.

[0192] FIG. 10A shows a film formation sequence using the ALD apparatus shown in FIG. 8A. First, the substrate 4530 is set on the substrate holder 4526 in the chamber 4520 (step S101). Next, the temperature of the heater 4527 is adjusted (step S102). At this time, the temperatures of the piping heaters 4534a and 4534b may also be adjusted. Next, the substrate 4530 is held on the substrate holder 4526 so that the temperature of the substrate 4530 is uniform within the substrate surface (step S103). Next, a metal oxide film is formed according to the first to fourth steps described above (step S104). Note that if the temperature adjustment of the heater 4527 is not required after the substrate 4530 is set (step S101), step S102 may be omitted.

[0193] In step S104, a first source gas (source gas having a precursor) and a second source gas (source gas having a reactant) are alternately introduced into the chamber 4520 to form a film on the substrate 4530. The first source gas and the second source gas are each introduced in a pulsed manner. In a period in which neither the first source gas nor the second source gas is introduced, the inside of the chamber 4520 is purged. In the film formation by the ALD method, one cycle is the introduction of the first source gas (first step above), purging of the first source gas (second step above), introduction of the second source gas (third step above), and purging of the second source gas (fourth step above), and this cycle is repeated to form a film having a desired thickness.

[0194] In addition, between steps S103 and S104, a second source gas having a reactant may be introduced into the chamber 4020. As the second source gas, ozone (O 3 ), oxygen (O2 ), and water (H 2 It is preferable to introduce one or more selected from the group consisting of water, oxygen, and argon. By introducing water as the second source gas, a hydrophilic group can be formed on the substrate 4530, and the adsorption of the precursor can be further improved. By introducing ozone and oxygen as the second source gas, the chamber is made into an oxygen atmosphere, and oxygen can be supplied to the base insulating film formed on the substrate 4530. This allows oxygen to be supplied to the metal oxide film formed on the base insulating film, and the oxygen concentration in the film can be increased. At this time, the second source gas is preferably introduced in a pulsed manner similar to the method shown in step S104, but the present invention is not limited to this. The second source gas may be introduced continuously. During the period when the second source gas is not introduced, the chamber 4520 is evacuated.

[0195] A layered crystalline oxide having a plurality of different oxide layers can be formed by forming a first oxide layer in one cycle using the above-mentioned first raw material gas, forming a second oxide layer in one cycle using a third raw material gas different from the first raw material gas, and forming a third oxide layer in one cycle using a fourth raw material gas different from the first raw material gas. In the following, as an example, a film formation sequence corresponding to the film formation process of In-Ga-Zn oxide shown in Figures 5A to 6C will be described with reference to Figure 10B.

[0196] 10B shows step S104 of a film formation sequence for an example in which a film is formed using a first source gas to a third source gas having a precursor. Note that steps S101 to S103 may be performed in the same manner as described above. Here, the first source gas contains a precursor having indium, the third source gas contains a precursor having gallium, and the fourth source gas contains a precursor having zinc.

[0197] As shown in Fig. 10B, first, a first source gas is introduced, and a precursor having indium is adsorbed onto a substrate 4530 (corresponding to Fig. 5A). Then, the introduction of the first source gas is stopped, and the excess first source gas in the chamber is purged.

[0198] Next, the second source gas is introduced, and the precursor having adsorbed indium is reacted with the oxidizing agent to form an indium oxide layer (corresponding to FIG. 5B). Then, the introduction of the second source gas is stopped, and the excess second source gas in the chamber is purged.

[0199] Next, the third source gas is introduced to adsorb a gallium-containing precursor onto the indium oxide layer (corresponding to FIG. 5C). Then, the introduction of the third source gas is stopped and the excess third source gas in the chamber is purged.

[0200] Next, the second source gas is introduced, and the precursor having the adsorbed gallium reacts with the oxidizing agent to form a layer of gallium oxide (corresponding to FIG. 5D). Then, the introduction of the second source gas is stopped, and the excess second source gas in the chamber is purged.

[0201] Next, the fourth source gas is introduced to adsorb the zinc-containing precursor onto the gallium oxide layer (corresponding to FIG. 6A). Then, the introduction of the fourth source gas is stopped and the excess fourth source gas in the chamber is purged.

[0202] Next, the second source gas is introduced, and the precursor having adsorbed zinc is reacted with the oxidizing agent to form a layer of zinc oxide (corresponding to FIG. 6B). Then, the introduction of the second source gas is stopped, and the excess second source gas in the chamber is purged. Furthermore, the precursor having indium is adsorbed on the zinc oxide using the method described above (corresponding to FIG. 6C).

[0203] The above process of forming indium oxide, gallium oxide, and zinc oxide constitutes one cycle, and by repeating the cycle, an In-Ga-Zn oxide with an atomic ratio of In:Ga:Zn=1:1:1 and a desired film thickness can be formed.

[0204] The first to fourth source gases are introduced in a pulsed manner. The pulse time for introducing the first, third, and fourth source gases into the chamber 4520 is preferably 0.05 to 1 second, and more preferably 0.1 to 0.5 seconds. The time for exhausting the first, third, and fourth source gases from the chamber 4520 is preferably 0.1 to 15 seconds, and more preferably 0.5 to 10 seconds. The pulse time for introducing the second source gas into the chamber 4520 is preferably 0.05 to 30 seconds, and more preferably 0.1 to 15 seconds. The time for exhausting the second source gas from the chamber 4520 is preferably 0.1 to 15 seconds, and more preferably 0.1 to 5 seconds.

[0205] In the sequence shown in FIG. 10B, the order of introduction of the first raw material gas, the third raw material gas, and the fourth raw material gas is not limited to this. For example, the fourth gas containing a precursor having zinc may be introduced first. Since zinc oxide is easier to form a crystal structure than indium oxide and gallium oxide, stable zinc oxide crystals can be formed in the bottom layer. This allows a layer of indium oxide and gallium oxide to be formed relatively easily on zinc oxide.

[0206] In the above, the formation of an In-Ga-Zn oxide film with an atomic ratio of In:Ga:Zn=1:1:1 has been described, but the present invention is not limited to this. In-Ga-Zn oxides with different atomic ratios can be formed using a similar method. It is preferable to set the number of pulses or pulse time of the precursor-containing source gas in one cycle according to the atomic ratio of the desired In-Ga-Zn oxide.

[0207] For example, in the sequence shown in Fig. 10B, in order to form an In-Ga-Zn oxide film with an atomic ratio of In:Ga:Zn = 1:1:1, the first source gas containing indium, the third source gas containing gallium, and the fourth source gas containing zinc are pulsed once each in one cycle. At this time, the pulse times of each precursor are the same.

[0208] FIG. 11A shows an example of a film formation sequence of In-Ga-Zn oxide with In:Ga:Zn=1:3:4 [atomic ratio]. In FIG. 11A, the number of pulses of the first source gas containing indium in one cycle is one, the number of pulses of the third source gas containing gallium is three, and the number of pulses of the fourth source gas containing zinc is four. In other words, the number of pulses of the source gas containing the precursor corresponds to In:Ga:Zn=1:3:4 [atomic ratio]. By forming the film in this manner, a metal oxide with a layered crystal structure according to FIG. 2D can be formed.

[0209] In addition, as described above, by performing film formation by the ALD method while heating the substrate, rearrangement of each oxide layer can be promoted. As a result, even if film formation is performed according to the sequence shown in Fig. 11A, a layer having two kinds of metal elements (indium and gallium) in one oxide layer can be formed, as in layer 22 shown in Fig. 2D.

[0210] In the above, different types of precursors are introduced between the introduction of the reactant-containing raw material gas, but the present invention is not limited to this. For example, the same type of precursor-containing raw material gas may be continuously introduced between the introduction of the reactant-containing raw material gas. In this case, the number of pulses of the precursor-containing raw material gas in one cycle is preferably the same as the atomic ratio of the desired In-Ga-Zn oxide.

[0211] In the above, only one type of precursor-containing raw material gas is introduced during the interval in which oxidation is performed with the second raw material gas, but the present invention is not limited to this. Two or more types of precursor-containing raw material gases may be introduced during the interval in which oxidation is performed with the second raw material gas. In this case, two or more types of precursor-containing raw material gases may be introduced simultaneously. Also, the same type of precursor may be introduced twice in succession during the interval in which oxidation is performed with the second raw material gas.

[0212] For example, when forming an In-Ga-Zn oxide film with an atomic ratio of In:Ga:Zn=1:3:4, the film may be formed in the sequence shown in FIG. 11B. In FIG. 11B, the first raw material gas, the third raw material gas, the fourth raw material gas, the third raw material gas, and the fourth raw material gas are introduced in this order in accordance with the crystal structure in which the layers 22, 41, 31, and 41 are stacked in this order as shown in FIG. 2D. However, the first raw material gas and the third raw material gas are introduced without the introduction of the second raw material gas in between. In other words, the oxidizing agent is introduced after the precursor containing indium contained in the first raw material gas and the precursor containing gallium contained in the third raw material gas are adsorbed. This makes it possible to form a layer containing two kinds of metal elements (indium and gallium) in one oxide layer, as in the layer 22 shown in FIG. 2D. At this time, it is preferable that the pulse time of the first raw material gas and the third raw material gas is about half the pulse time of the fourth raw material gas. As a result, as shown in FIG. 11B, the ratio of the pulse time of the first raw material gas containing indium to the pulse time of the third raw material gas containing gallium to the pulse time of the fourth raw material gas containing zinc during one cycle can be made 1:3:4, which is the same as the atomic number ratio.

[0213] In the above, the deposition of an oxide having a constant atomic ratio has been described, but the present invention is not limited thereto. Using a similar method, two or more oxides having different atomic ratios can be deposited continuously. In this case, it is preferable to set the number of pulses or pulse time of the precursor-containing source gas in one cycle according to the atomic ratio of each oxide in the laminated oxides having different atomic ratios. By depositing the film in this manner, laminated oxides having different atomic ratios can be deposited in a single chamber. Therefore, it is possible to prevent impurities such as hydrogen or carbon from entering during the intervals between deposition of each oxide.

[0214] FIG. 12 shows an example of a film formation sequence when an oxide having an atomic ratio of In:Ga:Zn=1:1:1 is laminated on an oxide having an atomic ratio of In:Ga:Zn=1:3:4. Step 104a corresponds to an oxide having an atomic ratio of In:Ga:Zn=1:3:4, and is the same as the sequence shown in FIG. 11A. Step 104b corresponds to an oxide having an atomic ratio of In:Ga:Zn=1:1:1, and is the same as the sequence shown in FIG. 10B. In this way, the first half of the process is performed with the number of pulses per cycle of the first raw material gas: the third raw material gas: the fourth raw material gas=1:3:4, and the second half of the process is performed with the number of pulses per cycle of the first raw material gas: the third raw material gas: the fourth raw material gas=1:1:1, so that a metal oxide having a laminated structure of the oxide 62 and the oxide 60 shown in FIG. 3B can be formed. In other words, the first half of the film is deposited with a pulse count corresponding to an atomic ratio of In:Ga:Zn=1:3:4, and the second half of the film is deposited with a pulse count corresponding to an atomic ratio of In:Ga:Zn=1:1:1.

[0215] In the above, the film forming method is described using In-Ga-Zn oxide as an example, but the present invention is not limited to this. Precursors may be appropriately selected according to the metal elements contained in the desired metal oxide. In the above, the number of precursors is one or three, but is not limited to this, and may be two or four or more.

[0216] In the above, an example of forming a film using a precursor having one type of metal element has been shown, but the present invention is not limited to this. A precursor having two or more types of metal elements may be used. For example, a precursor containing indium and gallium, or a precursor containing gallium and zinc may be used. In this case, the number of raw material supply parts 4521 shown in FIG. 8A etc. can be reduced.

[0217] <Classification of crystal structures> Below, classification of the crystal structures of the above metal oxides (oxide semiconductors) will be explained.

[0218] First, classification of crystal structures in oxide semiconductors will be described with reference to Fig. 13A. Fig. 13A is a diagram for explaining classification of crystal structures of oxide semiconductors, typically IGZO (metal oxide containing In, Ga, and Zn).

[0219] As shown in FIG. 13A, oxide semiconductors are broadly classified into "Amorphous", "Crystalline", and "Crystal". "Amorphous" includes completely amorphous. "Crystalline" includes c-axis-aligned crystalline (CAAC), nanocrystalline (nc), and cloud-aligned composite (CAC) (excluding single crystal and poly crystal). "Crystalline" excludes single crystal, poly crystal, and completely amorphous. "Crystal" includes single crystal and poly crystal.

[0220] The structure in the bold frame shown in Fig. 13A is an intermediate state between "Amorphous" and "Crystal" and belongs to a new boundary region (New crystalline phase). In other words, this structure is completely different from the energetically unstable "Amorphous" or "Crystal".

[0221] The crystal structure of the film or substrate can be evaluated using an X-ray diffraction (XRD) spectrum. FIG. 13B shows an XRD spectrum obtained by GIXD (Grazing-Incidence XRD) measurement of the CAAC-IGZO film classified as "Crystalline". The GIXD method is also called the thin film method or the Seemann-Bohlin method. Hereinafter, the XRD spectrum obtained by the GIXD measurement shown in FIG. 13B will be simply referred to as the XRD spectrum. The composition of the CAAC-IGZO film shown in FIG. 13B is in the vicinity of In:Ga:Zn=4:2:3 [atomic ratio]. The thickness of the CAAC-IGZO film shown in FIG. 13B is 500 nm.

[0222] As shown in Figure 13B, a clear peak indicating crystallinity is detected in the XRD spectrum of the CAAC-IGZO film. Specifically, a peak indicating c-axis orientation is detected near 2θ=31° in the XRD spectrum of the CAAC-IGZO film. Note that, as shown in Figure 13B, the peak near 2θ=31° is asymmetric with respect to the angle at which the peak intensity is detected.

[0223] In addition, the crystal structure of the film or substrate can be evaluated by the diffraction pattern (also referred to as the nano beam electron diffraction pattern) observed by the nano beam electron diffraction method (NBED). The diffraction pattern of the CAAC-IGZO film is shown in FIG. 13C. FIG. 13C is a diffraction pattern observed by NBED in which the electron beam is incident parallel to the substrate. Note that the composition of the CAAC-IGZO film shown in FIG. 13C is in the vicinity of In:Ga:Zn = 4:2:3 [atomic ratio]. In the nano beam electron diffraction method, electron diffraction is performed with a probe diameter of 1 nm.

[0224] As shown in FIG. 13C, in the diffraction pattern of the CAAC-IGZO film, a plurality of spots indicating c-axis orientation are observed.

[0225] <Metal oxide having a CAAC structure> Hereinafter, the details of the metal oxide having a CAAC structure will be described.

[0226] The CAAC structure has a plurality of crystals, and the c-axes of the plurality of crystals are oriented in a specific direction. Note that the specific direction is the thickness direction of the metal oxide having a CAAC structure, the normal direction of the surface on which the metal oxide having a CAAC structure is formed, or the normal direction of the surface of the metal oxide having a CAAC structure. Note that when referring to a crystal region, the crystal region refers to the crystal itself having a CAAC structure or the crystal having a CAAC structure and the region in the vicinity thereof. Therefore, the crystal having a CAAC structure may be referred to as a crystal region having a CAAC structure.

[0227] A crystalline region is a region in which the atomic arrangement has periodicity. If the atomic arrangement is considered as a lattice arrangement, the crystalline region is also a region in which the lattice arrangement is uniform. Furthermore, the CAAC structure has a region in which multiple crystalline regions are connected in the ab-plane direction, and the region may have distortion. The distortion refers to a portion in which the direction of the lattice arrangement changes between a region in which the lattice arrangement is uniform and another region in which the lattice arrangement is uniform in the region in which multiple crystalline regions are connected. In other words, a metal oxide having a CAAC structure is a metal oxide that is c-axis oriented and does not have a clear orientation in the ab-plane direction.

[0228] Each of the multiple crystalline regions is composed of one or more minute crystals (crystals with a maximum diameter of less than 10 nm). When a crystalline region is composed of one minute crystal, the maximum diameter of the crystalline region is less than 10 nm. When a crystalline region is composed of many minute crystals, the size of the crystalline region may be about several tens of nm.

[0229] In addition, in an In-M-Zn oxide (wherein element M is one or more elements selected from aluminum, gallium, yttrium, tin, titanium, etc.), the CAAC structure tends to have a layered crystal structure (also referred to as a layered structure) in which a layer having indium (In) and oxygen and a layer having element M, zinc (Zn), and oxygen are stacked. The layer having indium and oxygen may contain element M or zinc. The layer having element M, zinc, and oxygen may contain indium. The layered structure is observed as a lattice image in a high-resolution TEM image, for example.

[0230] When a metal oxide having a CAAC structure is subjected to structural analysis using, for example, an XRD device, a peak indicating c-axis orientation is detected at or near 2θ=31° in out-of-plane XRD measurement using θ / 2θ scan. Note that the position of the peak indicating c-axis orientation (2θ value) may vary depending on the type and composition of the metal element constituting the metal oxide.

[0231] For example, in the electron diffraction pattern of a metal oxide having a CAAC structure, multiple bright spots are observed, and one spot and another spot are observed at positions that are point-symmetric with respect to the spot of the incident electron beam that has passed through the sample (also called the direct spot).

[0232] When the crystal region is observed from the specific direction, the lattice arrangement in the crystal region is based on a hexagonal lattice, but the unit lattice is not necessarily a regular hexagon, and may be a non-regular hexagon. In addition, the above distortion may have a lattice arrangement such as a pentagon or heptagon. In addition, in a metal oxide having a CAAC structure, no clear crystal grain boundary can be confirmed even in the vicinity of the distortion. That is, it can be seen that the formation of crystal grain boundaries is suppressed by the distortion of the lattice arrangement. This is thought to be because the metal oxide having a CAAC structure can tolerate distortion because the arrangement of oxygen atoms in the ab-plane direction is not dense, or the bond distance between atoms changes due to the substitution of metal atoms.

[0233] Metal oxides having a CAAC structure are highly crystalline and have no clear crystal grain boundaries. In other words, it can be said that metal oxides having a CAAC structure are less susceptible to a decrease in electron mobility due to crystal grain boundaries. Therefore, metal oxides having a CAAC structure have stable physical properties. Therefore, metal oxides having a CAAC structure are resistant to heat and highly reliable. Therefore, metal oxides having a CAAC structure are one of the crystalline oxides having a crystal structure suitable for the semiconductor layer of a transistor.

[0234] <Transistors with metal oxide> Next, a case where a metal oxide (oxide semiconductor) is used for a transistor will be described.

[0235] By using the metal oxide (oxide semiconductor) of one embodiment of the present invention for a transistor, a transistor with high field-effect mobility can be realized. In addition, a highly reliable transistor can be realized. In addition, a miniaturized or highly integrated transistor can be realized. For example, a transistor with a channel length of 2 nm to 30 nm can be manufactured.

[0236] For the channel formation region of the transistor, an oxide semiconductor with a low carrier concentration is preferably used. For example, the carrier concentration of the channel formation region of the oxide semiconductor is 1×10 17 cm -3 Less than or equal to 1×10 15 cm -3 Less than 1×10, more preferably 13 cm -3 Less than or equal to 1×10 11 cm -3 Less than 1×10, more preferably 10 cm -3 Less than 1 x 10 -9 cm -3 The above is the case. Note that in order to reduce the carrier concentration of an oxide semiconductor film, the impurity concentration in the oxide semiconductor film may be reduced to reduce the density of defect states. In this specification and the like, an oxide semiconductor having a low impurity concentration and a low density of defect states is referred to as a high-purity intrinsic or substantially high-purity intrinsic oxide semiconductor. Note that an oxide semiconductor having a low carrier concentration may be referred to as a high-purity intrinsic or substantially high-purity intrinsic oxide semiconductor.

