Metal oxide film formation method

Abstract

To provide a novel metal oxide film formation method.SOLUTION: A metal oxide film formation method includes: 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 the third step. 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 higher than or equal to 300°C and lower than or equal to a decomposition temperature of the first to third precursors.SELECTED DRAWING: Figure 1

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 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 (liquid crystal display devices, light-emitting display devices, etc.), 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 fields. One aspect of the invention disclosed in this specification 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 has attracted 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 with high on-state current. Another object of one embodiment of the present invention is to provide a semiconductor device with 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 with excellent 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 other problems 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 step, 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 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 converting an oxidant into plasma 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 one cycle is defined as carrying out each of the first to fourth steps at least once, and that one cycle is repeated multiple 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 first steps to the number of second steps to the number of third steps 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, wherein 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 lower than 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 means for supplying a different type of precursor, the fourth raw material supply unit has means for supplying an oxidizing agent, and the heater has means for heating a substrate placed in the chamber to a temperature of 300°C or higher and lower than the lowest temperature among 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 containing indium, the second raw material supply unit has a means for supplying a precursor containing 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 containing zinc.

[0021] In the above, the precursor containing indium, the precursor containing element M, and the precursor containing zinc preferably contain no carbon or hydrogen. Also, 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 that covers pipes provided between the first to fourth raw material supply parts and the chamber.

[0023] In the above, it is preferable that the apparatus 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. [Effects 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 another embodiment of the present invention, a novel metal oxide film formation apparatus can be provided. According to another embodiment of the present invention, a semiconductor device with high on-state current can be provided. According to another embodiment of the present invention, a semiconductor device with high field-effect mobility can be provided. According to another embodiment of the present invention, a semiconductor device with high reliability can be provided. According to another embodiment of the present invention, a semiconductor device with excellent electrical characteristics can be provided. According to another embodiment of the present invention, a semiconductor device that can be miniaturized or highly integrated can be provided. According to another embodiment of the present invention, a method for manufacturing the 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 necessarily 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 other effects from the description in the specification, drawings, claims, etc. [Brief explanation of the drawings]

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

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

[0028] In addition, in the drawings, sizes, layer thicknesses, or regions may be exaggerated for clarity. Therefore, the drawings are not necessarily limited to the scale. The drawings are schematic representations of ideal examples and are not limited to the shapes or values shown in the drawings. For example, in actual manufacturing processes, layers or resist masks may be unintentionally thinned by processes such as etching, but this may not be reflected in the drawings to facilitate understanding. In addition, in the drawings, the same reference numerals may be used in common between different drawings for identical parts or parts having similar functions, and repeated explanations may be omitted. When referring to similar functions, the same hatch pattern may be used and no particular reference numeral may be assigned.

[0029] In order to make the invention easier to understand, 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 processes or stacking. Therefore, for example, "first" can be appropriately replaced with "second" or "third," etc. in the description. Furthermore, the ordinal numbers used to identify one embodiment of the present invention may not match the ordinal numbers used in this specification.

[0031] Furthermore, in this specification, terms indicating arrangement such as "above" and "below" are used for convenience in describing the positional relationship between components with reference to the drawings. Furthermore, the positional relationship between 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, if it is explicitly stated in this specification that X and Y are connected, it is assumed that the specification also discloses cases in which X and Y are electrically connected, cases in which X and Y are functionally connected, and cases in which X and Y are directly connected. Therefore, it is not limited to a specific connection relationship, for example, a connection relationship shown in a figure or text, and it is assumed that connections other than those shown in a figure or text are also disclosed in a figure or text. Here, X and Y are assumed to be objects (e.g., devices, elements, circuits, wiring, electrodes, terminals, conductive films, layers, etc.).

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

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

[0035] Note that 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 the distance between the source (source region or source electrode) and the drain (drain region or drain electrode) in the 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 a single 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 region where a semiconductor (or a portion of the semiconductor through which current flows when the transistor is on) and a gate electrode overlap in a top view of a transistor, or the length of the channel formation region in a direction perpendicular to the channel length direction in the channel formation region. Note that the channel width of a single transistor does not necessarily have the same value in all regions. That is, the channel width of a single transistor may not be determined to a single value. Therefore, in this specification, the channel width refers to 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 the side surface of a semiconductor, the effective channel width may be larger than the apparent channel width, and the influence thereof may not be negligible. For example, in a fine transistor in which a gate electrode covers the side surface of a semiconductor, the proportion of the channel formation region formed on the side surface of the semiconductor may be large. In such a case, the effective channel width is larger than the apparent channel width.

[0038] In such cases, 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 accurately known, it is difficult to accurately measure the effective channel width.

[0039] In this specification, when simply referred to as a channel width, it may refer to an apparent channel width. Alternatively, when simply referred to as a channel width, it may refer to an effective channel width. Note that 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 component constituting the semiconductor. For example, an element with a concentration of less than 0.1 atomic % can be considered an impurity. The presence of impurities can, for example, increase the defect state density of 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 deficiency (V) in the oxide semiconductor. O It may be 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, silicon oxynitride is a material whose composition contains more oxygen than nitrogen. Furthermore, a nitride oxide is a material whose composition contains more nitrogen than oxygen. For example, 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] Furthermore, 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 cases in which the angle is -5 degrees or more and 5 degrees or less. Furthermore, "substantially 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. Furthermore, "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 cases in which the angle is 85 degrees or more and 95 degrees or less. Furthermore, "substantially 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 as "OSs"). For example, when a metal oxide is used in 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 including a metal oxide or an oxide semiconductor.

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

[0046] Furthermore, 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 x 10 at 85°C -18A or less, or 1 x 10 at 125°C -16 This means that it is A or below.

[0047] In addition, in this specification, when upper and lower limit values are specified, it is also considered that a configuration in which they can be freely combined 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 a 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, planar defects such as grain boundaries, and volume defects such as voids. Factors that cause lattice defects include a discrepancy in the ratio of the number of atoms of the constituent elements (an excess or deficiency 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, if 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, the electrical characteristics may be easily changed and reliability may be reduced. In addition, hydrogen atoms near the oxygen vacancies may be introduced into the oxygen vacancies (hereinafter referred to as V OOxygen vacancies are sometimes called H defects. These vacancies may form and generate electrons that serve as carriers. Therefore, if the channel formation region in the metal oxide contains oxygen vacancies, the transistor is likely to have normally-on characteristics (a channel exists and 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 in 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 present 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) structures, and amorphous structures. The a-like structures are intermediate between the nc structures and amorphous structures. The classification of crystal structures will be discussed later.

[0054] Furthermore, metal oxides with an a-like structure and metal oxides with an amorphous structure have pores or low-density regions. That is, metal oxides with an a-like structure and metal oxides with an amorphous structure have lower crystallinity than metal oxides with an nc structure and metal oxides with a CAAC structure. Furthermore, metal oxides with an a-like structure have a higher hydrogen concentration than metal oxides with an nc structure and metal oxides with a CAAC structure. Therefore, lattice defects are likely to be generated in metal oxides with an a-like structure and metal oxides with 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 with a single crystal structure. By using such a metal oxide for a transistor, a transistor with good electrical characteristics can be realized. Furthermore, a highly reliable transistor can be realized.

[0056] The highly crystalline metal oxides 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 polycrystalline metal oxide is used in a semiconductor layer of a transistor, the crystal grain boundaries act as recombination centers, and carriers are likely to be captured, resulting in a decrease in the on-state current and field-effect mobility of the transistor.

[0057] Furthermore, it is preferable to use a metal oxide for the channel formation region of a transistor, which increases the on-state current of the transistor. To increase the on-state current of the transistor, it is preferable to increase the mobility of the metal oxide used in the transistor. To increase the mobility of the metal oxide, it is necessary to improve the transport of carriers (electrons in the case of an n-channel transistor) or reduce scattering factors that contribute to the transport of carriers. 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 the transistor can be increased.

[0058] Here, it is preferable to use a metal oxide with high crystallinity for the metal oxide including the channel formation region. Furthermore, the crystal preferably has 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 referred to as 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-OSs, which will be described later.

[0059] Furthermore, it is 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, so that the multiple layers are arranged approximately parallel to the surface on which the metal oxide is formed or the film surface, i.e., the multiple layers extend in the channel length direction.

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

[0061] Examples of the crystal structure of the above crystal include a YbFe2O4 type structure, a Yb2Fe3O7 type structure, and modified structures thereof.

[0062] Furthermore, each of the first to third layers is preferably composed of one metal element or multiple metal elements with the same valence and oxygen. The valence of the one or more metal elements constituting the first layer is preferably the same as the valence of the one or more metal elements constituting the second layer. The first and second layers may also contain the same metal element. The valence of the one or more metal elements constituting the first layer is preferably different from the valence of the one or more 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. 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. It is particularly preferable that it contains indium and zinc. In addition, it preferably contains a metal element having the same valence as that of indium or zinc. Examples of such metal elements include aluminum, gallium, and yttrium. It may also contain one or more elements selected from iron, cobalt, nickel, lanthanum, cerium, neodymium, magnesium, calcium, and the like.

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

[0066] To form the metal oxide having the layered crystal structure, it is preferable to deposit atoms one layer at a time, for example, by ALD (Atomic Layer Deposition).

[0067] The ALD method utilizes the self-regulating properties of precursor molecules or atoms contained in the precursors to deposit atoms layer by layer. This allows for the formation of ultrathin films, films with high aspect ratios, films with fewer defects such as pinholes, films with excellent coverage, and films formed at low temperatures. The ALD method also includes plasma-enhanced ALD (PEALD), a film formation method that uses plasma. The use of plasma can sometimes be preferable because it enables film formation at lower temperatures. Note that some precursors used in the ALD method contain elements such as carbon or chlorine. Therefore, films formed by the ALD method may contain higher amounts of elements such as carbon or chlorine than films formed by other film formation methods. The quantification of these elements can be performed using X-ray photoelectron spectroscopy (XPS).

[0068] Unlike film formation methods 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 a workpiece. Therefore, it is a film formation method that is less affected by the shape of the workpiece and has good step coverage. In particular, the ALD method has excellent step coverage and excellent thickness uniformity, making it suitable for coating the surface of openings with high aspect ratios. However, because 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 CVD, which has a faster film formation rate.

[0069] The ALD method can control the composition of the obtained film by adjusting the introduction amount of the source gas. 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 compared to the case of using a plurality of film formation chambers because there is no need for the time required for transfer and pressure adjustment. Therefore, the productivity of semiconductor devices may be increased.

[0070] <ALD Apparatus and Film Formation Method Using 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 metal precursor) and a second source gas (sometimes referred to as a reactant, an oxidant, 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, for example, by switching each switching valve (sometimes referred to as a high-speed valve). Further, when introducing the source gas, an inert gas such as nitrogen (N2), 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 when the volatility of the source gas is low or the vapor pressure is low, adsorption of the source gas to the inside of the pipe and the valve can be suppressed, and the source gas can be introduced into the chamber. Also, the uniformity of the formed film is improved, which is preferable.

[0072] An example of a method for forming a metal oxide film having the above-described three-layered crystal structure using the ALD method will be described with reference to FIGS. 1A to 1E. First, precursor 11a is introduced into a chamber and adsorbed onto the surface of substrate 10 (see FIG. 1A; hereinafter, this step may be referred to as the first step). As shown in FIG. 1A, adsorption of precursor 11a onto the surface of substrate 10 initiates a self-limiting mechanism for the surface chemical reaction, preventing further adsorption of precursor 11a onto the layer of precursor 11a on substrate 10. The optimum substrate temperature range within which the self-limiting mechanism for the surface chemical reaction operates is also referred to as the ALD window. The ALD window is determined by the temperature characteristics, vapor pressure, decomposition temperature, and other factors 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 remove excess precursor 11a and reaction products from the chamber (hereinafter, this step may be referred to as the second step). Alternatively, instead of introducing an inert gas into the chamber, excess precursor and reaction products may be removed from the chamber by vacuum evacuation. The second step is also called purging.

[0074] Next, reactant 12a (for example, an oxidizing agent (ozone (O3), oxygen (O2), water (H2O), and plasma, radicals, ions, etc.)) is introduced into the chamber and reacted with precursor 11a adsorbed on the surface of substrate 10, causing some of the components contained in precursor 11a to desorb while leaving the constituent molecules of precursor 11a adsorbed on 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 part of precursor 11a is formed on the surface of substrate 10.

[0075] When performing the plasma ALD method, oxygen may be continuously supplied as an oxidant and plasma may be generated in the third step. As a result, oxygen plasma is formed in the third step and functions as reactant 12a. In this case, 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, excess reactant 12a and reaction products are discharged from the chamber by introducing an inert gas or evacuating (hereinafter, this step may be referred to as the fourth step).

[0077] Next, precursor 11b having a metal element different from precursor 11a is introduced, and a process similar to the first step is performed to adsorb precursor 11b onto the surface of oxide 13a (see FIG. 1C). Here, as shown in FIG. 1C, the adsorption of precursor 11b onto the oxide 13a layer triggers a self-termination mechanism of the surface chemical reaction, preventing further adsorption of precursor 11b onto 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 (see FIG. 1D). As a result, a layer of oxide 13b, which is formed by oxidizing a portion 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 vacuum evacuation.

[0081] Furthermore, by similarly performing the first to fourth steps, a layer of oxide 13c can be formed on the layer of oxide 13b. In this way, by repeatedly performing the steps of forming oxides 13a to 13c, a metal oxide having a layered crystal structure in which the stacked structure of oxides 13a to 13c is repeated can be formed (see FIG. 1E). That is, 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] When forming a metal oxide having a layered crystal structure, particularly a metal oxide having the CAAC structure, it is preferable to perform the process 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 multiple different precursors, it is preferable to set the substrate temperature to the decomposition temperature of the lowest precursor among the multiple precursors. This allows the multiple precursors used to be adsorbed onto the target object (e.g., substrate) without being decomposed during film formation by the ALD method.

[0083] By performing the above film formation while heating the substrate within this temperature range, impurities such as hydrogen and carbon contained in the precursor or reactant can be removed from the metal oxide during each of steps 1 to 4. For example, carbon in the metal oxide can be released as CO and CO, and hydrogen in the metal oxide can be released as HO. Furthermore, simultaneously with the removal of the impurities, metal and oxygen atoms can be rearranged, resulting in highly ordered arrangement of each oxide layer. This allows for the formation of a highly crystalline, layered metal oxide, particularly a metal oxide with the CAAC structure. While FIG. 1A illustrates an example of a configuration in which the precursor 11a is formed on the substrate 10, this is not limiting. For example, the precursor 11a may be formed on an insulating film (insulating film containing oxygen, nitrogen, silicon, aluminum, hafnium, etc.) or a conductive film (conductive film containing tungsten, tantalum, molybdenum, zirconium, aluminum, titanium, etc.) provided on the substrate 10. 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 within 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 higher and 700°C or lower, and more preferably 300°C or higher and 600°C or lower. As a precursor with such a high decomposition temperature, it is preferable to use a precursor formed from an inorganic substance (hereinafter referred to as an inorganic precursor). Inorganic precursors generally tend to have a higher decomposition temperature than precursors formed from organic substances (hereinafter referred to as organic precursors), and therefore some have an ALD window within the above temperature range. Furthermore, since inorganic precursors do not contain impurities such as hydrogen or carbon, an increase in the concentration of impurities such as hydrogen or carbon in the metal oxide film formed can be prevented.

[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 immediately after the formation of the film by the ALD method without exposing it to the open air. The heat treatment may be performed at a temperature of 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 may be performed in a nitrogen gas or inert gas atmosphere, or in an atmosphere containing 10 ppm or more, 1% or more, or 10% or more of an oxidizing gas. The heat treatment may also be performed under reduced pressure. Alternatively, the heat treatment may be performed in a nitrogen gas or inert gas atmosphere, followed by an atmosphere containing 10 ppm or more, 1% or more, or 10% or more of an oxidizing gas to replenish desorbed oxygen. Furthermore, if the heat treatment temperature is high, the metal oxide may take on a polycrystalline structure. Therefore, the heat treatment temperature should be appropriately set within a range in which the metal oxide does not take on a polycrystalline structure.

[0086] By performing this heat treatment, impurities such as hydrogen and carbon contained in the metal oxide can be removed. For example, carbon in the metal oxide can be released as CO2 and CO, and hydrogen in the metal oxide can be released as HO. Furthermore, simultaneously with the removal of the impurities, metal atoms and oxygen atoms are rearranged, improving crystallinity. Therefore, it is possible to form a metal oxide with a highly crystalline layered crystal structure, particularly a metal oxide with the CAAC structure.

