Semiconductor device

Abstract

To provide a method for manufacturing a sputtering target capable of depositing an oxide semiconductor film with a small amount of defects. Alternatively, an oxide semiconductor film having a small amount of defects is formed.SOLUTION: A method for manufacturing a sputtering target includes forming a polycrystalline In-M-Zn oxide (M is aluminum, titanium, gallium, yttrium, zirconium, lanthanum, cesium, neodymium, or hafnium) powder by mixing, baking, and then pulverizing indium oxide, a metal oxide (the metal is aluminum, titanium, gallium, yttrium, zirconium, lanthanum, cesium, neodymium, or hafnium), and zinc oxide, forming a mixture by mixing the polycrystalline In-M-Zn oxide powder and the zinc oxide powder, forming a molded body by molding the mixture, and baking the molded body.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Sputtering target manufacturing method, oxide film forming method, and transistor do. [Background technology]

[0002] It is used in many flat panel displays, such as liquid crystal displays and light-emitting displays. The transistors used are made of amorphous silicon and single-crystal silicon formed on a glass substrate. It is made of silicon semiconductor such as silicon or polycrystalline silicon. Transistors using semiconductors are also used in integrated circuits (ICs).

[0003] In recent years, metal oxides that exhibit semiconductor properties have been used in transistors instead of silicon semiconductors. In this specification, metal oxides that exhibit semiconductor properties are referred to as oxides. We will call it a semiconductor.

[0004] For example, as an oxide semiconductor, InGaO3(ZnO) having a homologous phase m (m: natural numbers) are known (see Non-Patent Document 1 and Non-Patent Document 2).

[0005] In addition, Patent Document 1 discloses a homologous compound InMO3(ZnO) m (M=In, Fe, Transparent thin film field effect transistor using Ga or Al, m = integer 1 or more but less than 50 The data is disclosed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-103957 [Non-patent literature]

[0007] [Non-Patent Document 1] M. Nakamura, N. Kimizuka, and T. Mohri, “The Phase Relations in the In2O3-Ga2ZnO4-ZnO System at 1350℃”, J. Solid State Chem., 1991, Vol.93, p.298-315 [Non-patent document 2] Masaaki Nakamura, Noboru Kimizuka, Takahiko Mohri, Mitsumasa Isobe, "Synthesis and Crystal Structure of Homologous Phase, InFeO3(ZnO)m (m: natural number) and Its Isomorphic Compounds," Solid State Physics, 1993, Vol. 28, No. 5, pp. 317-327 Summary of the Invention [Problem to be solved by the invention]

[0008] However, if the crystallinity of an oxide semiconductor film is low, oxygen vacancies and dung may occur in the oxide semiconductor film. It is prone to contain defects such as ring bonds.

[0009] In addition, when oxide semiconductor films are stacked using sputtering targets with different compositions, If the crystallinity of each oxide semiconductor film is different, the interface between the stacked oxide semiconductor films may be damaged. Defects will occur on the surface.

[0010] The defects in the oxide semiconductor film or the bonds between the defects and hydrogen or the like cause capacitance in the film. This may cause a rear to occur, which may change the electrical properties of the oxide semiconductor film. This leads to poor electrical characteristics of the transistor, and also to deterioration over time and stress tests (e.g., BT( Bias-Temperature stress tests, optical BT stress tests, etc. This causes an increase in the amount of variation in the electrical characteristics of the transistor, typically the threshold voltage. .

[0011] In view of this, one embodiment of the present invention provides a semiconductor device capable of forming an oxide semiconductor film with few defects. It is an object of the present invention to provide a method for manufacturing a sputtering target. An object of one embodiment is to form an oxide semiconductor film with a small amount of defects. One embodiment of the present invention is to improve electrical characteristics of a semiconductor device or the like including an oxide semiconductor film. Another object of one embodiment of the present invention is to provide a semiconductor device using an oxide semiconductor film. An object of the present invention is to improve the reliability of the device. It is not necessary to solve all of these problems. [Means for solving the problem]

[0012] One aspect of the present invention is to provide a method for producing a crystalline silicon film using indium oxide, metal oxide (the metal is aluminum, titanium, gallium, etc.). Sodium, yttrium, zirconium, lanthanum, cesium, neodymium, or hafnium In-M-Zn oxide (M is Aluminum, titanium, gallium, yttrium, zirconium, lanthanum, cesium, Neodymium or hafnium) powder to form polycrystalline In-M-Zn oxide powder and oxide mixing the mixture with zinc powder to form a mixture, molding the mixture to form a compact, and firing the compact. This is a method for manufacturing a sputtering target.

[0013] In the sputtering target, M (M is aluminum, titanium, gallium) Sodium, yttrium, zirconium, lanthanum, cesium, neodymium, or hafnium The zinc composition is larger than that of the ZnO.

[0014] In addition, the polycrystalline In-M-Zn oxide powder used to manufacture the sputtering target is It is a morogus compound.

[0015] In addition, one embodiment of the present invention is a method for manufacturing a semiconductor device using indium, M (M is aluminum, titanium, gallium, yttrium, zirconium, lanthanum, cesium, neodymium, or hafnium), and Sputtering using a sputtering target with a zinc content greater than M In-M-Zn oxide (where M is aluminum, titanium, gallium, or yttrium) was prepared by the annealing method. depositing a thin film of cesium, zirconium, lanthanum, cesium, neodymium, or hafnium A method for forming an oxide film.

[0016] In-M-Zn oxide (where M is aluminum, titanium, gallium, or yttrium) , zirconium, lanthanum, cesium, neodymium, or hafnium) have homologous structures It has a structure.

[0017] In-M-Zn oxide (where M is aluminum, titanium, gallium, or yttrium) , zirconium, lanthanum, cesium, neodymium, or hafnium) is Z for M The atomic ratio of n is greater than 0.5.

[0018] Furthermore, one aspect of the present invention is the above-mentioned In-M-Zn oxide (M is aluminum, titanium, Gallium, yttrium, zirconium, lanthanum, cesium, neodymium, or hafnium It is a transistor having a gate insulating film. [Effects of the Invention]