[0237] Furthermore, a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film has a low density of defect states, and therefore the density of trap states might also be low.

[0238] In addition, charges trapped in the trap states of an oxide semiconductor take a long time to disappear and may behave as if they are fixed charges. Therefore, a transistor in which a channel formation region is formed in an oxide semiconductor with a high density of trap states may have unstable electrical characteristics.

[0239] Therefore, in order to stabilize the electrical characteristics of a transistor, it is effective to reduce the impurity concentration in the oxide semiconductor. In order to reduce the impurity concentration in the oxide semiconductor, it is preferable to also reduce the impurity concentration in a nearby film. Examples of impurities include hydrogen, nitrogen, alkali metals, alkaline earth metals, iron, nickel, silicon, and the like.

[0240] <Impurities in metal oxides> Here, the influence of each impurity in a metal oxide (oxide semiconductor) will be described.

[0241] When an oxide semiconductor contains silicon or carbon, which is one of the Group 14 elements, defect levels are formed in the oxide semiconductor. For this reason, the concentration of silicon or carbon in the channel formation region of the oxide semiconductor and the concentration of silicon or carbon near the interface with the channel formation region of the oxide semiconductor (concentration obtained by secondary ion mass spectrometry (SIMS)) are set to 2×10 18 atoms / cm 3 Less than or equal to 2×10 17 atoms / cm 3 The following applies.

[0242] In addition, when an oxide semiconductor contains an alkali metal or an alkaline earth metal, defect levels are formed and carriers are generated in some cases. Therefore, a transistor using an oxide semiconductor containing an alkali metal or an alkaline earth metal is likely to have normally-on characteristics. For this reason, when the concentration of the alkali metal or the alkaline earth metal in the channel formation region of the oxide semiconductor obtained by SIMS is set to 1×10 18 atoms / cm 3 Less than or equal to 2×10 16 atoms / cm 3 To the following:

[0243] Furthermore, when nitrogen is contained in an oxide semiconductor, electrons serving as carriers are generated, the carrier concentration increases, and the semiconductor is likely to become n-type. As a result, a transistor using an oxide semiconductor containing nitrogen as a semiconductor is likely to have normally-on characteristics. Alternatively, when nitrogen is contained in an oxide semiconductor, trap states may be formed. As a result, the electrical characteristics of the transistor may become unstable. For this reason, the nitrogen concentration in the channel formation region of the oxide semiconductor obtained by SIMS is set to 5×10 19 atoms / cm 3 Less than 5 x 10 18 atoms / cm 3 Less than or equal to 1×10 18 atoms / cm 3 Less than 5×10, more preferably 17 atoms / cm 3 To the following:

[0244] Furthermore, hydrogen contained in the oxide semiconductor reacts with oxygen bonded to a metal atom to form water, which may form an oxygen vacancy. When hydrogen enters the oxygen vacancy, electrons serving as carriers may be generated. In addition, some of the hydrogen may bond with oxygen bonded to a metal atom to generate electrons serving as carriers. Therefore, a transistor using an oxide semiconductor containing hydrogen is likely to have normally-on characteristics. For this reason, it is preferable to reduce hydrogen in the channel formation region of the oxide semiconductor as much as possible. Specifically, the hydrogen concentration measured by SIMS in the channel formation region of the oxide semiconductor is 1×10 20 atoms / cm 3 Less than 5 x 10 19 atoms / cm 3 less than 1×10 19 atoms / cm 3 less than 5×10 18 atoms / cm 3 less than 1×10 18 atoms / cm 3 Make it less than.

[0245] When an oxide semiconductor in which impurities are sufficiently reduced is used for a channel formation region of a transistor, stable electrical characteristics can be obtained.

[0246] <Other materials that can be used for the semiconductor layer of transistors> One embodiment of the present invention is not limited to the above metal oxide. For example, a layered substance may be used. A layered substance has high electrical conductivity within a unit layer, that is, high two-dimensional electrical conductivity. By using a material that functions as a semiconductor and has high two-dimensional electrical conductivity for a channel formation region, a transistor with a large on-state current can be provided.

[0247] Layered materials include graphene, silicene, and chalcogenides. Chalcogenides are compounds that contain chalcogen. Chalcogen is a general term for elements in group 16, including oxygen, sulfur, selenium, tellurium, polonium, and livermorium. Chalcogenides include transition metal chalcogenides and group 13 chalcogenides.

[0248] For example, a transition metal chalcogenide that functions as a semiconductor is preferably used as the semiconductor layer of a transistor. Specifically, molybdenum sulfide (representatively, MoS 2 ), molybdenum selenide (represented by MoSe 2 ), molybdenum tellurium (represented by MoTe 2 ), tungsten sulfide (represented by WS 2 ), tungsten selenide (represented by WSe 2 ), tungsten tellurium (represented by WTe 2 ), hafnium sulfide (represented by HfS 2 ), hafnium selenide (represented by HfSe 2 ), zirconium sulfide (typically ZrS 2 ), zirconium selenide (represented by ZrSe 2 ) etc.

[0249] The structures, methods, and the like described in this embodiment can be used in appropriate combination with other structures, methods, and the like described in this embodiment or structures, methods, and the like described in other embodiments.

[0250] (Embodiment 2) In this embodiment, an example of a semiconductor device including the transistor 200 using the metal oxide described in the above embodiment and a manufacturing method thereof will be described with reference to FIGS.

[0251] <Example of semiconductor device configuration> A configuration of a semiconductor device having a transistor 200 will be described with reference to FIG. 14. FIGS. 14A to 14D are a top view and a cross-sectional view of a semiconductor device having a transistor 200. FIG. 14A is a top view of the semiconductor device. FIGS. 14B to 14D are cross-sectional views of the semiconductor device. FIG. 14B is a cross-sectional view of a portion indicated by a dashed line A1-A2 in FIG. 14A, and is also a cross-sectional view of the transistor 200 in the channel length direction. FIG. 14C is a cross-sectional view of a portion indicated by a dashed line A3-A4 in FIG. 14A, and is also a cross-sectional view of the transistor 200 in the channel width direction. FIG. 14D is a cross-sectional view of a portion indicated by a dashed line A5-A6 in FIG. 14A. Note that some elements are omitted in the top view of FIG. 14A for clarity.

[0252] The semiconductor device of one embodiment of the present invention includes an insulator 212 on a substrate (not shown), an insulator 214 on the insulator 212, a transistor 200 on the insulator 214, an insulator 280 on the transistor 200, an insulator 282 on the insulator 280, an insulator 283 on the insulator 282, and an insulator 285 on the insulator 283. The insulators 212, 214, 280, 282, 283, and 285 function as interlayer insulating films. The semiconductor device also includes a conductor 240 (conductor 240a and conductor 240b) that is electrically connected to the transistor 200 and functions as a plug. Note that an insulator 241 (insulator 241a and insulator 241b) is provided in contact with a side surface of the conductor 240 that functions as a plug. In addition, on the insulator 285 and the conductor 240, a conductor 246 (conductor 246a and conductor 246b) is provided which is electrically connected to the conductor 240 and functions as wiring.

[0253] Insulator 241a is provided in contact with the inner wall of the opening of insulator 280, insulator 282, insulator 283, and insulator 285, and conductor 240a is provided in contact with the side of insulator 241a. Insulator 241b is provided in contact with the inner wall of the opening of insulator 280, insulator 282, insulator 283, and insulator 285, and conductor 240b is provided in contact with the side of insulator 241b. Insulator 241 has a structure in which a first insulator is provided in contact with the inner wall of the opening, and a second insulator is provided further inward. In addition, conductor 240 has a structure in which a first conductor is provided in contact with the side of insulator 241, and a second conductor is provided further inward.

[0254] In the transistor 200, a configuration in which the first insulator of the insulator 241 and the second insulator of the insulator 241 are stacked is shown, but the present invention is not limited to this. For example, the insulator 241 may be provided as a single layer or a stacked structure of three or more layers. In the transistor 200, a configuration in which the first conductor of the conductor 240 and the second conductor of the conductor 240 are stacked is shown, but the present invention is not limited to this. For example, the conductor 240 may be provided as a single layer or a stacked structure of three or more layers. When a structure has a stacked structure, an ordinal number may be given to the order of formation to distinguish them.

[0255] [Transistor 200] As shown in FIGS. 14A to 14D , the transistor 200 includes an insulator 216 on an insulator 214, a conductor 205 (conductor 205a and conductor 205b) disposed so as to be embedded in the insulator 216, an insulator 222 on the insulator 216 and on the conductor 205, an insulator 224 on the insulator 222, an oxide 230a on the insulator 224, an oxide 230b on the oxide 230a, a conductor 242a on the oxide 230b, an insulator 271a on the conductor 242a, and an oxide 272a on the oxide 272b. conductor 242b on oxide 230b, insulator 271b on conductor 242b, insulator 250 (insulator 250a and insulator 250b) on oxide 230b, conductor 260 (conductor 260a and conductor 260b) located on insulator 250 and overlapping part of oxide 230b, and insulator 275 arranged to cover insulator 222, insulator 224, oxide 230a, oxide 230b, conductor 242a, conductor 242b, insulator 271a, and insulator 271b.

[0256] In the following, the oxide 230a and the oxide 230b may be collectively referred to as the oxide 230. Furthermore, the conductor 242a and the conductor 242b may be collectively referred to as the conductor 242. Furthermore, the insulator 271a and the insulator 271b may be collectively referred to as the insulator 271.

[0257] An opening reaching the oxide 230b is provided in the insulator 280 and the insulator 275. The insulator 250 and the conductor 260 are disposed in the opening. In addition, in the channel length direction of the transistor 200, the conductor 260 and the insulator 250 are provided between the insulator 271a and the conductor 242a and the insulator 271b and the conductor 242b. The insulator 250 has a region in contact with a side surface of the conductor 260 and a region in contact with a bottom surface of the conductor 260.

[0258] The oxide 230 preferably has an oxide 230a disposed on the insulator 224 and an oxide 230b disposed on the oxide 230a. By having the oxide 230a below the oxide 230b, it is possible to suppress the diffusion of impurities from a structure formed below the oxide 230a to the oxide 230b.

[0259] Note that, in the transistor 200, the oxide 230 has a structure in which two layers of the oxide 230a and the oxide 230b are stacked, but the present invention is not limited to this. For example, the oxide 230b may have a single layer or a stacked structure of three or more layers, or each of the oxide 230a and the oxide 230b may have a stacked structure.

[0260] The conductor 260 functions as a first gate (also referred to as a top gate) electrode, and the conductor 205 functions as a second gate (also referred to as a back gate) electrode. The insulator 250 functions as a first gate insulating film, and the insulators 224 and 222 function as a second gate insulating film. The conductor 242a functions as one of a source electrode or a drain electrode, and the conductor 242b functions as the other of the source electrode or the drain electrode. At least a part of a region of the oxide 230 overlapping with the conductor 260 functions as a channel formation region.

[0261] In the transistor 200, the oxide 230 including the channel formation region (the oxide 230a and the oxide 230b) is preferably formed using the metal oxide (hereinafter also referred to as an oxide semiconductor) described in the above embodiment.

[0262] The metal oxide described in the above embodiment can function as a semiconductor. In this case, the metal oxide has a band gap of 2 eV or more, or 2.5 eV or more. By using such a metal oxide having a wide band gap, the off-state current of a transistor can be reduced.

[0263] As the oxide 230, for example, a metal oxide such as an In-M-Zn oxide having indium, an element M, and zinc (the element M is one or more selected from aluminum, gallium, yttrium, tin, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, etc.) may be used. Alternatively, as the oxide 230, an In-Ga oxide, an In-Zn oxide, or an indium oxide may be used.

[0264] Here, it is preferable that the atomic ratio of In to element M in the metal oxide used for the oxide 230b is greater than the atomic ratio of In to element M in the metal oxide used for the oxide 230a. For example, the metal oxide shown in FIG. 2D in the previous embodiment can be used as the oxide 230a. Also, for example, the metal oxide shown in FIG. 2B in the previous embodiment can be used as the oxide 230b.

[0265] In this manner, by disposing the oxide 230a below the oxide 230b, it is possible to suppress the diffusion of impurities and oxygen from structures formed below the oxide 230a into the oxide 230b.

[0266] In addition, the oxide 230a and the oxide 230b have a common element other than oxygen (as a main component), so that the defect state density at the interface between the oxide 230a and the oxide 230b can be reduced. Since the defect state density at the interface between the oxide 230a and the oxide 230b can be reduced, the effect of interface scattering on carrier conduction is small, and a high on-current can be obtained.

[0267] In addition, the oxide 230b is preferably crystalline. In particular, it is preferable to use a c-axis aligned crystalline oxide semiconductor (CAAC-OS) as the oxide 230b. By using the deposition method shown in the above embodiment, impurities are reduced and a CAAC-OS having good crystallinity can be formed.

[0268] CAAC-OS has a highly crystalline and dense structure and is free of impurities or defects (e.g., oxygen vacancies (V O ) is a metal oxide having a small amount of impurities. In particular, by performing heat treatment at a temperature at which the metal oxide does not become polycrystallized (for example, 400° C. or higher and 600° C. or lower) after the formation of the metal oxide, the CAAC-OS can have a dense structure with higher crystallinity. In this way, the density of the CAAC-OS can be increased, and the diffusion of impurities or oxygen in the CAAC-OS can be reduced.

[0269] On the other hand, it is difficult to identify clear grain boundaries in CAAC-OS, so it is said that the decrease in electron mobility caused by grain boundaries is unlikely to occur. Therefore, metal oxides with CAAC-OS have stable physical properties. Therefore, metal oxides with CAAC-OS are resistant to heat and highly reliable.

[0270] In addition, since a crystalline oxide such as CAAC-OS has few impurities or defects (such as oxygen vacancies) and a dense structure with high crystallinity, it is possible to suppress the extraction of oxygen from the oxide 230b by the source or drain electrode. As a result, even if a heat treatment is performed, the extraction of oxygen from the oxide 230b can be reduced, and the transistor 200 is stable against high temperatures (so-called thermal budget) in the manufacturing process.

[0271] Here, an enlarged view of the vicinity of the channel formation region of the transistor 200 is shown in FIG. 15A. When oxygen is supplied to the oxide 230b, a channel formation region is formed in a region between the conductor 242a and the conductor 242b. Thus, as shown in FIG. 15A, the oxide 230b has a region 230bc that functions as a channel formation region of the transistor 200, and regions 230ba and 230bb that are provided on either side of the region 230bc and function as a source region or a drain region. At least a portion of the region 230bc overlaps with the conductor 260. In other words, the region 230bc is provided in a region between the conductor 242a and the conductor 242b. The region 230ba is provided overlapping with the conductor 242a, and the region 230bb is provided overlapping with the conductor 242b.

[0272] The region 230bc, which functions as a channel formation region, is a high-resistance region with a low carrier concentration because it has fewer oxygen vacancies or a lower impurity concentration than the regions 230ba and 230bb. Therefore, the region 230bc can be said to be i-type (intrinsic) or substantially i-type.

[0273] Moreover, the regions 230ba and 230bb that function as source and drain regions have many oxygen vacancies and high concentrations of impurities such as hydrogen, nitrogen, and metal elements, which increases the carrier concentration and reduces resistance. That is, the regions 230ba and 230bb are n-type regions with a high carrier concentration and low resistance compared to the region 230bc.

[0274] Here, the carrier concentration of the region 230bc functioning as a channel forming region is 1×10 18 cm -3 It is preferable that the value is less than 1×10 17 cm -3 More preferably, it is less than 1×10 16 cm -3 More preferably, it is less than 1×10 13 cm -3 More preferably, it is less than 1×10 12 cm -3 The lower limit of the carrier concentration of the region 230bc that functions as a channel formation region is not particularly limited, but is, for example, 1×10 -9 cm -3 It can be said that:

[0275] In addition, a region having a carrier concentration equal to or lower than that of the region 230ba and the region 230bb, and equal to or higher than that of the region 230bc, may be formed between the region 230bc and the region 230ba or the region 230bb. That is, the region functions as a junction region between the region 230bc and the region 230ba or the region 230bb. The junction region may have a hydrogen concentration equal to or lower than that of the region 230ba and the region 230bb, and equal to or higher than that of the region 230bc. The junction region may have an oxygen vacancy equal to or less than that of the region 230ba and the region 230bb, and equal to or more than that of the region 230bc.

[0276] 15A shows an example in which the regions 230ba, 230bb, and 230bc are formed in the oxide 230b, but the present invention is not limited to this. For example, each of the above regions may be formed not only in the oxide 230b but also in the oxide 230a.

[0277] In addition, it may be difficult to clearly detect the boundaries between the regions in the oxide 230. The concentrations of metal elements, hydrogen, nitrogen, and other impurity elements detected in each region may not only vary stepwise from region to region, but may also vary continuously within each region. In other words, it is sufficient that the concentrations of metal elements, hydrogen, nitrogen, and other impurity elements decrease in the region closer to the channel formation region.

[0278] 14C , in a cross-sectional view in the channel width direction of the transistor 200, a curved surface may be formed between the side surface of the oxide 230b and the top surface of the oxide 230b. In other words, the end of the side surface and the end of the top surface may be curved (also referred to as rounded).

[0279] The radius of curvature of the curved surface is preferably greater than 0 nm and smaller than the film thickness of the oxide 230b in the region overlapping with the conductor 242, or smaller than half the length of the region not having the curved surface. Specifically, the radius of curvature of the curved surface is greater than 0 nm and less than 20 nm, preferably greater than 1 nm and less than 15 nm, and more preferably greater than 2 nm and less than 10 nm. By forming the curved surface in this manner, the coverage of the oxide 230b by the insulator 250 and the conductor 260 can be improved.

[0280] The oxide 230 preferably has a laminated structure of a plurality of oxide layers having different chemical compositions. Specifically, in the metal oxide used for the oxide 230a, the atomic ratio of element M to the metal element that is the main component is preferably larger than the atomic ratio of element M to the metal element that is the main component in the metal oxide used for the oxide 230b. In addition, in the metal oxide used for the oxide 230a, the atomic ratio of element M to In is preferably larger than the atomic ratio of element M to In in the metal oxide used for the oxide 230b. In addition, in the metal oxide used for the oxide 230b, the atomic ratio of In to element M is preferably larger than the atomic ratio of In to element M in the metal oxide used for the oxide 230a. By using the film formation method shown in the above embodiment, the oxide 230a and the oxide 230b having different atomic ratios can be continuously formed in a single chamber. This makes it possible to prevent impurities such as hydrogen from being excessively mixed into the interface between the oxide 230a and the oxide 230b.

[0281] Here, the conduction band minimum changes gradually at the junction between the oxide 230a and the oxide 230b. In other words, the conduction band minimum at the junction between the oxide 230a and the oxide 230b can be said to change continuously or to be a continuous junction. To achieve this, it is preferable to reduce the defect level density of the mixed layer formed at the interface between the oxide 230a and the oxide 230b.

[0282] Specifically, the oxide 230a and the oxide 230b have a common element other than oxygen as a main component, so that a mixed layer with a low density of defect states can be formed. For example, when the oxide 230b is an In-M-Zn oxide, the oxide 230a may be an In-M-Zn oxide, an M-Zn oxide, an oxide of element M, an In-Zn oxide, an indium oxide, or the like.

[0283] Specifically, the oxide 230a may be a metal oxide having a composition of In:M:Zn=1:3:4 [atomic ratio] or a composition close thereto, or In:M:Zn=1:1:0.5 [atomic ratio] or a composition close thereto. The oxide 230b may be a metal oxide having a composition of In:M:Zn=1:1:1 [atomic ratio] or a composition close thereto, or In:M:Zn=4:2:3 [atomic ratio] or a composition close thereto, or In:M:Zn=5:1:3 [atomic ratio] or a composition close thereto. The composition close thereto includes a range of ±30% of the desired atomic ratio. Gallium is preferably used as the element M. By using the film formation method shown in the previous embodiment, metal oxides having various atomic ratios as described above can be formed relatively easily.