[0087] Although FIG. 1 illustrates a structure in which oxides 13a to 13c are stacked repeatedly, the present invention is not limited to this. For example, a metal oxide may be used in which a single layer, two layers, or four or more oxide layers are repeatedly stacked. Although FIG. 1 illustrates the oxides 13a, 13b, and 13c repeatedly stacked in the same order, the present invention is not limited to this. For example, the order of the oxides 13a, 13b, and 13c may be reversed. Furthermore, the compositions of the oxides 13a, 13b, and 13c may be changed midway through the film. Although FIG. 1 illustrates different oxide layers adjacent to each other, such as the oxides 13a, 13b, and 13c, the present invention is not limited to this. For example, the same oxide layers may be continuously stacked, such as the oxides 13a, 13a, 13b, 13b, 13c, and 13c.

[0088] Furthermore, in the following description of this specification, unless otherwise specified, when ozone, oxygen, or water is used as a reactant or oxidant, it is understood that 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, which will be described later, may be used.

[0089] To remove impurities such as carbon or hydrogen contained in the precursor, it is preferable to allow the precursor to react sufficiently with the oxidizing agent. For example, the pulse time for introducing the oxidizing agent can be lengthened. Alternatively, the oxidizing agent can be introduced multiple times. When introducing the oxidizing agent multiple times, the same type of oxidizing agent or different types of oxidizing agents can be introduced. For example, water can be introduced into the chamber as a first oxidizing agent, followed by evacuation. Then, ozone or oxygen containing no hydrogen can be introduced into the chamber as a second oxidizing agent, followed by evacuation.

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

[0091] In this way, performing the third and fourth steps once or multiple times before the first step is preferable because it allows for control of the film formation atmosphere in the chamber. For example, introducing O3 and O2 as oxidizing agents in the third step can create an oxygen atmosphere in the chamber. Depositing a film in an oxygen atmosphere in the chamber is preferable because it increases the oxygen concentration in the film formed. Furthermore, oxygen can also be supplied to the insulator and oxide underlying the film. A semiconductor device formed using this method has excellent characteristics and high reliability. Furthermore, introducing water as an oxidizing agent in the third step can form hydrophilic groups on the formation surface, for example. This further improves the adsorption of the precursor.

[0092] Furthermore, after the first and second steps, the introduction of the second source gas in the third step and the evacuation or introduction of an 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, and so on.

[0093] For example, O3 and O2 may be introduced as oxidizing agents in the third step, and an inert gas may be introduced in the fourth step, and this process may be repeated multiple times. Furthermore, when repeating the third and fourth steps, it is not necessary to repeatedly introduce the same type of source gas. For example, H2O may be used as the oxidizing agent in the first third step, and O3 may be used as the oxidizing agent in the second or subsequent third steps.

[0094] In this way, by repeatedly introducing an oxidizing agent and an inert gas (or evacuating) into the chamber multiple times in a short period of time, excess hydrogen atoms, carbon atoms, chlorine atoms, etc. can be more reliably removed from the precursor adsorbed on the substrate surface and expelled to the outside of the chamber. Furthermore, by increasing the number of types of oxidizing agents to two, more excess hydrogen atoms, etc. can be removed from the precursor adsorbed on the substrate surface. In this way, by preventing hydrogen atoms from being incorporated into the film during film formation, the amount of water, hydrogen, etc. contained in the formed film can be reduced.

[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 in TDS analysis. 13 molecule / cm 2 Over 1.0 x 10 16 molecule / cm 2 Less than or equal to 1.0 × 10 13 molecule / cm 2 Over 3.0 x 10 15 molecule / cm 2 The following films can be formed:

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

[0097] Furthermore, ALD methods that involve the reaction of the precursor and reactant described above and the introduction of a plasma-excited reactant as a third source gas into the chamber are sometimes called plasma ALD methods. In this case, a plasma generator is installed at the introduction point for the third source gas. Inductively coupled plasma (ICP) can be used to generate plasma. In contrast, ALD methods that use thermal energy to cause the reaction of the precursor and reactant are sometimes called thermal ALD methods.

[0098] In the plasma ALD method, a plasma-excited reactant is introduced in the third step to form a film. Alternatively, a plasma-excited reactant (second reactant) is introduced simultaneously while repeating the first through fourth steps. 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 source gas can be the same material as the oxidizer. That is, plasma-excited ozone, oxygen, and water can be used as the second reactant. In addition to the oxidizer, a nitriding agent can also be used as the second reactant. Nitrogen (N2) or ammonia (NH3) can be used as the nitriding agent. A mixed gas of nitrogen (N2) and hydrogen (H2) can also be used as the nitriding agent. For example, a mixed gas of 5% nitrogen (N2) and 95% hydrogen (H2) can be used as the nitriding agent. Nitride films such as metal nitride films can be formed by introducing plasma-excited nitrogen or ammonia during film formation.

[0099] Argon (Ar), helium (He), or nitrogen (N2) may also be used as a carrier gas for the second reactant. Using a carrier gas such as argon, helium, or nitrogen facilitates plasma discharge and facilitates the generation of a plasma-excited second reactant, which is preferable. When forming an oxide film such as a metal oxide film using the plasma ALD method, using nitrogen as a carrier gas may result in nitrogen contamination in the film, making it difficult to obtain the desired film quality. In this case, it is preferable to use argon or helium as a 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] Furthermore, plasma ALD allows for film formation at even lower temperatures than thermal ALD. For example, plasma ALD can sometimes achieve film formation at temperatures below 100°C without reducing the film formation rate. Furthermore, plasma ALD can use many reactants, including not only oxidizing agents but also nitriding agents, allowing for the formation of many types of films, including not only oxides but also nitrides, fluorides, and metals.

[0102] Furthermore, when performing plasma ALD, plasma damage can be reduced by generating plasma from a plasma source such as an inductively coupled plasma (ICP) or electron cyclotron resonance plasma (ECR) at a distance 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 using Figures 2A to 3D. In Figures 2B, 2D, 3B, and 3D, atoms are represented by spheres (circles), and bonds between metal atoms and oxygen atoms are represented by lines. In Figures 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. 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 Figures 2B, 2D, 3B, and 3D.

[0104] FIG. 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, gate electrode, source electrode, and 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 to be deposited is arranged parallel to the substrate (or base, 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 oxide 60 shown in FIGS. 2A and 2B has a composition of In:M:Zn=1:1:1 [atomic ratio] and a crystal structure of YbFe2O4 type. The element M is a +3 valent metal element.

[0106] 2B, the crystals of the oxide 60 are formed by repeatedly stacking a layer 21 containing indium (In) and oxygen, a layer 31 containing the element M and oxygen, and a layer 41 containing zinc (Zn) and oxygen in this order. The layers 21, 31, and 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 stacking order of layers 21, 31, and 41 may be changed. For example, layers 21, 41, and 31 may be repeatedly stacked in this order. Alternatively, layers 21, 31, 41, 21, 41, and 31 may be repeatedly stacked in this order. Furthermore, part of the element M in layer 31 may be substituted with zinc, and part of the zinc in layer 41 may be substituted with element M.

[0109] In the above, an example of forming an In-M-Zn oxide with a composition of In:M:Zn=1:1:1 [atomic ratio] was shown. (1+α) M (1-α) O3(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, Figures 2C and 2D show an In-M-Zn oxide with a composition of In:M:Zn = 1:3:4 [atomic ratio].

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

[0111] 2D , the crystals of the oxide 62 include a layer 22 containing indium (In), an element M, and oxygen, a layer 41 containing zinc (Zn) and oxygen, and a layer 31 containing the element M and oxygen. In the oxide 62, multiple layers are repeatedly stacked in the order of layer 22, layer 41, layer 31, and layer 41. The layers 22, 31, and 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] The In-M-Zn oxide with an atomic ratio of In:M:Zn=1:3:4 is not limited to the structure shown in FIG. 2D , and the structure may be changed within the range of the atomic ratio of In:M:Zn=1:3:4. For example, the stacking order of layers 22, 31, and 41 may be changed. Furthermore, part of the element M in layer 31 may be substituted with zinc, and part of the zinc in layer 41 may be substituted with element M. Furthermore, layer 21 or layer 31 may be formed instead of layer 22.

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

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

[0115] 3B, the structures of the oxide 62 and the oxide 60 may be changed as described above. 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 for deposition on structures with high aspect ratios and can also form films with excellent coverage on the side surfaces of structures. Using the ALD method, crystalline metal oxides, such as those with a CAAC structure, can be easily formed regardless of the orientation of the surface on which the film is to be formed. For example, even if the structure has a convex or concave shape, metal oxides can be formed with good coverage on the top, bottom, side, and inclined surfaces of the structure. That is, metal oxides can be formed with a substantially constant film thickness in the normal direction on each surface on which the film is to be formed. The ratio of the minimum film thickness to the maximum film thickness of the metal oxide formed on each of the top, bottom, side, and inclined surfaces of the structure can be 0.5 to 1, preferably 0.7 to 1, and more preferably 0.9 to 1. In this case, if the metal oxide has a crystalline structure, its c-axis is oriented in a direction substantially parallel to the normal direction of each surface on which the film is to be formed. That is, the c-axis is oriented perpendicular to each surface on which the film is to be formed.

[0117] FIG. 3C shows a case where the deposition surface of the structure 50 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 stacked on the side surface of the structure 50. The indium-containing layer 21 is arranged parallel to the deposition surface of the structure 50, the layer 31 containing element M is arranged on top of it, parallel to the deposition surface of the structure 50, and the zinc-containing layer 41 is arranged on top of it, 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. Although Figures 3C and 3D show an example of In-M-Zn oxide with an atomic ratio of In:M:Zn=1:1:1, 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] Furthermore, in the above, examples of metal oxides with 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 these.

[0119] 4A, 4B, and 4C are used to explain preferred ranges of the atomic ratio of indium, the element M, and zinc in a metal oxide that can be used for the oxide shown in one embodiment of the present invention. Note that the atomic ratio of oxygen is not shown in FIGS. 4A, 4B, and 4C. The atomic ratios of indium, the element M, and zinc in a metal oxide are represented by [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] Furthermore, metal oxides with an atomic ratio of [In]:[M]:[Zn]=0:2:1, as shown in FIGS. 4A, 4B, and 4C, and values close thereto, 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. Also, 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 the 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] Increasing the indium content of a metal oxide can increase the carrier mobility (electron mobility) of the metal oxide. Therefore, a metal oxide with a high indium content has higher carrier mobility than a metal oxide with a low indium content.

[0126] On the other hand, as the indium and zinc contents in the metal oxide decrease, the carrier mobility decreases. Therefore, when the atomic ratio is [In]:[M]:[Zn]=0:1:0 or a value close to that (e.g., region C shown in Figure 4C), the insulating properties are high. Note that region C includes the region that is likely to form the spinel crystal structure described above, so it is preferable to use a composition that avoids the region that is likely to form the spinel crystal structure.

[0127] For example, the metal oxide used in the channel formation region and the low-resistivity region preferably has an atomic ratio shown in region A of FIG. 4A, which provides high carrier mobility. The metal oxide used in the channel formation region and the low-resistivity region may have an atomic ratio of, for example, In:Ga:Zn=4:2:3 to 4.1 or a value close to it. Alternatively, the metal oxide may have an atomic ratio of, for example, In:Ga:Zn=1:1:1 or a value close to it. On the other hand, when a metal oxide is provided to surround the channel formation region and the low-resistivity region, it preferably has an atomic ratio shown in region C of FIG. 4C, which provides relatively high insulating properties. The metal oxide provided to surround the channel formation region and the low-resistivity region may have an atomic ratio of, for example, In:Ga:Zn=1:3:4 or a value close to it, or In:Ga:Zn=1:3:2 or a value close to it. Alternatively, the metal oxide provided to surround the channel formation region and the low-resistivity region may be the same as the metal oxide used in the channel formation region and the low-resistivity 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] Note that 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 a metal oxide vary significantly 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 with a layered crystal structure that corresponds to each atomic ratio. Therefore, by using the ALD method, it is possible to form a metal oxide film that corresponds to the desired 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 an indium-containing precursor is introduced into the chamber, and the precursor is adsorbed onto the surface of the structure 50 (see FIG. 5A). Here, the source gas contains the precursor and a carrier gas such as argon, helium, or nitrogen. Examples of indium-containing precursors that can be used include trimethylindium, triethylindium, tris(2,2,6,6-tetramethyl-3,5-heptanedionate)indium, cyclopentadienylindium, indium(III) acetylacetonate, and (3-(dimethylamino)propyl)dimethylindium.

[0133] Alternatively, an inorganic precursor containing no hydrocarbon may be used as the indium-containing precursor. Examples of inorganic precursors that can be used include halogen-based indium compounds such as indium trichloride, indium tribromide, and indium triiodide. The decomposition temperature of indium trichloride is approximately 500°C to 700°C. Therefore, by using indium trichloride, film formation can be performed by the ALD method while heating the substrate at approximately 400°C to 600°C, for example, at 500°C.

[0134] Next, the introduction of the source gas 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, leaving indium adsorbed on the substrate while releasing components other than indium, forming a layer 21 in which indium and oxygen are combined (see FIG. 5B). Examples of oxidizing agents that can be used include ozone, oxygen, and water. Next, the introduction of the oxidizing agent is stopped, and the chamber is purged to remove excess reactant 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). The source gas contains the precursor and a carrier gas such as argon, helium, or nitrogen. When gallium is used as element M, examples of precursors containing gallium include trimethylgallium, triethylgallium, tris(dimethylamido)gallium, gallium(III) acetylacetonate, tris(2,2,6,6-tetramethyl-3,5-heptanedionate)gallium, dimethylchlorogallium, diethylchlorogallium, and dimethylgallium isopropoxide.

[0137] Alternatively, an inorganic precursor containing no hydrocarbon may be used as the gallium-containing precursor. Examples of the gallium-containing inorganic precursor include halogen-based gallium compounds such as gallium trichloride, gallium tribromide, and gallium triiodide. Gallium trichloride has a decomposition temperature of approximately 550°C to 700°C. Therefore, by using gallium trichloride, film formation can be performed by the ALD method while heating the substrate at approximately 450°C to 650°C, 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, leaving element M adsorbed on the substrate while components other than element M are removed, thereby forming layer 31 in which element M and oxygen are combined (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 layer 31 (see FIG. 6A). At this time, a portion of layer 41 in which zinc and oxygen are combined may be formed. In addition to the precursor, the source gas contains a carrier gas such as argon, helium, or nitrogen. Examples of zinc-containing precursors that can be used include dimethylzinc, diethylzinc, zinc bis(2,2,6,6-tetramethyl-3,5-heptanedionate), and zinc acetate.

[0141] Alternatively, an inorganic precursor containing no hydrocarbon may be used as the zinc-containing precursor. Examples of the zinc-containing inorganic precursor include halogen-based zinc compounds such as zinc dichloride, zinc dibromide, and zinc diiodide. The decomposition temperature of zinc dichloride is approximately 450°C to 700°C. Therefore, by using zinc dichloride, film formation can be performed by the ALD method while heating the substrate at approximately 350°C to 550°C, 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 remove excess reactant and reaction products from the chamber.

[0144] Next, the layer 21 is formed again on the layer 41 by the above-described method (see FIG. 6C). By repeating the above-described method, an oxide 60 can be formed on the substrate or 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 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] The processes shown in Figures 5A to 6C are preferably performed 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 this temperature range, impurities such as hydrogen and carbon contained in the precursor or reactant can be removed from the metal oxide during each process shown in Figures 5A to 6C. For example, carbon in the metal oxide can be released as CO2 and CO, and hydrogen in the metal oxide can be released as HO. Furthermore, simultaneously with the removal of the impurities, metal and oxygen atoms are rearranged, resulting in a highly ordered arrangement of each oxide layer. This allows the formation of a highly crystalline metal oxide with a layered crystal structure, such as a metal oxide with a CAAC structure.

[0148] In order to form a film while heating the substrate within 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 higher and 700°C or lower, and more preferably 300°C or higher and 600°C or lower. As a precursor with such a high decomposition temperature, it is preferable to use an inorganic precursor. Inorganic precursors generally tend to have a higher decomposition temperature than organic precursors, so even if film formation is performed while heating the substrate as described above, the precursor is less likely to decompose.

[0149] Examples of inorganic precursors that can be used include the aforementioned indium trichloride, gallium trichloride, and zinc dichloride. As mentioned above, these precursors have decomposition temperatures of approximately 350°C to 700°C, which is significantly higher than the decomposition temperatures of typical organic precursors. However, as mentioned above, the decomposition temperatures of indium trichloride, gallium trichloride, and zinc dichloride are different from one another. When forming a film using multiple different precursors by the ALD method, it is preferable to set the substrate temperature below the decomposition temperature of the lowest precursor among the multiple precursors. In the above example, the substrate temperature can be set within a range in which zinc dichloride, the precursor with the lowest decomposition temperature, does not decompose. This allows other precursors, such as indium trichloride and gallium trichloride, to be adsorbed onto the target object (e.g., a substrate) without decomposing.