[0019] According to one embodiment of the present invention, a sputtering method capable of forming an oxide semiconductor film with few defects can be provided. According to one aspect of the present invention, a method for manufacturing a targeting target can be provided. In this way, an oxide semiconductor film with few defects can be formed. As a result, electrical characteristics of a semiconductor device including an oxide semiconductor film can be improved. According to one embodiment of the present invention, a semiconductor device including an oxide semiconductor film can be provided with high reliability. It can improve the performance. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram illustrating the crystal structure of a homologous compound. [Figure 2] 1A to 1C are diagrams illustrating a manufacturing process of a sputtering target. [Figure 3] 1A to 1C are diagrams illustrating a manufacturing process of a sputtering target. [Figure 4] Schematic diagrams illustrating a method for producing an oxide. [Figure 5] Schematic diagram illustrating oxides. [Figure 6] FIG. 2 is a schematic diagram illustrating sputtering particles. [Figure 7] FIG. 1 is a diagram illustrating the crystal structure of a homologous compound. [Figure 8] Schematic diagrams illustrating a method for producing an oxide. [Figure 9] Schematic diagram illustrating oxides. [Figure 10] 1 shows nanobeam electron diffraction patterns of CAAC-OS and nc-OS. [Figure 11] 1 is a diagram illustrating the process of zinc oxide crystal growth. [Figure 12] 1 is a diagram illustrating the process of zinc oxide crystal growth. [Figure 13] 1 is a diagram illustrating the process of zinc oxide crystal growth. [Figure 14] Schematic diagrams illustrating a method for producing an oxide. [Figure 15]Schematic diagram illustrating oxides. [Figure 16] Schematic diagrams illustrating a method for producing an oxide. [Figure 17] Schematic diagrams illustrating a method for producing an oxide. [Figure 18] Schematic diagrams illustrating a method for producing an oxide. [Figure 19] FIG. [Figure 20] FIG. 2 is a cross-sectional view illustrating a film forming apparatus. [Figure 21] 1A and 1B are diagrams illustrating plasma discharge in a sputtering method using a DC power supply and an AC power supply. [Figure 22] 1A and 1B are a top view and a cross-sectional view illustrating one embodiment of a transistor. [Figure 23] FIG. 1 is a cross-sectional view illustrating one embodiment of a transistor. [Figure 24] FIG. 1 is a cross-sectional view illustrating one embodiment of a transistor. [Figure 25] 1A and 1B are a top view and a cross-sectional view illustrating one embodiment of a transistor. [Figure 26] FIG. 1 is a cross-sectional view illustrating one embodiment of a transistor. [Figure 27] 1A and 1B are a top view and a cross-sectional view illustrating one embodiment of a transistor. [Figure 28] 1A and 1B are a top view and a cross-sectional view illustrating one embodiment of a transistor. [Figure 29] 1A and 1B are a top view and a cross-sectional view illustrating one embodiment of a transistor. [Figure 30] 1A to 1C are cross-sectional views illustrating one embodiment of a method for manufacturing a transistor. [Figure 31] 1A to 1C are cross-sectional views illustrating one embodiment of a method for manufacturing a transistor. [Figure 32] FIG. 1 is a diagram showing the atomic ratio of an In—Ga—Zn oxide film obtained from the results of XPS analysis. [Figure 33] X-ray diffraction measurement results of In-Ga-Zn oxide film. [Figure 34] X-ray diffraction measurement results of In-Ga-Zn oxide film. [Figure 35]X-ray diffraction measurement results of In-Ga-Zn oxide film. [Figure 36] Ternary phase diagram of sputtering target and In-Ga-Zn oxide film. [Figure 37] Cross-sectional TEM images of sample 2 and sample 3. [Figure 38] Cross-sectional image observed by HAADF-STEM. [Figure 39] Band diagram of In-Ga-Zn oxide film. [Figure 40] Band diagram of In-Ga-Zn oxide film. [Figure 41] TEM cross-sectional images of Samples 11 to 13. [Figure 42] TEM cross-sectional images of Samples 11 to 13. [Figure 43] Cross-sectional images of sample 12 and sample 13 observed by TEM. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the following description, and the embodiments and methods thereof may be modified without departing from the spirit and scope of the present invention. It will be readily apparent to those skilled in the art that various modifications may be made to the design and details of the present invention. However, the present invention should not be construed as being limited to the description of the following embodiments and examples. In the embodiments and examples described below, the same parts or parts having similar functions In the case of parts, the same symbols or the same hatch patterns are used in common among different drawings, and the repetition The explanation of repetition will be omitted.

[0022] In each figure described in this specification, the size of each component, the thickness of the film, or the area is The figures may be exaggerated for clarity and are not necessarily limited to that scale. stomach.

[0023] In addition, terms such as first, second, and third used in this specification are used interchangeably to avoid confusion of components. It is not intended to limit the number of items. The terms "second" or "third" can be used interchangeably to explain the present invention.

[0024] The functions of the "source" and "drain" are also different when the direction of the current changes during circuit operation. For this reason, in this specification, the terms "sauce" and "dressing" are used interchangeably. The terms "in" and "in" may be used interchangeably.

[0025] Voltage refers to the potential difference between two points, and potential refers to the electrostatic field at a certain point. This refers to the electrostatic energy (electrical potential energy) of a unit charge in a particle. However, in general, the potential difference between the potential at a certain point and a reference potential (for example, ground potential) This is simply called potential or voltage, and potential and voltage are often used synonymously. Therefore, in this specification, unless otherwise specified, the term "potential" may be read as "voltage." , voltage may be read as potential.

[0026] In this specification, when an etching step is performed after a photolithography step, After the etching process, the mask formed in the photolithography process is removed. .

[0027] (Embodiment 1) In this embodiment, a method for manufacturing a sputtering target will be described.

[0028] <Homologous compounds and homologous structures> First, InMO3(ZnO) m(M is Al, Ti, Ga, Y, Zr, La, Cs, This section explains homologous compounds represented by InM (Nd or Hf, m is a natural number). O3(ZnO) m The crystal structure of the homologous compound represented by - layer and (FeZn m )O m+1 1+ LuFeO3(Z) has a layered structure in which layers are regularly stacked alternately. nO) m When m is odd, it has the space group R-3m, and when m is even, it has the same structure as It has the space group P63 / mmc. m (m=1) In this case, it is also called YbFe2O4 type. Such a crystal structure is called a homologous structure. In the specification, the crystal structure is based on the hexagonal crystal representation.

[0029] Next, InMO3(ZnO) m A typical example is InGaO3(ZnO) m Using Explain the crystal structure of the molybdenum compound InGaO3(ZnO) m In this case, m=1 (i.e. The crystal structure of InGaO3(ZnO)1) is shown in Figure 1(A), and m=2 (i.e., InGa The crystal structure of InGaO3(ZnO)2 is shown in Figure 1(B), where m=3 (i.e., InGaO3(Z The crystal structure of nO)3) is shown in Figure 1(C).

[0030] As shown in Figure 1, InMO3(ZnO) m The homologous compound represented by It has a crystal structure in which a plurality of repeating units u1 to u3 composed of In are stacked. Between the O2 layers, a layer having gallium atoms or / and zinc atoms and oxygen atoms (Zn O, GaO, and (Ga,Zn)O have a crystal structure with (m + 1) layers provided. Thus such a structure is referred to as a homologous structure. In addition, for a homologous m compound represented by InMO3(ZnO) even outside of it, it is possible to form a homologous structure.

[0031] <CAAC-OS film> Next, CAAC-OS (C Axis Aligned Crystalline Oxide Semiconductor) will be described. Here, only the crystal structure of CAAC-OS will be described, and the details of CAAC-OS will be described in Embodiment 2. For CAAC-OS, here, only the crystal structure of CAAC-OS will be described, and the details of CAAC-OS will be described in Embodiment 2. -OS will be described in Embodiment 2.

[0032] CAAC-OS is an oxide semiconductor having CAAC (C Axis Aligned Crystal).