[0284] By configuring the oxide 230a and the oxide 230b as described above, the defect state density at the interface between the oxide 230a and the oxide 230b can be reduced, so that the effect of interface scattering on carrier conduction is reduced, and the transistor 200 can obtain a large on-current and high frequency characteristics.

[0285] In the transistor 200, the oxide 230 has a two-layer structure of the oxide 230a and the oxide 230b, but the present invention is not limited to this. For example, the oxide 230b may have a single layer or a stacked structure of three or more layers. The oxide 230a and the oxide 230b may each have a stacked structure. When the oxide 230 has a stacked structure of three or more layers, a part of the stacked structure of the oxide 230 may be formed in the openings formed in the insulator 280 and the insulator 275, as in the case of the insulator 250.

[0286] At least one of the insulators 212, 214, 271, 275, 282, and 283 preferably functions as a barrier insulating film that suppresses the diffusion of impurities such as water and hydrogen from the substrate side or from above the transistor 200 to the transistor 200. Therefore, at least one of the insulators 212, 214, 271, 275, 282, and 283 preferably suppresses the diffusion of impurities such as hydrogen, hydrogen, and nitrogen atoms, hydrogen molecules, water molecules, nitrogen atoms, nitrogen molecules, and nitrogen oxide molecules (N 2 O, NO, NO 2 It is preferable to use an insulating material that has a function of suppressing the diffusion of impurities such as copper atoms (the impurities are unlikely to permeate through the insulating material), or that has a function of suppressing the diffusion of oxygen (for example, at least one of oxygen atoms, oxygen molecules, etc.) (the oxygen is unlikely to permeate through the insulating material).

[0287] In this specification, a barrier insulating film refers to an insulating film having a barrier property. In this specification, the barrier property refers to a function of suppressing the diffusion of a corresponding substance (also referred to as low permeability) or a function of capturing and fixing a corresponding substance (also referred to as gettering).

[0288] For example, aluminum oxide, magnesium oxide, hafnium oxide, gallium oxide, indium gallium zinc oxide, silicon nitride, or silicon nitride oxide can be used for the insulators 212, 214, 271, 275, 282, and 283. For example, it is preferable to use silicon nitride or the like, which has a higher hydrogen barrier property, for the insulators 212, 275, and 283. For example, it is preferable to use aluminum oxide or magnesium oxide, which has a higher function of capturing and fixing hydrogen, for the insulators 214, 271, and 282. This can suppress impurities such as water and hydrogen from diffusing from the substrate side to the transistor 200 side through the insulators 212 and 214. Alternatively, it is possible to suppress impurities such as water and hydrogen from diffusing from an interlayer insulating film disposed outside the insulator 283 to the transistor 200 side. Alternatively, oxygen contained in the insulator 224 or the like can be suppressed from diffusing toward the substrate side through the insulator 212 and the insulator 214. Alternatively, oxygen contained in the insulator 280 or the like can be suppressed from diffusing upward from the transistor 200 through the insulator 282 or the like. In this manner, it is preferable to have a structure in which the transistor 200 is surrounded by the insulators 212, 214, 271, 275, 282, and 283, which have a function of suppressing the diffusion of impurities such as water and hydrogen, and oxygen.

[0289] Here, it is preferable to use an oxide having an amorphous structure as at least one of the insulators 212, 214, 271, 275, 282, and 283. For example, AlO x (x is any number greater than 0), or MgO yIt is preferable to use a metal oxide such as y (y is any number greater than 0). In such a metal oxide having an amorphous structure, oxygen atoms have dangling bonds, and the dangling bonds may have the property of capturing or fixing hydrogen. By using such a metal oxide having an amorphous structure as a component of the transistor 200 or providing it around the transistor 200, hydrogen contained in the transistor 200 or hydrogen present around the transistor 200 can be captured or fixed. In particular, it is preferable to capture or fix hydrogen contained in the channel formation region of the transistor 200. By using a metal oxide having an amorphous structure as a component of the transistor 200 or providing it around the transistor 200, a transistor 200 and a semiconductor device having good characteristics and high reliability can be manufactured.

[0290] At least one of the insulators 212, 214, 271, 275, 282, and 283 is preferably an amorphous structure, but may have a polycrystalline structure region in a portion thereof. At least one of the insulators 212, 214, 271, 275, 282, and 283 may have a multilayer structure in which a layer of an amorphous structure and a layer of a polycrystalline structure are stacked. For example, a layered structure in which a layer of a polycrystalline structure is formed on a layer of an amorphous structure may be used.

[0291] The insulators 212, 214, 271, 275, 282, and 283 may be formed by, for example, a sputtering method. Since the sputtering method does not require the use of hydrogen in the film formation gas, the hydrogen concentration of the insulators 212, 214, 271, 275, 282, and 283 can be reduced. Note that the film formation method is not limited to the sputtering method, and a chemical vapor deposition (CVD) method, a molecular beam epitaxy (MBE) method, a pulsed laser deposition (PLD) method, an atomic layer deposition (ALD) method, or the like may be used as appropriate. For example, the insulator 275 may be formed by an ALD method, which has relatively good coverage. Among the ALD methods, the PEALD method, which can reduce the film formation temperature, may be used.

[0292] In addition, it may be preferable to reduce the resistivity of the insulator 212 and the insulator 283. For example, it is preferable to reduce the resistivity of the insulator 212 and the insulator 283 to approximately 1×10 13 By setting the resistivity at Ωcm, the insulator 212 and the insulator 283 may be able to reduce charge-up of the conductor 205, the conductor 242, the conductor 260, or the conductor 246 in a process using plasma or the like in a semiconductor device manufacturing process. 10 Ωcm or more 1×10 15 Ωcm or less.

[0293] The insulator 216 and the insulator 280 preferably have a lower dielectric constant than the insulator 214. By using a material with a low dielectric constant as an interlayer insulating film, the parasitic capacitance generated between wirings can be reduced. For example, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide to which fluorine has been added, silicon oxide to which carbon has been added, silicon oxide to which carbon and nitrogen have been added, silicon oxide having vacancies, or the like may be used as the insulator 216 and the insulator 280 as appropriate.

[0294] The conductor 205 is disposed so as to overlap the oxide 230 and the conductor 260. Here, the conductor 205 is preferably provided by being embedded in an opening formed in the insulator 216. Also, a part of the conductor 205 may be embedded in the insulator 214.

[0295] The conductor 205 includes conductor 205a and conductor 205b. The conductor 205a is provided in contact with the bottom surface and side wall of the opening. The conductor 205b is provided so as to be embedded in a recess formed in the conductor 205a. Here, the height of the upper surface of the conductor 205b is approximately the same as the height of the top of the conductor 205a and the height of the upper surface of the insulator 216.

[0296] Here, the conductor 205a is a hydrogen atom, a hydrogen molecule, a water molecule, a nitrogen atom, a nitrogen molecule, a nitrogen oxide molecule (N 2 O, NO, NO 2 It is preferable to use a conductive material having a function of suppressing the diffusion of impurities such as copper atoms, etc., or oxygen (e.g., at least one of oxygen atoms, oxygen molecules, etc.).

[0297] By using a conductive material having a function of reducing hydrogen diffusion for the conductor 205a, it is possible to prevent impurities such as hydrogen contained in the conductor 205b from diffusing into the oxide 230 via the insulator 224 and the like. In addition, by using a conductive material having a function of suppressing oxygen diffusion for the conductor 205a, it is possible to suppress the conductor 205b from being oxidized and its conductivity from decreasing. As the conductive material having a function of suppressing oxygen diffusion, it is preferable to use, for example, titanium, titanium nitride, tantalum, tantalum nitride, ruthenium, ruthenium oxide, or the like. Therefore, the conductor 205a may be a single layer or a multilayer of the above conductive material. For example, the conductor 205a may be made of titanium nitride.

[0298] The conductor 205b is preferably made of a conductive material containing tungsten, copper, or aluminum as a main component, for example, tungsten.

[0299] The conductor 205 may function as a second gate electrode. In this case, the threshold voltage (Vth) of the transistor 200 can be controlled by changing the potential applied to the conductor 205 independently of the potential applied to the conductor 260. In particular, by applying a negative potential to the conductor 205, the Vth of the transistor 200 can be increased and the off-current can be reduced compared to when no potential is applied to the conductor 205. Therefore, the drain current when the potential applied to the conductor 260 is 0 V can be reduced by applying a negative potential to the conductor 205 compared to when no potential is applied.

[0300] As shown in FIG. 14A, the conductor 205 is preferably larger than the size of the region of the oxide 230 that does not overlap with the conductor 242a and the conductor 242b. In particular, as shown in FIG. 14C, the conductor 205 preferably extends to the region outside the end of the oxide 230a and the oxide 230b that intersects with the channel width direction. In other words, the conductor 205 and the conductor 260 preferably overlap with each other via an insulator on the outside of the side surface of the oxide 230 in the channel width direction. With this configuration, the channel formation region of the oxide 230 can be electrically surrounded by the electric field of the conductor 260 that functions as the first gate electrode and the electric field of the conductor 205 that functions as the second gate electrode. In this specification, a structure of a transistor in which the channel formation region is electrically surrounded by the electric fields of the first gate and the second gate is called a surrounded channel (S-channel) structure.

[0301] In this specification and the like, a transistor with an S-channel structure refers to a transistor structure in which a channel formation region is electrically surrounded by the electric fields of one and the other of a pair of gate electrodes. The S-channel structure disclosed in this specification and the like is different from a fin type structure and a planar type structure. By adopting the S-channel structure, it is possible to improve resistance to the short channel effect, in other words, to make a transistor in which the short channel effect is unlikely to occur.

[0302] 14C, the conductor 205 is extended to function as a wiring. However, the present invention is not limited to this, and a conductor functioning as a wiring may be provided below the conductor 205. Also, it is not necessary to provide one conductor 205 for each transistor. For example, the conductor 205 may be shared by multiple transistors.

[0303] Note that, although the conductor 205 in the transistor 200 has a stacked structure of the conductor 205a and the conductor 205b, the present invention is not limited to this. For example, the conductor 205 may have a single layer or a stacked structure of three or more layers.

[0304] The insulators 222 and 224 function as gate insulating films.

[0305] The insulator 222 preferably has a function of suppressing the diffusion of hydrogen (e.g., at least one of hydrogen atoms, hydrogen molecules, etc.). The insulator 222 preferably has a function of suppressing the diffusion of oxygen (e.g., at least one of oxygen atoms, oxygen molecules, etc.). For example, the insulator 222 preferably has a function of suppressing the diffusion of one or both of hydrogen and oxygen more than the insulator 224.

[0306] The insulator 222 may be an insulator containing an oxide of one or both of aluminum and hafnium, which are insulating materials. As the insulator, it is preferable to use aluminum oxide, hafnium oxide, an oxide containing aluminum and hafnium (hafnium aluminate), or the like. When the insulator 222 is formed using such a material, the insulator 222 functions as a layer that suppresses release of oxygen from the oxide 230 to the substrate side, or diffusion of impurities such as hydrogen from the periphery of the transistor 200 to the oxide 230. Thus, by providing the insulator 222, it is possible to suppress diffusion of impurities such as hydrogen into the inside of the transistor 200 and suppress generation of oxygen vacancies in the oxide 230. In addition, it is possible to suppress reaction of the conductor 205 with oxygen contained in the insulator 224 or the oxide 230.

[0307] Alternatively, for example, aluminum oxide, bismuth oxide, germanium oxide, niobium oxide, silicon oxide, titanium oxide, tungsten oxide, yttrium oxide, or zirconium oxide may be added to the insulator. Alternatively, these insulators may be nitrided. The insulator 222 may be formed by stacking silicon oxide, silicon oxynitride, or silicon nitride on these insulators.

[0308] The insulator 222 may be made of, for example, aluminum oxide, hafnium oxide, tantalum oxide, zirconium oxide, lead zirconate titanate (PZT), strontium titanate (SrTiO 3 ), (Ba,Sr)TiO 3 Insulators containing so-called high-k materials such as (BST) may be used in a single layer or a multilayer. As transistors become smaller and more highly integrated, problems such as leakage current may occur due to the thinning of the gate insulator. By using a high-k material for the insulator that functions as the gate insulator, it is possible to reduce the gate potential during transistor operation while maintaining the physical film thickness.

[0309] The insulator 224 in contact with the oxide 230 may be made of, for example, silicon oxide, silicon oxynitride, or the like as appropriate. By providing the insulator 224 containing oxygen in contact with the oxide 230, oxygen vacancies in the oxide 230 can be reduced and the reliability of the transistor 200 can be improved. The insulator 224 is preferably processed into an island shape so as to overlap with the oxide 230a. In this case, the insulator 275 is configured to be in contact with the side surface of the insulator 224 and the top surface of the insulator 222. With this configuration, the volume of the insulator 224 can be significantly reduced and the insulator 224 and the insulator 280 can be separated by the insulator 275. Therefore, the oxygen contained in the insulator 280 can be diffused into the insulator 224, and the oxygen in the insulator 224 can be prevented from becoming excessive.

[0310] The insulator 222 and the insulator 224 may have a laminated structure of two or more layers. In that case, the laminated structure is not limited to being made of the same material, and may be made of different materials. Although FIG. 14B and other figures show a configuration in which the insulator 224 is formed in an island shape by overlapping with the oxide 230a, the present invention is not limited to this. If the amount of oxygen contained in the insulator 224 can be appropriately adjusted, the insulator 224 may be configured not to be patterned, similar to the insulator 222.

[0311] In addition, in the manufacturing process of the transistor 200, it is preferable to perform heat treatment while the surface of the oxide 230 is exposed. The heat treatment may be performed, for example, at a temperature of 100° C. or higher and 600° C. or lower, more preferably 350° C. or higher and 550° C. or lower. Note that the heat treatment is performed in an atmosphere of nitrogen gas or an inert gas, or an atmosphere containing an oxidizing gas at 10 ppm or higher, 1% or higher, or 10% or higher. For example, the heat treatment is preferably performed in an oxygen atmosphere. This supplies oxygen to the oxide 230 to reduce oxygen deficiencies (V O) can be reduced. The heat treatment may be performed under reduced pressure. Alternatively, the heat treatment may be performed in an atmosphere containing 10 ppm or more, 1% or more, or 10% or more of an oxidizing gas in order to compensate for the desorbed oxygen after the heat treatment in a nitrogen gas or inert gas atmosphere. Alternatively, the heat treatment may be performed in an atmosphere containing 10 ppm or more, 1% or more, or 10% or more of an oxidizing gas in order to compensate for the desorbed oxygen. Alternatively, the heat treatment may be performed in an atmosphere containing 10 ppm or more, 1% or more, or 10% or more of an oxidizing gas in succession to a heat treatment in a nitrogen gas or inert gas atmosphere.

[0312] In addition, by subjecting the oxide 230 to an oxygen addition treatment, the oxygen vacancies in the oxide 230 are repaired by the supplied oxygen. In other words, O +O→null. Furthermore, the reaction of the supplied oxygen with the hydrogen remaining in the oxide 230 can be accelerated to convert the hydrogen into H 2 O. This causes the hydrogen remaining in the oxide 230 to recombine with the oxygen vacancies and form V. O The formation of H can be suppressed.

[0313] The conductor 242a and the conductor 242b are preferably provided in contact with the top surface of the oxide 230b. The conductor 242a and the conductor 242b function as a source electrode and a drain electrode of the transistor 200, respectively.

[0314] As the conductor 242 (conductor 242a and conductor 242b), for example, a nitride containing tantalum, a nitride containing titanium, a nitride containing molybdenum, a nitride containing tungsten, a nitride containing tantalum and aluminum, a nitride containing titanium and aluminum, or the like is preferably used. In one embodiment of the present invention, a nitride containing tantalum is particularly preferable. Also, for example, ruthenium oxide, ruthenium nitride, an oxide containing strontium and ruthenium, an oxide containing lanthanum and nickel, or the like may be used. These materials are preferable because they are conductive materials that are difficult to oxidize, or materials that maintain their conductivity even when they absorb oxygen.

[0315] Here, it is preferable to use a film having a large compressive stress as the conductor 242, for example, a tantalum nitride film formed by sputtering. The stress of the conductor 242 causes distortion in the crystal structure of the regions 230ba and 230bb, which causes oxygen deficiency (V O ) is easily formed. As a result, V O Since the amount of H increases, the carrier concentration in the regions 230ba and 230bb can be increased to make them n-type.

[0316] Note that hydrogen contained in the oxide 230b etc. may diffuse into the conductor 242a or the conductor 242b. In particular, by using a nitride containing tantalum for the conductor 242a and the conductor 242b, hydrogen contained in the oxide 230b etc. is likely to diffuse into the conductor 242a or the conductor 242b, and the diffused hydrogen may bond with nitrogen contained in the conductor 242a or the conductor 242b. In other words, hydrogen contained in the oxide 230b etc. may be absorbed by the conductor 242a or the conductor 242b.

[0317] Moreover, it is preferable that no curved surface is formed between the side surface of the conductor 242 and the top surface of the conductor 242. By forming the conductor 242 without such a curved surface, it is possible to increase the cross-sectional area of ​​the conductor 242 in the cross section in the channel width direction as shown in Fig. 14D. This can increase the conductivity of the conductor 242 and the on-current of the transistor 200.

[0318] The insulator 271a is provided in contact with the upper surface of the conductor 242a, and the insulator 271b is provided in contact with the upper surface of the conductor 242b. The insulator 271 preferably has a function of capturing impurities such as hydrogen. In that case, an insulator such as a metal oxide having an amorphous structure, for example, aluminum oxide or magnesium oxide, may be used as the insulator 271. In particular, it is preferable to use aluminum oxide having an amorphous structure or aluminum oxide having an amorphous structure as the insulator 271, because hydrogen can be captured or fixed more effectively. This makes it possible to manufacture a transistor 200 and a semiconductor device having excellent characteristics and high reliability.

[0319] The insulator 271 preferably functions as a barrier insulating film against oxygen. Therefore, the insulator 271 preferably has a function of suppressing oxygen diffusion. For example, the insulator 271 preferably has a function of suppressing oxygen diffusion more than the insulator 280. In this case, the insulator 271 may be, for example, a nitride containing silicon, such as silicon nitride.

[0320] The insulator 275 is provided in contact with the upper surface of the insulator 222, the side surface of the insulator 224, the side surface of the oxide 230a, the side surface of the oxide 230b, the side surface of the conductor 242, and the side surface and upper surface of the insulator 271. The insulator 275 has openings formed in the regions where the insulator 250 and the conductor 260 are provided.

[0321] The insulator 275 preferably functions as a barrier insulating film that suppresses oxygen permeation. The insulator 275 preferably functions as a barrier insulating film that suppresses the diffusion of impurities such as water and hydrogen, and preferably has a function of capturing impurities such as hydrogen. The insulator 275 may be, for example, a single layer or a stack of insulators such as aluminum oxide or silicon nitride. For example, an aluminum oxide film having an amorphous structure may be provided, and a silicon nitride film may be stacked thereon. Such a stacked structure is preferable because it can enhance the barrier properties against hydrogen and oxygen more than a single layer of an aluminum oxide film or a single layer of a silicon nitride film.

[0322] By providing the insulators 271 and 275 as described above, the conductor 242 can be wrapped in an insulator having a barrier property against oxygen. That is, it is possible to prevent oxygen contained in the insulators 224, 280, and 250a from diffusing into the conductor 242. This makes it possible to suppress a decrease in on-current due to an increase in resistivity caused by direct oxidation of the conductor 242 caused by the oxygen contained in the insulators 224, 280, and 250a.