[0150] Although the above example uses an inorganic precursor, the present invention is not limited thereto. For example, the present invention can also be applied to an ALD method using an organic precursor. For example, when forming a metal oxide film (e.g., an In-M-Zn metal oxide) using an organic precursor, it is preferable to set the substrate temperature below the decomposition temperature of the lowest precursor among multiple organic precursors. This allows the multiple precursors used to be adsorbed onto the target object (e.g., a substrate) without being decomposed during ALD film formation. In this case, the substrate temperature can also be set within a range from 100°C to the lowest decomposition temperature of the precursors (typically, 200°C to 300°C).

[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 immediately after the formation of the film by the ALD method without exposing it to the open air. The heat treatment is preferably performed at a temperature of 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 this heat treatment, impurities such as hydrogen and carbon contained in the metal oxide can be removed. For example, carbon in the metal oxide can be released as CO2 and CO, and hydrogen in the metal oxide can be released as HO. Furthermore, simultaneously with the removal of the impurities, metal and oxygen atoms can be rearranged, improving crystallinity. Therefore, a highly crystalline metal oxide with a layered crystal structure, particularly the above-mentioned metal oxide with the CAAC structure, can be formed.

[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 this 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] Furthermore, when forming a metal oxide having an atomic ratio different from In:M:Zn=1:1:1 (atomic ratio), the layers 21, 31, and 41 may be formed appropriately according to the atomic ratio. For example, as shown in FIG. 6A, by repeating the formation of layer 41 multiple times before and after the formation of layer 31, a stack of layers 31 and 41 having the desired number of atoms, number of layers, and thickness may be formed between two layers 21.

[0154] <Configuration example of film formation equipment> As an example of an apparatus capable of forming a film using the ALD method, the configuration of a film formation 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 formation apparatus 4000, and Figures 8A and 8B are cross-sectional views of an ALD apparatus that can be used for the film formation apparatus 4000.

[0155] The film formation apparatus 4000 includes a loading / unloading chamber 4002, a loading / unloading chamber 4004, a transfer chamber 4006, a film formation chamber 4008, a film formation chamber 4009, a processing chamber 4011, and a transfer arm 4014. The loading / unloading chamber 4002, the loading / unloading chamber 4004, the film formation chamber 4008, the film formation 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 formation chamber 4008, the film formation chamber 4009, and the processing chamber 4011 without exposure to the atmosphere, preventing impurities from being mixed into the film. Furthermore, contamination of the interface between the substrate and the film and the interface between each film is reduced, resulting in clean interfaces.

[0156] In addition, it is preferable that 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 are filled with an inert gas (such as nitrogen gas) with a controlled dew point to prevent moisture from adhering, 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) or 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 deposited in the deposition chamber 4009, an oxide semiconductor film that functions as an active layer can be deposited in the deposition chamber 4008, and heat treatment can be performed after the oxide semiconductor film deposition in the treatment chamber 4011. In this case, the deposition of the base insulating film, the deposition of the oxide semiconductor film, and the heat treatment can be performed successively without exposure to the air.

[0160] Furthermore, although the film formation apparatus 4000 is configured to include the load / unload chamber 4002, the load / unload chamber 4004, the film formation chamber 4008, the film formation chamber 4009, and the processing chamber 4011, the present invention is not limited to this. The film formation apparatus 4000 may be configured to include one film formation chamber or three or more processing chambers. The film formation apparatus 4000 may be configured to include two or more processing chambers. The film formation apparatus 4000 may be a single-wafer type or 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 heats using a resistance heating element or the like. Alternatively, it may be a mechanism that heats by thermal conduction or thermal radiation from a medium such as heated gas. 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. An LRTA heats the workpiece by radiating light (electromagnetic waves) emitted from a lamp such as a halogen lamp, metal halide lamp, xenon arc lamp, carbon arc lamp, high-pressure sodium lamp, or high-pressure mercury lamp. A GRTA performs heat processing using high-temperature gas.

[0162] The heat treatment using the heating device may be performed at a temperature of 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 may be performed in a nitrogen gas or inert gas atmosphere, or in 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 concentration may be approximately 20%. The heat treatment may also be performed under reduced pressure. Alternatively, the heat treatment may be performed in a nitrogen gas or inert gas atmosphere, followed by 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, 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] The gas used in the heat treatment is preferably highly purified. For example, the moisture content of 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, the incorporation of moisture into the metal oxide can be prevented as much as possible.

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

[0165] 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 released as CO2 and CO, and hydrogen in the metal oxide can be released as H2O. As described above, since the processing chamber 4011 is connected to the film formation 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, rearrangement of metal atoms and oxygen atoms is 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 description, an example of using a heat treatment apparatus in the processing chamber 4011 has been described, but the present invention is not limited thereto. For example, a configuration using a microwave processing apparatus 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 formation apparatus 4000 will be described with reference to Fig. 8A. The thermal ALD apparatus includes a film formation 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 inlet 4523, a raw material outlet 4524, and an exhaust unit 4525. The raw material inlet 4523 installed in the chamber 4520 is connected to the raw material supply units 4521a, 4521b, 4521c, 4531, and 4532 via supply pipes and valves, respectively, and the raw material outlet 4524 is connected to the exhaust unit 4525 via an exhaust pipe, a valve, and a pressure regulator.

[0168] Chamber 4520 contains a substrate holder 4526, on which a substrate 4530 is placed. Substrate holder 4526 may have a rotation mechanism. A heater 4527 is provided on the outer wall of chamber 4520, allowing for temperature control of the interior of chamber 4520, substrate holder 4526, and the surface of substrate 4530. Heater 4527 can preferably control the surface temperature of substrate 4530 to between 100°C and 600°C, preferably between 200°C and 600°C, and more preferably between 300°C and the decomposition temperature of the precursor. The temperature of heater 4527 itself can preferably be set to between 100°C and 600°C. By heating the substrate within this temperature range during film formation, impurities such as hydrogen and carbon contained in the precursor or reactant can be suitably reduced from the metal oxide. Furthermore, simultaneously with the removal of the impurities, metal and oxygen atoms are rearranged, allowing each oxide layer to be arranged in a highly ordered manner. Therefore, a metal oxide film having a highly crystalline layered crystal structure can be formed. Heat treatment may be performed using the heater 4527 after the metal oxide film is formed.

[0169] In raw material supply unit 4521a, raw material supply unit 4521b, raw material supply unit 4521c, and raw material supply unit 4531, a raw material gas is formed from a solid raw material or a liquid raw material by a vaporizer, a heating means, etc. Alternatively, raw material supply unit 4521a, raw material supply unit 4521b, raw material supply unit 4521c, and raw material supply 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) to be used in raw material supply unit 4521 and raw material supply unit 4531 and introducing the selected raw materials 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 configuration may be adopted in which a precursor containing indium is supplied from raw material supply unit 4521a, a precursor containing gallium is supplied from raw material supply unit 4521b, and a precursor containing zinc is supplied from raw material supply unit 4521c. The precursors containing indium, gallium, and zinc can be the precursors described above. The precursors containing indium, gallium, and zinc preferably have high decomposition temperatures, and it is preferable to use inorganic precursors, for example. Note that when halogen-based compounds or the like are used as inorganic precursors, the gas may be highly corrosive. Therefore, it is preferable to use highly corrosion-resistant materials, such as titanium, for components that come into contact with gas, such as chambers, piping, and various gas supply units.

[0172] Furthermore, 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. An inert gas such as argon (Ar), helium (He), or nitrogen (N) can be used as the carrier gas. 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] Furthermore, a piping heater 4534a is provided to cover piping or valves between the chamber 4520 and 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. A piping heater 4534b is provided to cover piping or valves between the exhaust device 4525 and the chamber 4520. The temperatures of piping heater 4534a and piping heater 4534b may be appropriately set, for example, within a range from room temperature to 300°C. By providing such a piping heater, it is possible to prevent 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. Therefore, when using such precursors, 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 pipe heater 4534a, pipe heater 4534b, and heater 4527 may be configured to be controlled independently. By controlling pipe heater 4534a, pipe heater 4534b, and heater 4527 independently, the temperature of each heater can be controlled individually. However, this is not limited thereto, and the temperature control of pipe heater 4534a, pipe heater 4534b, and heater 4527 may be configured to be linked with each other. In this case, temperature control can be adjusted collectively, which reduces the cost of device components, etc.

[0175] High-speed valves 4522a to 4522d can be precisely controlled in time, thereby enabling the source gases supplied from raw material supply units 4521a, 4521b, 4521c, and 4531 to be controlled and introduced into chamber 4520.

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

[0178] 8A, heater 4527, raw material inlet 4523, and raw material outlet 4524 are arranged in the lower part of chamber 4520, but the arrangement is not limited to this and can be set appropriately. Also, 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 combined into raw material inlet 4523, but the arrangement is not limited to this and a different inlet may be provided for each.

[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, valve, and pressure regulator. Substrate holder 4026 is located inside chamber 4020, and substrate 4030 is placed on substrate holder 4026. Heater 4027 is provided on the outer wall of the chamber, and piping heaters 4034a and 4034b are provided to cover the piping and the like connected to the chamber.

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

[0181] As shown in FIG. 8B, by connecting a plasma generator 4028 to the chamber 4020, the plasma ALD apparatus can perform film formation by the plasma ALD method in addition to the thermal ALD method. 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, and more preferably 2 MHz to 60 MHz. For example, it can output power having a frequency of 13.56 MHz. Since the plasma ALD method allows film formation without reducing the film formation rate even at low temperatures, it is suitable for use in single-wafer film formation equipment with low film formation efficiency.

[0182] The reactant discharged from the raw material supply unit 4031 passes through the plasma generator 4028 and is converted into 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 configured to 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 located at the top of chamber 4520, heater 4027 and raw material inlet 4023 are located on the side of chamber 4520, and raw material outlet 4524 is located at the bottom of chamber 4520, but the arrangement is not limited to this and can be set appropriately.

[0185] 9A to 9C illustrate 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 referred to as a chamber. Alternatively, the reaction chamber 4120 and the plasma generation chamber 4111 can be collectively referred to as 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. Furthermore, a plasma generation device 4128 can apply high frequency waves such as RF or microwaves to gas introduced into the plasma generation chamber 4111 to generate plasma 4131 within the plasma generation chamber 4111. When generating plasma 4131 using microwaves, microwaves with a frequency of 2.45 GHz are typically used. Furthermore, plasma generated by applying such microwaves and a magnetic field is sometimes referred to as ECR (Electron Cyclotron Resonance) plasma.

[0187] The reaction chamber 4120 also has a substrate holder 4126, on which a substrate 4130 is placed. The source gas introduced through the source gas inlet 4123 is decomposed by heat from a heater installed in the reaction chamber 4120 and deposited on the substrate 4130. The source gas introduced through the source gas inlet 4133 is converted into a plasma state by the plasma generator 4128. The plasma-state source gas recombines with electrons or other molecules before reaching the surface of the substrate 4130, becoming radicals that reach the substrate 4130. An ALD apparatus that uses radicals to form a film in this way is sometimes called a radical-enhanced ALD (radical-enhanced ALD) apparatus. While the plasma ALD apparatus 4100 has a configuration in which the plasma generation chamber 4111 is installed above the reaction chamber 4120, this embodiment is not limited to this. The plasma generation chamber 4111 may also be installed 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 includes a chamber 4220. The chamber 4220 includes an electrode 4213, a raw material outlet 4224, and a substrate holder 4226. A substrate 4230 is placed on the substrate holder 4226. The electrode 4213 includes a raw material inlet 4223 and a showerhead 4214 that supplies the introduced raw material gas into the chamber 4220. The electrode 4213 is connected to a power supply 4215 capable of applying high-frequency power via a capacitor 4217. The substrate holder 4226 may be provided with a mechanism for applying a constant potential or high-frequency power. 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, respectively, for generating a plasma 4231. 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 a 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 includes a chamber 4320. The chamber 4320 includes an electrode 4313, a raw material outlet 4324, and a substrate holder 4326. A substrate 4330 is placed on the substrate holder 4326. The electrode 4313 includes a raw material inlet 4323 and a showerhead 4314 that supplies the introduced raw material gas into the chamber 4320. A power supply 4315 capable of applying high frequency power is connected to the electrode 4313 via a capacitor 4317. A mechanism for applying a constant potential or high frequency power may be provided to the substrate holder 4326. 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, respectively, for generating plasma 4331. The plasma ALD apparatus 4300 differs from the plasma ALD apparatus 4200 in that it includes a mesh 4319 connected to a power supply 4321 capable of applying high-frequency voltage via a capacitor 4322 between an electrode 4313 and a substrate holder 4326. The provision of the mesh 4319 allows the plasma 4231 to be separated from the substrate 4130. The source gas introduced through the source gas 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 through the source gas inlet 4323 becomes a plasma between the electrode 4313 and the substrate holder 4326. The charge of the plasma-state source gas is removed by the mesh 4319, and the source gas reaches the substrate 4130 in an electrically neutral state, such as in the form of radicals. This allows for film formation with reduced ion incidence and plasma damage.

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

[0191] <Film formation 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 periods when no source gases are introduced are indicated by OFF.

[0192] FIG. 10A shows a film formation sequence using the ALD apparatus shown in FIG. 8A. First, a substrate 4530 is set on a substrate holder 4526 in a chamber 4520 (step S101). Next, the temperature of a heater 4527 is adjusted (step S102). At this time, the temperatures of pipe 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 across 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 temperature adjustment of the heater 4527 is not required after setting the substrate 4530 (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. The chamber 4520 is purged during periods when neither the first source gas nor the second source gas is being introduced. In film formation by the ALD method, one cycle consists of introducing the first source gas (first step above), purging the first source gas (second step above), introducing the second source gas (third step above), and purging the second source gas (fourth step above), and by repeating this cycle, a film having a desired thickness is formed.

[0194] Alternatively, a second source gas having a reactant may be introduced into chamber 4020 between steps S103 and S104. Preferably, the second source gas is one or more oxidizing agents selected from ozone (O), oxygen (O), and water (H). Introducing water as the second source gas can form hydrophilic groups on substrate 4530, further improving the precursor adsorption. Introducing ozone and oxygen as the second source gas creates an oxygen atmosphere in the chamber, supplying oxygen to the insulating film underlayer formed on substrate 4530. This supplies oxygen to the metal oxide film formed on the insulating film underlayer, increasing the oxygen concentration in the film. The second source gas is preferably introduced in pulses, as in step S104, but the present invention is not limited to this. The second source gas may also be introduced continuously. During periods when the second source gas is not being introduced, the chamber 4520 is evacuated.

[0195] A layered crystalline oxide film having multiple different oxide layers can be formed by forming a first oxide layer in one cycle using the above-mentioned first source gas, forming a second oxide layer in one cycle using a third source gas different from the first source gas, and forming a third oxide layer in one cycle using a fourth source gas different from the first source gas. Hereinafter, 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 the film formation sequence for an example in which a film is formed using first to third source gases each containing 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 containing indium, the third source gas contains a precursor containing gallium, and the fourth source gas contains a precursor containing zinc.

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

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

[0199] Next, a third source gas is introduced to adsorb a gallium-containing precursor onto the indium oxide layer (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, a second source gas is introduced, and the precursor with adsorbed gallium reacts with the oxidizing agent to form a layer of gallium oxide (Figure 5D).Then, the introduction of the second source gas is stopped, and the excess second source gas in the chamber is purged.

[0201] Next, a fourth source gas is introduced to adsorb a 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, a second source gas is introduced, and the adsorbed zinc-containing precursor reacts with the oxidizing agent to form a zinc oxide layer (Figure 6B). The introduction of the second source gas is then stopped, and excess second source gas is purged from the chamber. Using the method described above, an indium-containing precursor is then adsorbed onto the zinc oxide (Figure 6C).

[0203] The above process of forming indium oxide, gallium oxide, and zinc oxide constitutes one cycle, and by repeating this cycle, an In-Ga-Zn oxide with an In:Ga:Zn=1:1:1 [atomic ratio] of the 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 0.05 to 1 second, preferably 0.1 to 0.5 seconds. The time for exhausting the first, third, and fourth source gases from the chamber 4520 is 0.1 to 15 seconds, preferably 0.5 to 10 seconds. The pulse time for introducing the second source gas into the chamber 4520 is 0.05 to 30 seconds, preferably 0.1 to 15 seconds. The time for exhausting the second source gas from the chamber 4520 is 0.1 to 15 seconds, preferably 0.1 to 5 seconds.

[0205] In the sequence shown in FIG. 10B, the order of introducing the first, third, and fourth source gases is not limited to this. For example, the fourth gas containing a zinc precursor may be introduced first. Zinc oxide forms a crystalline structure more easily than indium oxide and gallium oxide, so stable zinc oxide crystals can be formed in the bottom layer. This allows for relatively easy formation of layers of indium oxide and gallium oxide on the zinc oxide.