[0033] CAAC-OS, for example, has a plurality of crystal parts, and in the plurality of crystal parts, the c-axes may be aligned in a direction parallel to the normal vector of the formation surface or the upper surface. Also, for CAAC-OS, for example, when analyzed by the out-of-plane method using an X-ray diffraction (XRD: X-Ray Diffraction) apparatus, peaks identified as c-axis orientation, for example, peaks identified as plane orientation (00x) may appear. Also, for CAAC-OS, for example, spots (bright spots) are observed in an electron diffraction pattern. Also, for CAAC-OS, for example, in different crystal parts, the directions of the a-axis and the b-axis may not be aligned. -OS, for example, when analyzed by the out-of-plane method using an X-ray diffraction (XRD: X-Ray Diffraction) apparatus, peaks identified as c-axis orientation, for example, peaks identified as plane orientation (00x) may appear. Also, for CAAC-OS, for example, in different crystal parts, the directions of the a-axis and the b-axis may not be aligned. using an X-ray diffraction (XRD: X-Ray Diffraction) apparatus, peaks identified as c-axis orientation, for example, peaks identified as plane orientation (00x) may appear. Also, for CAAC-OS, for example, in different crystal parts, the directions of the a-axis and the b-axis may not be aligned. -OS, for example, spots (bright spots) are observed in an electron diffraction pattern. Also, for CAAC-OS, for example, in different crystal parts, the directions of the a-axis and the b-axis may not be aligned. -OS, for example, in different crystal parts, the directions of the a-axis and the b-axis may not be aligned.

[0034] Observe the CAAC-OS film by TEM from a direction substantially parallel to the sample surface (cross-sectional TEM observation). ​​​​​When observed, it can be confirmed that metal atoms are arranged in layers in the crystalline part. Each layer of the CAAC-OS film is formed on a surface (also called a surface to be formed) or on a concave surface of the upper surface. The shape reflects the convexity and is aligned parallel to the surface on which the CAAC-OS film is formed or the upper surface.

[0035] On the other hand, the CAAC-OS film was observed by TEM from a direction approximately perpendicular to the sample surface (plane T EM observation reveals that metal atoms are arranged in triangular or hexagonal shapes in the crystalline region. However, no regularity was observed in the arrangement of metal atoms between different crystal regions. do not have.

[0036] In this specification, when simply referring to vertical, it means 80° or more and 100° or less, or 85° Also, when simply describing it as parallel, it is -10° This also includes ranges of 10° or more, or -5° or more and 5° or less.

[0037] In addition, in CAAC-OS, gallium atoms and / or zinc atoms are interposed between the InO2 layers. It has one or more layers containing ZnO, GaO, (Ga,Zn)O and oxygen atoms. In this case, it becomes a homologous structure.

[0038] <First sputtering target manufacturing method> Next, we developed a spatula that can form an In-Ga-Zn oxide film with a homologous structure. The manufacturing method of the targeting target will be explained with reference to FIG. A method for manufacturing a sputtering target capable of depositing a CAAC-OS film having a structure The method will be explained using FIG.

[0039] As shown in FIG. 2, in step S101, a raw material for In-Ga-Zn oxide is Indium oxide powder, gallium oxide powder, and zinc oxide powder are prepared, milled, and mixed. Indium oxide powder, gallium oxide powder, and zinc oxide powder are mixed together to form a mixture. indicates powder with purity of 99.9%, 99.99%, or 99.999% or higher, respectively. As a result, the concentration of impurities contained in an oxide semiconductor film to be formed later can be reduced. This makes it possible to manufacture a transistor with excellent electrical characteristics.

[0040] Alternatively, as a raw material for In-Ga-Zn oxide, the following steps S111 to S114 in FIG. 3 can be used. The polycrystalline In-Ga-Zn oxide powder and zinc oxide powder prepared in step S113 were used. Alternatively, as a raw material for In-Ga-Zn oxide, the following can be used: The polycrystalline In-Ga-Zn oxide powder and Ga-Zn prepared in steps S11 to S113 n-oxide powder can be used.

[0041] The atomic ratio of Zn to Ga in the mixture is Ga <Znとなるように、In-Ga- Prepare Zn oxide raw material. For example, In:Ga:Zn=1:3:4, In:Ga:Z n=1:3:5, In:Ga:Zn=1:3:6, In:Ga:Zn=1:3:7, In :Ga:Zn=1:3:8, In:Ga:Zn=1:3:9, In:Ga:Zn=1:3 :10, In:Ga:Zn=1:4:5, In:Ga:Zn=1:4:6, In:Ga: Zn=1:4:7, In:Ga:Zn=1:4:8, In:Ga:Zn=1:4:9, I n:Ga:Zn=1:4:10, In:Ga:Zn=1:5:6, In:Ga:Zn=1 :5:7, In:Ga:Zn=1:5:8, In:Ga:Zn=1:5:9, In:Ga :Zn=1:5:10, In:Ga:Zn=1:6:7, In:Ga:Zn=1:6:8 , In:Ga:Zn=1:6:9, In:Ga:Zn=1:6:10 As a result, in the subsequent firing process, the homologous Ga-Zn oxide powder is obtained. It is possible to produce a sputtering target containing In-Ga-Zn oxide with a silicon dioxide structure. do.

[0042] For grinding and mixing of the raw materials of In-Ga-Zn oxide, ball mills, bead mills, and roll mills are used. A mixer / mill such as a mill, a jet mill, or an ultrasonic device can be used. By doing so, the raw material of In-Ga-Zn oxide is crushed to the specified particle size and mixed. It is possible.

[0043] The average particle size of the crushed In-Ga-Zn oxide raw material is between 0.01 μm and 3.0 μm. It is preferable that the thickness is not more than 0.1 μm or not less than 2.0 μm.

[0044] Next, in step S102, the mixture is molded to form a molded body.

[0045] Methods for forming the compact include die molding and cold isostatic pressing. In the treatment, polyvinyl alcohol, methyl cellulose, polywax, olein may be used as appropriate. A molding aid such as an acid may be used.

[0046] In step S101, water, a dispersant, and a binder are added to the raw material of In-Ga-Zn oxide. The binder is mixed to form a slurry, and in step S102, the slurry is poured into a mold. The molded body may be formed by sucking water from the bottom of the mold and performing a drying process. The process involves natural drying followed by heat treatment at 300°C to 700°C to form a compact. The moisture contained in the

[0047] Next, in step S103, the compact is sintered to form a sintered body.

[0048] In the firing step in step S103, the temperature is 1200°C or higher and 1600°C or lower, The mixture is heated at a temperature of 1300°C to 1500°C. Crystalline In-Ga-Zn oxide can be formed. Polycrystalline In-Ga-Zn oxide can be formed. In this case, the atomic ratio of Zn to Ga is Ga <Znとなる。

[0049] After this, the sintered body is heated in a reducing atmosphere such as hydrogen, methane, or carbon monoxide, or in a reducing atmosphere such as nitrogen or rare gas. As a result, the variation in the resistance of the sintered body can be reduced. It is possible.

[0050] Step S102 (molding step) and step S103 (firing step) are performed simultaneously. As a method for forming such a sputtering target, Examples of methods include hot pressing and hot isostatic pressing.

[0051] Next, in step S104, the sintered body is processed to manufacture a sputtering target. do.

[0052] In step S104, the sintered body is cut and processed, and a backing plate or the like is attached. After cutting, the sintered body is mirror-finished to a surface roughness (Ra) of 5 μm. The mirror finishing method is mechanical polishing, chemical polishing, CM There are P etc.

[0053] Through the above steps, a sputtering target can be manufactured. The sputtering target manufactured by the method has an atomic ratio of Zn to Ga of Ga. <Znと By using such a sputtering target, homologous It is possible to form an In-Ga-Zn oxide film with a homologous structure. and an In-Ga-Zn oxide film that is CAAC-OS can be formed. .