[0323] Furthermore, by providing insulators 214, 271, and 275, which have the function of capturing impurities such as hydrogen, in the region sandwiched between insulators 212 and 275, impurities such as hydrogen contained in insulator 224 or insulator 216 can be captured and the amount of hydrogen in the region can be kept constant. In this case, it is preferable that at least a portion of insulator 275 contains aluminum oxide with an amorphous structure.

[0324] The insulator 250 has an insulator 250a and an insulator 250b on the insulator 250a, and functions as a gate insulating film. The insulator 250a is preferably disposed in contact with the top surface of the oxide 230b and the side surface of the insulator 280. The thickness of the insulator 250 is preferably 1 nm or more and 20 nm or less.

[0325] The insulator 250a may be made of silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide doped with fluorine, silicon oxide having vacancies, etc. In particular, silicon oxide and silicon oxynitride are preferred because they are stable against heat. Note that the insulator 250a is preferably one having a low carbon content in the film.

[0326] However, one embodiment of the present invention is not limited thereto, and the insulator 250a may contain carbon. For example, the carbon concentration of the insulator 250a is preferably 1×10 18 atoms / cm 3 5×10 or more 20 atoms / cm 3 Less than or equal to 5×10 18 atoms / cm 3 More than 1×10 20 atoms / cm 3 The carbon concentration in the film of the insulator 250a can be measured by SIMS analysis or the like.

[0327] Similar to the insulator 224, the insulator 250a preferably has a reduced concentration of impurities such as water and hydrogen.

[0328] It is preferable that the insulator 250a is formed using an insulator through which oxygen can easily diffuse when heated, and the insulator 250b is formed using an insulator that has a function of suppressing the diffusion of oxygen. With this configuration, when the oxygen contained in the insulator 250a is diffused, the diffusion of oxygen to the conductor 260 can be suppressed. In other words, a decrease in the amount of oxygen supplied to the oxide 230 can be suppressed. In addition, the oxidation of the conductor 260 due to the oxygen contained in the insulator 250a can be suppressed. For example, the insulator 250b can be provided using the same material as the insulator 222.

[0329] When silicon oxide or silicon oxynitride is used for the insulator 250a, the insulator 250b may be an insulating material that is a high-k material with a high dielectric constant. The gate insulator can be made into a laminated structure of the insulators 250a and 250b, which is stable against heat and has a high dielectric constant. This makes it possible to reduce the gate potential applied during transistor operation while maintaining the physical thickness of the gate insulator. It also makes it possible to reduce the equivalent oxide thickness (EOT) of the insulator that functions as the gate insulator.

[0330] Specifically, the insulator 250b may be a metal oxide containing one or more of hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, magnesium, or the like, or a metal oxide that can be used as the oxide 230. In particular, it is preferable to use an insulator containing an oxide of one or both of aluminum and hafnium. It is preferable to use aluminum oxide, hafnium oxide, an oxide containing aluminum and hafnium (hafnium aluminate), or the like, as the insulator. Alternatively, the insulator 250b may be a stacked film in which a hafnium oxide film and a silicon nitride film are provided on the hafnium oxide film.

[0331] In addition, in FIG. 14B and FIG. 14C, the insulator 250 is illustrated as a two-layer laminated structure, but the present invention is not limited thereto. The insulator 250 may be a single layer or a laminated structure of three or more layers. For example, as shown in FIG. 15B, a configuration may be adopted in which an insulator 250c is provided between the insulator 250b and the conductor 260a. As the insulator 250c, an insulator that can be used for the insulator 283 described above may be used. As the insulator 250c, it is preferable to use a barrier insulating film against hydrogen. This can prevent impurities such as hydrogen contained in the conductor 260 from diffusing into the insulator 250b, the insulator 250a, and the oxide 230b. For example, silicon nitride formed by the PEALD method may be used as the insulator 250c.

[0332] Furthermore, a metal oxide may be provided between the insulator 250 and the conductor 260. The metal oxide preferably suppresses the diffusion of oxygen from the insulator 250 to the conductor 260. By providing a metal oxide that suppresses the diffusion of oxygen, the diffusion of oxygen from the insulator 250 to the conductor 260 is suppressed. In other words, a decrease in the amount of oxygen supplied to the oxide 230 can be suppressed. Furthermore, oxidation of the conductor 260 due to oxygen from the insulator 250 can be suppressed.

[0333] The metal oxide may be configured to function as a part of the first gate electrode. For example, the metal oxide that can be used as the oxide 230 may be used as the metal oxide. In this case, the electric resistance value of the metal oxide can be reduced to make it a conductor by forming the conductor 260a by a sputtering method. This can be called an OC (Oxide Conductor) electrode.

[0334] By including the metal oxide, the on-state current of the transistor 200 can be improved without weakening the influence of the electric field from the conductor 260.

[0335] The conductor 260 is provided on the insulator 250b and functions as a first gate electrode of the transistor 200. The conductor 260 preferably includes a conductor 260a and a conductor 260b disposed on the conductor 260a. For example, the conductor 260a is preferably disposed so as to surround the bottom and side surfaces of the conductor 260b. As shown in FIGS. 14B and 14C, the top surface of the conductor 260 is substantially flush with the top surface of the insulator 250. Note that, although the conductor 260 is shown as having a two-layer structure of the conductor 260a and the conductor 260b in FIGS. 14B and 14C, the conductor 260 may have a single-layer structure or a stacked structure of three or more layers.

[0336] The conductor 260a is preferably made of a conductive material having a function of suppressing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, nitrogen atoms, nitrogen molecules, nitrogen oxide molecules, copper atoms, etc. Alternatively, it is preferably made of a conductive material having a function of suppressing the diffusion of oxygen (for example, at least one of oxygen atoms, oxygen molecules, etc.).

[0337] Furthermore, since the conductor 260a has a function of suppressing oxygen diffusion, it is possible to suppress a decrease in conductivity due to oxidation of the conductor 260b caused by oxygen contained in the insulator 250. As a conductive material having a function of suppressing oxygen diffusion, it is preferable to use, for example, titanium, titanium nitride, tantalum, tantalum nitride, ruthenium, ruthenium oxide, or the like.

[0338] In addition, since the conductor 260 also functions as wiring, it is preferable to use a conductor with high conductivity. For example, the conductor 260b can be a conductive material mainly composed of tungsten, copper, or aluminum. The conductor 260b may also have a laminated structure, for example, a laminated structure of titanium or titanium nitride and the above-mentioned conductive material.

[0339] In addition, in the transistor 200, the conductor 260 is formed in a self-aligned manner so as to fill an opening formed in the insulator 280 or the like. By forming the conductor 260 in this manner, the conductor 260 can be reliably disposed in the region between the conductor 242a and the conductor 242b without alignment. Note that, as shown in FIG. 15A and other figures, when the upper part of the opening is wider than the lower part of the opening, the conductor 260 also has a shape wider than the lower part.

[0340] 14C, in the channel width direction of the transistor 200, the height of the bottom surface of the conductor 260 in the region where the conductor 260 and the oxide 230b do not overlap is preferably lower than the height of the bottom surface of the oxide 230b when the bottom surface of the insulator 222 is used as a reference. The conductor 260, which functions as a gate electrode, is configured to cover the side and upper surface of the channel formation region of the oxide 230b via the insulator 250 or the like, so that the electric field of the conductor 260 can be easily applied to the entire channel formation region of the oxide 230b. This makes it possible to increase the on-current of the transistor 200 and improve the frequency characteristics. When the bottom surface of the insulator 222 is used as a reference, the difference between the height of the bottom surface of the conductor 260 in the region where the oxide 230a and the oxide 230b do not overlap with the conductor 260 and the height of the bottom surface of the oxide 230b is 0 nm or more and 100 nm or less, preferably 3 nm or more and 50 nm or less, and more preferably 5 nm or more and 20 nm or less.

[0341] The insulator 280 is provided on the insulator 275, and openings are formed in the regions where the insulator 250 and the conductor 260 are provided. The upper surface of the insulator 280 may be flattened. In this case, it is preferable that the upper surface of the insulator 280 is roughly aligned with the upper surfaces of the insulator 250 and the conductor 260.

[0342] The insulator 280 that functions as an interlayer insulating film preferably has a low dielectric constant. By using a material with a low dielectric constant as the interlayer insulating film, the parasitic capacitance that occurs between wirings can be reduced. The insulator 280 is preferably provided using, for example, the same material as the insulator 216. In particular, silicon oxide and silicon oxynitride are preferable because they are thermally stable. In particular, materials such as silicon oxide, silicon oxynitride, and silicon oxide having vacancies are preferable because they can easily form a region containing oxygen that is desorbed by heating.

[0343] Like the insulator 224, the insulator 280 may have excess oxygen. The insulator 280 preferably has a reduced concentration of impurities such as water and hydrogen. For example, the insulator 280 may be an oxide containing silicon, such as silicon oxide or silicon oxynitride, as appropriate. By providing the insulator 280 in contact with the insulator 250a, oxygen can be supplied to the oxide 230 through the insulator 250a. The oxygen can reduce oxygen vacancies in the oxide 230, thereby improving the reliability of the transistor 200.

[0344] The insulator 282 is provided in contact with the top surface of the insulator 280, the top surface of the insulator 250, and the top surface of the conductor 260. For example, an insulator such as aluminum oxide may be used as the insulator 282. By forming aluminum oxide as the insulator 282 by a sputtering method, the insulator 280 can contain excess oxygen. The insulator 282 preferably functions as a barrier insulating film that suppresses impurities such as water and hydrogen from diffusing from above into the insulator 280, and preferably has a function of capturing impurities such as hydrogen. The insulator 282 also preferably functions as a barrier insulating film that suppresses oxygen permeation. By providing the insulator 282 in contact with the insulator 280 in a region sandwiched between the insulator 212 and the insulator 283 and having a function of capturing impurities such as hydrogen, impurities such as hydrogen contained in the insulator 280 can be captured, and the amount of hydrogen in the region can be kept constant. In particular, aluminum oxide having an amorphous structure or aluminum oxide having an amorphous structure is preferably used as the insulator 282 because hydrogen can be captured or fixed more effectively in some cases. This makes it possible to manufacture a transistor 200 and a semiconductor device having favorable characteristics and high reliability.

[0345] The insulator 283 functions as a barrier insulating film that suppresses the diffusion of impurities such as water and hydrogen from above into the insulator 280. The insulator 283 is disposed on the insulator 282. As the insulator 283, it is preferable to use a nitride containing silicon, such as silicon nitride or silicon nitride oxide. For example, the insulator 283 may be silicon nitride formed by a sputtering method. By forming the insulator 283 by a sputtering method, a silicon nitride film that is high in density and unlikely to form voids can be formed. Furthermore, as the insulator 283, silicon nitride formed by an ALD method may be stacked on silicon nitride formed by a sputtering method. With such a structure, even if defects, such as voids, occur in the silicon nitride formed by the sputtering method, the voids can be filled by the silicon nitride formed by the ALD method, which has good coverage, and thus the sealing performance can be improved.

[0346] The insulator 285 is provided on the insulator 283. The insulator 285 is preferably provided using, for example, the same material as the insulator 280. In particular, silicon oxide and silicon oxynitride are preferable because they are thermally stable. Note that, although a structure in which the insulator 285 is provided is illustrated in Fig. 14B and Fig. 14C, the present invention is not limited to this. A configuration in which the insulator 285 is not provided and the conductor 246 is provided in contact with the insulator 283 may also be used.

[0347] The conductor 240a and the conductor 240b are preferably made of a conductive material containing tungsten, copper, or aluminum as a main component. The conductor 240a and the conductor 240b may have a layered structure.

[0348] Furthermore, when the conductor 240 has a laminated structure, it is preferable to use a conductive material having a function of suppressing the permeation of impurities such as water and hydrogen for the first conductor in contact with the insulator 241. For example, it is preferable to use tantalum, tantalum nitride, titanium, titanium nitride, ruthenium, ruthenium oxide, etc. Furthermore, the conductive material having a function of suppressing the permeation of impurities such as water and hydrogen may be used in a single layer or a laminated layer. Furthermore, it is possible to suppress impurities such as water and hydrogen contained in layers above the insulator 283 from being mixed into the oxide 230 through the conductor 240a and the conductor 240b.

[0349] The insulator 241a and the insulator 241b may be a barrier insulating film that can be used for the insulator 275 or the like. For example, the insulator 241a and the insulator 241b may be an insulator such as silicon nitride, aluminum oxide, or silicon nitride oxide. The insulator 241a and the insulator 241b are provided in contact with the insulator 283, the insulator 282, and the insulator 271, and therefore can prevent impurities such as water and hydrogen contained in the insulator 280 or the like from being mixed into the oxide 230 through the conductor 240a and the conductor 240b. In particular, silicon nitride is preferable because it has high barrier properties against hydrogen. In addition, it can prevent oxygen contained in the insulator 280 from being absorbed by the conductor 240a and the conductor 240b.

[0350] When the insulators 241a and 241b are formed into a layered structure as shown in FIG. 14A, it is preferable that the first insulator in contact with the inner wall of an opening such as insulator 280 and the second insulator inside it are made of a combination of a barrier insulating film against oxygen and a barrier insulating film against hydrogen.

[0351] For example, the first insulator may be made of aluminum oxide formed by the ALD method, and the second insulator may be made of silicon nitride formed by the PEALD method. This structure can suppress oxidation of the conductor 240 and reduce hydrogen contamination of the conductor 240.

[0352] Conductors 246 (conductors 246a and 246b) may be disposed in contact with the upper surface of conductor 240a and the upper surface of conductor 240b to function as wiring. Conductor 246 is preferably made of a conductive material containing tungsten, copper, or aluminum as a main component. The conductor may have a laminated structure, for example, a laminate of titanium or titanium nitride and the above conductive material. The conductor may be formed so as to be embedded in an opening provided in an insulator.

[0353] <Materials for semiconductor devices> The following describes constituent materials that can be used in the semiconductor device.

[0354] <<Substrate>> The substrate on which the transistor 200 is formed may be, for example, an insulating substrate, a semiconductor substrate, or a conductive substrate. Examples of insulating substrates include a glass substrate, a quartz substrate, a sapphire substrate, a stabilized zirconia substrate (such as an yttria stabilized zirconia substrate), and a resin substrate. Examples of semiconductor substrates include a semiconductor substrate made of silicon or germanium, or a compound semiconductor substrate made of silicon carbide, silicon germanium, gallium arsenide, indium phosphide, zinc oxide, and gallium oxide. Examples of semiconductor substrates include a semiconductor substrate having an insulating region inside the semiconductor substrate, such as an SOI (Silicon On Insulator) substrate. Examples of conductive substrates include a graphite substrate, a metal substrate, an alloy substrate, and a conductive resin substrate. Examples of substrates include a substrate having a metal nitride, a substrate having a metal oxide, and the like. Examples of substrates include a substrate having a conductor or semiconductor provided on an insulating substrate, a substrate having a conductor or insulator provided on a semiconductor substrate, and a substrate having a semiconductor or insulator provided on a conductive substrate. Alternatively, a substrate provided with elements may be used. The elements provided on the substrate include a capacitor element, a resistor element, a switch element, a light-emitting element, a memory element, and the like.

[0355] <<Insulators>> Examples of the insulator include oxides, nitrides, oxynitrides, nitride oxides, metal oxides, metal oxynitrides, and metal nitride oxides, each of which has insulating properties.

[0356] For example, as transistors become more miniaturized and highly integrated, problems such as leakage current can occur due to thinner gate insulators. By using a high-k material for the insulator that functions as the gate insulator, it is possible to reduce the voltage required for transistor operation while maintaining the physical film thickness. On the other hand, by using a material with a low dielectric constant for the insulator that functions as the interlayer insulating film, it is possible to reduce the parasitic capacitance that occurs between wiring. Therefore, it is best to select materials according to the insulator's functions.

[0357] Further, examples of insulators with a high relative dielectric constant include gallium oxide, hafnium oxide, zirconium oxide, oxides having aluminum and hafnium, oxynitrides having aluminum and hafnium, oxides having silicon and hafnium, oxynitrides having silicon and hafnium, and nitrides having silicon and hafnium.

[0358] Examples of insulators with a low dielectric constant include silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide with fluorine added, silicon oxide with carbon added, silicon oxide with carbon and nitrogen added, silicon oxide with voids, or resin.

[0359] In addition, the transistor using metal oxide can have stable electrical characteristics by being surrounded by an insulator having a function of suppressing the permeation of impurities such as hydrogen and oxygen. As the insulator having a function of suppressing the permeation of impurities such as hydrogen and oxygen, for example, an insulator containing boron, carbon, nitrogen, oxygen, fluorine, magnesium, aluminum, silicon, phosphorus, chlorine, argon, gallium, germanium, yttrium, zirconium, lanthanum, neodymium, hafnium, or tantalum may be used in a single layer or a stacked layer. Specifically, as the insulator having a function of suppressing the permeation of impurities such as hydrogen and oxygen, metal oxides such as aluminum oxide, magnesium oxide, gallium oxide, germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, hafnium oxide, and tantalum oxide, and metal nitrides such as aluminum nitride, silicon nitride oxide, and silicon nitride can be used.

[0360] The insulator that functions as the gate insulator is preferably an insulator having a region containing oxygen that is released by heating. For example, by using a structure in which silicon oxide or silicon oxynitride having a region containing oxygen that is released by heating is in contact with the oxide 230, oxygen vacancies in the oxide 230 can be compensated for.

[0361] <<Conductors>> As the conductor, it is preferable to use a metal element selected from aluminum, chromium, copper, silver, gold, platinum, tantalum, nickel, titanium, molybdenum, tungsten, hafnium, vanadium, niobium, manganese, magnesium, zirconium, beryllium, indium, ruthenium, iridium, strontium, lanthanum, etc., or an alloy containing the above-mentioned metal elements as a component, or an alloy combining the above-mentioned metal elements. For example, it is preferable to use tantalum nitride, titanium nitride, tungsten, nitride containing titanium and aluminum, nitride containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, oxide containing strontium and ruthenium, oxide containing lanthanum and nickel, etc. In addition, tantalum nitride, titanium nitride, nitride containing titanium and aluminum, nitride containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, oxide containing strontium and ruthenium, oxide containing lanthanum and nickel are conductive materials that are difficult to oxidize, or materials that maintain conductivity even when oxygen is absorbed, so they are preferable. Furthermore, a semiconductor having high electrical conductivity, typified by polycrystalline silicon containing an impurity element such as phosphorus, or a silicide such as nickel silicide may be used.

[0362] A plurality of conductive layers formed of the above-mentioned materials may be stacked. For example, a stacked structure may be formed by combining the above-mentioned material containing a metal element and a conductive material containing oxygen. A stacked structure may be formed by combining the above-mentioned material containing a metal element and a conductive material containing nitrogen. A stacked structure may be formed by combining the above-mentioned material containing a metal element, a conductive material containing oxygen, and a conductive material containing nitrogen.

[0363] In addition, when an oxide is used for the channel formation region of a transistor, a conductor functioning as a gate electrode preferably has a stacked structure in which a material containing a metal element and a conductive material containing oxygen are combined. In this case, the conductive material containing oxygen is preferably provided on the channel formation region side. By providing the conductive material containing oxygen on the channel formation region side, oxygen released from the conductive material is easily supplied to the channel formation region.

[0364] In particular, it is preferable to use a conductive material containing oxygen and a metal element contained in the metal oxide in which the channel is formed as a conductor functioning as a gate electrode. The conductive material containing the metal element and nitrogen described above may also be used. For example, a conductive material containing nitrogen, such as titanium nitride or tantalum nitride, may also be used. Indium tin oxide, indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium zinc oxide, or indium tin oxide to which silicon is added may also be used. Indium gallium zinc oxide containing nitrogen may also be used. By using such a material, hydrogen contained in the metal oxide in which the channel is formed may be captured. Alternatively, hydrogen mixed in from an external insulator may be captured.