[0206] Although the above describes the formation of an In-Ga-Zn oxide film with an In:Ga:Zn=1:1:1 atomic ratio, the present invention is not limited to this. Similar methods can be used to form In-Ga-Zn oxide films with different atomic ratios. It is preferable to set the number of pulses or pulse time of the precursor-containing source gas in one cycle according to the desired atomic ratio of the In-Ga-Zn oxide.

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

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

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

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

[0211] In the above, a configuration in which only one precursor-containing source gas is introduced during the interval in which oxidation is performed with the second source gas is shown, but the present invention is not limited to this. Two or more precursor-containing source gases may be introduced during the interval in which oxidation is performed with the second source gas. In this case, two or more precursor-containing source gases may be introduced simultaneously. Furthermore, the same type of precursor may be introduced twice consecutively during the interval in which oxidation is performed with the second source 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 using the sequence shown in FIG. 11B. In FIG. 11B, the first source gas, the third source gas, the fourth source gas, the third source gas, the fourth source gas, the third source gas, and the fourth source gas are introduced in this order, in accordance with the crystal structure shown in FIG. 2D, in which layers 22, 41, 31, and 41 are stacked in this order. However, the first and third source gases are initially introduced without the second source gas being introduced in between. In other words, the oxidizing agent is introduced after the indium-containing precursor contained in the first source gas and the gallium-containing precursor contained in the third source gas are adsorbed. This allows the formation of a layer containing two types of metal elements (indium and gallium) in a single oxide layer, as in layer 22 shown in FIG. 2D. In this case, it is preferable to set the pulse times of the first and third source gases to about half the pulse time of the fourth source gas. As a result, as shown in FIG. 11B, the ratio of the pulse time of the first source gas containing indium to the pulse time of the third source gas containing gallium to the pulse time of the fourth source gas containing zinc in one cycle can be set to 1:3:4, which is the same as the atomic ratio.

[0213] Although the above describes the deposition of an oxide film with a constant atomic ratio, the present invention is not limited to this. Using a similar method, two or more oxides with different atomic ratios can be deposited consecutively. 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 layered oxides with different atomic ratios. By depositing the film in this manner, layered oxides with different atomic ratios can be deposited in a single chamber. This prevents 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 for stacking an oxide with an atomic ratio of In:Ga:Zn=1:1:1 on an oxide with an atomic ratio of In:Ga:Zn=1:3:4. Step 104a corresponds to an oxide with 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 with an atomic ratio of In:Ga:Zn=1:1:1 and is the same as the sequence shown in FIG. 10B. In this way, by performing the first half of the process with the number of pulses per cycle of the first source gas, the third source gas, and the fourth source gas in the ratio of 1:3:4, and performing the second half of the process with the number of pulses per cycle of the first source gas, the third source gas, and the fourth source gas in the ratio of 1:1:1, a metal oxide film having a stacked structure of oxide 62 and oxide 60 shown in FIG. 3B can be formed. That is, the first half of the film was deposited with a pulse count corresponding to an atomic ratio of In:Ga:Zn=1:3:4, and the second half of the film was deposited with a pulse count corresponding to an atomic ratio of In:Ga:Zn=1:1:1.

[0215] Although the film formation method has been described above using In-Ga-Zn oxide as an example, the present invention is not limited to this. Precursors may be selected appropriately depending on the metal elements contained in the desired metal oxide. Furthermore, while the number of precursors used in the above example is one or three, it is not limited to this and may be two or four or more.

[0216] Although the above example shows a film formation using a precursor containing one type of metal element, the present invention is not limited to this. A precursor containing two or more types of metal elements may also be used. For example, a precursor containing indium and gallium, or a precursor containing gallium and zinc, may also be used. In this case, the number of raw material supply units 4521 shown in FIG. 8A and other figures can be reduced.

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

[0218] First, classification of crystal structures in oxide semiconductors will be described with reference to Fig. 13A. Fig. 13A is a diagram illustrating classification of crystal structures of oxide semiconductors, typically IGZO (a 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 polycrystal). "Crystalline" excludes single crystal, polycrystal, and completely amorphous. "Crystalline" includes single crystal and polycrystal.

[0220] The structure within the bold frame in Figure 13A is an intermediate state between "amorphous" and "crystal," and is a structure that belongs to a new boundary region (new crystalline phase). In other words, this structure can be described as a structure that is completely different from the energetically unstable "amorphous" or "crystal."

[0221] The crystalline structure of a film or substrate can be evaluated using X-ray diffraction (XRD) spectroscopy. Figure 13B shows the XRD spectrum obtained by GIXD (Grazing-Incidence XRD) measurement of a CAAC-IGZO film classified as "Crystalline." The GIXD method is also known as the thin-film method or the Seemann-Bohlin method. Hereinafter, the XRD spectrum obtained by GIXD measurement shown in Figure 13B will be simply referred to as the XRD spectrum. The composition of the CAAC-IGZO film shown in Figure 13B is approximately In:Ga:Zn = 4:2:3 [atomic ratio]. The thickness of the CAAC-IGZO film shown in Figure 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. 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 an electron beam is incident parallel to the substrate. 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 showing 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. 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. 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 its vicinity. 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 is periodic. If the atomic arrangement is considered as a lattice arrangement, then a crystalline region is also a region in which the lattice arrangement is aligned. Furthermore, the CAAC structure has a region in which multiple crystalline regions are connected in the ab-plane direction, and this region may have distortion. Note that distortion refers to a location in a region in which multiple crystalline regions are connected, where the lattice arrangement changes direction between a region with a aligned lattice arrangement and a region with a different aligned lattice arrangement. In other words, a metal oxide with a CAAC structure is a metal oxide that is c-axis oriented and does not clearly have an 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 several tens of nm.

[0229] Furthermore, in In-M-Zn oxides (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 containing indium (In) and oxygen and a layer containing element M, zinc (Zn), and oxygen are stacked. The layer containing indium and oxygen may contain element M or zinc. The layer containing 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 elements that make up the metal oxide.

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

[0232] When observing the crystalline region from the specific direction, the lattice arrangement within the crystalline region is based on a hexagonal lattice, but the unit cell is not necessarily a regular hexagon and may be non-regular hexagonal. Furthermore, the distortion may have a pentagonal, heptagonal, or other lattice arrangement. In metal oxides with a CAAC structure, no clear grain boundaries can be identified even near the distortion. This indicates that the formation of grain boundaries is suppressed by the distortion of the lattice arrangement. This is thought to be because metal oxides with a CAAC structure can tolerate distortion due to the lack of close-packed arrangement of oxygen atoms in the ab-plane direction or the change in interatomic bond distance caused by metal atom substitution.

[0233] Metal oxides with a CAAC structure are highly crystalline and have no clearly defined grain boundaries. In other words, metal oxides with a CAAC structure are less likely to experience a decrease in electron mobility due to grain boundaries. Therefore, metal oxides with a CAAC structure have stable physical properties. As a result, metal oxides with a CAAC structure are heat-resistant and highly reliable. Therefore, metal oxides with a CAAC structure are one of the crystalline oxides with a crystal structure suitable for the semiconductor layer of a transistor.

[0234] <Transistors with metal oxides> Next, a case where a metal oxide (oxide semiconductor) is used in 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. Furthermore, a highly reliable transistor can be realized. Furthermore, 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] The channel formation region of the transistor is preferably formed using an oxide semiconductor with a low carrier concentration. For example, the carrier concentration of the channel formation region of the oxide semiconductor is 1×10 17 cm -3 Less than 1 × 10 15 cm -3 or less, more preferably 1 × 10 13 cm -3 Less than or equal to 1×10 11 cm -3 or less, more preferably 1 × 10 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, a semiconductor having a low impurity concentration and a low density of defect states is referred to as a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor. Note that an oxide semiconductor having a low carrier concentration may also be referred to as a highly purified intrinsic or substantially highly purified 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 may also be low.

[0238] Furthermore, charges trapped in the trap states of an oxide semiconductor take a long time to dissipate and may behave like 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. Furthermore, in order to reduce the impurity concentration in the oxide semiconductor, it is preferable to also reduce the impurity concentration in the adjacent film. Examples of impurities include hydrogen, nitrogen, alkali metals, alkaline earth metals, iron, nickel, and silicon.

[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. Therefore, 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 calculated to be 2×10 18 atoms / cm 3 Less than or equal to 2 x 10 17 atoms / cm 3 The following applies.

[0242] Furthermore, when an oxide semiconductor contains an alkali metal or alkaline earth metal, defect states may be formed and carriers may be generated. Therefore, a transistor using an oxide semiconductor containing an alkali metal or alkaline earth metal is likely to have normally-on characteristics. For this reason, when the concentration of the alkali metal or 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 x 10 16 atoms / cm 3 Do 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 tends 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 an 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 Do the following:

[0244] Furthermore, hydrogen contained in an oxide semiconductor may react 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. Furthermore, 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 the amount of 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 with sufficiently reduced impurities 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 metal oxides described above. 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 high on-state current can be provided.

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

[0248] For example, it is preferable to use a transition metal chalcogenide that functions as a semiconductor as the semiconductor layer of a transistor.Specific examples of transition metal chalcogenides that can be used as the semiconductor layer of a transistor include molybdenum sulfide (typically MoS2), molybdenum selenide (typically MoSe2), molybdenum tellurium (typically MoTe2), tungsten sulfide (typically WS2), tungsten selenide (typically WSe2), tungsten tellurium (typically WTe2), hafnium sulfide (typically HfS2), hafnium selenide (typically HfSe2), zirconium sulfide (typically ZrS2), and zirconium selenide (typically ZrSe2).

[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 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 previous embodiment and a manufacturing method thereof will be described with reference to FIGS.

[0251] <Configuration example of semiconductor device> The structure of a semiconductor device including a transistor 200 will be described with reference to FIG. 14. FIGS. 14A to 14D are top and cross-sectional views of a semiconductor device including 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 dotted 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 dotted 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 dotted line A5-A6 in FIG. 14A. Note that some elements are omitted from the top view of FIG. 14A for clarity.

[0252] A semiconductor device of one embodiment of the present invention includes an insulator 212 over a substrate (not shown), an insulator 214 over the insulator 212, a transistor 200 over the insulator 214, an insulator 280 over the transistor 200, an insulator 282 over the insulator 280, an insulator 283 over the insulator 282, and an insulator 285 over 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) electrically connected to the transistor 200 and functioning 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 functioning 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 walls of the openings of insulators 280, 282, 283, and 285, and conductor 240a is provided in contact with the side surface of insulator 241a. Insulator 241b is provided in contact with the inner walls of the openings of insulators 280, 282, 283, and 285, and conductor 240b is provided in contact with the side surface 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 surface of insulator 241, and a second conductor is provided further inward.

[0254] Although the transistor 200 has been described as having a stacked structure of the first insulator of the insulator 241 and the second insulator of the insulator 241, 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. Furthermore, the transistor 200 has been described as having a stacked structure of the first conductor of the conductor 240 and the second conductor of the conductor 240, 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, ordinal numbers may be assigned to indicate the order of formation to distinguish the structures.

[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 271b on the oxide 271b. 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. The conductor 242a and the conductor 242b may be collectively referred to as the conductor 242. The insulator 271a and the insulator 271b may be collectively referred to as the insulator 271.

[0257] Openings that reach the oxide 230b are provided in the insulator 280 and the insulator 275. The insulator 250 and the conductor 260 are disposed in the openings. In addition, the conductor 260 and the insulator 250 are disposed between the insulator 271a and the conductor 242a and the insulator 271b and the conductor 242b in the channel length direction of the transistor 200. The insulator 250 has a region that contacts the side surface of the conductor 260 and a region that contacts the bottom surface of the conductor 260.

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

[0259] Note that 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, 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 and a drain electrode, and the conductor 242b functions as the other of the source electrode and the drain electrode. At least a part of a region of the oxide 230 that overlaps with the conductor 260 functions as a channel formation region.

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

[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 with a wide band gap, the off-state current of a transistor can be reduced.

[0263] For example, a metal oxide such as In-M-Zn oxide containing indium, element M, and zinc (element M is one or more elements 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 as oxide 230. Alternatively, In-Ga oxide, In-Zn oxide, or indium oxide may be used as oxide 230.

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

[0265] In this way, 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] Furthermore, since the oxide 230a and the oxide 230b have a common element other than oxygen (as a main component), the defect state density at the interface between the oxide 230a and the oxide 230b can be reduced. Because 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 reduced, and a high on-current can be obtained.

[0267] The oxide 230b preferably has crystallinity. In particular, it is preferable to use a c-axis aligned crystalline oxide semiconductor (CAAC-OS) as the oxide 230b. By using the film formation method described in the above embodiment, impurities can be reduced and a CAAC-OS with 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 ) and the like. In particular, by subjecting the formed metal oxide to heat treatment at a temperature (e.g., 400°C or higher and 600°C or lower) at which the metal oxide does not polycrystallize, the CAAC-OS can be made to have a dense structure with higher crystallinity. In this way, the density of the CAAC-OS can be increased, thereby further reducing the diffusion of impurities or oxygen in the CAAC-OS.

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

[0270] Furthermore, crystalline oxides such as CAAC-OS have few impurities or defects (such as oxygen vacancies) and a dense structure with high crystallinity, which can suppress the extraction of oxygen from the oxide 230b by the source or drain electrode. This reduces the extraction of oxygen from the oxide 230b even during heat treatment, making the transistor 200 stable against high temperatures (so-called thermal budget) in the manufacturing process.

[0271] FIG. 15A shows an enlarged view of the vicinity of the channel formation region of the transistor 200. When oxygen is supplied to the oxide 230b, a channel formation region is formed in the region between the conductor 242a and the conductor 242b. Therefore, as shown in FIG. 15A, the oxide 230b includes a region 230bc that functions as the 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 source and drain regions. At least a portion of the region 230bc overlaps with the conductor 260. In other words, the region 230bc is located in the region between the conductor 242a and the conductor 242b. The region 230ba overlaps with the conductor 242a, and the region 230bb overlaps with the conductor 242b.

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

[0273] The regions 230ba and 230bb, which 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 higher carrier concentration and lower resistance than the region 230bc.

[0274] Here, the carrier concentration of the region 230bc that functions as a channel forming region is 1×10 18 cm -3 Preferably, it is 1×10 or less. 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 preferably, for example, 1×10 -9 cm -3 It can be said that:

[0275] Furthermore, a region having a carrier concentration equal to or lower than that of regions 230ba and 230bb and equal to or higher than that of region 230bc may be formed between region 230bc and regions 230ba or 230bb. That is, this region functions as a junction region between region 230bc and regions 230ba or 230bb. The junction region may have a hydrogen concentration equal to or lower than that of regions 230ba and 230bb and equal to or higher than that of region 230bc. The junction region may also have oxygen vacancies equal to or lower than those of regions 230ba and 230bb and equal to or higher than those of 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] Furthermore, it may be difficult to clearly detect the boundaries between regions in the oxide 230. The concentrations of metal elements and impurity elements such as hydrogen and nitrogen detected in each region may not necessarily 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 and impurity elements such as hydrogen and nitrogen decrease in regions closer to the channel formation region.

[0278] 14C , in a cross-sectional view of the transistor 200 in the channel width direction, a curved surface may be formed between the side surface of the oxide 230b and the top surface of the oxide 230b. That is, 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 smaller than 20 nm, preferably greater than 1 nm and smaller than 15 nm, and more preferably greater than 2 nm and smaller than 10 nm. This shape can improve the coverage of the oxide 230b with the insulator 250 and the conductor 260.

[0280] The oxide 230 preferably has a stacked structure of multiple oxide layers with different chemical compositions. Specifically, the atomic ratio of the element M to the main metal element in the metal oxide used for the oxide 230a is preferably greater than the atomic ratio of the element M to the main metal element in the metal oxide used for the oxide 230b. Furthermore, the atomic ratio of the element M to In in the metal oxide used for the oxide 230a is preferably greater than the atomic ratio of the element M to In in the metal oxide used for the oxide 230b. Furthermore, the atomic ratio of In to M in the metal oxide used for the oxide 230b is preferably greater than the atomic ratio of In to M in the metal oxide used for the oxide 230a. By using the film formation method described in the previous embodiment, the oxides 230a and 230b with different atomic ratios can be continuously formed in a single chamber. This prevents excessive impurities such as hydrogen from being mixed into the interface between the oxides 230a and 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 changes continuously or can be said to be a continuous junction. To achieve this, it is advisable to reduce the defect level density of the mixed layer formed at the interface between the oxide 230a and the oxide 230b.