[0054] <Second method for producing sputtering target> Here, InGaO3(ZnO) m It is possible to form a film of a homologous compound represented by the formula A method for manufacturing a sputtering target that can be used for this purpose will be described with reference to FIG. GaO3(ZnO) m and forming a CAAC-OS film. A method for manufacturing a sputtering target capable of forming a film will be described with reference to FIG. do.

[0055] As shown in FIG. 3, first, an In—Ga—Zn oxide powder is prepared.

[0056] In step S111, indium oxide, which is the raw material for the In-Ga-Zn oxide powder, is The amounts of powder, gallium oxide powder, and zinc oxide powder are prepared and mixed to form a mixture. The indium oxide powder, gallium oxide powder, and zinc oxide powder each have a purity of 9%. Powder with a purity of 9.9%, 99.99%, or 99.999% or higher is used. As a result, The concentration of impurities contained in the oxide semiconductor film formed later can be reduced, and Therefore, a transistor having the desired electrical characteristics can be manufactured.

[0057] In the mixture, the atomic ratio of the metal elements is In:Ga:Zn=1:1:m (m is a natural number). The amounts of indium oxide powder, gallium oxide powder, and zinc oxide powder are adjusted so that As a result, in the firing process of step S112, InGaO3(Z nO) m Sputtering target containing In-Ga-Zn oxide with a homologous structure represented by A get can be manufactured.

[0058] Next, in step S112, the mixture is fired to form polycrystalline In-Ga-Zn oxide. Form.

[0059] The firing step can be performed in the same manner as the firing step shown in step S103 of FIG. This process allows the formation of polycrystalline In-Ga-Zn oxide. n-Ga-Zn oxide is InGaO3(ZnO) m There are homologous compounds represented by Representative examples include InGaZnO4, InGaZn2O5, InGaZn3O6, and InGaZ Examples include In4O7 and InGaZn5O8.

[0060] Next, in step S113, the polycrystalline In-Ga-Zn oxide is crushed to obtain polycrystalline Form In-Ga-Zn oxide powder.

[0061] The polycrystalline In-Ga-Zn oxide can be pulverized using a ball mill, a bead mill, a roll mill, or a die mill. The crushing is carried out using a crushing method such as a micromill or ultrasonic device.

[0062] The average particle size of the crushed polycrystalline In-Ga-Zn oxide powder is 0.01 μm or more and 3.0 It is preferable that the thickness is 0.1 μm or less, or 0.1 μm or more and 2.0 μm or less.

[0063] In addition, when the average particle size of the crushed polycrystalline In-Ga-Zn oxide powder is 3.0 μm or more, In this case, it is preferable to perform the pulverization step shown in step S113 again.

[0064] Next, the manufacturing process of the sputtering target will be described.

[0065] In step S114, the polycrystalline In-Ga-Zn oxide powder and the zinc oxide powder are mixed. In this mixing step, polycrystalline In-Ga-Zn The oxide powder and zinc oxide powder may be individually pulverized to improve the uniformity of the particle size of the powders.

[0066] Here, the polycrystalline In- The Ga-Zn oxide powder and the zinc oxide powder are mixed to form a mixture. The atomic ratio of Zn to Ga is (m+0.05) or more and (m+0.5) or less. Polycrystalline In-Ga-Zn oxide powder and zinc oxide powder are prepared. For example, In:Ga: Zn=1:1:1.05, In:Ga:Zn=1:1:2.05, In:Ga:Zn=1 Polycrystalline In-Ga-Zn oxide powder and zinc oxide powder were mixed in a ratio of 1:3.05. As a result, in the subsequent firing process of step S116, InGaO3(ZnO) m The sputtering reaction has a larger number of zinc atoms than the gallium atoms contained in the homologous compound represented by It is possible to manufacture a target.

[0067] Next, in step S115, the mixture is formed into a formed body.

[0068] As a method of forming the mixture into a formed body, it can be performed in the same manner as the forming process shown in step S102 of FIG. 2. It can be carried out in the same manner as the forming process shown in step S102 of FIG. 2.

[0069] Also, in step S114, water, a dispersant, and a binder are mixed with the polycrystalline In-Ga-Zn oxide powder and zinc oxide powder to form a slurry. In step S115, the slurry is poured into a mold, water is sucked from the bottom surface of the mold, and a drying process is performed to form a formed body. The drying process can remove the moisture contained in the formed body by performing natural drying and then heating at a temperature of 300 °C or higher and 700 °C or lower. The drying process can remove the moisture contained in the formed body by performing natural drying and then heating at a temperature of 300 °C or higher and 700 °C or lower. The drying process can remove the moisture contained in the formed body by performing natural drying and then heating at a temperature of 300 °C or higher and 700 °C or lower.

[0070] Next, in step S116, the formed body is sintered to form a sintered body.

[0071] In the firing process in step S116, the mixture is heated at 800 °C or higher and 1600 °C or lower, or 1300 °C or higher and 1500 °C or lower. By this process, polycrystalline In- Ga-Zn oxide can be formed as a sintered body. In the polycrystalline In-Ga-Zn oxide, the atomic ratio of Zn to Ga is Ga < Zn. The polycrystalline In-Ga-Zn oxide is a mixed crystal of a homologous compound represented by In GaO3(ZnO) and ZnO. m It is a mixed crystal of a homologous compound represented by InGaO3(ZnO) and ZnO.

[0072] After that, the sintered body may be heat-treated in a reducing atmosphere such as hydrogen, methane, carbon monoxide, or an inert gas atmosphere such as nitrogen or a noble gas. As a result, the variation in the resistance of the sintered body can be reduced. After that, the sintered body may be heat-treated in a reducing atmosphere such as hydrogen, methane, carbon monoxide, or an inert gas atmosphere such as nitrogen or a noble gas. As a result, the variation in the resistance of the sintered body can be reduced. After that, the sintered body may be heat-treated in a reducing atmosphere such as hydrogen, methane, carbon monoxide, or an inert gas atmosphere such as nitrogen or a noble gas. As a result, the variation in the resistance of the sintered body can be reduced.

[0073] Step S115 (molding step) and step S116 (firing step) are performed simultaneously. Such a molding method can be used for forming a sintered body. There are hot isostatic firing methods.

[0074] Next, in step S117, the sintered body is processed to manufacture a sputtering target. do.

[0075] In step S117, the processing step shown in step S104 in FIG. 2 is used as appropriate. It is possible.

[0076] Through the above steps, a sputtering target can be manufactured. The sputtering target produced by InGaO3(ZnO) m Homologous It is a mixed crystal of gas compounds and ZnO, and the ratio of Z to Ga in the sputtering target The atomic ratio of n is (m+0.05) or more and (m+0.5) or less. The homologous compound In-Ga- Furthermore, a Zn oxide film can be formed. It is possible to form an In-Ga-Zn oxide film, which is an AC-OS.

[0077] (Embodiment 2) In this embodiment, oxidation using the sputtering target manufactured in the first embodiment is performed. The method for forming the In-M-Zn film will be described with reference to FIGS. Representative examples of oxides (M is Al, Ti, Ga, Y, Zr, La, Cs, Nd, or Hf) This will be explained using In-Ga-Zn oxide.