[0365] <<Metal oxides>> It is preferable to use a metal oxide that functions as a semiconductor (oxide semiconductor) as the oxide 230. Hereinafter, metal oxides that can be applied to the oxide 230 according to the present invention will be described.

[0366] The metal oxide preferably contains at least indium or zinc. In particular, it is preferable that the metal oxide contains indium and zinc. In addition to these, it is preferable that the metal oxide contains aluminum, gallium, yttrium, tin, etc. In addition, it may contain one or more elements selected from boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, cobalt, etc.

[0367] Here, the case where the metal oxide is an In-M-Zn oxide having indium, element M, and zinc is considered. The element M is aluminum, gallium, yttrium, or tin. Other elements applicable to the element M include boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, and cobalt. However, there are cases where the element M may be a combination of multiple elements mentioned above.

[0368] <Method for manufacturing semiconductor device> Next, a manufacturing method of the semiconductor device of one embodiment of the present invention shown in FIGS. 14A to 14D will be described with reference to FIGS. 16A to 25A, 16B to 25B, 16C to 25C, and 16D to 25D.

[0369] 16A to 25A are top views. FIG. 16B to 25B are cross-sectional views corresponding to the portion indicated by the dashed line A1-A2 in FIG. 16A to FIG. 25A, and are cross-sectional views in the channel length direction of the transistor 200. FIG. 16C to FIG. 25C are cross-sectional views corresponding to the portion indicated by the dashed line A3-A4 in FIG. 16A to FIG. 25A, and are cross-sectional views in the channel width direction of the transistor 200. FIG. 16D to FIG. 25D are cross-sectional views of the portion indicated by the dashed line A5-A6 in FIG. 16A to FIG. 25A. Note that some elements are omitted in the top views in FIG. 16A to FIG. 25A for clarity.

[0370] In the following, insulating materials for forming insulators, conductive materials for forming conductors, or semiconductor materials for forming semiconductors can be formed as films by appropriately using a sputtering method, a CVD method, an MBE method, a PLD method, an ALD method, or the like.

[0371] There are three types of sputtering: RF sputtering, which uses a high-frequency power source for the sputtering power supply, DC sputtering, which uses a direct current power source, and pulsed DC sputtering, which changes the voltage applied to the electrode in a pulsed manner. RF sputtering is mainly used when depositing insulating films, while DC sputtering is mainly used when depositing metal conductive films. Pulsed DC sputtering is mainly used when depositing compounds such as oxides, nitrides, and carbides using reactive sputtering.

[0372] CVD methods can be classified into plasma CVD (PECVD) methods (sometimes called plasma chemical vapor deposition), which use plasma, thermal CVD (TCVD: Thermal CVD), which uses heat, and photo CVD (Photo CVD), which uses light. They can also be further divided into metal CVD (MCVD: Metal CVD) and metal organic CVD (MOCVD: Metal Organic CVD), which are sometimes called metal organic chemical vapor deposition, depending on the source gas used.

[0373] The plasma CVD method can obtain a high-quality film at a relatively low temperature. Moreover, the thermal CVD method is a film formation method that can reduce plasma damage to the object to be processed because it does not use plasma. For example, wiring, electrodes, elements (transistors, capacitive elements, etc.) included in a semiconductor device may be charged up by receiving electric charge from plasma. At this time, the wiring, electrodes, elements, etc. included in the semiconductor device may be destroyed by the accumulated electric charge. On the other hand, in the case of the thermal CVD method that does not use plasma, such plasma damage does not occur, so the yield of the semiconductor device can be increased. Furthermore, in the thermal CVD method, plasma damage does not occur during film formation, so a film with few defects can be obtained.

[0374] As the ALD method, a thermal ALD method in which a reaction between a precursor and a reactant is carried out using only thermal energy, a PEALD method in which a plasma-excited reactant is used, or the like can be used.

[0375] In addition, the ALD method utilizes the self-regulating nature of atoms to deposit atoms one layer at a time, and thus has the following advantages: extremely thin films can be formed; films can be formed on structures with high aspect ratios; films can be formed with fewer defects such as pinholes; films can be formed with excellent coverage; and films can be formed at low temperatures. In the PEALD method, the use of plasma can be preferable because it allows films to be formed at lower temperatures. Note that some precursors used in the ALD method contain impurities such as carbon. For this reason, films formed by the ALD method may contain more impurities such as carbon than films formed by other film formation methods. Note that the amount of impurities can be quantified using X-ray photoelectron spectroscopy (XPS).

[0376] The CVD method and the ALD method are different from the film formation method in which particles emitted from a target or the like are deposited, and are film formation methods in which a film is formed by a reaction on the surface of a workpiece. Therefore, they are film formation methods that are not easily affected by the shape of the workpiece and have good step coverage. In particular, the ALD method has excellent step coverage and excellent thickness uniformity, so it is suitable for coating the surface of an opening with a high aspect ratio. However, since the ALD method has a relatively slow film formation speed, it may be preferable to use it in combination with other film formation methods such as the CVD method, which has a fast film formation speed.

[0377] In the CVD method and the ALD method, the composition of the film obtained can be controlled by the flow rate ratio of the raw material gas. For example, in the CVD method and the ALD method, a film of any composition can be formed by changing the flow rate ratio of the raw material gas. In addition, for example, in the CVD method and the ALD method, a film whose composition changes continuously can be formed by changing the flow rate ratio of the raw material gas while forming the film. When forming a film while changing the flow rate ratio of the raw material gas, the time required for film formation can be shortened compared to the case of forming a film using multiple film formation chambers because no time is required for transport and pressure adjustment. Therefore, the productivity of semiconductor devices can be increased in some cases.

[0378] First, a substrate (not shown) is prepared, and the insulator 212 is formed on the substrate (see FIGS. 16A to 16D). The insulator 212 is preferably formed by a sputtering method. By using a sputtering method that does not require hydrogen as a deposition gas, the hydrogen concentration in the insulator 212 can be reduced. However, the method for forming the insulator 212 is not limited to the sputtering method, and a CVD method, an MBE method, a PLD method, an ALD method, or the like may be used as appropriate.

[0379] In this embodiment, a silicon nitride film is formed as the insulator 212 by pulsed DC sputtering using a silicon target in an atmosphere containing nitrogen gas. By using pulsed DC sputtering, the generation of particles due to arcing on the target surface can be suppressed, making the film thickness distribution more uniform. In addition, by using a pulsed voltage, the rise and fall of the discharge can be made steeper than with a high-frequency voltage. This allows power to be supplied to the electrodes more efficiently, improving the sputtering rate and film quality.

[0380] By using an insulator such as silicon nitride through which impurities such as water and hydrogen do not easily permeate, it is possible to suppress the diffusion of impurities such as water and hydrogen contained in layers below the insulator 212. Furthermore, by using an insulator such as silicon nitride through which copper does not easily permeate as the insulator 212, even if a metal that easily diffuses, such as copper, is used for a conductor in a layer (not shown) below the insulator 212, it is possible to suppress the diffusion of the metal upward through the insulator 212.

[0381] Next, the insulator 214 is deposited on the insulator 212 (see FIGS. 16A to 16D). The insulator 214 is preferably deposited by a sputtering method. By using a sputtering method that does not require hydrogen as a deposition gas, the hydrogen concentration in the insulator 214 can be reduced. However, the deposition of the insulator 214 is not limited to the sputtering method, and a CVD method, an MBE method, a PLD method, an ALD method, or the like may also be used as appropriate.

[0382] In this embodiment, an aluminum oxide film is formed as the insulator 214 by pulsed DC sputtering using an aluminum target in an atmosphere containing oxygen gas. By using the pulsed DC sputtering method, the film thickness distribution can be made more uniform, and the sputtering rate and film quality can be improved. Here, RF (Radio Frequency) power may be applied to the substrate. For example, a configuration may be adopted in which no RF power is applied when forming the lower layer of the insulator 214, and RF power is applied when forming the upper layer of the insulator 214. The amount of oxygen injected into the layer below the insulator 214 can be controlled by the magnitude of the RF power applied to the substrate. The RF power is set to 0 W / cm. 2 Above 1.86W / cm 2 The following is set forth. In other words, the amount of oxygen suitable for the transistor characteristics can be changed and injected by adjusting the RF power when forming the insulator 214. Therefore, it is possible to inject an amount of oxygen suitable for improving the reliability of the transistor. In addition, the RF frequency is preferably 10 MHz or higher. Typically, it is 13.56 MHz. The higher the RF frequency, the less damage can be caused to the substrate.

[0383] It is preferable to use a metal oxide having an amorphous structure, such as aluminum oxide, which has a high function of trapping and fixing hydrogen, as the insulator 214. This makes it possible to trap or fix hydrogen contained in the insulator 216 and the like and prevent the hydrogen from diffusing into the oxide 230. In particular, it is preferable to use aluminum oxide having an amorphous structure or aluminum oxide having an amorphous structure as the insulator 214, because hydrogen can be more effectively trapped or fixed. This makes it possible to manufacture a transistor 200 and a semiconductor device having excellent characteristics and high reliability.

[0384] Next, the insulator 216 is deposited over the insulator 214. The insulator 216 is preferably deposited by a sputtering method. By using a sputtering method that does not require hydrogen as a deposition gas, the hydrogen concentration in the insulator 216 can be reduced. However, the deposition of the insulator 216 is not limited to the sputtering method, and a CVD method, an MBE method, a PLD method, an ALD method, or the like may also be used as appropriate.

[0385] In this embodiment, a silicon oxide film is formed by pulsed DC sputtering using a silicon target in an atmosphere containing oxygen gas as the insulator 216. By using the pulsed DC sputtering method, the film thickness distribution can be made more uniform, and the sputtering rate and film quality can be improved.

[0386] It is preferable that the insulators 212, 214, and 216 are successively formed without exposure to the air. For example, a multi-chamber film formation apparatus can be used. This allows the insulators 212, 214, and 216 to be formed with reduced hydrogen in the films, and further reduces the incorporation of hydrogen into the films between each film formation process.

[0387] Next, an opening is formed in the insulator 216, reaching the insulator 214. The opening may be, for example, a groove or a slit. The opening may be an area where the opening is formed. The opening may be formed by wet etching, but dry etching is preferable for fine processing. It is preferable to select an insulator that functions as an etching stopper film when etching the insulator 216 to form a groove as the insulator 214. For example, when silicon oxide or silicon oxynitride is used for the insulator 216 that forms the groove, the insulator 214 may be silicon nitride, aluminum oxide, or hafnium oxide. Note that a recess may be formed in the insulator 214, overlapping the opening of the insulator 216.

[0388] As the dry etching apparatus, a capacitively coupled plasma (CCP) etching apparatus having parallel plate electrodes can be used. The capacitively coupled plasma etching apparatus having parallel plate electrodes can be configured to apply a high frequency voltage to one of the parallel plate electrodes. Alternatively, it can be configured to apply a plurality of different high frequency voltages to one of the parallel plate electrodes. Alternatively, it can be configured to apply a high frequency voltage of the same frequency to each of the parallel plate electrodes. Alternatively, it can be configured to apply high frequency voltages of different frequencies to each of the parallel plate electrodes. Alternatively, a dry etching apparatus having a high density plasma source can be used. As the dry etching apparatus having a high density plasma source, for example, an inductively coupled plasma (ICP) etching apparatus or the like can be used.

[0389] After the opening is formed, a conductive film that becomes the conductor 205a is formed. The conductive film that becomes the conductor 205a preferably contains a conductor that has a function of suppressing oxygen permeation. For example, tantalum nitride, tungsten nitride, titanium nitride, or the like can be used. Alternatively, it can be a laminated film of a conductor that has a function of suppressing oxygen permeation and tantalum, tungsten, titanium, molybdenum, aluminum, copper, or a molybdenum-tungsten alloy. The conductive film that becomes the conductor 205a can be formed by a sputtering method, a CVD method, an MBE method, a PLD method, an ALD method, or the like.

[0390] In this embodiment, titanium nitride is formed as the conductive film that becomes the conductor 205a. By providing such a metal nitride in contact with the lower surface and side surface of the conductor 205b, it is possible to prevent the conductor 205b from being oxidized by the insulator 216 or the like. Even if a metal that easily diffuses, such as copper, is used as the conductor 205b, it is possible to prevent the metal from diffusing out of the conductor 205a.

[0391] Next, a conductive film to be the conductor 205b is formed. As the conductive film to be the conductor 205b, tantalum, tungsten, titanium, molybdenum, aluminum, copper, a molybdenum-tungsten alloy, or the like can be used. The conductive film can be formed by a plating method, a sputtering method, a CVD method, an MBE method, a PLD method, an ALD method, or the like. In this embodiment, tungsten is formed as the conductive film to be the conductor 205b.

[0392] Next, a CMP process is performed to remove a portion of the conductive film that will become the conductor 205a and a portion of the conductive film that will become the conductor 205b, thereby exposing the insulator 216 (see FIGS. 16A to 16D). As a result, the conductor 205a and the conductor 205b remain only in the openings. This makes it possible to form a conductor 205 with a flat upper surface. Note that the CMP process may remove a portion of the insulator 216.

[0393] Next, the insulator 222 is formed on the insulator 216 and the conductor 205 (see FIGS. 17A to 17D). As the insulator 222, an insulator containing one or both of an oxide of aluminum and hafnium may be formed. Note that as the insulator containing one or both of an oxide of aluminum and hafnium, it is preferable to use aluminum oxide, hafnium oxide, an oxide containing aluminum and hafnium (hafnium aluminate), or the like. An insulator containing one or both of an oxide of aluminum and hafnium has a barrier property against oxygen, hydrogen, and water. When the insulator 222 has a barrier property against hydrogen and water, the hydrogen and water contained in the structure provided around the transistor 200 are prevented from diffusing into the inside of the transistor 200 through the insulator 222, and the generation of oxygen vacancies in the oxide 230 can be suppressed.

[0394] The insulator 222 can be formed by a sputtering method, a CVD method, an MBE method, a PLD method, an ALD method, etc. In this embodiment, hafnium oxide is formed as the insulator 222 by an ALD method.

[0395] It is preferable to carry out a heat treatment subsequently. The heat treatment may be carried out at 250°C or higher and 650°C or lower, preferably 300°C or higher and 500°C or lower, and more preferably 320°C or higher and 450°C or lower. The heat treatment may be carried out in an atmosphere of nitrogen gas or an inert gas, or an atmosphere containing 10 ppm or higher, 1% or higher, or 10% or higher of an oxidizing gas. For example, when the heat treatment is carried out in a mixed atmosphere of nitrogen gas and oxygen gas, the oxygen gas may be about 20%. The heat treatment may be carried out under reduced pressure. Alternatively, the heat treatment may be carried out in an atmosphere of nitrogen gas or an inert gas, and then in an atmosphere containing 10 ppm or higher, 1% or higher, or 10% or higher of an oxidizing gas to compensate for the desorbed oxygen.

[0396] In addition, it is preferable that the gas used in the heat treatment is highly purified. For example, the amount of moisture contained in the gas used in the heat treatment is 1 ppb or less, preferably 0.1 ppb or less, and more preferably 0.05 ppb or less. By performing the heat treatment using a highly purified gas, it is possible to prevent moisture and the like from being taken into the insulator 222 as much as possible.

[0397] In this embodiment, after the insulator 222 is formed, heat treatment is performed at a flow rate ratio of nitrogen gas and oxygen gas of 4 slm:1 slm at a temperature of 400° C. for one hour. The heat treatment can remove impurities such as water and hydrogen contained in the insulator 222. When an oxide containing hafnium is used as the insulator 222, the heat treatment may cause part of the insulator 222 to crystallize. The heat treatment can also be performed at a timing such as after the insulator 224 is formed.

[0398] Next, the insulating film 224A is formed on the insulator 222 (see FIGS. 17A to 17D). The insulating film 224A can be formed by a sputtering method, a CVD method, an MBE method, a PLD method, an ALD method, or the like. In this embodiment, a silicon oxide film is formed as the insulating film 224A by a sputtering method. By using a sputtering method that does not require hydrogen as a film formation gas, the hydrogen concentration in the insulating film 224A can be reduced. Since the insulating film 224A comes into contact with the oxide 230a in a later process, it is preferable that the hydrogen concentration is reduced in this manner.

[0399] Next, oxide film 230A and oxide film 230B are sequentially formed on insulating film 224A (see FIGS. 17A to 17D). Note that oxide film 230A and oxide film 230B are preferably formed successively without being exposed to the air environment. By forming the films without being exposed to the air, it is possible to prevent impurities or moisture from the air environment from adhering to oxide film 230A and oxide film 230B, and it is possible to keep the vicinity of the interface between oxide film 230A and oxide film 230B clean.

[0400] The oxide film 230A and the oxide film 230B are preferably formed by the ALD method as described in the previous embodiment, which allows the oxide film 230A and the oxide film 230B to be formed as oxides having a layered crystal structure.

[0401] It is preferable to form the insulating film 224A, the oxide film 230A, and the oxide film 230B by the ALD method without exposing them to the atmosphere. For example, the multi-chamber film forming apparatus shown in the above embodiment may be used. This can reduce the inclusion of hydrogen in the insulating film 224A, the oxide film 230A, and the oxide film 230B between the film forming steps.

[0402] Next, it is preferable to perform a heat treatment. The heat treatment may be performed in a temperature range where the oxide film 230A and the oxide film 230B are not polycrystallized, and may be performed at 100°C to 1200°C, preferably 200°C to 1000°C, more preferably 250°C to 650°C, even more preferably 300°C to 600°C, even more preferably 400°C to 550°C, and even more preferably 420°C to 480°C. The heat treatment is performed in an atmosphere of nitrogen gas or an inert gas, or an atmosphere containing 10 ppm or more, 1% or more, or 10% or more of an oxidizing gas. For example, when the heat treatment is performed in a mixed atmosphere of nitrogen gas and oxygen gas, the oxygen gas may be about 20%. The heat treatment may be performed under reduced pressure. Alternatively, the heat treatment may be performed in an atmosphere of nitrogen gas or an inert gas, and then in an atmosphere containing 10 ppm or more, 1% or more, or 10% or more of an oxidizing gas to compensate for the desorbed oxygen. Note that when the heat treatment temperature is increased, the metal oxide may have a polycrystalline structure, so the heat treatment temperature may be appropriately set within a range in which the metal oxide does not have a polycrystalline structure. However, in one embodiment of the present invention, the metal oxide may have a polycrystalline structure. The heat treatment may be performed in the treatment chamber 4011 shown in FIG. 7 of the previous embodiment.

[0403] In addition, the gas used in the heat treatment is preferably highly purified. For example, the amount of moisture contained in the gas used in the heat treatment may be 1 ppb or less, preferably 0.1 ppb or less, and more preferably 0.05 ppb or less. By using a highly purified gas to perform the heat treatment, it is possible to prevent moisture and the like from being taken into the oxide film 230A and the oxide film 230B as much as possible.

[0404] In this embodiment, the heat treatment is performed at a temperature of 450° C. for 1 hour with a flow rate ratio of nitrogen gas to oxygen gas of 4 slm:1 slm. Such heat treatment including oxygen gas can reduce impurities such as carbon, water, and hydrogen in the oxide film 230A and the oxide film 230B. By reducing the impurities in the film in this way, the crystallinity of the oxide film 230B can be improved, and a denser and more compact structure can be obtained. This increases the crystalline regions in the oxide film 230A and the oxide film 230B, and reduces the in-plane variation of the crystalline regions in the oxide film 230A and the oxide film 230B. Therefore, the in-plane variation of the electrical characteristics of the transistor 200 can be reduced.