[0282] Specifically, when the oxide 230a and the oxide 230b contain a common element other than oxygen as a main component, 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 an atomic ratio of In:M:Zn=1:3:4 or a similar composition, or an atomic ratio of In:M:Zn=1:1:0.5 or a similar composition. The oxide 230b may be a metal oxide having an atomic ratio of In:M:Zn=1:1:1 or a similar composition, or an atomic ratio of In:M:Zn=4:2:3 or a similar composition, or an atomic ratio of In:M:Zn=5:1:3 or a similar composition. Note that a similar composition includes a range of ±30% of the desired atomic ratio. Gallium is preferably used as the element M. By using the film formation method described in the previous embodiment, metal oxides with various atomic ratios such as those 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, which reduces the influence of interface scattering on carrier conduction, and the transistor 200 can achieve a large on-state current and high frequency characteristics.

[0285] Note that, 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 230 may have a single layer or a stacked structure of three or more layers. Furthermore, each of the oxide 230a and the oxide 230b may have a stacked structure. Furthermore, when the oxide 230 has a stacked structure of three or more layers, part of the stacked structure of the oxide 230 may be formed in the openings formed in the insulators 280 and 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 into the transistor 200. Therefore, at least one of the insulators 212, 214, 271, 275, 282, and 283 is preferably an insulating material that suppresses the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, nitrogen atoms, nitrogen molecules, nitrogen oxide molecules (NO, NO, NO, etc.), and copper atoms (i.e., through which the above impurities are less likely to permeate). Alternatively, it is preferably an insulating material that suppresses the diffusion of oxygen (e.g., at least one of oxygen atoms, oxygen molecules, etc.) (i.e., through which the above oxygen is less likely to permeate).

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

[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, silicon nitride, which has a higher hydrogen barrier property, is preferably used for the insulators 212, 275, and 283. Furthermore, for example, aluminum oxide or magnesium oxide, which has a high ability to capture and fix hydrogen, is preferably used for the insulators 214, 271, and 282. This can prevent 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 can prevent 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 prevented from diffusing toward the substrate side through the insulators 212 and 214. Alternatively, oxygen contained in the insulator 280 or the like can be prevented from diffusing upward from the transistor 200 through the insulator 282 or the like. In this way, 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 the function of preventing 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 (where y is any number greater than 0). In such metal oxides 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 highly reliable transistor 200 and a semiconductor device can be manufactured that have excellent characteristics.

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

[0291] The insulators 212, 214, 271, 275, 282, and 283 may be deposited by, for example, sputtering. Sputtering does not require the use of hydrogen as a deposition gas, and therefore can reduce the hydrogen concentration of the insulators 212, 214, 271, 275, 282, and 283. Note that the deposition method is not limited to sputtering, and other methods such as chemical vapor deposition (CVD), molecular beam epitaxy (MBE), pulsed laser deposition (PLD), and atomic layer deposition (ALD) may also be used as appropriate. For example, the insulator 275 may be deposited by ALD, which has relatively good coverage. Furthermore, among the ALD methods, the PEALD method, which allows the film formation temperature to be relatively low, may also be used.

[0292] It may also be preferable to reduce the resistivity of the insulators 212 and 283. For example, it is preferable to reduce the resistivity of the insulators 212 and 283 to approximately 1×10 13 By setting the resistivity to 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. The resistivity of the insulator 212 and the insulator 283 is preferably 1×10 10 Ωcm or more 1×10 15 Ωcm or less.

[0293] Furthermore, the insulators 216 and 280 preferably have a lower dielectric constant than the insulator 214. Using a material with a low dielectric constant as an interlayer insulating film can reduce parasitic capacitance between wirings. For example, the insulators 216 and 280 may be made of silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide doped with fluorine, silicon oxide doped with carbon, silicon oxide doped with carbon and nitrogen, silicon oxide having vacancies, or the like, as appropriate.

[0294] The conductor 205 is arranged 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 a conductor 205a and a conductor 205b. The conductor 205a is provided in contact with the bottom surface and sidewall 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 preferably made of a conductive material that has the function of suppressing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, nitrogen atoms, nitrogen molecules, nitrogen oxide molecules (NO, NO, NO, etc.), copper atoms, etc. Alternatively, it is preferably made of a conductive material that has the function of suppressing the diffusion of oxygen (for example, at least one of oxygen atoms, oxygen molecules, etc.).

[0297] By using a conductive material for the conductor 205a that has the function of reducing hydrogen diffusion, it is possible to prevent impurities such as hydrogen contained in the conductor 205b from diffusing into the oxide 230 via the insulator 224 or the like. Furthermore, by using a conductive material for the conductor 205a that has the function of suppressing oxygen diffusion, it is possible to suppress oxidation of the conductor 205b and a decrease in conductivity. Examples of conductive materials that have the function of suppressing oxygen diffusion include titanium, titanium nitride, tantalum, tantalum nitride, ruthenium, and ruthenium oxide. Therefore, the conductor 205a may be formed as a single layer or a multilayer of the above conductive materials. 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, applying a negative potential to the conductor 205 can increase the Vth of the transistor 200 and reduce the off-state current compared to when no potential is applied to the conductor 205. Therefore, applying a negative potential to the conductor 205 can reduce the drain current when the potential applied to the conductor 260 is 0 V compared to when no potential is applied.

[0300] As shown in FIG. 14A, the conductor 205 is preferably larger than the area of the oxide 230 that does not overlap with the conductors 242a and 242b. In particular, as shown in FIG. 14C, the conductor 205 preferably extends to areas outside the ends of the oxides 230a and 230b that intersect with the channel width direction. That is, outside the side surfaces of the oxide 230 in the channel width direction, the conductor 205 and the conductor 260 preferably overlap with each other via an insulator. This structure allows the channel formation region of the oxide 230 to be electrically surrounded by the electric field of the conductor 260, which functions as the first gate electrode, and the electric field of the conductor 205, which functions as the second gate electrode. In this specification, a transistor structure in which the channel formation region is electrically surrounded by the electric fields of the first and second gates is referred to as 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 differs from a fin structure and a planar structure. By adopting the S-channel structure, the transistor can be made more resistant to the short-channel effect, in other words, less susceptible to the short-channel effect.

[0302] 14C, the conductor 205 is extended to function as wiring. However, the present invention is not limited to this, and a conductor functioning as wiring may be provided below the conductor 205. Furthermore, 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 transistor 200 illustrates a structure in which the conductor 205 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 structure 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 also 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. Aluminum oxide, hafnium oxide, or an oxide containing aluminum and hafnium (hafnium aluminate) is preferably used as the insulator. When the insulator 222 is formed using such a material, the insulator 222 functions as a layer that suppresses oxygen release from the oxide 230 to the substrate side or the diffusion of impurities such as hydrogen from the periphery of the transistor 200 to the oxide 230. Therefore, the insulator 222 can suppress the diffusion of impurities such as hydrogen into the inside of the transistor 200 and the generation of oxygen vacancies in the oxide 230. Furthermore, the conductor 205 can be prevented from reacting with oxygen contained in the insulator 224 or the oxide 230.

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

[0308] The insulator 222 may be a single layer or a multilayer of an insulator containing a so-called high-k material, such as aluminum oxide, hafnium oxide, tantalum oxide, zirconium oxide, lead zirconate titanate (PZT), strontium titanate (SrTiO3), or (Ba,Sr)TiO3 (BST). As transistors become smaller and more highly integrated, thinning the gate insulator can cause problems such as leakage current. Using a high-k material for the insulator that functions as the gate insulator allows for a reduction in 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 or silicon oxynitride as appropriate. Providing the insulator 224 containing oxygen in contact with the oxide 230 reduces oxygen vacancies in the oxide 230 and improves the reliability of the transistor 200. 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 in contact with the side surface of the insulator 224 and the top surface of the insulator 222. This structure significantly reduces the volume of the insulator 224 and separates the insulator 224 from the insulator 280. Therefore, oxygen contained in the insulator 280 can diffuse into the insulator 224, preventing excessive oxygen in the insulator 224.

[0310] The insulators 222 and 224 may have a stacked structure of two or more layers. In this case, the stacked structures are not limited to those made of the same material, and may be stacked structures made of different materials. While FIG. 14B and other figures illustrate 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. As long as the amount of oxygen contained in the insulator 224 can be appropriately adjusted, the insulator 224 may be configured without being patterned, similar to the insulator 222.

[0311] In addition, during 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, thereby eliminating oxygen vacancies (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 after the heat treatment in a nitrogen gas or inert gas atmosphere 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, and then the heat treatment may be performed in a nitrogen gas or inert gas atmosphere.

[0312] By subjecting the oxide 230 to oxygen addition treatment, oxygen vacancies in the oxide 230 are repaired by the supplied oxygen. In other words, O Furthermore, the reaction of the hydrogen remaining in the oxide 230 with the supplied oxygen can be removed as H2O (dehydration). As a result, the hydrogen remaining in the oxide 230 recombines with the oxygen vacancies to 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), it is preferable to use, for example, a nitride containing tantalum, a nitride containing titanium, a nitride containing molybdenum, a nitride containing tungsten, a nitride containing tantalum and aluminum, or a nitride containing titanium and aluminum. 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, or an oxide containing lanthanum and nickel may be used. These materials are preferable because they are conductive materials that are resistant to oxidation or that maintain conductivity even when they absorb oxygen.

[0315] Here, it is preferable to use a film with 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 in the region 230ba and the region 230bb. 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 and the like 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 and the like 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 and the like may be absorbed by the conductor 242a or the conductor 242b.

[0317] Preferably, 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, the cross-sectional area of the conductor 242 in the cross section in the channel width direction can be increased, as shown in Fig. 14D. This increases the conductivity of the conductor 242 and the on-state current of the transistor 200.

[0318] The insulator 271a is provided in contact with the top surface of the conductor 242a, and the insulator 271b is provided in contact with the top surface of the conductor 242b. The insulator 271 preferably has a function of capturing impurities such as hydrogen. In this case, the insulator 271 may be an insulator made of a metal oxide having an amorphous structure, such as aluminum oxide or magnesium oxide. In particular, using aluminum oxide having an amorphous structure or aluminum oxide having an amorphous structure as the insulator 271 is preferable because it may be possible to more effectively capture or fix hydrogen. This enables the manufacture of a transistor 200 and a semiconductor device with 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 top 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 top surface of the insulator 271. Openings are formed in the insulator 275 in 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 amorphous aluminum oxide film 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 compared to a single layer of aluminum oxide or a single layer of silicon nitride.

[0322] By providing the insulators 271 and 275 as described above, the conductor 242 can be surrounded by insulators that have 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 the conductor 242 from being directly oxidized by the oxygen contained in the insulators 224, 280, and 250a, which would increase the resistivity and reduce the on-current.

[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 can be made of silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide doped with fluorine, silicon oxide with vacancies, etc. Silicon oxide and silicon oxynitride are particularly preferred because they are stable against heat. Note that the insulator 250a preferably has a low carbon content.

[0326] However, one embodiment of the present invention is not limited to this, and the insulator 250a may contain carbon. For example, the carbon concentration of the insulator 250a is preferably 1×10 18 atoms / cm 3 5x10 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] As with the insulator 224, the insulator 250a preferably has a reduced concentration of impurities such as water and hydrogen.

[0328] Preferably, the insulator 250a is formed using an insulator that allows oxygen to diffuse easily when heated, and the insulator 250b is formed using an insulator that has a function of suppressing oxygen diffusion. With this structure, when the oxygen contained in the insulator 250a is diffused, the diffusion of oxygen into the conductor 260 can be suppressed. In other words, a decrease in the amount of oxygen supplied to the oxide 230 can be suppressed. Also, oxidation of the conductor 260 due to the oxygen contained in the insulator 250a can be suppressed. For example, the insulator 250b can be formed 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, such as a high-k material with a high dielectric constant. By forming the gate insulator as a stacked structure of the insulators 250a and 250b, a thermally stable stacked structure with a high dielectric constant can be achieved. This allows the gate potential applied during transistor operation to be reduced while maintaining the physical thickness of the gate insulator. Furthermore, the equivalent oxide thickness (EOT) of the insulator functioning as the gate insulator can be reduced.

[0330] Specifically, the insulator 250b may be a metal oxide containing one or more elements selected from 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. It is preferable to use aluminum oxide, hafnium oxide, or an oxide containing aluminum and hafnium (hafnium aluminate) as the insulator. Alternatively, the insulator 250b may be a stacked film including a hafnium oxide film and a silicon nitride film provided on the hafnium oxide film.

[0331] Although the insulator 250 is illustrated as having a two-layer stacked structure in FIGS. 14B and 14C, the present invention is not limited to this. The insulator 250 may be a single layer or a stacked structure of three or more layers. For example, as shown in FIG. 15B, an insulator 250c may be provided between the insulator 250b and the conductor 260a. The insulator 250c may be an insulator that can be used for the insulator 283 described above. A barrier insulating film against hydrogen is preferably used for the insulator 250c. This prevents impurities such as hydrogen contained in the conductor 260 from diffusing into the insulator 250b, the insulator 250a, and the oxide 230b. For example, the insulator 250c may be a silicon nitride film formed by the PEALD method.

[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 by oxygen from the insulator 250 can be suppressed.

[0333] The metal oxide may function as 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 electrical conductor 260a may be formed by sputtering to reduce the electrical resistance of the metal oxide, thereby making it a conductor. This may be called an OC (Oxide Conductor) electrode.

[0334] The presence of the metal oxide can improve the on-state current of the transistor 200 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, it 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 that has the 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 that has the 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 the 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 the 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] Furthermore, 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 made of a conductive material containing tungsten, copper, or aluminum as a main component. The conductor 260b may also have a layered structure, such as a layered structure of titanium or titanium nitride and the above-mentioned conductive material.

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

[0340] 14C , in the channel width direction of the transistor 200, the height of the bottom surface of the conductor 260 in a 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, relative to the bottom surface of the insulator 222. The conductor 260, which functions as a gate electrode, covers the side and top surfaces of the channel formation region of the oxide 230b via the insulator 250 or the like, making it easier for the electric field of the conductor 260 to act on the entire channel formation region of the oxide 230b. This increases the on-state current of the transistor 200 and improves its frequency characteristics. The difference between the height of the bottom surface of the conductor 260 and the height of the bottom surface of the oxide 230b in a region where the oxides 230a and 230b do not overlap with the conductor 260, relative to the bottom surface of the insulator 222, 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 be roughly flush with the upper surfaces of the insulator 250 and the conductor 260.

[0342] The insulator 280, which functions as an interlayer insulating film, preferably has a low dielectric constant. Using a material with a low dielectric constant as the interlayer insulating film can reduce the parasitic capacitance that occurs between wirings. The insulator 280 is preferably formed using, for example, the same material as the insulator 216. Silicon oxide and silicon oxynitride are particularly preferred because they are thermally stable. Materials such as silicon oxide, silicon oxynitride, and silicon oxide with vacancies are particularly preferred because they can easily form regions containing oxygen that is released by heating.

[0343] Like the insulator 224, the insulator 280 may contain excess oxygen. The insulator 280 preferably has a reduced concentration of impurities such as water and hydrogen. For example, the insulator 280 may be formed using 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 reduces 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. The insulator 282 may be, for example, an insulator such as aluminum oxide. 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 the diffusion of impurities such as water and hydrogen 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 the permeation of oxygen. By providing the insulator 282 in contact with the insulator 280 in the region sandwiched between the insulator 212 and the insulator 283 and having a function of capturing impurities such as hydrogen, the insulator 282 can capture impurities such as hydrogen contained in the insulator 280 and maintain a constant amount of hydrogen in the region. In particular, using aluminum oxide having an amorphous structure or aluminum oxide having an amorphous structure as the insulator 282 is preferable because hydrogen can be captured or fixed more effectively in some cases, which enables the manufacture of a highly reliable transistor 200 and semiconductor device with favorable characteristics.

[0345] The insulator 283 functions as a barrier insulating film that prevents impurities such as water and hydrogen from diffusing from above into the insulator 280. The insulator 283 is disposed on the insulator 282. The insulator 283 is preferably a nitride containing silicon, such as silicon nitride or silicon nitride oxide. For example, the insulator 283 may be formed using silicon nitride deposited by a sputtering method. By depositing the insulator 283 by a sputtering method, a silicon nitride film that is high in density and less likely to form voids can be formed. Alternatively, the insulator 283 may be formed by stacking a silicon nitride film deposited by an ALD method on a silicon nitride film deposited by a sputtering method. This structure is preferable because even if defects, such as voids, occur in the silicon nitride film deposited by the sputtering method, the voids can be filled by the silicon nitride film deposited by the ALD method, which has good coverage, thereby improving sealing performance.

[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. Silicon oxide and silicon oxynitride are particularly preferred because they are thermally stable. Note that although FIGS. 14B and 14C illustrate a structure in which the insulator 285 is provided, 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 conductors 240a and 240b are preferably made of a conductive material containing tungsten, copper, or aluminum as a main component. The conductors 240a and 240b may have a layered structure.