[0078] 4, 8, 14, 16, 17, and 18 are diagrams showing sputtering in a film formation chamber of a film formation apparatus. 1 is a schematic diagram of a film forming process. The details will be explained in the third embodiment.

[0079] <Heated deposition (deposition temperature: 150°C or higher but less than 600°C)> As shown in FIG. 4(A), a substrate stage 12 and a substrate holder 13 are provided in a film-forming chamber 11 of a film-forming apparatus. The sputtering target 13 manufactured in the manner 1 is provided facing the substrate. A substrate 121 is placed on the board 12 .

[0080] In the film-forming chamber 11, an inert gas such as argon or a sputtering gas such as oxygen is introduced. A voltage is applied to the sputtering target 13 to generate plasma 17. The sputtering gas is ionized in the plasma 17, generating ions 15. When the ions 15 collide with the ring target 13, the ions 15 are released from the ring target 13. The interatomic bonds between the particles are broken, and the particles are separated from the sputtering target 13. Therefore, ions, sputtering particles, electrons, etc. exist in the plasma 17. The particles that peel off from the sputtering target are called sputtered particles.

[0081] The ions 15 may be, for example, positive ions of oxygen. By using the ion, for example, plasma damage during film formation can be reduced. By using oxygen cations as the ions 15, for example, the ions 15 can be sputtered. The crystallinity of the sputtering target 13 when colliding with the surface of the target 13 In addition, the use of oxygen cations as the ions 15 can suppress the deterioration or amorphization. For example, when ions 15 collide with the surface of the sputtering target 13, The crystallinity of the target 13 can be improved in some cases. For example, the positive charge of noble gases (helium, neon, argon, krypton, xenon, etc.) Ions may also be used.

[0082] Sputtering particles include zinc particles, oxygen particles, zinc oxide particles, and In-Ga-Zn. The sputtering target produced in the first embodiment has a higher content of Ga than that of Ga oxide particles. Therefore, in this case, zinc particles, After oxygen particles or zinc oxide particles are preferentially peeled off, zinc particles, oxygen particles, zinc oxide particles This will be explained using a model in which particles of In-Ga-Zn oxide are peeled off.

[0083] First, zinc particles 123a and oxygen particles 123b are sputtered as sputtering particles. The zinc particles 123a and oxygen particles 123b are then peeled off from the plating target 13. By moving onto the substrate 121, hexagonal crystal grains 123c formed of zinc oxide are formed on the substrate. is formed.

[0084] FIG. 5(A) shows a model of the top surface shape of a hexagonal crystal grain 123c formed of zinc oxide. As shown in Figure 5(A), the hexagonal crystal grains 123c formed in zinc oxide are The electron and oxygen atoms are bonded in a hexagonal configuration.

[0085] As will be described later in the section "Crystal Growth Mechanism of Zinc Oxide," zinc oxide grows in the direction parallel to the ab plane. Since the crystal growth is fast, when the substrate temperature is between 150°C and 600°C, the film is formed from zinc oxide. The hexagonal crystal grains 123c are aligned in a direction parallel to the surface of the substrate 121, that is, in a direction parallel to the cross section of the zinc oxide film. As a result, the hexagonal crystals grow laterally on the surface as shown in Figure 4(B). A zinc film 125 is formed. That is, the hexagonal zinc oxide film 125 has a single crystal region. The hexagonal zinc oxide film 125 may contain regions that are not single crystal regions.

[0086] FIG. 5B shows a model of the top surface shape of the region 126 of the hexagonal zinc oxide film 125. (C) shows a model of the cross-sectional shape of the region 126. As shown in FIG. 5(B), the hexagonal oxide In the zinc film 125, Zn atoms and O atoms are bonded in a hexagonal shape. The bond between the n atom and the O atom is spread across the ab plane.

[0087] Next, sputtering particles are ejected from the sputtering target. As the sputtering particles, In-Ga-Zn oxide particles were peeled off, as shown in Figure 4(C). In-Ga-Zn oxide particles 127 are deposited on the hexagonal zinc oxide film 125, and In-Ga A film 129 containing Zn oxide particles is formed. Zinc particles, oxygen particles, and zinc oxide particles are also peeled off as coating particles, but these are omitted here. do.

[0088] The In-Ga-Zn oxide particles 127 have crystallinity and are typically single crystals. In some cases, the In-Ga-Zn oxide particles 127 are polycrystalline.

[0089] Here, the shape of the In—Ga—Zn oxide particles 127 will be described with reference to FIG. As shown in FIG. 6(A), the In—Ga—Zn oxide particle 127 has an aspect ratio of 1 / 2 mm in cross section. Unlike the granular material, it is a flat or plate-like structure whose width is longer than its length. In the n-Ga-Zn oxide particle 127, the side parallel to the c-axis corresponds to This corresponds to the side of the In-Ga-Zn oxide particle 127 that is parallel to the axis that intersects with the c-axis. As shown in Figure 6(A), there are two parallel hexagons (regular hexagons) with all interior angles of 120°. Alternatively, as shown in FIG. 6(C), it is preferable that all of the interior angles are 6. It is preferable to have two parallel faces 127s of a 0° triangle (equilateral triangle). The In-Ga-Zn oxide particles 127 can be called pellets. For example, the surface 127s is parallel to the ab plane of the crystal. The direction perpendicular to this is the c-axis direction of the crystal. The thickness is 100 nm or less, 1 nm to 30 nm, or 1 nm to 10 nm.

[0090] The In-Ga-Zn oxide particles 127 are positively or negatively charged. In the case of the In-Ga-Zn oxide particles 127a, some of the oxygen atoms in the particles 127a are charged by the ion collision. Alternatively, by being exposed to plasma, one of the oxygen atoms of the In-Ga-Zn oxide particles 127a may be removed. FIG. 6B shows a negatively charged In-Ga-Zn oxide particle 127a. As shown in FIG. 6(B), the In—Ga—Zn oxide particles 127a Some of the oxygen in the In-Ga-Zn oxide particles may be negatively charged. Oxygen ions may bond to 27a.

[0091] Here, an example of the crystal contained in the sputtering target is InGaO3(Zn O) m The crystal structure of a homologous compound represented by m=1 (m is a natural number) is called the ab plane. The figure is shown from a parallel perspective (see FIG. 7(A)). In FIG. 7(A), the area surrounded by the dashed line The portion is enlarged and shown in Figure 7(B).

[0092] For example, in the crystals contained in the sputtering target, the gallium oxide shown in FIG. a first layer having gallium atoms or / and zinc atoms and oxygen atoms; and / or a second layer having zinc atoms and oxygen atoms, This is because the oxygen atoms in the first layer and the oxygen atoms in the second layer are in close proximity. This is due to the fact that the oxygen atom has a negative charge (see the boxed area in Figure 7(B)). Therefore, if oxygen atoms are close to each other, the bond between the layers may be weakened. The chemical bonds in the first layer and the second layer are bonded to the bonds between the first layer and the second layer. The chemical bond between the first and second layers becomes much larger than that in the first layer, and a cleavage plane is formed between the first and second layers. In this way, the cleavage plane may be a plane parallel to the ab plane.