[0405] Next, the conductive film 242A is formed on the oxide film 230B (see FIGS. 17A to 17D). The conductive film 242A can be formed by sputtering, CVD, MBE, PLD, ALD, or the like. For example, tantalum nitride may be formed as the conductive film 242A by sputtering. Note that heat treatment may be performed before the conductive film 242A is formed. The heat treatment may be performed under reduced pressure, and the conductive film 242A may be formed continuously without exposure to the air. By performing such treatment, moisture and hydrogen adsorbed on the surface of the oxide film 230B and the like can be removed, and the moisture concentration and hydrogen concentration in the oxide film 230A, the oxide film 230B, and the oxide film 230B can be further reduced. The temperature of the heat treatment is preferably 100° C. or higher and 400° C. or lower. In this embodiment, the temperature of the heat treatment is set to 200° C.

[0406] Next, the insulating film 271A is formed on the conductive film 242A (see FIGS. 17A to 17D). The insulating film 271A can be formed by a sputtering method, a CVD method, an MBE method, a PLD method, an ALD method, or the like. The insulating film 271A is preferably an insulating film having a function of suppressing oxygen permeation. For example, the insulating film 271A may be formed of aluminum oxide by a sputtering method.

[0407] Note that the conductive film 242A and the insulating film 271A are preferably formed by a sputtering method without exposure to the air. For example, a multi-chamber film formation apparatus may be used. This allows the conductive film 242A and the insulating film 271A to be formed with reduced hydrogen in the films, and further reduces the inclusion of hydrogen in the films between film formation steps. In addition, when a hard mask is provided on the insulating film 271A, the film to be the hard mask may also be formed continuously without exposure to the air.

[0408] Next, the insulating film 224A, the oxide film 230A, the oxide film 230B, the conductive film 242A, and the insulating film 271A are processed into an island shape by using a lithography method to form the insulator 224, the oxide 230a, the oxide 230b, the conductive layer 242B, and the insulating layer 271B (see FIGS. 18A to 18D). Here, the insulator 224, the oxide 230a, the oxide 230b, the conductive layer 242B, and the insulating layer 271B are formed so that at least a part of them overlaps with the conductor 205. The above processing can be performed by a dry etching method or a wet etching method. Processing by the dry etching method is suitable for fine processing. In addition, the insulating film 224A, the oxide film 230A, the oxide film 230B, the conductive film 242A, the insulating film 271A, and the insulating layer 271B may be processed under different conditions.

[0409] In the lithography method, first, the resist is exposed through a mask. Next, the exposed area is removed or left using a developer to form a resist mask. Next, a conductor, a semiconductor, an insulator, or the like can be processed into a desired shape by etching through the resist mask. For example, a resist mask may be formed by exposing the resist using KrF excimer laser light, ArF excimer laser light, EUV (Extreme Ultraviolet) light, or the like. Also, a liquid immersion technique may be used in which a liquid (e.g., water) is filled between the substrate and the projection lens and exposure is performed. Also, an electron beam or an ion beam may be used instead of the light described above. When an electron beam or an ion beam is used, a mask is not required. The resist mask can be removed by performing a dry etching process such as ashing, a wet etching process, a wet etching process after a dry etching process, or a dry etching process after a wet etching process.

[0410] Furthermore, a hard mask made of an insulator or a conductor may be used under the resist mask. When using a hard mask, an insulating film or a conductive film that will be the hard mask material is formed on the conductive film 242A, a resist mask is formed thereon, and the hard mask material is etched to form a hard mask of a desired shape. Etching of the conductive film 242A and the like may be performed after removing the resist mask, or may be performed while leaving the resist mask. In the latter case, the resist mask may disappear during etching. After etching of the conductive film 242A and the like, the hard mask may be removed by etching. On the other hand, if the material of the hard mask does not affect the subsequent process or can be used in the subsequent process, it is not necessarily necessary to remove the hard mask. In this embodiment, the insulating layer 271B is used as the hard mask.

[0411] Here, since the insulating layer 271B functions as a mask for the conductive layer 242B, the conductive layer 242B does not have a curved surface between the side surface and the top surface, as shown in FIG. 18B to FIG. 18D. As a result, the conductors 242a and 242b shown in FIG. 14B and FIG. 14D have angular ends where the side surface and the top surface intersect. The angular end where the side surface and the top surface of the conductor 242 intersect increases the cross-sectional area of ​​the conductor 242 compared to when the end has a curved surface. This reduces the resistance of the conductor 242, and therefore the on-current of the transistor 200 can be increased.

[0412] As shown in FIG. 18B to FIG. 18D, the cross sections of the insulator 224, the oxide 230a, the oxide 230b, the conductive layer 242B, and the insulating layer 271B may be tapered. In this specification and the like, the tapered shape refers to a shape in which at least a part of the side surface of the structure is inclined with respect to the substrate surface. For example, it is preferable that the angle between the inclined side surface and the substrate surface (hereinafter, sometimes referred to as the taper angle) is less than 90°. For example, the insulator 224, the oxide 230a, the oxide 230b, the conductive layer 242B, and the insulating layer 271B may have a taper angle of 60° or more and less than 90°. By making the cross sections tapered in this way, the coverage of the insulator 275 and the like can be improved in the subsequent steps, and defects such as voids can be reduced.

[0413] However, the present invention is not limited to the above, and the side surfaces of the insulator 224, the oxide 230a, the oxide 230b, the conductive layer 242B, and the insulating layer 271B may be configured to be approximately perpendicular to the upper surface of the insulator 222. With such a configuration, it is possible to reduce the area and increase the density when providing multiple transistors 200.

[0414] Furthermore, by-products generated in the above etching process may be formed in layers on the side surfaces of the insulator 224, the oxide 230a, the oxide 230b, the conductive layer 242B, and the insulating layer 271B. In this case, the layered by-products are formed between the insulator 224, the oxide 230a, the oxide 230b, the conductive layer 242B, and the insulating layer 271B and the insulator 275. Therefore, it is preferable to remove the layered by-products.

[0415] Next, the insulator 275 is formed to cover the insulator 224 and the insulating layer 271B, etc. (see FIGS. 19A to 19D). Here, it is preferable that the insulator 275 is in close contact with the upper surface of the insulator 222 and the side surface of the insulator 224. The insulator 275 can be formed by a sputtering method, a CVD method, an MBE method, a PLD method, an ALD method, etc. It is preferable that the insulator 275 is an insulating film having a function of suppressing oxygen permeation. For example, as the insulator 275, a film of aluminum oxide may be formed by a sputtering method, and a film of silicon nitride may be formed thereon by a PEALD method. By forming the insulator 275 in such a layered structure, the function of suppressing the diffusion of impurities such as water and hydrogen, and oxygen may be improved.

[0416] In this manner, the insulator 224, the oxide 230a, the oxide 230b, and the conductive layer 242B can be covered with the insulator 275 and the insulating layer 271B, which have a function of suppressing the diffusion of oxygen. This makes it possible to reduce the direct diffusion of oxygen from the insulator 280, etc., to the insulator 224, the oxide 230a, the oxide 230b, and the conductive layer 242B in a later process.

[0417] Next, an insulating film to be the insulator 280 is formed on the insulator 275. The insulating film can be formed by a sputtering method, a CVD method, an MBE method, a PLD method, an ALD method, or the like. For example, a silicon oxide film may be formed by a sputtering method as the insulating film. The insulating film to be the insulator 280 can be formed by a sputtering method in an atmosphere containing oxygen, thereby forming the insulator 280 containing excess oxygen. In addition, the hydrogen concentration in the insulator 280 can be reduced by using a sputtering method that does not require hydrogen as a deposition gas. Note that a heat treatment may be performed before the insulating film is formed. The heat treatment may be performed under reduced pressure, and the insulating film may be formed continuously without exposure to the atmosphere. By performing such a treatment, moisture and hydrogen adsorbed on the surface of the insulator 275 and the like can be removed, and the moisture concentration and hydrogen concentration in the oxide 230a, the oxide 230b, and the insulator 224 can be further reduced. The heat treatment conditions described above can be used for the heat treatment.

[0418] Next, the insulating film that will become the insulator 280 is subjected to CMP processing to form the insulator 280 with a flat upper surface (see FIGS. 19A to 19D). Note that a silicon nitride film may be formed on the insulator 280 by, for example, a sputtering method, and the CMP processing may be performed until the silicon nitride reaches the insulator 280.

[0419] Next, a part of the insulator 280, a part of the insulator 275, a part of the insulating layer 271B, and a part of the conductive layer 242B are processed to form an opening that reaches the oxide 230b. The opening is preferably formed so as to overlap the conductor 205. By forming the opening, the insulator 271a, the insulator 271b, the conductor 242a, and the conductor 242b are formed (see FIGS. 20A to 20D).

[0420] 20B and 20C, the side surfaces of the insulator 280, the insulator 275, the insulator 271, and the conductor 242 may have a tapered shape. Also, the taper angle of the insulator 280 may be larger than the taper angle of the conductor 242. Also, although not shown in FIGS. 20A to 20C, the upper part of the oxide 230b may be removed when the opening is formed.

[0421] Furthermore, a part of the insulator 280, a part of the insulator 275, a part of the insulating layer 271B, and a part of the conductive layer 242B can be processed by dry etching or wet etching. Processing by dry etching is suitable for fine processing. Moreover, the processing may be performed under different conditions. For example, a part of the insulator 280 may be processed by dry etching, a part of the insulator 275 and a part of the insulating layer 271B may be processed by wet etching, and a part of the conductive layer 242B may be processed by dry etching.

[0422] Here, impurities may adhere to the side of the oxide 230a, the top and side of the oxide 230b, the side of the conductor 242, the side of the insulator 280, etc., and may diffuse into these. A step of removing such impurities may be performed. In addition, a damaged area may be formed on the surface of the oxide 230b by the dry etching. Such a damaged area may be removed. The impurities include those caused by components contained in the insulator 280, the insulator 275, a part of the insulating layer 271B, and the conductive layer 242B, components contained in the members used in the device used to form the opening, and components contained in the gas or liquid used in etching. The impurities include, for example, hafnium, aluminum, silicon, tantalum, fluorine, and chlorine.

[0423] In particular, impurities such as aluminum or silicon inhibit the oxide 230b from becoming a CAAC-OS. Therefore, it is preferable that impurity elements such as aluminum or silicon that inhibit the CAAC-OS formation are reduced or removed. For example, the concentration of aluminum atoms in the oxide 230b and its vicinity may be 5.0 atomic % or less, preferably 2.0 atomic % or less, more preferably 1.5 atomic % or less, even more preferably 1.0 atomic % or less, and even more preferably less than 0.3 atomic %.

[0424] In addition, the region of the metal oxide in which the CAAC-OS formation is inhibited by impurities such as aluminum or silicon and which becomes an amorphous-like oxide semiconductor (a-like OS) is sometimes called a non-CAAC region. In the non-CAAC region, the density of the crystal structure is reduced, so the V O A large amount of H is formed, which makes the transistor more likely to be normally on. Therefore, it is preferable that the non-CAAC region of the oxide 230b is reduced or eliminated.

[0425] In contrast, it is preferable that the oxide 230b has a layered CAAC structure. In particular, it is preferable that the oxide 230b has the CAAC structure up to the lower end of the drain. Here, in the transistor 200, the conductor 242a or the conductor 242b and its vicinity function as the drain. In other words, it is preferable that the oxide 230b near the lower end of the conductor 242a (conductor 242b) has the CAAC structure. In this way, even at the drain end, which significantly affects the drain breakdown voltage, the damaged region of the oxide 230b is removed, and by having the CAAC structure, the fluctuation in the electrical characteristics of the transistor 200 can be further suppressed. In addition, the reliability of the transistor 200 can be improved.

[0426] A cleaning process is performed to remove impurities that have adhered to the surface of the oxide 230b in the etching process. The cleaning method includes wet cleaning using a cleaning solution (which can also be called wet etching), plasma processing using plasma, and cleaning by heat treatment, and the above cleaning methods may be combined as appropriate. Note that the cleaning process may deepen the grooves.

[0427] For wet cleaning, a cleaning process may be performed using an aqueous solution of ammonia water, oxalic acid, phosphoric acid, hydrofluoric acid, or the like diluted with carbonated water or pure water, pure water, carbonated water, or the like. Alternatively, ultrasonic cleaning may be performed using these aqueous solutions, pure water, or carbonated water. Alternatively, these cleaning methods may be combined as appropriate.

[0428] In this specification, an aqueous solution obtained by diluting commercially available hydrofluoric acid with pure water may be called diluted hydrofluoric acid, and an aqueous solution obtained by diluting commercially available ammonia water with pure water may be called diluted ammonia water. The concentration and temperature of the aqueous solution may be appropriately adjusted depending on the impurities to be removed and the configuration of the semiconductor device to be cleaned. The ammonia concentration of the diluted ammonia water may be 0.01% or more and 5% or less, preferably 0.1% or more and 0.5% or less. The hydrogen fluoride concentration of the diluted hydrofluoric acid may be 0.01 ppm or more and 100 ppm or less, preferably 0.1 ppm or more and 10 ppm or less.

[0429] In addition, it is preferable to use a frequency of 200 kHz or more, and more preferably 900 kHz or more, for ultrasonic cleaning. By using such a frequency, damage to the oxide 230b and the like can be reduced.

[0430] The above cleaning process may be performed multiple times, and the cleaning solution may be changed for each cleaning process. For example, a first cleaning process may be performed using diluted hydrofluoric acid or diluted ammonia water, and a second cleaning process may be performed using pure water or carbonated water.

[0431] As the cleaning process, in this embodiment, wet cleaning is performed using diluted ammonia water. By performing this cleaning process, impurities attached to the surfaces of the oxides 230a and 230b or diffused inside the oxides 230a and 230b can be removed.

[0432] After the etching or cleaning, a heat treatment may be performed. The heat treatment may be performed at a temperature of 100°C to 500°C, preferably 300°C to 500°C, and more preferably 350°C to 400°C. The heat treatment may be performed in an atmosphere of nitrogen gas, inert gas, or oxidizing gas. Alternatively, the heat treatment may be performed in an atmosphere of nitrogen gas or inert gas containing 10 ppm or more, 1% or more, or 10% or more of oxidizing gas. For example, the heat treatment is preferably performed in a mixed atmosphere of oxygen gas and nitrogen gas. This supplies oxygen to the oxide 230a and the oxide 230b, thereby reducing the oxygen deficiency (V O ) can be reduced. In addition, by performing such a heat treatment, the crystallinity of the oxide 230b can be improved. The heat treatment may be performed under reduced pressure. Alternatively, after the heat treatment in an oxygen atmosphere, the heat treatment may be performed continuously in a nitrogen atmosphere without exposure to the air. In addition, when the heat treatment in an oxygen atmosphere is performed continuously in a nitrogen atmosphere without exposure to the air, the heat treatment in the oxygen atmosphere may be performed for a longer period of time than the heat treatment in the nitrogen atmosphere.

[0433] Next, the insulating film 250A is formed (see FIGS. 21A to 21D). A heat treatment may be performed before the formation of the insulating film 250A, and the heat treatment may be performed under reduced pressure, and the insulating film 250A may be formed continuously without exposure to the atmosphere. The heat treatment is preferably performed in an atmosphere containing oxygen. By performing such a treatment, moisture and hydrogen adsorbed on the surface of the oxide 230b can be removed, and the moisture concentration and hydrogen concentration in the oxide 230a and the oxide 230b can be further reduced. The temperature of the heat treatment is preferably 100° C. or higher and 400° C. or lower.

[0434] The insulating film 250A can be formed by sputtering, CVD, PECVD, MBE, PLD, ALD, or the like. The insulating film 250A is preferably formed by a film formation method using a gas in which hydrogen atoms are reduced or removed. This allows the hydrogen concentration of the insulating film 250A to be reduced. Since the insulating film 250A becomes the insulator 250a that contacts the oxide 230b in a later process, it is preferable that the hydrogen concentration is reduced in this manner.

[0435] In addition, it is preferable to form the insulating film 250A by using the ALD method. The thickness of the insulator 250 functioning as the gate insulating film of the miniaturized transistor 200 must be extremely thin (for example, about 5 nm to 30 nm) and have small variations. In contrast, the ALD method is a film formation method in which a precursor and a reactant (for example, an oxidizing agent, etc.) are alternately introduced, and the thickness can be adjusted by the number of times this cycle is repeated, so that precise thickness adjustment is possible. Therefore, the precision of the thickness of the gate insulating film required by the miniaturized transistor 200 can be achieved. In addition, as shown in FIG. 21B and FIG. 21C, the insulating film 250A must be formed with good coverage on the bottom and side of the opening formed by the insulator 280, etc. Since layers of atoms can be deposited one by one on the bottom and side of the opening, the insulating film 250A can be formed with good coverage on the opening.

[0436] Also, for example, SiH 4 (or Si 2 H 6 When the insulating film 250A is formed by the PECVD method using a gas containing hydrogen such as SiO 2 , the hydrogen-containing gas is decomposed in the plasma to generate a large amount of hydrogen radicals. OWhen H is formed, the hydrogen concentration in the oxide 230b increases. However, when the insulating film 250A is formed using the ALD method, the generation of hydrogen radicals can be suppressed both when the precursor and the reactant are introduced. Therefore, by forming the insulating film 250A using the ALD method, the hydrogen concentration in the oxide 230b can be prevented from increasing.

[0437] In this embodiment, the insulating film 250A is formed of silicon oxide by the PEALD method.

[0438] If the above-mentioned impurities are not removed before forming the insulating film 250A, the impurities may remain between the oxide 230a, the oxide 230b, the conductor 242, the insulator 280, etc. and the insulator 250a.

[0439] Next, it is preferable to perform microwave treatment in an atmosphere containing oxygen (see Figs. 21A to 21D). Here, the microwave treatment refers to treatment using, for example, a device having a power source that generates high-density plasma using microwaves. In addition, in this specification and the like, microwave refers to electromagnetic waves having a frequency of 300 MHz or more and 300 GHz or less.

[0440] In FIG. 21B to FIG. 21D, the dotted lines indicate high-frequency oxygen plasma such as microwaves or RF, or oxygen radicals. For the microwave treatment, it is preferable to use a microwave treatment device having a power source that generates high-density plasma using microwaves. Here, the frequency of the microwave treatment device may be 300 MHz or more and 300 GHz or less, preferably 2.4 GHz or more and 2.5 GHz or less, for example, 2.45 GHz. In addition, the power of the power source that applies the microwave of the microwave treatment device may be 1000 W or more and 10000 W or less, preferably 2000 W or more and 5000 W or less. In addition, the microwave treatment device may have a power source that applies RF to the substrate side. By using high-density plasma, high-density oxygen radicals can be generated. In addition, by applying RF to the substrate side, oxygen ions generated by high-density plasma can be efficiently guided into the oxide 230b.

[0441] The microwave treatment is preferably carried out under reduced pressure, with the pressure being 60 Pa or more, preferably 133 Pa or more, more preferably 200 Pa or more, and even more preferably 400 Pa or more. For example, 10 Pa or more and 1000 Pa or less, preferably 300 Pa or more and 700 Pa or less. The treatment temperature is 750° C. or less, preferably 500° C. or less, for example, about 400° C. After the oxygen plasma treatment, a heat treatment may be carried out continuously without exposure to the outside air. For example, the temperature may be 100° C. or more and 750° C. or less, preferably 300° C. or more and 500° C. or less.

[0442] For example, the microwave treatment may be performed using oxygen gas and argon gas. Here, the oxygen flow rate ratio (O 2 / (O 2 The oxygen flow rate (O + Ar)) should be greater than 0% and less than 100%. 2 / (O 2 The oxygen flow rate (O + Ar) should be greater than 0% and less than 50%. 2 / (O 2 The oxygen flow rate ratio (O + Ar) should be 10% or more and 40% or less.2 / (O 2 +Ar)) may be set to 10% or more and 30% or less. In this way, by performing microwave treatment in an atmosphere containing oxygen, the carrier concentration in the region 230bc can be reduced. In addition, by preventing an excessive amount of oxygen from being introduced into the chamber during microwave treatment, it is possible to prevent the carrier concentration in the regions 230ba and 230bb from being excessively reduced.