[0348] Furthermore, when the conductor 240 has a layered structure, it is preferable to use a conductive material that has the 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 that has the function of suppressing the permeation of impurities such as water and hydrogen may be used in a single layer or a layered structure. Furthermore, it is possible to suppress impurities such as water and hydrogen contained in layers above the insulator 283 from mixing into the oxide 230 through the conductor 240a and the conductor 240b.

[0349] The insulators 241a and 241b may be a barrier insulating film that can be used for the insulator 275, etc. For example, the insulators 241a and 241b may be made of an insulator such as silicon nitride, aluminum oxide, or silicon nitride oxide. The insulators 241a and 241b are provided in contact with the insulators 283, 282, and 271, and therefore can prevent impurities such as water and hydrogen contained in the insulator 280 from mixing with the oxide 230 through the conductors 240a and 240b. Silicon nitride is particularly suitable because it has high barrier properties against hydrogen. Furthermore, it can prevent oxygen contained in the insulator 280 from being absorbed by the conductors 240a and 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 the opening, such as the insulator 280, and the second insulator inside it be formed by combining a barrier insulating film against oxygen and a barrier insulating film against hydrogen.

[0351] For example, the first insulator may be aluminum oxide formed by ALD, and the second insulator may be silicon nitride formed by PEALD. This configuration 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 surfaces of the conductors 240a and 240b, functioning as wiring. Conductor 246 is preferably made of a conductive material containing tungsten, copper, or aluminum as its main component. The conductor may have a layered structure, for example, a layered structure of titanium or titanium nitride and the above-mentioned 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 semiconductor devices.

[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 glass substrates, quartz substrates, sapphire substrates, stabilized zirconia substrates (e.g., yttria-stabilized zirconia substrates), and resin substrates. Examples of semiconductor substrates include semiconductor substrates made of silicon or germanium, or compound semiconductor substrates made of silicon carbide, silicon germanium, gallium arsenide, indium phosphide, zinc oxide, and gallium oxide. Examples of semiconductor substrates include those having an insulating region within the semiconductor substrate, such as an SOI (Silicon-On-Insulator) substrate. Examples of conductive substrates include graphite substrates, metal substrates, alloy substrates, and conductive resin substrates. Other examples include substrates having a metal nitride and a metal oxide. Examples of other substrates include a substrate in which a conductor or semiconductor is provided on an insulating substrate, a substrate in which a conductor or insulator is provided on a semiconductor substrate, and a substrate in which a semiconductor or insulator is provided on a conductive substrate. Alternatively, a substrate provided with elements may be used, such as 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, all of which have insulating properties.

[0356] For example, as transistors become more miniaturized and highly integrated, thinner gate insulators can cause problems such as leakage current. Using high-k materials for the gate insulator allows for lower voltage operation of the transistor while maintaining the physical film thickness. On the other hand, using a material with a low dielectric constant for the interlayer insulating film can reduce the parasitic capacitance between wiring. Therefore, it is best to select materials based on the insulator's function.

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

[0359] Furthermore, a transistor using a metal oxide can have stable electrical characteristics by being surrounded by an insulator that has a function of suppressing the permeation of impurities such as hydrogen and oxygen. Examples of insulators that have a function of suppressing the permeation of impurities such as hydrogen and oxygen include insulators containing boron, carbon, nitrogen, oxygen, fluorine, magnesium, aluminum, silicon, phosphorus, chlorine, argon, gallium, germanium, yttrium, zirconium, lanthanum, neodymium, hafnium, and tantalum, and can be used in a single layer or a stacked layer. Specifically, examples of insulators that have a function of suppressing the permeation of impurities such as hydrogen and oxygen include 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.

[0360] The insulator functioning 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>> The conductor is preferably 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 metal elements as a component, or an alloy combining the above metal elements. For example, tantalum nitride, titanium nitride, tungsten, nitrides containing titanium and aluminum, nitrides containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, oxides containing strontium and ruthenium, oxides containing lanthanum and nickel, etc. Furthermore, tantalum nitride, titanium nitride, nitrides containing titanium and aluminum, nitrides containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, oxides containing strontium and ruthenium, and oxides containing lanthanum and nickel are preferred because they are conductive materials that are resistant to oxidation or maintain conductivity even when absorbing oxygen. Furthermore, semiconductors with high electrical conductivity, such as polycrystalline silicon containing impurity elements such as phosphorus, and silicides such as nickel silicide may also be used.

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

[0363] 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 the 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, as a conductor functioning as a gate electrode, 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. Alternatively, a conductive material containing the aforementioned metal element and nitrogen may be used. For example, a conductive material containing nitrogen, such as titanium nitride or tantalum nitride, may be used. Alternatively, 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 doped with silicon may be used. Furthermore, indium gallium zinc oxide containing nitrogen may be used. Using such a material may allow hydrogen contained in the metal oxide in which the channel is formed to be captured. Alternatively, hydrogen introduced from an external insulator or the like may be captured.

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

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

[0367] Here, we consider a case where the metal oxide is an In-M-Zn oxide containing indium, element M, and zinc. The element M is aluminum, gallium, yttrium, or tin. Other elements that can be used for element M include boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, and cobalt. However, there are cases where a combination of the aforementioned elements can be used as element M.

[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. FIGS. 16B to 25B are cross-sectional views corresponding to the portion indicated by the dashed dotted line A1-A2 in FIGS. 16A to 25A, and are also cross-sectional views of the transistor 200 in the channel length direction. FIGS. 16C to 25C are cross-sectional views corresponding to the portion indicated by the dashed dotted line A3-A4 in FIGS. 16A to 25A, and are also cross-sectional views of the transistor 200 in the channel width direction. FIGS. 16D to 25D are cross-sectional views of the portion indicated by the dashed dotted line A5-A6 in FIGS. 16A to 25A. Note that some elements are omitted from the top views in FIGS. 16A to 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 using a sputtering method, a CVD method, an MBE method, a PLD method, an ALD method, or the like, as appropriate.

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

[0372] CVD methods can be classified into plasma CVD (PECVD) methods (sometimes called plasma enhanced 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 produce high-quality films at relatively low temperatures. Furthermore, because the thermal CVD method does not use plasma, it is a film formation method that can minimize plasma damage to the workpiece. For example, wiring, electrodes, elements (transistors, capacitors, etc.) included in a semiconductor device may become charged up by receiving electric charge from the plasma. In this case, the accumulated electric charge may destroy the wiring, electrodes, elements, etc. included in the semiconductor device. On the other hand, the thermal CVD method, which does not use plasma, does not cause such plasma damage, and therefore can increase the yield of semiconductor devices. Furthermore, because the thermal CVD method does not cause plasma damage during film formation, it can produce films with fewer defects.

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

[0375] Furthermore, the ALD method utilizes the self-regulating properties of atoms to deposit atoms layer by layer, enabling the formation of ultrathin films, films with high aspect ratios, films with fewer defects such as pinholes, films with excellent coverage, and films at low temperatures. The PEALD method utilizes plasma, which can be preferable because it allows film formation at lower temperatures. Note that some precursors used in the ALD method contain impurities such as carbon. Therefore, films formed by the ALD method may contain higher amounts of impurities such as carbon than films formed by other film formation methods. Quantitative determination of impurities can be performed using X-ray photoelectron spectroscopy (XPS).

[0376] Unlike film formation methods in which particles emitted from a target or the like are deposited, CVD and ALD are film formation methods in which a film is formed by a reaction on the surface of the workpiece. Therefore, these film formation methods are less affected by the shape of the workpiece and have good step coverage. In particular, ALD has excellent step coverage and excellent thickness uniformity, making it suitable for coating the surface of openings with high aspect ratios. However, because ALD has a relatively slow film formation rate, it may be preferable to use it in combination with other film formation methods, such as CVD, which has a faster film formation rate.

[0377] The CVD method and the ALD method can control the composition of the resulting film by adjusting the flow rate ratio of the source gases. For example, the CVD method and the ALD method can form a film of any composition by adjusting the flow rate ratio of the source gases. Furthermore, for example, the CVD method and the ALD method can form a film with a continuously changing composition by changing the flow rate ratio of the source gases while forming the film. When forming a film while changing the flow rate ratio of the source gases, the time required for film formation can be shortened compared to when forming a film using multiple film formation chambers because no time is required for transportation and pressure adjustment. Therefore, the productivity of semiconductor devices can be improved in some cases.

[0378] First, a substrate (not shown) is prepared, and an insulator 212 is formed on the substrate (see FIGS. 16A to 16D). The insulator 212 is preferably formed by sputtering. By using sputtering, which does not require the use of 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 sputtering, and a CVD method, an MBE method, a PLD method, an ALD method, or the like may also 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. The use of pulsed DC sputtering can suppress particle generation due to arcing on the target surface, resulting in a more uniform film thickness distribution. Furthermore, the use of pulsed voltage can make the discharge rise and fall steeper than with high-frequency voltage. This allows for more efficient supply of power to the electrodes, improving the sputtering rate and film quality.

[0380] By using an insulator that is impermeable to impurities such as water and hydrogen, such as silicon nitride, 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 that is impermeable to copper, such as silicon nitride, 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 upward diffusion of the metal 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 sputtering. By using sputtering, which does not require the use of 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 sputtering, and CVD, MBE, PLD, ALD, 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 pulsed DC sputtering, 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 RF power is not 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 implanted 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 Over 1.86W / cm 2 The following is true. In other words, the amount of oxygen suitable for the transistor characteristics can be changed and implanted by adjusting the RF power used when forming the insulator 214. Therefore, an amount of oxygen suitable for improving the reliability of the transistor can be implanted. Furthermore, 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 ability to capture and fix hydrogen, as the insulator 214. This allows hydrogen contained in the insulator 216 to be captured or fixed and prevents the hydrogen from diffusing into the oxide 230. In particular, using aluminum oxide having an amorphous structure or aluminum oxide having an amorphous structure as the insulator 214 is preferable because it may be possible to more effectively capture or fix hydrogen. This enables the manufacture of a highly reliable transistor 200 and semiconductor device with favorable characteristics.

[0384] Next, the insulator 216 is deposited over the insulator 214. The insulator 216 is preferably deposited by sputtering. By using sputtering, which does not require the use of 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 sputtering, 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 pulse DC sputtering using a silicon target in an atmosphere containing oxygen gas as the insulator 216. 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.

[0386] The insulators 212, 214, and 216 are preferably successively deposited without exposure to the atmosphere. For example, a multi-chamber deposition apparatus can be used. This allows the insulators 212, 214, and 216 to be deposited with reduced hydrogen content and also reduces the amount of hydrogen mixed into the films between deposition steps.

[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 region where the opening is formed may be referred to as an opening. The opening may be formed by wet etching, but dry etching is preferable for fine processing. It is also preferable to select an insulator for the insulator 214 that functions as an etching stopper film when etching the insulator 216 to form the groove. For example, if silicon oxide or silicon oxynitride is used for the insulator 216 that forms the groove, the insulator 214 may be made of silicon nitride, aluminum oxide, or hafnium oxide. A recess may be formed in the insulator 214, overlapping the opening in the insulator 216.

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

[0389] After the openings are formed, a conductive film that becomes the conductor 205a is formed. The conductive film that becomes the conductor 205a preferably includes 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, the conductive film can be a stacked 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 sputtering, CVD, MBE, PLD, ALD, 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 bottom and side surfaces of the conductor 205b, it is possible to prevent the conductor 205b from being oxidized by the insulator 216 or the like. Furthermore, 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 allows the formation of 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 over the insulator 216 and the conductor 205 (see FIGS. 17A to 17D). The insulator 222 may be an insulator containing one or both of aluminum and hafnium oxides. Note that aluminum oxide, hafnium oxide, or an oxide containing aluminum and hafnium (hafnium aluminate) is preferably used as the insulator containing one or both of aluminum and hafnium oxides. An insulator containing one or both of aluminum and hafnium oxides has barrier properties against oxygen, hydrogen, and water. The insulator 222 having barrier properties against hydrogen and water can prevent hydrogen and water contained in structures provided around the transistor 200 from diffusing into the inside of the transistor 200 through the insulator 222, thereby preventing oxygen vacancies from being generated in the oxide 230.

[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] Subsequently, heat treatment is preferably performed. The heat treatment may be performed at a temperature of 250°C to 650°C, preferably 300°C to 500°C, and more preferably 320°C to 450°C. The heat treatment may be performed in a nitrogen gas or inert gas atmosphere, or in 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 concentration may be about 20%. The heat treatment may also be performed under reduced pressure. Alternatively, the heat treatment may be performed in a nitrogen gas or inert gas atmosphere, followed by another heat treatment 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.

[0396] 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 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, moisture and the like can be prevented from being introduced into the insulator 222 as much as possible.

[0397] In this embodiment, after the insulator 222 is formed, heat treatment is performed at 400° C. for 1 hour with a flow rate ratio of nitrogen gas and oxygen gas set to 4 slm:1 slm. This 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, an insulating film 224A is formed on the insulator 222 (see FIGS. 17A to 17D). The insulating film 224A can be formed by sputtering, CVD, MBE, PLD, ALD, or the like. In this embodiment, silicon oxide is formed as the insulating film 224A by sputtering. By using a sputtering method that does not require the use of hydrogen as a deposition gas, the hydrogen concentration in the insulating film 224A can be reduced. Since the insulating film 224A will come into contact with the oxide 230a in a later step, it is preferable that the hydrogen concentration be reduced in this manner.

[0399] Next, oxide films 230A and 230B are sequentially formed on insulating film 224A (see FIGS. 17A to 17D). It is preferable to form oxide films 230A and 230B consecutively without exposing them to the atmosphere. By forming the films without exposing them to the atmosphere, it is possible to prevent impurities or moisture from the atmosphere from adhering to oxide films 230A and 230B, and to keep the vicinity of the interface between oxide films 230A and 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 formation apparatus shown in the previous embodiment may be used. This reduces the amount of hydrogen that gets mixed into the insulating film 224A, the oxide film 230A, and the oxide film 230B between the film formation steps.

[0402] Next, heat treatment is preferably performed. The heat treatment may be performed within a temperature range in which the oxide film 230A and the oxide film 230B do not polycrystallize, such as 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 a nitrogen gas or inert gas atmosphere, or in 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 concentration should be approximately 20%. The heat treatment may also be performed under reduced pressure. Alternatively, the heat treatment may be performed in a nitrogen gas or inert gas atmosphere, followed by an atmosphere containing 10 ppm or more, 1% or more, or 10% or more of an oxidizing gas to replenish the desorbed oxygen. Note that, 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. The heat treatment may be performed in the processing chamber 4011 shown in FIG. 7 of the previous embodiment.

[0403] Furthermore, it is preferable that the gas used in the heat treatment be highly purified. For example, the moisture content of the gas used in the heat treatment should 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 other contaminants from being absorbed into the oxide film 230A and the oxide film 230B as much as possible.

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

[0405] Next, a 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 formation of the conductive film 242A. The heat treatment may be performed under reduced pressure, and the conductive film 242A may be formed successively without exposure to the air. By performing such treatment, moisture and hydrogen adsorbed on the surface of the oxide film 230B can be removed, and the moisture and hydrogen concentrations in the oxide film 230A, the oxide film 230B, and the oxide film 230B can be further reduced. The heat treatment temperature is preferably 100° C. or higher and 400° C. or lower. In this embodiment, the heat treatment temperature is 200° C.

[0406] Next, an 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 that has a function of suppressing oxygen permeation. For example, aluminum oxide may be formed as the insulating film 271A by a sputtering method.

[0407] Note that the conductive film 242A and the insulating film 271A are preferably formed by sputtering without exposure to the atmosphere. 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 content and also reduces the amount of hydrogen mixed into the films between film formation steps. Furthermore, when a hard mask is provided on the insulating film 271A, the film that will become the hard mask may also be formed continuously without exposure to the atmosphere.

[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 island shapes using lithography 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). 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 portion of each overlaps the conductor 205. This processing can be performed using a dry etching method or a wet etching method. Processing using a dry etching method is suitable for microfabrication. 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 lithography, a resist is first exposed through a mask. The exposed area is then removed or left using a developer to form a resist mask. A conductor, semiconductor, or insulator can then be processed into a desired shape by etching through the resist mask. For example, a resist mask can be formed by exposing the resist to KrF excimer laser light, ArF excimer laser light, or EUV (Extreme Ultraviolet) light. An immersion technique may also be used, in which a liquid (e.g., water) is filled between the substrate and the projection lens for exposure. An electron beam or ion beam may also be used instead of the light described above. When an electron beam or ion beam is used, a mask is not required. The resist mask can be removed by dry etching such as ashing, wet etching, dry etching followed by wet etching, or wet etching followed by dry etching.