[0093] In addition, the crystal structure shown in Figure 7 has gold atoms arranged in equilateral triangles and equilateral hexagons when viewed from a perspective perpendicular to the ab plane. Therefore, the sputtering process containing the crystals with the crystal structure shown in Figure 7 When a target is used, the In-Ga-Zn oxide particles 127 have an interior angle of 120°. There is a high probability that the shape will have regular hexagonal faces or equilateral triangular faces with 60° interior angles. It is thought that...

[0094] Here, the In-Ga-Zn oxide formed by peeling off at the cleavage plane shown in FIG. 7(B) Representative examples of the crystal structure of the particle 127 are shown in FIG. 5(D) and FIG. 5(E).

[0095] The In-Ga-Zn oxide particles 127a shown in FIG. 5(D) contain gallium atoms and / or The first layer (denoted as (Ga,Zn)O) has zinc and oxygen atoms, and the second layer (denoted as (Ga,Zn)O) has zinc and oxygen atoms. Indium layer (InO2) and gallium atoms or / and zinc atoms and oxygen atoms The first layer (indicated as (Ga,Zn)O) is a layer that supports the first layer, and the second layer (indicated as (Ga,Zn)O) is a layer that supports the second layer.

[0096] In addition, the In-Ga-Zn oxide particles 127b shown in FIG. 5(E) contain gallium atoms or and a first layer having zinc atoms and oxygen atoms (denoted as (Ga,Zn)O); A second layer having gallium atoms and / or zinc atoms and oxygen atoms ((Ga,Zn )O. ) and an indium oxide layer (InO2) and gallium atoms or / and zinc A third layer (denoted as (Ga,Zn)O) containing gallium atoms and oxygen atoms. and / or a fourth layer having zinc atoms and oxygen atoms (denoted as (Ga,Zn)O). ) and five layers are bonded in order.

[0097] When the hexagonal zinc oxide film 125 is formed on the substrate 121, the hexagonal zinc oxide film 1 In-Ga-Zn oxide particles 127 are deposited in the direction of 25. Since the hexagonal zinc oxide film 125 The c-axis of the In-Ga-Zn oxide particles 127 was aligned parallel to the c-axis of the In-Ga-Zn oxide particles 127. The In-Ga-Zn oxide particles 127 peeled off from the target 13 are hexagonal zinc oxide. After being moved or rotated in the vicinity of the film 125, it is deposited on the hexagonal zinc oxide film 125.

[0098] At this time, the a-axis and b-axis directions of the In-Ga-Zn oxide particles already deposited are aligned. Similarly, the In-Ga-Zn oxide particles 127 may rotate and bond in the ab plane. As a result, the a-axis and b-axis directions of adjacent In-Ga-Zn oxide particles are aligned. Therefore, a single crystal region is formed in the film 129 having In-Ga-Zn oxide particles. The film 12 having In-Ga-Zn oxide particles is formed on the entire surface of the cubic zinc oxide film 125. The crystal orientation of the In-Ga-Zn oxide particles 9 is aligned, and the film 129 having the In-Ga-Zn oxide particles becomes a single crystal region. Alternatively, in the film 129 having In-Ga-Zn oxide particles, single crystal Multiple regions are formed, and in each region, the c-axis direction of the In-Ga-Zn oxide grains Only the a-axis and b-axis may be aligned, but the orientations of the two axes may not be aligned.

[0099] Here, FIG. 5(F) shows the zinc oxide film and In-Ga-Z A model of the cross-sectional shape near the interface of the film 129 having n oxide particles is shown in FIG. As shown in the figure, the Zn in the hexagonal zinc oxide film and the film 129 having In-Ga-Zn oxide particles A layer having gallium atoms or / and zinc atoms and oxygen atoms ((Ga, Zn)O.) is bonded to the oxygen.

[0100] Since the hexagonal zinc oxide film 125 has high crystallinity, the hexagonal zinc oxide film 125 is used as a seed crystal. By doing so, it is possible to improve the crystallinity of the film 129 having In-Ga-Zn oxide particles. is.

[0101] Next, as in FIG. 4(A), zinc particles 123a and oxygen particles are mixed together as shown in FIG. 8(A). 123b peels off from the sputtering target and deposits on the In-Ga-Zn oxide particles 127. , hexagonal crystal grains 123c made of zinc oxide are formed on the substrate. .

[0102] Since zinc oxide crystals grow quickly in the direction parallel to the ab plane, the oxide The hexagonal crystal grains 123c formed of zinc chloride are oriented in a direction parallel to the surface of the substrate 121, i.e., in the direction of the oxide. Crystal growth occurs laterally in the cross section of the zinc oxide film, forming a hexagonal zinc oxide film 131. (See FIG. 8B.) That is, the hexagonal zinc oxide film 131 has a single crystal region.

[0103] After this, sputtering particles are emitted from the sputtering target, as in Figure 4(C). As shown in FIG. 8(C), an In-Ga-Zn oxide film is formed on the hexagonal zinc oxide film 131. Particles 133 are deposited. In addition, another In-Ga- Zn oxide particles are deposited.

[0104] The process of forming the hexagonal zinc oxide film 131 shown in FIG. 8(B) and the process of forming the In By repeating the process of depositing Ga-Zn oxide particles 133, a highly crystalline oxide film is formed. A film can be formed.

[0105] Formed by sputtering using the sputtering target of embodiment 1 The atomic ratio of Ga to In in In-Ga-Zn oxide (Ga / In), Z to In The atomic ratio of n (Zn / In) is smaller than the atomic ratio contained in the sputtering target. In addition, in the In-Ga-Zn oxide film, the atomic ratio of Zn to Ga (Zn / Ga) is 0.5 or more.

[0106] In addition, the In-Ga-Zn oxide particles are deposited in the c-axis direction of the hexagonal zinc oxide film. Therefore, the oxide film obtained by this process has a c-axis that is perpendicular to the normal vector of the surface on which it is formed or the surface The CAAC-OS film is aligned parallel to the normal vector of the

[0107] In addition, the crystal structure of the oxide film obtained by the film formation process shown in Figs. 4 and 8 will be explained using Fig. 9. The oxide film obtained by the film formation process shown in FIGS. 4 and 8 is composed of two indium oxide (I nO2), a layer having gallium atoms or / and zinc atoms and oxygen atoms is formed between the layers. Since multiple layers of In-Ga-Zn oxide particles having the above properties are stacked, it has a homologous structure. .

[0108] As shown in FIG. 9(A), the oxide film obtained by the film forming process of FIGS. 4 and 8 is a first oxide film. Indium layer (InO2) and gallium atoms or / and zinc atoms and oxygen atoms A layer having a thickness of 1000 nm (denoted as (Ga,Zn)O) and a second indium oxide layer (InO2). The structure is three layers bonded in order. That is, gallium atoms or and / or one layer having zinc atoms and oxygen atoms.

[0109] As shown in FIG. 9(B), the oxide film obtained by the film forming process shown in FIGS. Indium oxide layer (InO2) and gallium atoms or / and zinc atoms and oxygen The first layer (denoted as (Ga,Zn)O) has gallium atoms and / or zinc atoms. A second layer (denoted as (Ga,Zn)O) containing lead and oxygen atoms and a second oxide layer (denoted as (Ga,Zn)O) The structure is made up of four layers bonded in order, including an indium layer (InO2). Between the silicon layers, two layers having gallium atoms or / and zinc atoms and oxygen atoms are provided. It is being used.