[0443] As shown in Figures 21B to 21D, by performing microwave processing in an atmosphere containing oxygen, oxygen gas can be turned into plasma using microwaves or high frequency waves such as RF, and the oxygen plasma can be applied to the region between the conductors 242a and 242b of the oxide 230b. At this time, microwaves or high frequency waves such as RF can also be irradiated to the region 230bc. In other words, microwaves or high frequency oxygen plasma such as RF can be applied to the region 230bc shown in Figure 15A. The action of the plasma, microwaves, etc., causes the V of the region 230bc to increase. O H can be split off and hydrogen H can be removed from the region 230bc. O H→H+V O " occurs, and the V in the region 230bc O H can be reduced. Therefore, the oxygen vacancies in the region 230bc and V O By supplying oxygen radicals generated by the oxygen plasma or oxygen contained in the insulator 250 to the oxygen vacancies formed in the region 230bc, the oxygen vacancies in the region 230bc can be further reduced, and the carrier concentration can be reduced.

[0444] On the other hand, conductors 242a and 242b are provided on regions 230ba and 230bb shown in Fig. 15A. Here, conductor 242 preferably functions as a shielding film against the action of microwaves, high frequencies such as RF, oxygen plasma, etc., when performing microwave processing in an atmosphere containing oxygen. For this reason, conductor 242 preferably has a function of shielding electromagnetic waves of 300 MHz or more and 300 GHz or less, for example, 2.4 GHz or more and 2.5 GHz or less.

[0445] 21B to 21D, the conductors 242a and 242b shield the effects of microwaves or high-frequency oxygen plasma such as RF, so that these effects do not reach the regions 230ba and 230bb. As a result, the microwave treatment causes the V O Since there is no reduction in H and no excessive supply of oxygen, a decrease in the carrier concentration can be prevented.

[0446] In this manner, oxygen vacancies and V are selectively formed in the oxide semiconductor region 230bc. O By removing H, the region 230bc can be made i-type or substantially i-type. Furthermore, the supply of excess oxygen to the regions 230ba and 230bb that function as source and drain regions can be suppressed, and the n-type can be maintained. This suppresses fluctuations in the electrical characteristics of the transistor 200, and suppresses variations in the electrical characteristics of the transistor 200 within the substrate surface.

[0447] In addition, in the microwave treatment, thermal energy may be directly transferred to the oxide 230b due to electromagnetic interaction between the microwaves and the molecules in the oxide 230b. The oxide 230b may be heated by this thermal energy. Such a heating treatment may be called microwave annealing. By performing the microwave treatment in an atmosphere containing oxygen, an effect equivalent to that of oxygen annealing may be obtained. In addition, if the oxide 230b contains hydrogen, it is considered that the thermal energy is transferred to the hydrogen in the oxide 230b, and the activated hydrogen is released from the oxide 230b.

[0448] Next, the insulating film 250B is formed (see FIG. 22A to FIG. 22D). The insulating film 250B can be formed by sputtering, CVD, MBE, PLD, ALD, or the like. The insulating film 250B is preferably formed using an insulator having a function of suppressing oxygen diffusion. With such a configuration, it is possible to suppress the oxygen contained in the insulator 250a from diffusing into the conductor 260. That is, it is possible to suppress a decrease in the amount of oxygen supplied to the oxide 230. In addition, it is possible to suppress the oxidation of the conductor 260 due to the oxygen contained in the insulator 250a. For example, the insulating film 250A can be provided using a material that can be used for the insulator 250a described above, and the insulating film 250B can be provided using a material similar to that of the insulator 222.

[0449] Specifically, the insulating film 250B may be a metal oxide containing one or more of hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, magnesium, etc., or a metal oxide that can be used as the oxide 230. In particular, it is preferable to use an insulator containing an oxide of one or both of aluminum and hafnium.

[0450] In this embodiment, the insulating film 250B is formed by depositing hafnium oxide using a thermal ALD method.

[0451] A microwave treatment may be performed after the formation of the insulating film 250B (see FIGS. 22A to 22D). The microwave treatment may be performed under the conditions of the microwave treatment performed after the formation of the insulating film 250A described above. Alternatively, the microwave treatment may be performed after the formation of the insulating film 250B without performing the microwave treatment after the formation of the insulating film 250A.

[0452] Also, after the formation of the insulating film 250A and after the formation of the insulating film 250B, a heating treatment may be performed while maintaining the reduced pressure state. By performing such a treatment, hydrogen in the insulating film 250A, the insulating film 250B, the oxide 230b, and the oxide 230a can be efficiently removed. Also, some of the hydrogen may be gettered to the conductor 242 (the conductor 242a and the conductor 242b). Alternatively, a step of performing a heating treatment may be repeated multiple times while maintaining the reduced pressure state after the microwave treatment. By repeatedly performing the heating treatment, hydrogen in the insulating film 250A, the oxide 230b, and the oxide 230a can be more efficiently removed. The heating treatment temperature is preferably 300° C. or more and 500° C. or less. Also, the microwave treatment, i.e., microwave annealing, may serve as the heating treatment. If the oxide 230b, etc. is sufficiently heated by the microwave annealing, the heating treatment may not be performed.

[0453] Furthermore, by modifying the film quality of the insulating film 250A and the insulating film 250B by microwave processing, it is possible to suppress the diffusion of hydrogen, water, impurities, etc. Therefore, it is possible to suppress the diffusion of hydrogen, water, impurities, etc. into the oxide 230b, the oxide 230a, etc. through the insulator 250 by a post-process such as film formation of a conductive film that becomes the conductor 260, or a post-process such as heat treatment.

[0454] Next, a conductive film that becomes the conductor 260a and a conductive film that becomes the conductor 260b are formed in this order. The conductive film that becomes the conductor 260a and the conductive film that becomes the conductor 260b can be formed using a sputtering method, a CVD method, an MBE method, a PLD method, an ALD method, or the like. In this embodiment, the conductive film that becomes the conductor 260a is formed using the ALD method, and the conductive film that becomes the conductor 260b is formed using the CVD method.

[0455] Next, the insulating film 250A, the insulating film 250B, the conductive film to be the conductor 260a, and the conductive film to be the conductor 260b are polished by CMP until the insulator 280 is exposed, thereby forming the insulator 250a, the insulator 250b, the conductor 260a, and the conductor 260b (see FIGS. 23A to 23D). As a result, the insulator 250 is disposed so as to cover the opening that reaches the oxide 230b and the inner wall (side wall and bottom surface) of the groove of the oxide 230b. The conductor 260 is disposed so as to fill the opening and the groove through the insulator 250.

[0456] Next, heat treatment may be performed under the same conditions as the above heat treatment. In this embodiment, the treatment is performed in a nitrogen atmosphere at a temperature of 400° C. for 1 hour. The heat treatment can reduce the moisture and hydrogen concentrations in the insulators 250 and 280. Note that after the heat treatment, the insulator 282 may be formed without exposure to the air.

[0457] Next, the insulator 282 is formed over the insulator 250, the conductor 260, and the insulator 280 (see FIGS. 24A to 24D). The insulator 282 can be formed by a sputtering method, a CVD method, an MBE method, a PLD method, an ALD method, or the like. The insulator 282 is preferably formed by a sputtering method. By using a sputtering method that does not require the use of hydrogen in the film formation gas, the hydrogen concentration in the insulator 282 can be reduced. In addition, by forming the insulator 282 in an atmosphere containing oxygen by using a sputtering method, oxygen can be added to the insulator 280 while forming the film. This allows the insulator 280 to contain excess oxygen. At this time, the insulator 282 is preferably formed while heating the substrate.

[0458] In this embodiment, an aluminum oxide film is formed by pulse DC sputtering using an aluminum target in an atmosphere containing oxygen gas as the insulator 282. By using the pulse DC sputtering method, the film thickness distribution can be made more uniform, and the sputtering rate and film quality can be improved.

[0459] Next, it is preferable to perform heat treatment. The heat treatment can be performed under the same conditions as the above-mentioned heat treatment. In this embodiment, the treatment is performed in a nitrogen atmosphere at a temperature of 400° C. for one hour. By the heat treatment, oxygen added by the formation of the insulator 282 can be diffused into the insulator 280 and the insulator 250a and selectively supplied to the channel formation region of the oxide 230. As a result, a semiconductor device with favorable electrical characteristics can be provided. In addition, a semiconductor device with favorable reliability can be provided.

[0460] Note that the above heat treatment may be performed not only after the formation of the insulator 282 but also after the formation of the insulator 283, or the like.

[0461] Next, the insulator 283 is formed over the insulator 282 (see FIGS. 24A to 24D). The insulator 283 can be formed by a sputtering method, a CVD method, an MBE method, a PLD method, an ALD method, or the like. The insulator 283 is preferably formed by a sputtering method. By using a sputtering method that does not require hydrogen as a deposition gas, the hydrogen concentration in the insulator 283 can be reduced. The insulator 283 may also be multi-layered. For example, a silicon nitride film may be formed by a sputtering method, and a silicon nitride film may be formed on the silicon nitride by a CVD method.

[0462] Next, an insulator 285 is formed over the insulator 283. The insulating film can be formed by a sputtering method, a CVD method, an MBE method, a PLD method, an ALD method, or the like. For example, a silicon oxide film may be formed as the insulating film by a CVD method.

[0463] Next, openings reaching the conductor 242 are formed in the insulators 271, 275, 280, 282, 283, and 285 (see FIGS. 25A to 25D). The openings may be formed by using a lithography method. Note that, although the shape of the openings is circular in top view in FIG. 25A, the shape is not limited to this. For example, the openings may be substantially circular such as an ellipse, polygonal such as a rectangle, or polygonal such as a rectangle with rounded corners in top view.

[0464] Next, an insulating film that will become the insulator 241 is formed, and the insulating film is anisotropically etched to form the insulator 241 (see FIGS. 25A to 25D). The insulating film that will become the insulator 241 can be formed by sputtering, CVD, MBE, PLD, ALD, or the like. It is preferable to use an insulating film that has a function of suppressing oxygen permeation as the insulating film that will become the insulator 241. For example, it is preferable to form a film of aluminum oxide by the ALD method, and then form a film of silicon nitride thereon by the PEALD method. Silicon nitride is preferable because it has high barrier properties against hydrogen.

[0465] Moreover, for example, a dry etching method or the like may be used as the anisotropic etching of the insulating film that becomes the insulator 241. By providing the insulator 241 on the side wall of the opening, it is possible to suppress the permeation of oxygen from the outside and prevent the oxidation of the conductor 240a and the conductor 240b to be formed next. It is also possible to prevent impurities such as water and hydrogen contained in the insulator 280 from diffusing into the conductor 240a and the conductor 240b.

[0466] Next, a conductive film that becomes the conductor 240a and the conductor 240b is formed. The conductive film that becomes the conductor 240a and the conductor 240b is preferably a laminated structure including a conductor that has a function of suppressing the permeation of impurities such as water and hydrogen. For example, it can be a laminated structure of tantalum nitride, titanium nitride, or the like, and tungsten, molybdenum, copper, or the like. The conductive film that becomes the conductor 240 can be formed by using a sputtering method, a CVD method, an MBE method, a PLD method, an ALD method, or the like.

[0467] Next, a CMP process is performed to remove parts of the conductive film that will become the conductors 240a and 240b, exposing the upper surface of the insulator 285. As a result, the conductive film remains only in the openings, forming the conductors 240a and 240b with flat upper surfaces (see Figures 25A to 25D). Note that the CMP process may remove part of the upper surface of the insulator 285.

[0468] Next, a conductive film is formed to become the conductor 246. The conductive film to become the conductor 246 can be formed by sputtering, CVD, MBE, PLD, ALD, or the like.

[0469] Next, the conductive film that becomes the conductor 246 is processed by lithography to form the conductor 246a in contact with the top surface of the conductor 240a and the conductor 246b in contact with the top surface of the conductor 240b. At this time, a part of the insulator 285 in the region where the conductor 246a and the conductor 246b do not overlap with the insulator 285 may be removed.

[0470] Through the above steps, a semiconductor device including the transistor 200 illustrated in Figures 14A to 14D can be manufactured. As illustrated in Figures 16A to 25A, 16B to 25B, 16C to 25C, and 16D to 25D, the transistor 200 can be manufactured by using the method for manufacturing a semiconductor device described in this embodiment.

[0471] <Microwave processing equipment> A microwave processing apparatus that can be used in the above-described method for manufacturing a semiconductor device will be described below.

[0472] First, the configuration of a manufacturing apparatus capable of reducing the inclusion of impurities during the manufacture of a semiconductor device or the like will be described with reference to FIGS.

[0473] 26 is a schematic top view of a single-wafer multi-chamber manufacturing apparatus 2700. The manufacturing apparatus 2700 includes an atmosphere-side substrate supply chamber 2701 having a cassette port 2761 for accommodating a substrate and an alignment port 2762 for aligning the substrate, an atmosphere-side substrate transfer chamber 2702 for transferring the substrate from the atmosphere-side substrate supply chamber 2701, a load lock chamber 2703a for loading the substrate and for reducing the pressure in the chamber from atmospheric pressure or from reduced pressure to atmospheric pressure, an unload lock chamber 2703b for unloading the substrate and for switching the pressure in the chamber from reduced pressure to atmospheric pressure or from atmospheric pressure to reduced pressure, a transfer chamber 2704 for transferring the substrate in a vacuum, a chamber 2706a, a chamber 2706b, a chamber 2706c, and a chamber 2706d.

[0474] The atmospheric side substrate transfer chamber 2702 is connected to a load lock chamber 2703a and an unload lock chamber 2703b, the load lock chamber 2703a and the unload lock chamber 2703b are connected to a transfer chamber 2704, and the transfer chamber 2704 is connected to a chamber 2706a, a chamber 2706b, a chamber 2706c, and a chamber 2706d.

[0475] A gate valve GV is provided at the connection between each chamber, and each chamber can be independently maintained in a vacuum state, except for the atmosphere side substrate supply chamber 2701 and the atmosphere side substrate transfer chamber 2702. A transfer robot 2763a is provided in the atmosphere side substrate transfer chamber 2702, and a transfer robot 2763b is provided in the transfer chamber 2704. Substrates can be transferred within the manufacturing apparatus 2700 by the transfer robot 2763a and the transfer robot 2763b.

[0476] The back pressure (total pressure) of the transfer chamber 2704 and each chamber is, for example, 1×10 -4 Pa or less, preferably 3×10 -5 Pa or less, more preferably 1×10 -5 The partial pressure of gas molecules (atoms) with a mass-to-charge ratio (m / z) of 18 in the transfer chamber 2704 and each chamber is, for example, 3×10 -5 Pa or less, preferably 1×10 -5 Pa or less, more preferably 3×10 -6 The partial pressure of gas molecules (atoms) with m / z of 28 in the transfer chamber 2704 and each chamber is, for example, 3×10 -5 Pa or less, preferably 1×10 -5 Pa or less, more preferably 3×10 -6 The partial pressure of gas molecules (atoms) with m / z of 44 in the transfer chamber 2704 and each chamber is, for example, 3×10 -5 Pa or less, preferably 1×10 -5 Pa or less, more preferably 3×10 -6 Pa or less.

[0477] The total pressure and partial pressure in the transfer chamber 2704 and each chamber can be measured using a mass spectrometer. For example, a quadrupole mass spectrometer (also called Q-mass) Qulee CGM-051 manufactured by ULVAC, Inc. may be used.

[0478] In addition, it is desirable that the transfer chamber 2704 and each chamber have a configuration with little external or internal leakage. For example, the leak rate of the transfer chamber 2704 and each chamber is 3×10 -6 Pa·m 3 / s or less, preferably 1×10 -6 Pa·m 3 / s or less. For example, the leak rate of a gas molecule (atom) with m / z of 18 is 1×10 -7 Pa·m 3 / s or less, preferably 3×10 -8 Pa·m 3 / s or less. For example, the leak rate of a gas molecule (atom) with m / z of 28 is 1×10 -5 Pa·m 3 / s or less, preferably 1×10 -6 Pa·m 3 / s or less. For example, the leak rate of a gas molecule (atom) with m / z of 44 is 3×10 -6 Pa·m 3 / s or less, preferably 1×10 -6 Pa·m 3 / s or less.

[0479] The leak rate can be derived from the total pressure and partial pressure measured using the mass spectrometer mentioned above. The leak rate depends on external and internal leaks. External leaks are gases that flow in from outside the vacuum system due to tiny holes or poor seals. Internal leaks are caused by leakage from partitions such as valves in the vacuum system, or gases released from internal components. To keep the leak rate below the above values, measures must be taken to prevent both external and internal leaks.

[0480] For example, the opening and closing parts of the transfer chamber 2704 and each chamber may be sealed with a metal gasket. The metal gasket is preferably made of a metal coated with iron fluoride, aluminum oxide, or chromium oxide. Metal gaskets have higher adhesion than O-rings and can reduce external leakage. In addition, by using a passivated metal coated with iron fluoride, aluminum oxide, chromium oxide, or the like, the release of gas containing impurities from the metal gasket is suppressed, and internal leakage can be reduced.

[0481] In addition, aluminum, chromium, titanium, zirconium, nickel, or vanadium, which emits less gas containing impurities, is used as a member constituting the manufacturing apparatus 2700. In addition, the above-mentioned metals which emit less gas containing impurities may be used by coating an alloy containing iron, chromium, nickel, etc. Alloys containing iron, chromium, nickel, etc. are rigid, heat-resistant, and suitable for processing. Here, if the surface irregularities of the members are reduced by polishing or the like in order to reduce the surface area, the amount of emitted gas can be reduced.

[0482] Alternatively, the components of the manufacturing apparatus 2700 described above may be coated with iron fluoride, aluminum oxide, chromium oxide, or the like.

[0483] It is preferable that the components of the manufacturing apparatus 2700 are constructed solely from metal as much as possible. For example, even if a viewing window made of quartz or the like is installed, it is advisable to thinly coat the surface with iron fluoride, aluminum oxide, chromium oxide, or the like to suppress outgassing.

[0484] The adsorbed matter present in the transfer chamber 2704 and each chamber does not affect the pressure of the transfer chamber 2704 and each chamber because it is adsorbed to the inner walls, but it causes gas emission when the transfer chamber 2704 and each chamber are evacuated. Therefore, although there is no correlation between the leak rate and the exhaust speed, it is important to use a pump with high exhaust capacity to desorb as much of the adsorbed matter present in the transfer chamber 2704 and each chamber and evacuate them in advance. In addition, the transfer chamber 2704 and each chamber may be baked to promote the desorption of the adsorbed matter. By baking, the desorption speed of the adsorbed matter can be increased by about 10 times. Baking may be performed at 100°C or higher and 450°C or lower. At this time, if the adsorbed matter is removed while introducing an inert gas into the transfer chamber 2704 and each chamber, the desorption speed of water and the like that is difficult to desorb by only exhausting can be further increased. In addition, the desorption speed of the adsorbed matter can be further increased by heating the inert gas introduced to the same temperature as the baking temperature. Here, it is preferable to use a rare gas as the inert gas.