[0410] Furthermore, a hard mask made of an insulator or conductor may be used under the resist mask. When using a hard mask, an insulating or conductive film serving as 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 with 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 be lost during etching. The hard mask may be removed by etching after etching the conductive film 242A and the like. On the other hand, if the hard mask material does not affect subsequent processes or can be used in subsequent processes, 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 its side surface and top surface, as shown in FIGS. 18B to 18D. As a result, the conductors 242a and 242b shown in FIGS. 14B and 14D have angular ends where their side surfaces and top surfaces intersect. Because the angular ends where the side surfaces and top surfaces of the conductor 242 intersect are angular, the cross-sectional area of the conductor 242 is larger than when the ends have a curved surface. This reduces the resistance of the conductor 242, thereby increasing the on-current of the transistor 200.

[0412] 18B to 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, a tapered shape refers to a shape in which at least a portion of the side surface of the structure is inclined with respect to the substrate surface. For example, the angle between the inclined side surface and the substrate surface (hereinafter, sometimes referred to as the taper angle) is preferably less than 90°. The insulator 224, the oxide 230a, the oxide 230b, the conductive layer 242B, and the insulating layer 271B may have a taper angle of, for example, 60° or more and less than 90°. By tapering the cross sections in this way, the coverage of the insulator 275 and the like can be improved in subsequent processes, 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 top 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 etching process may form 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 layer-like 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 layer-like 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 be 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, or the like. It is preferable that the insulator 275 be an insulating film having the function of suppressing oxygen permeation. For example, the insulator 275 may be formed by depositing an aluminum oxide film by a sputtering method, and then depositing a silicon nitride film 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 way, 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 the function of suppressing the diffusion of oxygen. This makes it possible to reduce the direct diffusion of oxygen from the insulator 280 and the like into 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 sputtering, CVD, MBE, PLD, ALD, or the like. For example, a silicon oxide film can be formed by sputtering. The insulating film to be the insulator 280 can be formed by sputtering in an oxygen-containing atmosphere, thereby forming the insulator 280 containing excess oxygen. Furthermore, the hydrogen concentration in the insulator 280 can be reduced by using a sputtering method that does not require hydrogen as a deposition gas. Heat treatment may be performed before the formation of the insulating film. The heat treatment may be performed under reduced pressure, and the insulating film may be formed successively without exposure to the atmosphere. By performing such treatment, moisture and hydrogen adsorbed on the surface of the insulator 275 can be removed, and the moisture and hydrogen concentrations in the oxide 230a, the oxide 230b, and the insulator 224 can be 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). Alternatively, a silicon nitride film may be formed on the insulator 280 by, for example, a sputtering method, and the CMP processing may be performed on the silicon nitride until it reaches the insulator 280.

[0419] Next, a portion of the insulator 280, a portion of the insulator 275, a portion of the insulating layer 271B, and a portion 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. Furthermore, 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 portion of the insulator 280, a portion of the insulator 275, a portion of the insulating layer 271B, and a portion of the conductive layer 242B can be processed by dry etching or wet etching. Processing by dry etching is suitable for fine processing. Furthermore, the processing may be performed under different conditions. For example, a portion of the insulator 280 may be processed by dry etching, a portion of the insulator 275 and a portion of the insulating layer 271B may be processed by wet etching, and a portion of the conductive layer 242B may be processed by dry etching.

[0422] Here, impurities may adhere to the side surfaces of the oxide 230a, the top and side surfaces of the oxide 230b, the side surfaces of the conductor 242, and the side surfaces of the insulator 280, and may diffuse into these surfaces. A process for removing such impurities may be performed. Furthermore, the dry etching may result in damaged regions being formed on the surface of the oxide 230b. Such damaged regions may be removed. Examples of such impurities include those derived from components contained in the insulator 280, the insulator 275, part of the insulating layer 271B, and the conductive layer 242B, components contained in the materials used in the device used to form the opening, and components contained in the gas or liquid used in etching. Examples of such impurities include hafnium, aluminum, silicon, tantalum, fluorine, and chlorine.

[0423] In particular, impurities such as aluminum or silicon inhibit the formation of a CAAC-OS oxide 230b. Therefore, it is preferable to reduce or eliminate impurity elements such as aluminum or silicon that inhibit the formation of a CAAC-OS oxide. For example, the concentration of aluminum atoms in and around the oxide 230b 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] Note that the region of the metal oxide where the CAAC-OS transformation is inhibited by impurities such as aluminum or silicon and 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 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 be 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 bottom edge 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 bottom edge of the conductor 242a (conductor 242b) has the CAAC structure. In this way, even at the drain edge, which significantly affects the drain breakdown voltage, the damaged region of the oxide 230b is removed, and by having the CAAC structure, fluctuations in the electrical characteristics of the transistor 200 can be further suppressed. Furthermore, the reliability of the transistor 200 can be improved.

[0426] A cleaning process is performed to remove impurities and the like that have adhered to the surface of the oxide 230b during the etching process. Cleaning methods include wet cleaning using a cleaning solution (also known as 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, cleaning treatment 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 used in combination as appropriate.

[0428] In this specification, an aqueous solution obtained by diluting commercially available hydrofluoric acid with pure water may be referred to as "diluted hydrofluoric acid," and an aqueous solution obtained by diluting commercially available ammonia water with pure water may be referred to as "diluted ammonia water." The concentration, temperature, and other parameters of the aqueous solution may be adjusted appropriately 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 set to 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 set to 0.01 ppm or more and 100 ppm or less, preferably 0.1 ppm or more and 10 ppm or less.

[0429] It is preferable to use a frequency of 200 kHz or more, and more preferably 900 kHz or more, for ultrasonic cleaning, as this frequency can reduce damage to the oxide 230b and the like.

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

[0431] In this embodiment, the cleaning process is performed by wet cleaning using diluted ammonia water, which can remove impurities that have adhered to the surfaces of the oxides 230a and 230b or that have diffused into the oxides 230a and 230b.

[0432] After the etching or cleaning, a heat treatment may be performed. The heat treatment may be performed at a temperature of 100°C or higher and 500°C or lower, preferably 300°C or higher and 500°C or lower, and more preferably 350°C or higher and 400°C or lower. 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 higher, 1% or higher, or 10% or higher 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 eliminating oxygen deficiencies (V O ) can be reduced. Furthermore, by performing such 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 successively in a nitrogen atmosphere without exposure to the air. Furthermore, when the heat treatment in an oxygen atmosphere is performed successively in a nitrogen atmosphere without exposure to the air, the heat treatment in the oxygen atmosphere may be performed for a longer 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. The heat treatment may be performed under reduced pressure, and the insulating film 250A may be formed immediately without exposure to the atmosphere. The heat treatment is preferably performed in an oxygen-containing atmosphere. By performing such a treatment, moisture and hydrogen adsorbed on the surface of the oxide 230b can be removed, and the moisture and hydrogen concentrations 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 a method such as sputtering, CVD, PECVD, MBE, PLD, or ALD. The insulating film 250A is preferably formed by a film formation method using a gas in which hydrogen atoms are reduced or removed. This reduces the hydrogen concentration in the insulating film 250A. The insulating film 250A will become the insulator 250a that contacts the oxide 230b in a later process, so it is preferable that the hydrogen concentration be reduced in this manner.

[0435] Furthermore, the insulating film 250A is preferably formed using the ALD method. The insulator 250, which functions as the gate insulating film of the miniaturized transistor 200, must be extremely thin (e.g., between 5 nm and 30 nm) and have minimal variation in thickness. In contrast, the ALD method is a film formation method in which a precursor and a reactant (e.g., an oxidizer) are alternately introduced. The thickness can be adjusted by the number of times this cycle is repeated, allowing for precise film thickness adjustment. Therefore, the precision of the gate insulating film thickness required for the miniaturized transistor 200 can be achieved. Furthermore, as shown in FIGS. 21B and 21C , the insulating film 250A must be formed with good coverage on the bottom and side surfaces of the opening formed by the insulator 280, etc. Because atomic layers can be deposited one by one on the bottom and side surfaces of the opening, the insulating film 250A can be formed with good coverage on the opening.

[0436] Furthermore, when the insulating film 250A is formed by the PECVD method using a gas containing hydrogen such as SiH4 (or Si2H6) as the film formation gas, the film formation gas containing hydrogen is decomposed in the plasma to generate a large amount of hydrogen radicals. The reduction reaction of the hydrogen radicals extracts oxygen from the oxide 230b, resulting in V 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 introducing the precursor and when introducing the reactant. 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, microwave treatment is preferably performed in an oxygen-containing atmosphere (see FIGS. 21A to 21D). Here, microwave treatment refers to treatment using, for example, a device with a power source that generates high-density plasma using microwaves. In this specification and elsewhere, microwaves refer to electromagnetic waves having a frequency of 300 MHz or more and 300 GHz or less.

[0440] In Figures 21B to 21D, dotted lines indicate high-frequency oxygen plasma such as microwaves or RF, or oxygen radicals. For microwave processing, it is preferable to use a microwave processing device having a power supply that generates high-density plasma using microwaves. Here, the frequency of the microwave processing device may be 300 MHz to 300 GHz, preferably 2.4 GHz to 2.5 GHz, for example, 2.45 GHz. Furthermore, the power of the power supply that applies microwaves to the microwave processing device may be 1000 W to 10,000 W, preferably 2000 W to 5,000 W. Furthermore, the microwave processing device may also have a power supply that applies RF to the substrate side. Using high-density plasma allows for the generation of high-density oxygen radicals. Furthermore, applying RF to the substrate side allows for the efficient introduction of oxygen ions generated by high-density plasma into the oxide 230b.

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

[0442] Furthermore, for example, the microwave treatment may be performed using oxygen gas and argon gas. Here, the oxygen flow ratio (O2 / (O2+Ar)) may be greater than 0% and less than or equal to 100%. Preferably, the oxygen flow ratio (O2 / (O2+Ar)) may be greater than 0% and less than or equal to 50%. More preferably, the oxygen flow ratio (O2 / (O2+Ar)) may be greater than 10% and less than or equal to 40%. Even more preferably, the oxygen flow ratio (O2 / (O2+Ar)) may be greater than 10% and less than or equal to 30%. In this way, by performing microwave treatment in an oxygen-containing atmosphere, the carrier concentration in the region 230bc can be reduced. Furthermore, by preventing excessive oxygen from being introduced into the chamber during microwave treatment, an excessive reduction in the carrier concentration in the regions 230ba and 230bb can be prevented.

[0443] As shown in Figures 21B to 21D, microwave processing is performed in an atmosphere containing oxygen, whereby oxygen gas is converted 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 onto 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 plasma, microwaves, etc., can increase the V of the region 230bc. O H can be split off and hydrogen H can be removed from the region 230bc. O H→H+V O " reaction occurs, and V contained in region 230bc O Therefore, oxygen vacancies and V in the region 230bc can be reduced. 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 lowered.

[0444] 15A, conductors 242a and 242b are provided on regions 230ba and 230bb. Here, conductor 242 preferably functions as a shielding film against the effects of microwaves, high-frequency waves such as RF, oxygen plasma, and the like when microwave processing is performed in an oxygen-containing atmosphere. Therefore, conductor 242 preferably has the function of blocking electromagnetic waves of 300 MHz or higher and 300 GHz or lower, for example, 2.4 GHz or higher and 2.5 GHz or lower.

[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. O Since there is no reduction in H and no excessive supply of oxygen, it is possible to prevent a decrease in the carrier concentration.

[0446] In this way, 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, which function as source and drain regions, can be prevented, maintaining the n-type conductivity. This prevents fluctuations in the electrical characteristics of the transistor 200 and prevents the electrical characteristics of the transistor 200 from varying across the substrate.

[0447] In microwave processing, thermal energy may be transferred directly to the oxide 230b due to electromagnetic interaction between the microwaves and molecules in the oxide 230b. This thermal energy may heat the oxide 230b. This type of heat treatment is sometimes called microwave annealing. Performing microwave processing in an oxygen-containing atmosphere may produce an effect equivalent to oxygen annealing. Furthermore, if the oxide 230b contains hydrogen, this thermal energy may be transferred to the hydrogen in the oxide 230b, which may activate and release the hydrogen from the oxide 230b.

[0448] Next, the insulating film 250B is formed (see FIGS. 22A to 22D). The insulating film 250B 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 250B is preferably formed using an insulator that has a function of suppressing oxygen diffusion. This configuration can suppress the oxygen contained in the insulator 250a from diffusing into the conductor 260. That is, it can suppress a decrease in the amount of oxygen supplied to the oxide 230. It can also suppress oxidation of the conductor 260 due to the oxygen contained in the insulator 250a. For example, the insulating film 250A can be formed using a material that can be used for the insulator 250a described above, and the insulating film 250B can be formed using a material similar to that for the insulator 222.

[0449] Specifically, the insulating film 250B can be a metal oxide containing one or more elements selected from 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 same conditions as those used for the microwave treatment performed after the formation of the insulating film 250A. Alternatively, the microwave treatment may be performed after the formation of the insulating film 250B without performing the microwave treatment performed after the formation of the insulating film 250A.

[0452] Furthermore, after the formation of the insulating film 250A and the formation of the insulating film 250B, a heat treatment may be performed while maintaining the reduced pressure after each microwave treatment. 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. Some of the hydrogen may be gettered to the conductor 242 (the conductor 242a and the conductor 242b). Alternatively, a heat treatment step may be performed multiple times while maintaining the reduced pressure after the microwave treatment. Repeated heat treatments can more efficiently remove hydrogen from the insulating film 250A, the oxide 230b, and the oxide 230a. The heat treatment temperature is preferably 300°C or higher and 500°C or lower. The microwave treatment, i.e., microwave annealing, may also serve as the heat treatment. If the oxide 230b and the like are sufficiently heated by microwave annealing, the heat treatment may not be necessary.

[0453] Furthermore, by modifying the film quality of the insulating film 250A and the insulating film 250B by microwave treatment, 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-treatment such as heat treatment.

[0454] Next, a conductive film that will become the conductor 260a and a conductive film that will become the conductor 260b are formed in this order. The conductive film that will become the conductor 260a and the conductive film that will become 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 will become the conductor 260a is formed using an ALD method, and the conductive film that will become the conductor 260b is formed using a CVD method.

[0455] Next, the insulating film 250A, the insulating film 250B, the conductive film that will become the conductor 260a, and the conductive film that will become the conductor 260b are polished by CMP until the insulator 280 is exposed, thereby forming the insulators 250a, 250b, the conductors 260a, and 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 walls (side walls and bottom surface) of the groove in the oxide 230b. The conductor 260 is disposed so as to fill the opening and the groove via 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 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 as a deposition gas, the hydrogen concentration in the insulator 282 can be reduced. Furthermore, by forming the insulator 282 by a sputtering method in an atmosphere containing oxygen, oxygen can be added to the insulator 280 during deposition. 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, heat treatment is preferably performed. This heat treatment can be performed under the same conditions as the above-described heat treatment. In this embodiment, the treatment is performed in a nitrogen atmosphere at 400° C. for 1 hour. This heat treatment allows oxygen added by the formation of the insulator 282 to diffuse into the insulator 280 and the insulator 250a and to be selectively supplied to the channel formation region of the oxide 230. This makes it possible to provide a semiconductor device with favorable electrical characteristics. Furthermore, it is possible to provide a semiconductor device with favorable reliability.

[0460] Note that the heat treatment may be performed not only after the insulator 282 is formed but also after the insulator 283 is formed.

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

[0462] Next, an insulator 285 is formed on 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 are formed in the insulators 271, 275, 280, 282, 283, and 285, reaching the conductor 242 (see FIGS. 25A to 25D). The openings may be formed using lithography. 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 have a substantially circular shape such as an ellipse, a polygonal shape such as a rectangle, or a polygonal shape 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 using a sputtering method, a CVD method, an MBE method, a PLD method, an ALD method, or the like. It is preferable to use an insulating film that has the 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 using the ALD method, and then form a film of silicon nitride thereon using the PEALD method. Silicon nitride is preferable because it has a high barrier property against hydrogen.

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

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

[0467] Next, CMP processing is performed to remove portions 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, thereby forming the conductors 240a and 240b with flat upper surfaces (see Figures 25A to 25D). Note that the CMP processing may remove portions 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 will become the conductor 246 is processed by lithography to form the conductor 246a that contacts the upper surface of the conductor 240a and the conductor 246b that contacts the upper 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] 14A to 14D can be manufactured. As shown in FIGS. 16A to 25A, 16B to 25B, 16C to 25C, and 16D to 25D, the transistor 200 can be manufactured by the manufacturing method of a semiconductor device described in this embodiment.

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

[0472] First, the configuration of a manufacturing apparatus capable of reducing the amount of impurities mixed in during the manufacturing of semiconductor devices and the like will be described with reference to FIGS.