[0110] As shown in FIG. 9(C), the oxide film obtained by the film forming process of FIGS. 4 and 8 is Indium oxide layer (InO2) and gallium atoms or / and zinc atoms and oxygen The first layer (denoted as (Ga,Zn)O) has atoms, the second layer has zinc oxide (ZnO), and the third layer has gallium. The second layer ((Ga,Zn)O) has aluminum atoms and / or zinc atoms and oxygen atoms. The structure is composed of five layers, namely, a first layer of indium oxide (InO2), and a second layer of indium oxide (InO2). That is, gallium atoms and / or zinc atoms and oxide atoms are present between the indium oxide layers. Two layers containing atomic atoms and a zinc oxide film are provided.

[0111] In addition, a layer (G) having a plurality of gallium atoms and / or zinc atoms and oxygen atoms The structure of the repeating unit with a zinc oxide film between the two is shown in Figure 8(C). As shown, the In-Ga-Zn oxide particles 127, the hexagonal zinc oxide film 131, and the In -Ga-Zn oxide particles 133 are formed in the region where they are stacked.

[0112] Here, the process of forming the hexagonal zinc oxide film 131 shown in FIG. 8(B) and the process of forming the hexagonal zinc oxide film 131 shown in FIG. Although the process of depositing the In-Ga-Zn oxide particles 133 shown in (C) has been described separately, In this case, in the step of FIG. 8(B), In-Ga-Zn oxide In some cases, the hexagonal zinc oxide film 131 is formed not only on the top surface of the solid particle but also on the side surface.

[0113] By the above process, a CAAC-OS film can be formed. In addition, the In-Ga-Zn oxide film can be formed. In place of Ga, Al, Ti, Y, Zr, La, Cs, Nd, or Hf may be used as appropriate. By using In-M-Zn oxide (M is Al, Ti, Y, Zr, La, Cs, Nd In this model, a crystal film of Hf can be formed on the substrate 121. Instead of forming the grains 123c, the In-Ga-Zn oxide grains 127 shown in FIG. 5(D) are formed. 5(a), or In-Ga-Zn oxide particles 127b shown in FIG. 5(E) are formed on the substrate 121. The model allows the deposition of CAAC-OS films. An In-Ga-Zn oxide film can be formed.

[0114] Here, the formed CAAC-OS will be described in detail.

[0115] The CAAC-OS film is one of the oxide semiconductor films that has multiple crystal parts aligned along the c-axis. .

[0116] The CAAC-OS film was observed under a transmission electron microscope (TEM). When observed under a tron ​​microscope, clear boundaries between the crystals are observed. It is difficult to identify the grain boundary. It can be said that the AC-OS film is less susceptible to the decrease in electron mobility caused by grain boundaries.

[0117] Cross-sectional and planar TEM observations revealed that the crystals in the CAAC-OS film had an orientation. It can be seen that this is the case.

[0118] Most of the crystals in the CAAC-OS film are cubic crystals with sides of less than 100 nm. Therefore, the crystal part in the CAAC-OS film has a side length of 10 This also includes cases where the size fits within a cube of less than 5 nm, or less than 3 nm. However, multiple crystals in the CAAC-OS film are connected to form a single large crystal domain. For example, in a planar TEM image, 2 Over 5μm 2 More than or equal to 1000 μm 2 Crystal regions with more than this size may be observed.

[0119] The CAAC-OS has, for example, a plurality of crystal parts, and the c-axes of the crystal parts are aligned. They may be aligned along the normal vector of the forming plane or parallel to the normal vector of the surface. Therefore, CAAC-OS can be easily analyzed by, for example, X-ray diffraction (XRD). When an out-of-plane analysis was performed using a ion device, the c-axis orientation was In some cases, a peak identified to the crystal plane orientation, for example, a peak identified to the crystal plane orientation (00x), may appear.

[0120] In the CAAC-OS film, the orientation of the a-axis and b-axis is irregular between different crystalline regions. It has a c-axis orientation, and the c-axis is oriented in a direction parallel to the normal vector of the surface to be formed or the upper surface. Therefore, it is clear that the layers of metal atoms arranged in layers confirmed by cross-sectional TEM observation are is a plane parallel to the ab plane of the crystal.

[0121] The crystalline part is formed when the CAAC-OS film is formed or after a crystallization treatment such as a heat treatment. As described above, the c-axis of the crystal is aligned with the surface on which the CAAC-OS film is to be formed. Therefore, for example, in the CAAC-OS film, When the shape is changed by etching, the c-axis of the crystal is aligned with the CAAC-OS film. It may not be parallel to the normal vector of the face or top surface.

[0122] Furthermore, the distribution of c-axis oriented crystals in the CAAC-OS film does not need to be uniform. For example, the crystalline part of the CAAC-OS film is grown from the top surface of the CAAC-OS film. Therefore, when the crystal is formed, the region near the top surface has a crystal orientation that is more c-axis oriented than the region near the surface on which the crystal is formed. In addition, when impurities are added to the CAAC-OS film, the proportion of the impurity The region where the material was added was transformed, and regions with different proportions of c-axis oriented crystals were formed. It may also be possible.

[0123] In addition, for example, spots (bright points) are observed in the electron diffraction pattern of CAAC-OS. In addition, the probe diameter is close to or smaller than the size of the crystal part (for example, 1 nm or more). Electron beam diffraction using an electron beam of 30 nm or less is also called nanobeam electron beam diffraction.

[0124] FIG. 10(A) shows an example of a nanobeam electron diffraction pattern of a sample having a CAAC-OS. Here, the sample was cut in a direction perpendicular to the CAAC-OS surface, and the thickness was 4 mm. In this case, the electron beam with a beam diameter of 1 nm is used. The incident light is perpendicular to the cut surface of the sample. The electron diffraction pattern shows that spots are observed.

[0125] The CAAC-OS film is an oxide semiconductor film with a low concentration of impurities. The oxide semiconductor film is made of an element other than the main component, such as silicon or a transition metal element. The elements such as ZnO, which have stronger bonding strength with oxygen than the metal elements constituting the oxide semiconductor film, By removing oxygen from the oxide semiconductor film, the atomic arrangement of the oxide semiconductor film is disrupted, and the crystallinity is reduced. In addition, heavy metals such as iron and nickel, argon, and carbon dioxide are Because the diameter (or molecular radius) is large, when the molecule is contained inside the oxide semiconductor film, The impurities contained in the oxide semiconductor film are likely to disturb the atomic arrangement of the oxide semiconductor film, which may result in a decrease in crystallinity. The pure material may act as a carrier trap or a carrier generation source.

[0126] The CAAC-OS film is an oxide semiconductor film with a low density of defect states. Oxygen vacancies in semiconductor films can act as carrier traps and trap hydrogen. This can become a carrier generation source.