[0485] Alternatively, it is preferable to increase the pressure in the transfer chamber 2704 and each chamber by introducing an inert gas such as a heated rare gas or oxygen, and then evacuate the transfer chamber 2704 and each chamber again after a certain time has passed. By introducing a heated gas, it is possible to desorb adsorbed substances in the transfer chamber 2704 and each chamber, and it is possible to reduce impurities present in the transfer chamber 2704 and each chamber. It is effective to repeat this process 2 to 30 times, preferably 5 to 15 times. Specifically, by introducing an inert gas or oxygen having a temperature of 40° C. to 400° C., preferably 50° C. to 200° C., the pressure in the transfer chamber 2704 and each chamber is set to 0.1 Pa to 10 kPa, preferably 1 Pa to 1 kPa, and more preferably 5 Pa to 100 Pa, and the period for maintaining the pressure is 1 minute to 300 minutes, preferably 5 minutes to 120 minutes. Thereafter, the transfer chamber 2704 and each chamber are evacuated for a period of 5 to 300 minutes, preferably 10 to 120 minutes.

[0486] Next, chamber 2706b and chamber 2706c will be described with reference to the schematic cross-sectional view shown in FIG.

[0487] The chamber 2706b and the chamber 2706c are chambers capable of performing microwave processing on an object to be processed, for example. The chamber 2706b and the chamber 2706c differ only in the atmosphere during microwave processing. Since the other configurations are common, they will be described together below.

[0488] The chamber 2706b and the chamber 2706c have a slot antenna plate 2808, a dielectric plate 2809, a substrate holder 2812, and an exhaust port 2819. In addition, outside the chamber 2706b and the chamber 2706c, a gas supply source 2801, a valve 2802, a high frequency generator 2803, a waveguide 2804, a mode converter 2805, a gas pipe 2806, a waveguide 2807, a matching box 2815, a high frequency power supply 2816, a vacuum pump 2817, and a valve 2818 are provided.

[0489] The high frequency generator 2803 is connected to the mode converter 2805 via a waveguide 2804. The mode converter 2805 is connected to a slot antenna plate 2808 via a waveguide 2807. The slot antenna plate 2808 is disposed in contact with a dielectric plate 2809. The gas supply source 2801 is connected to the mode converter 2805 via a valve 2802. Gas is sent to the chambers 2706b and 2706c through a gas pipe 2806 passing through the mode converter 2805, the waveguide 2807, and the dielectric plate 2809. The vacuum pump 2817 has a function of exhausting gas and the like from the chambers 2706b and 2706c via a valve 2818 and an exhaust port 2819. The high frequency power supply 2816 is connected to the substrate holder 2812 via a matching box 2815.

[0490] The substrate holder 2812 has a function of holding the substrate 2811. For example, the substrate holder 2812 has a function of electrostatically or mechanically chucking the substrate 2811. The substrate holder 2812 also has a function as an electrode to which power is supplied from a high frequency power supply 2816. The substrate holder 2812 also has an internal heating mechanism 2813 and has a function of heating the substrate 2811.

[0491] For example, a dry pump, a mechanical booster pump, an ion pump, a titanium sublimation pump, a cryopump, or a turbo molecular pump can be used as the vacuum pump 2817. A cryotrap may be used in addition to the vacuum pump 2817. The use of a cryopump and a cryotrap is particularly preferable because water can be efficiently exhausted.

[0492] The heating mechanism 2813 may be, for example, a heating mechanism that uses a resistance heating element or the like for heating. Alternatively, it may be a heating mechanism that uses heat conduction or heat radiation from a medium such as a heated gas for heating. For example, RTA (Rapid Thermal Annealing) such as GRTA (Gas Rapid Thermal Annealing) or LRTA (Lamp Rapid Thermal Annealing) can be used. GRTA performs heating processing using high-temperature gas. An inert gas is used as the gas.

[0493] The gas supply source 2801 may be connected to a refiner via a mass flow controller. It is preferable to use a gas with a dew point of -80° C. or less, preferably -100° C. or less. For example, oxygen gas, nitrogen gas, and rare gas (such as argon gas) may be used.

[0494] The dielectric plate 2809 may be made of, for example, silicon oxide (quartz), aluminum oxide (alumina), or yttrium oxide (yttria). A separate protective layer may be formed on the surface of the dielectric plate 2809. The protective layer may be made of magnesium oxide, titanium oxide, chromium oxide, zirconium oxide, hafnium oxide, tantalum oxide, silicon oxide, aluminum oxide, or yttrium oxide. The dielectric plate 2809 is exposed to a particularly high-density region of the high-density plasma 2810 described later, and thus damage to the dielectric plate 2809 can be mitigated by providing a protective layer. As a result, an increase in particles during processing can be suppressed.

[0495] The high frequency generator 2803 has a function of generating microwaves of, for example, 0.3 GHz to 3.0 GHz, 0.7 GHz to 1.1 GHz, or 2.2 GHz to 2.8 GHz. The microwaves generated by the high frequency generator 2803 are transmitted to the mode converter 2805 via the waveguide 2804. In the mode converter 2805, the microwaves transmitted as TE mode are converted to TEM mode. Then, the microwaves are transmitted to the slot antenna plate 2808 via the waveguide 2807. The slot antenna plate 2808 is provided with a plurality of slot holes, and the microwaves pass through the slot holes and the dielectric plate 2809. Then, an electric field is generated below the dielectric plate 2809, and a high density plasma 2810 can be generated. In the high density plasma 2810, ions and radicals according to the gas species supplied from the gas supply source 2801 exist. For example, oxygen radicals and the like exist.

[0496] At this time, the film on the substrate 2811 can be modified by the ions and radicals generated by the high-density plasma 2810. It may be preferable to apply a bias to the substrate 2811 side using a high-frequency power supply 2816. For the high-frequency power supply 2816, an RF power supply with a frequency of, for example, 13.56 MHz or 27.12 MHz may be used. By applying a bias to the substrate side, the ions in the high-density plasma 2810 can be efficiently delivered to the depths of the openings of the film on the substrate 2811.

[0497] For example, oxygen can be introduced from a gas supply source 2801 into the chamber 2706b or the chamber 2706c to perform oxygen radical treatment using a high density plasma 2810.

[0498] Next, chamber 2706a and chamber 2706d will be described with reference to the schematic cross-sectional view shown in FIG.

[0499] The chamber 2706a and the chamber 2706d are chambers capable of irradiating the object to be treated with electromagnetic waves, for example. The only difference between the chamber 2706a and the chamber 2706d is the type of electromagnetic waves. As the other configurations are largely common, they will be described together below.

[0500] The chamber 2706a and the chamber 2706d each have one or more lamps 2820, a substrate holder 2825, a gas inlet 2823, and an exhaust port 2830. In addition, a gas supply source 2821, a valve 2822, a vacuum pump 2828, and a valve 2829 are provided outside the chamber 2706a and the chamber 2706d.

[0501] The gas supply source 2821 is connected to a gas inlet 2823 via a valve 2822. The vacuum pump 2828 is connected to an exhaust port 2830 via a valve 2829. The lamp 2820 is disposed facing a substrate holder 2825. The substrate holder 2825 has a function of holding a substrate 2824. The substrate holder 2825 also has an internal heating mechanism 2826 and has a function of heating the substrate 2824.

[0502] A light source having a function of emitting electromagnetic waves such as visible light or ultraviolet light may be used as the lamp 2820. For example, a light source having a function of emitting electromagnetic waves having a peak wavelength of 10 nm to 2500 nm, 500 nm to 2000 nm, or 40 nm to 340 nm may be used.

[0503] For example, lamp 2820 may be a light source such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, or a high pressure mercury lamp.

[0504] For example, the electromagnetic waves emitted from the lamps 2820 can be absorbed in part or in whole by the substrate 2824 to modify a film on the substrate 2824. For example, defects can be generated or reduced, or impurities can be removed. If the process is performed while the substrate 2824 is heated, defects can be generated or reduced, or impurities can be removed efficiently.

[0505] Alternatively, for example, the substrate holder 2825 may be heated by electromagnetic waves emitted from the lamps 2820, thereby heating the substrate 2824. In that case, the substrate holder 2825 does not need to have the heating mechanism 2826 inside.

[0506] For the vacuum pump 2828, refer to the description of the vacuum pump 2817. For the heating mechanism 2826, refer to the description of the heating mechanism 2813. For the gas supply source 2821, refer to the description of the gas supply source 2801.

[0507] The microwave processing device that can be used in this embodiment is not limited to the above. A microwave processing device 2900 shown in FIG. 29 can be used. The microwave processing device 2900 has a quartz tube 2901, a gas supply source 2801, a valve 2802, a high frequency generator 2803, a waveguide 2804, a gas pipe 2806, a vacuum pump 2817, a valve 2818, and an exhaust port 2819. The microwave processing device 2900 also has a substrate holder 2902 that holds a plurality of substrates 2811 (2811_1 to 2811_n, n is an integer of 2 or more) in the quartz tube 2901. The microwave processing device 2900 may also have a heating means 2903 on the outside of the quartz tube 2901.

[0508] Microwaves generated by a high frequency generator 2803 are irradiated to a substrate provided in a quartz tube 2901 through a waveguide 2804. A vacuum pump 2817 is connected to an exhaust port 2819 through a valve 2818, and can adjust the pressure inside the quartz tube 2901. A gas supply source 2801 is connected to a gas pipe 2806 through a valve 2802, and can introduce a desired gas into the quartz tube 2901. A heating means 2903 can heat a substrate 2811 in the quartz tube 2901 to a desired temperature. Alternatively, the heating means 2903 may heat a gas supplied from the gas supply source 2801. The microwave processing device 2900 can simultaneously perform a heat treatment and a microwave treatment on the substrate 2811. Also, a microwave treatment can be performed after the substrate 2811 is heated. Also, a heat treatment can be performed on the substrate 2811 after the microwave treatment.

[0509] The substrates 2811_1 to 2811_n may all be processing substrates for forming semiconductor devices or memory devices, or some of the substrates may be dummy substrates. For example, the substrates 2811_1 and 2811_n may be dummy substrates, and the substrates 2811_2 to 2811_n-1 may be processing substrates. Also, the substrates 2811_1, 2811_2, 2811_n-1, and 2811_n may be dummy substrates, and the substrates 2811_3 to 2811_n-2 may be processing substrates. By using a dummy substrate, a plurality of processing substrates are uniformly processed during microwave processing or heat processing, and the variation between the processing substrates can be reduced, which is preferable. For example, by arranging a dummy substrate on the processing substrate closest to the high frequency generator 2803 and the waveguide 2804, the processing substrate can be prevented from being directly exposed to microwaves, which is preferable.

[0510] By using the above manufacturing apparatus, it is possible to modify the film while suppressing the inclusion of impurities in the processed object.

[0511] Moreover, the microwave processing apparatus shown in FIGS. 27 to 29 can also be used in the processing chamber 4011 shown in FIG. 7 of the previous embodiment.

[0512] <Modifications of the semiconductor device> An example of a semiconductor device which is one embodiment of the present invention will be described below with reference to FIG.

[0513] FIG. 30A shows a top view of the semiconductor device 500. The x-axis shown in FIG. 30A is parallel to the channel length direction of the transistor 200, and the y-axis is perpendicular to the x-axis. FIG. 30B is a cross-sectional view corresponding to the portion indicated by the dashed line A1-A2 shown in FIG. 30A, and is also a cross-sectional view in the channel length direction of the transistor 200. FIG. 30C is a cross-sectional view corresponding to the portion indicated by the dashed line A3-A4 shown in FIG. 30A, and is also a cross-sectional view of the opening region 400 and its vicinity. Note that some elements are omitted in the top view of FIG. 30A for clarity.

[0514] 30A to 30C, structures having the same functions as those of the structures constituting the semiconductor device shown in <Configuration example of semiconductor device> are denoted by the same reference numerals. Note that, in this section as well, the materials described in detail in <Configuration example of semiconductor device> can be used as the materials constituting the semiconductor device.

[0515] The semiconductor device 500 shown in Figures 30A to 30C is a modified example of the semiconductor device shown in Figures 14A to 14D. The semiconductor device 500 shown in Figures 30A to 30C differs from the semiconductor device shown in Figures 14A to 14D in that an opening region 400 is formed in the insulator 282 and the insulator 280. Also, the semiconductor device 500 differs from the semiconductor device shown in Figures 14A to 14D in that a sealing portion 265 is formed so as to surround the multiple transistors 200.

[0516] The semiconductor device 500 has a plurality of transistors 200 and a plurality of opening regions 400 arranged in a matrix. A plurality of conductors 260 functioning as gate electrodes of the transistors 200 are provided extending in the y-axis direction. The opening region 400 is formed in a region that does not overlap with the oxide 230 and the conductors 260. A sealing portion 265 is formed to surround the plurality of transistors 200, the plurality of conductors 260, and the plurality of opening regions 400. The number, arrangement, and size of the transistors 200, the conductors 260, and the opening regions 400 are not limited to the structure shown in FIG. 30, and may be appropriately set according to the design of the semiconductor device 500.

[0517] As shown in FIG. 30B and FIG. 30C, the sealing portion 265 is provided so as to surround the multiple transistors 200, the insulators 216, the insulators 222, the insulators 275, the insulators 280, and the insulators 282. In other words, the insulators 283 are provided so as to cover the insulators 216, the insulators 222, the insulators 275, the insulators 280, and the insulators 282. In addition, in the sealing portion 265, the insulators 283 are in contact with the upper surface of the insulators 214. In addition, in the sealing portion 265, the insulators 274 are provided between the insulators 283 and 285. The upper surface of the insulator 274 is approximately the same height as the uppermost surface of the insulator 283. In addition, the insulators 274 may be the same as the insulators 280.

[0518] With such a structure, the multiple transistors 200 can be enclosed by the insulator 283, the insulator 214, and the insulator 212. Here, it is preferable that one or more of the insulators 283, 214, and 212 function as a barrier insulating film against hydrogen. This can prevent hydrogen contained outside the region of the sealing portion 265 from entering the region of the sealing portion 265.

[0519] 30C, insulator 282 has an opening in opening region 400. In addition, insulator 280 may have a groove overlapping the opening of insulator 282 in opening region 400. The depth of the groove in insulator 280 may be at most until the top surface of insulator 275 is exposed, and may be, for example, approximately ¼ to ½ of the maximum film thickness of insulator 280.

[0520] 30C, insulator 283 contacts the side surface of insulator 282, the side surface of insulator 280, and the top surface of insulator 280 inside opening region 400. Also, a part of insulator 274 may be formed so as to fill a recess formed in insulator 283 within opening region 400. At this time, the height of the top surface of insulator 274 formed within opening region 400 and the top surface of insulator 283 may roughly match.

[0521] By performing heat treatment in a state where such an opening region 400 is formed and the insulator 280 is exposed through the opening of the insulator 282, part of the oxygen contained in the insulator 280 can be diffused outward from the opening region 400 while oxygen is supplied to the oxide 230. In this way, sufficient oxygen can be supplied from the insulator 280 containing oxygen released by heating to a region in the oxide semiconductor layer that functions as a channel formation region and its vicinity, while preventing an excessive amount of oxygen from being supplied.

[0522] At this time, the hydrogen contained in the insulator 280 can be bonded with oxygen and released to the outside through the opening region 400. The hydrogen bonded with oxygen is released as water. Therefore, the hydrogen contained in the insulator 280 can be reduced, and the hydrogen contained in the insulator 280 can be prevented from mixing with the oxide 230.

[0523] In addition, in FIG. 30A, the shape of the opening region 400 in top view is substantially rectangular, but the present invention is not limited to this. For example, the shape of the opening region 400 in top view may be rectangular, elliptical, circular, rhombic, or a combination of these. The area and arrangement interval of the opening region 400 can be appropriately set accordi...

Claims

1. a first step of providing a first precursor to a chamber; a second step of providing a second precursor to the chamber; a third step of providing a third precursor to the chamber; a fourth step of introducing an oxidizing agent into the chamber after each of the first step, the second step, and the third step; the first to third precursors are different types of precursors, In the first to fourth steps, the substrate placed in the chamber is heated to a temperature of 300° C. or higher and not higher than the lowest temperature among the decomposition temperatures of the first to third precursors; the first precursor comprises indium; the second precursor has an element M, where M is one or more of gallium, aluminum, yttrium, and tin; the third precursor comprises zinc; the first to third precursors are free of carbon and hydrogen; the first to third precursors each contain chlorine; The oxidizing agent is ozone and oxygen. A method for forming a metal oxide film.

2. a first step of providing a first precursor to a chamber; a second step of providing a second precursor to the chamber; a third step of providing a third precursor to the chamber; a fourth step of generating an oxidizing agent into plasma and introducing the plasma into the chamber after each of the first step, the second step, and the third step; the first to third precursors are different types of precursors, In the first to fourth steps, the substrate placed in the chamber is heated to a temperature of 300° C. or higher and not higher than the lowest temperature among the decomposition temperatures of the first to third precursors; the first precursor comprises indium; the second precursor has an element M, where M is one or more of gallium, aluminum, yttrium, and tin; the third precursor comprises zinc; the first to third precursors are free of carbon and hydrogen; the first to third precursors each contain chlorine; The oxidizing agent is ozone and oxygen. A method for forming a metal oxide film.

3. In claim 1 or 2, One cycle is defined as one or more times of each of the first to fourth steps, and the one cycle is repeated a plurality of times. A method for forming a metal oxide film.

4. In claim 3, The ratio of the number of times of the first step, the number of times of the second step, and the number of times of the third step in one cycle is The ratio of the indium, the element M, and the zinc contained in the metal oxide is the same as that of the zinc contained in the metal oxide. A method for forming a metal oxide film.

5. In claim 3 or claim 4, After repeating the cycle multiple times, a heat treatment is performed. A method for forming a metal oxide film.

6. 1. A method for forming a first metal oxide film and a second metal oxide film on and in contact with the first metal oxide film, comprising: a ratio of indium, an element M (M is one or more of gallium, aluminum, yttrium, and tin), and zinc contained in the first metal oxide is different from a ratio of indium, an element M (M is one or more of gallium, aluminum, yttrium, and tin), and zinc contained in the second metal oxide; The deposition of the first metal oxide includes: a first step of providing a first precursor to a chamber; a second step of providing a second precursor to the chamber; a third step of providing a third precursor to the chamber; a fourth step of introducing an oxidizing agent into the chamber after each of the first step, the second step, and the third step; the first to third precursors are different types of precursors, In the first to fourth steps, the substrate placed in the chamber is heated to a temperature of 300° C. or higher and not higher than the lowest temperature among the decomposition temperatures of the first to third precursors; the first precursor comprises indium; the second precursor has an element M, where M is one or more of gallium, aluminum, yttrium, and tin; the third precursor comprises zinc; One cycle is defined as one or more times of each of the first to fourth steps, and the one cycle is repeated a plurality of times; a ratio of the number of times the first step is performed to the number of times the second step is performed to the number of times the third step is performed in one cycle is the same as a ratio of indium, element M, and zinc contained in the first metal oxide; The deposition of the second metal oxide includes: a fifth step of providing a fourth precursor to the chamber; a sixth step of providing a fifth precursor to the chamber; a seventh step of providing a sixth precursor to the chamber; an eighth step of introducing an oxidizing agent into the chamber after each of the fifth step, the sixth step, and the seventh step; the fourth to sixth precursors are different types of precursors, In the fifth to eighth steps, the substrate placed in the chamber is heated to a temperature of 300° C. or higher and not higher than the lowest temperature among the decomposition temperatures of the fourth to sixth precursors; the fourth precursor comprises indium; the fifth precursor has an element M, where M is one or more of gallium, aluminum, yttrium, and tin; the sixth precursor comprises zinc; one cycle is defined as one cycle in which each of the fifth to eighth steps is performed at least once, and one cycle of forming the second metal oxide film is repeated a plurality of times; a ratio of the number of times the fifth step is performed, the number of times the sixth step is performed, and the number of times the seventh step is performed in one cycle of film formation of the second metal oxide is the same as a ratio of indium, element M, and zinc contained in the second metal oxide; the first to sixth precursors are free of carbon and hydrogen; the first to sixth precursors each contain chlorine; The oxidizing agent is ozone and oxygen. A method for forming a metal oxide film.

Images