[0473] 26 is a schematic top view of a single-wafer processing multi-chamber manufacturing apparatus 2700. The manufacturing apparatus 2700 has an atmosphere-side substrate supply chamber 2701 equipped with a cassette port 2761 for accommodating substrates and an alignment port 2762 for aligning the substrates, an atmosphere-side substrate transfer chamber 2702 for transferring substrates from the atmosphere-side substrate supply chamber 2701, a load lock chamber 2703a for loading substrates and for switching the pressure inside the chamber from atmospheric pressure to reduced pressure or from reduced pressure to atmospheric pressure, an unload lock chamber 2703b for unloading substrates and for switching the pressure inside the chamber from reduced pressure to atmospheric pressure or from atmospheric pressure to reduced pressure, a transfer chamber 2704 for transferring substrates in a vacuum, chambers 2706a, 2706b, 2706c, and 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 chambers 2706a, 2706b, 2706c and 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 robots 2763a and 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 In addition, 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.

[0478] It is also 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, if 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, if 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 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 caused by gases entering from outside the vacuum system due to tiny holes or poor seals. Internal leaks are caused by leaks from partitions such as valves within the vacuum system, or gases released from internal components. In order to keep the leak rate below the above-mentioned values, measures must be taken to prevent both external and internal leaks.

[0480] For example, it is advisable to seal the opening and closing portions of the transfer chamber 2704 and each chamber with a metal gasket. It is preferable to use a metal gasket coated with iron fluoride, aluminum oxide, or chromium oxide. Metal gaskets have higher adhesion than O-rings and can reduce external leakage. Furthermore, 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 can be suppressed, thereby reducing internal leakage.

[0481] Furthermore, aluminum, chromium, titanium, zirconium, nickel, or vanadium, which emit little impurity-containing gases, are used as components constituting the manufacturing apparatus 2700. Furthermore, the aforementioned metals that emit little impurity-containing gases may be coated on alloys containing iron, chromium, nickel, and the like. Alloys containing iron, chromium, nickel, and the like are rigid, heat-resistant, and suitable for processing. Here, reducing the surface roughness of the components by polishing or the like to reduce the surface area can reduce the amount of emitted gases.

[0482] Alternatively, the components of the manufacturing apparatus 2700 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 be constructed solely from metal as much as possible, and 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 gas emissions.

[0484] The adsorbed matter present in the transfer chamber 2704 and each chamber is adsorbed to the inner walls and does not affect the pressure of the transfer chamber 2704 or each chamber. However, it can cause gas emissions when the transfer chamber 2704 or each chamber is evacuated. Therefore, although there is no correlation between the leak rate and the evacuation speed, it is important to use a pump with high evacuation capacity to desorb as much adsorbed matter as possible from the transfer chamber 2704 and each chamber and evacuate them in advance. To promote the desorption of adsorbed matter, the transfer chamber 2704 and each chamber may be baked. Baking can increase the desorption rate of adsorbed matter by approximately 10 times. Baking can be performed at temperatures between 100°C and 450°C. In this case, introducing an inert gas into the transfer chamber 2704 and each chamber while removing adsorbed matter can further increase the desorption rate of water and other substances that are difficult to desorb by evacuation alone. Heating the introduced inert gas to the same temperature as the baking temperature can further increase the desorption rate of adsorbed matter. A rare gas is preferably used 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 evacuating the transfer chamber 2704 and each chamber again after a certain period of time has elapsed. The introduction of heated gas can desorb adsorbed substances from the transfer chamber 2704 and each chamber, thereby reducing impurities present in the transfer chamber 2704 and each chamber. It is effective to repeat this process two to 30 times, preferably five to 15 times. Specifically, by introducing an inert gas or oxygen at a temperature of 40°C to 400°C, preferably 50°C to 200°C, the pressure in the transfer chamber 2704 and each chamber can be adjusted to 0.1 Pa to 10 kPa, preferably 1 Pa to 1 kPa, and more preferably 5 Pa to 100 Pa. The pressure can be maintained for a period of 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 minutes to 300 minutes, preferably 10 minutes to 120 minutes.

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

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

[0488] Chamber 2706b and chamber 2706c have a slot antenna plate 2808, a dielectric plate 2809, a substrate holder 2812, and an exhaust port 2819. Also provided outside chamber 2706b and chamber 2706c are 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.

[0489] The high-frequency generator 2803 is connected to a 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 delivered to chambers 2706b and 2706c via a gas pipe 2806 that passes through the mode converter 2805, the waveguide 2807, and the dielectric plate 2809. The vacuum pump 2817 evacuates gases and other gases from chambers 2706b and 2706c via a valve 2818 and an exhaust port 2819. The high-frequency power supply 2816 is connected to a substrate holder 2812 via a matching box 2815.

[0490] The substrate holder 2812 has a function of holding the substrate 2811. For example, it has a function of electrostatically or mechanically chucking the substrate 2811. It also has a function as an electrode to which power is supplied from a high-frequency power supply 2816. It 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 turbomolecular pump can be used as the vacuum pump 2817. A cryotrap may also be used in addition to the vacuum pump 2817. The use of a cryopump or a cryotrap is particularly preferable because it allows water to be efficiently pumped out.

[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. The gas used preferably has a dew point of -80°C or lower, preferably -100°C or lower. 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). Furthermore, another protective layer may be formed on the surface of the dielectric plate 2809. The protective layer may be made of, for example, magnesium oxide, titanium oxide, chromium oxide, zirconium oxide, hafnium oxide, tantalum oxide, silicon oxide, aluminum oxide, or yttrium oxide. Because the dielectric plate 2809 is exposed to a particularly high-density region of the high-density plasma 2810 (described later), providing a protective layer can mitigate damage. As a result, an increase in particles during processing can be suppressed.

[0495] The high-frequency generator 2803 has the function of generating microwaves in the range 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 a mode converter 2805 via a waveguide 2804. The mode converter 2805 converts the microwaves transmitted in TE mode to TEM mode. The microwaves are then transmitted to a slot antenna plate 2808 via a waveguide 2807. The slot antenna plate 2808 has multiple slot holes, and the microwaves pass through the slot holes and a dielectric plate 2809. An electric field is then generated below the dielectric plate 2809, generating a high-density plasma 2810. The high-density plasma 2810 contains ions and radicals depending on the gas species supplied from the gas supply source 2801. For example, oxygen radicals are present.

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

[0497] For example, oxygen radical treatment using high density plasma 2810 can be performed in chamber 2706b or chamber 2706c by introducing oxygen from gas supply source 2801.

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

[0499] Chamber 2706a and chamber 2706d are chambers capable of irradiating an object to be treated with electromagnetic waves, for example. Chamber 2706a and chamber 2706d differ only in the type of electromagnetic waves. Since the other configurations are largely common, they will be described together below.

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

[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 opposite 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 that has a function of heating the substrate 2824.

[0502] A light source capable of emitting electromagnetic waves such as visible light or ultraviolet light may be used as the lamp 2820. For example, a light source capable 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, the 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 partially or completely absorbed by the substrate 2824, thereby modifying the film on the substrate 2824. For example, defects can be generated or reduced, or impurities can be removed. Note that 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 lamp 2820, thereby heating the substrate 2824. In this 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 apparatus that can be used in this embodiment is not limited to the above. A microwave processing apparatus 2900 shown in Fig. 29 can be used. The microwave processing apparatus 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 apparatus 2900 also has a substrate holder 2902 that holds multiple substrates 2811 (2811_1 to 2811_n, n is an integer of 2 or more) inside the quartz tube 2901. The microwave processing apparatus 2900 may also have heating means 2903 outside the quartz tube 2901.

[0508] Microwaves generated by a high-frequency generator 2803 are irradiated onto a substrate placed in a quartz tube 2901 via a waveguide 2804. A vacuum pump 2817 is connected to an exhaust port 2819 via a valve 2818, allowing adjustment of the pressure inside the quartz tube 2901. A gas supply source 2801 is connected to a gas pipe 2806 via a valve 2802, allowing a desired gas to be introduced into the quartz tube 2901. A heating means 2903 can heat the substrate 2811 in the quartz tube 2901 to a desired temperature. Alternatively, the heating means 2903 may heat the 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. Alternatively, the microwave treatment can be performed after the substrate 2811 is heated. Alternatively, 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. Alternatively, 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. Using dummy substrates is preferable because multiple processing substrates can be uniformly processed during microwave processing or heat treatment, reducing variations between processing substrates. For example, placing a dummy substrate on the processing substrate closest to the high-frequency generator 2803 and the waveguide 2804 is preferable because it prevents the processing substrate from being directly exposed to microwaves.

[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] 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] <Modification of Semiconductor Device> An example of a semiconductor device according to one embodiment of the present invention will be described below with reference to FIG.

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

[0514] 30A to 30C, the same reference numerals are used to designate structures having the same functions as those constituting the semiconductor device shown in <Configuration Example of Semiconductor Device>. Also in this section, the materials described in detail in <Configuration Example of Semiconductor Device> can be used as the materials constituting the semiconductor device.

[0515] 30A to 30C is a modified example of the semiconductor device shown in FIGS. 14A to 14D. The semiconductor device 500 shown in FIGS. 30A to 30C differs from the semiconductor device shown in FIGS. 14A to 14D in that an opening region 400 is formed in the insulator 282 and the insulator 280. The semiconductor device 500 also differs from the semiconductor device shown in FIGS. 14A to 14D in that a sealing portion 265 is formed 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 regions 400 are formed in regions that do 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. Note that 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 set appropriately according to the design of the semiconductor device 500.

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

[0518] With this structure, the multiple transistors 200 can be enclosed by the insulators 283, 214, and 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 mixing into 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 in opening region 400, overlapping the opening of insulator 282. The depth of the groove in insulator 280 may be at most deep enough to expose the top surface of insulator 275, 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. In addition, a portion of insulator 274 may be formed in opening region 400 so as to fill a recess formed in insulator 283. In this case, the height of the top surface of insulator 274 formed in opening region 400 may roughly match the height of the top surface of insulator 283.

[0521] By performing heat treatment with the opening region 400 formed and the insulator 280 exposed through the opening of the insulator 282, oxygen can be supplied to the oxide 230 while some of the oxygen contained in the insulator 280 diffuses outward from the opening region 400. This allows sufficient oxygen to be supplied from the insulator 280, which contains oxygen released by heating, to a region in the oxide semiconductor layer that functions as a channel formation region and its vicinity, while preventing excessive 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] 30A, the shape of the opening region 400 in a top view is substantially rectangular, but the present invention is not limited to this. For example, the shape of the opening region 400 in a top view may be rectangular, elliptical, circular, diamond-shaped, or a combination of these. The area and spacing of the opening regions 400 can be set appropriately in accordance with the design of the semiconductor device including the transistors 200. For example, in a region where the density of the transistors 200 is low, the area of the opening regions 400 can be increased or the spacing between the opening regions 400 can be narrowed. For example, in a region where the density of the transistors 200 is high, the area of the opening regions 400 can be narrowed or the spacing between the opening regions can be widened.

[0524] According to one embodiment of the present invention, a novel transistor can be provided. Alternatively, according to one embodiment of the present invention, a semiconductor device with high on-state current can be provided. Alternatively, according to one embodiment of the present invention, a semiconductor device with high frequency characteristics can be provided. Alternatively, according to one embodiment of the present invention, a semiconductor device with high reliability can be provided. Alternatively, according to one embodiment of the present invention, a semiconductor device with excellent electrical characteristics can be provided.

[0525] 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 other embodiments.

[0526] (Embodiment 3) In this embodiment mode, one mode of a semiconductor device will be described with reference to FIGS.

[0527] [Storage device 1] 31 illustrates an example of a semiconductor device (memory device) according to one embodiment of the present invention. In the semiconductor device according to one embodiment of the present invention, a transistor 200 is provided above a transistor 300, and a capacitor 100 is provided above the transistors 300 and 200. Note that the transistor 200 described in the above embodiment can be used as the transistor 200.

[0528] The transistor 200 is a transistor in which a channel is formed in a semiconductor layer containing an oxide semiconductor. The transistor 200 has a low off-state current; therefore, when used in a memory device, the stored data can be retained for a long time. That is, a refresh operation is not required or the frequency of the refresh operation is extremely low; therefore, the power consumption of the memory device can be sufficiently reduced.

[0529] 31 , a wiring 1001 is electrically connected to the source of a transistor 300, and a wiring 1002 is electrically connected to the drain of the transistor 300. A wiring 1003 is electrically connected to one of the source and drain of a transistor 200, a wiring 1004 is electrically connected to the first gate of the transistor 200, and a wiring 1006 is electrically connected to the second gate of the transistor 200. The gate of the transistor 300 and the other of the source and drain of the transistor 200 are electrically connected to one electrode of a capacitor 100, and a wiring 1005 is electrically connected to the other electrode of the capacitor 100.

[0530] Moreover, the memory device shown in FIG. 31 can be arranged in a matrix to form a memory cell array.

[0531] <Transistor 300> The transistor 300 is provided on a substrate 311 and includes a conductor 316 functioning as a gate, an insulator 315 functioning as a gate insulator, a semiconductor region 313 formed of part of the substrate 311, and low-resistance regions 314a and 314b functioning as source and drain regions. The transistor 300 may be either a p-channel type or an n-channel type.

[0532] Here, in the transistor 300 shown in FIG. 31, a semiconductor region 313 (a part of a substrate 311) where a channel is formed has a convex shape. In addition, a conductor 316 is provided to cover the side and top surfaces of the semiconductor region 313 with an insulator 315 interposed therebetween. Note that the conductor 316 may be made of a material that adjusts the work function. Such a transistor 300 is also called a FIN-type transistor because it utilizes the convex portion of the semiconductor substrate. Note that an insulator may be provided in contact with the top of the convex portion and function as a mask for forming the convex portion. In addition, although the case where the convex portion is formed by processing a part of the semiconductor substrate has been shown, a semiconductor film having a convex shape may also be formed by processing an SOI substrate.

[0533] Note that the transistor 300 illustrated in FIG. 31 is just an example, and the structure is not limited thereto. An appropriate transistor may be used depending on the circuit configuration or driving method.

[0534] <Capacitor element 100> The capacitor 100 is provided above the transistor 200. The capacitor 100 includes a conductor 110 that functions as a first electrode, a conductor 120 that functions as a second electrode, and an insulator 130 that functions as a dielectric. Here, the insulator 130 is preferably the same as the insulator 275 described in the above embodiment.

[0535] For example, the conductor 112 and the conductor 110 can be formed simultaneously over the conductor 240. The conductor 112 functions as a plug or a wiring electrically connected to the capacitor 100, the transistor 200, or the transistor 300. The conductor 112 and the conductor 110 correspond to the conductor 246 in the above embodiment.

[0536] 31, the conductor 112 and the conductor 110 are shown as having a single l...

Claims

[Claim 1] a first step of introducing a first precursor into a chamber and adsorbing the first precursor onto a surface of a substrate; a second step of introducing a first inert gas into the chamber after the first step and discharging excess first precursor from the chamber; a third step of introducing a first reactant into the chamber after the second step, causing the first reactant to react with the first precursor adsorbed on the surface of the substrate, thereby separating a portion of the components contained in the first precursor while leaving constituent molecules of the first precursor adsorbed on the surface of the substrate, thereby forming a first oxide layer formed by oxidizing a portion of the first precursor on the surface of the substrate; a fourth step of introducing a second inert gas into the chamber after the third step and discharging the excess first reactant from the chamber; a fifth step of introducing a second precursor into the chamber after the fourth step and allowing the second precursor to be adsorbed on the surface of the first oxide layer; a sixth step of introducing a third inert gas into the chamber after the fifth step to exhaust excess second precursor from the chamber; a seventh step, after the sixth step, of introducing a second reactant into the chamber and reacting it with the second precursor adsorbed on the surface of the substrate, thereby separating a part of the components contained in the second precursor while leaving the constituent molecules of the second precursor adsorbed on the surface of the substrate, thereby forming a second oxide layer formed by oxidizing a part of the second precursor on the surface of the substrate; an eighth step of introducing a fourth inert gas into the chamber after the seventh step and discharging excess first reactant from the chamber; a ninth step of introducing a third precursor into the chamber after the eighth step and allowing the third precursor to be adsorbed on the surface of the second oxide layer; a tenth step of introducing a fifth inert gas into the chamber after the ninth step to exhaust excess third precursor from the chamber; an eleventh step, after the tenth step, of introducing a third reactant into the chamber and reacting it with the third precursor adsorbed on the surface of the substrate, thereby separating a part of the components contained in the third precursor while leaving the constituent molecules of the third precursor adsorbed on the surface of the substrate, thereby forming a third oxide layer formed by oxidizing a part of the third precursor on the surface of the substrate; a twelfth step of introducing a sixth inert gas into the chamber after the eleventh step and discharging excess third reactant from the chamber; A method for forming a metal oxide film, comprising carrying out the first step to the twelfth step in order.

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