[0127] The low impurity concentration and low defect level density (low oxygen vacancies) are called high-purity intrinsic or The term "high-purity intrinsic" refers to a substantially high-purity intrinsic oxide semiconductor. Since the film has a small number of carrier generation sources, the carrier density can be reduced. The transistor using the oxide semiconductor film has electrical characteristics (noise) such that the threshold voltage is negative. It is also called "marine.") It is rare for it to become pure or substantially pure. An intrinsic oxide semiconductor film has few carrier traps. Transistors using this film have little fluctuation in electrical characteristics and are highly reliable. Note that it takes time for the charges trapped in the carrier traps in the oxide semiconductor film to be released. The time is long and the charge may behave as if it is fixed. Therefore, a transistor using an oxide semiconductor film with a high density of defect states has unstable electrical characteristics. This may be the case.

[0128] In addition, transistors using high-purity intrinsic or substantially high-purity intrinsic CAAC-OS are The electrical characteristics of the capacitor change little when exposed to visible light or ultraviolet light.

[0129] <Crystal growth mechanism of zinc oxide> Here, the crystal growth mechanism of the zinc oxide film 125 shown in FIG. 4(B) will be explained with reference to FIGS. 3 will be used to explain.

[0130] The atomic motion during heat treatment was investigated using classical molecular dynamics. So, the force acting on atoms can be defined by defining an empirical potential that characterizes the interatomic interaction. Here, we apply the laws of classical mechanics to each atom and calculate Newton's motion. The motion (time evolution) of each atom was verified by solving the equations numerically. As an empirical potential, the Born-Mayer-Huggins potential was used.

[0131] As shown in FIG. 11, amorphous zinc oxide (hereinafter referred to as a-ZnO) has a width of 1 nm. Single crystal zinc oxide (hereinafter referred to as c-ZnO) was arranged at equal intervals as crystal nuclei 180. The density of a-ZnO and c-ZnO was set to 5.5 g / cm 3 It was decided. The vertical direction was defined as the c-axis direction.

[0132] Next, in the model of Fig. 11, c-ZnO is fixed and the 3D periodic boundary conditions are Classical molecular dynamics at 0°C for 100 psec (time step width 0.2 fsec x 500,000 steps) The results of the mathematical calculations are shown in Figures 12 and 13.

[0133] Figure 12(A), Figure 12(B), and Figure 12(C) show the time periods of 20 psec, 40 psec, and The change in atomic configuration over 60 psec is shown in Figure 13(A) and Figure 13(B). The changes in atomic configuration after 80psec and 100psec are shown. In each figure, the distance and direction of crystal growth are indicated by the length and direction of the arrow.

[0134] The crystal growth rates in the vertical direction (c-axis

[0001] ) and the horizontal direction perpendicular to it are shown in Table 1. .

[0135] [Table 1]

[0136] In FIG. 12, the arrows 182, 186, and 190 in the vertical direction (c-axis direction) are Arrows 184a, 184b, 188a, 188b, 192a, 1 The longer length of 92b indicates that lateral crystal growth is predominant, as shown in Figure 12(C ) indicates that crystal growth has terminated between adjacent crystal nuclei.

[0137] In FIG. 13, the crystalline regions formed on the surface are used as seeds, and are indicated by arrows 194 and 196. As can be seen, the crystal grows in the vertical direction (c-axis direction).

[0138] In addition, from Table 1, it is clear that the crystal growth is more rapid in the horizontal direction, which is perpendicular to the vertical direction (c-axis

[0001] ), than in the vertical direction. From these results, it can be seen that the growth rate is about 4.9 times faster. Crystal growth proceeds in a direction parallel to the ab plane. At this time, crystal growth proceeds in the lateral direction on the ab plane. Next, the single crystal region formed on the surface (ab plane) is used as a seed to form a single crystal region on the surface ( Crystal growth proceeds along the c-axis, which is perpendicular to the ab plane. Thus, after the crystals grow preferentially in the direction parallel to the surface (ab plane), The crystal grows along the c-axis, which is perpendicular to the surface (epitaxial growth, or axial growth). This process (also called crystalline growth) forms a single crystal region.

[0139] <Heated deposition (deposition temperature: 600°C or higher but below the substrate distortion point)> Next, a film formation method different from that shown in FIGS. 4 to 9 will be described with reference to FIGS. The film formation methods shown in FIGS. 14 to 16 have a higher film formation temperature than the film formation methods shown in FIGS. Zinc oxide is easily evaporated at temperatures above 600°C in a reduced pressure atmosphere. 9 and the oxide film formed by the film formation method shown in FIGS. 14 to 16. The crystal structure is different.

[0140] As shown in FIG. 14(A), similarly to FIG. 4(A), the sputtering target 13 is The particles 15 collide with the sputtering target 13, causing sputtering particles to be ejected. Therefore, the plasma 17 contains ions, sputtering particles, electrons, and the like.

[0141] Sputtering particles include zinc particles, oxygen particles, zinc oxide particles, and In-Ga-Zn. The sputtering target manufactured in the first embodiment contains Z particles rather than Ga particles. Therefore, in this case, zinc particles, acid After the elementary particles or zinc oxide particles are preferentially peeled off, zinc particles, oxygen particles, zinc oxide particles This will be explained using a model in which In-Ga-Zn oxide particles peel off.

[0142] First, zinc particles 143a and oxygen particles 143b are sputtered. Next, the zinc particles 143a and the oxygen particles 143b are peeled off from the pulverizing target 13. As a result, the hexagonal crystal grains 143c formed of zinc oxide move onto the substrate 141. formed on top.

[0143] Here, since the substrate temperature is 600° C. or higher, the direction parallel to the surface of the substrate 141 is As a result, a hexagonal crystal is grown on the ab plane. In other words, the hexagonal zinc oxide film 145 has a single crystal region. Unlike the film formation process shown in FIG. 4(B), part of the zinc oxide evaporates. The hexagonal zinc oxide film 145 is separated.

[0144] FIG. 15 shows a model of the top surface shape of the hexagonal zinc oxide film 145. As shown in FIG. In the hexagonal zinc oxide film 145, Zn atoms and O atoms are bonded in a hexagonal shape. The hexagonal bonds between Zn and O atoms are spread across the ab plane.

[0145] Next, sputtering particles are ejected from the sputtering target. As the sputtering particles, In-Ga-Zn oxide particles peeled off, as shown in Figure 14(C). In-Ga-Zn oxide particles 147 are deposited on the hexagonal zinc oxide film 145, and the In-G A film 149 having In-Ga-Zn oxide particles is formed. has the same structure as the In-Ga-Zn oxide particles 127. Although zinc particles and oxygen particles are also peeled off as sputtering particles, their description is omitted here. .

[0146] Here, the hexagonal zinc oxide film 145 formed on the substrate 141 is separated. Therefore, the hexagonal zinc oxide film 145 does not cover the entire surface of the substrate 141. In-Ga-Zn oxide particles 147 are deposited in alignment with the crystal orientation of the zinc oxide film 145. Specifically, the c-axis of the hexagonal zinc oxide film 145 and the c-axis of the In-Ga-Zn oxide particles 147 The In-Ga- After the Zn oxide particles 147 move or rotate in the vicinity of the hexagonal zinc oxide film 145, The film is deposited on the crystalline zinc oxide film 145 .

[0147] On the other hand, in the region where the hexagonal zinc oxide film 145 is not formed, In-Ga-Z The crystal orientation of the n oxide particles 147 is random.

[0148] Next, as in FIG. 14(A), zinc particles 143a and oxygen are mixed together as shown in FIG. 16(A). Particles 143b peel off from the sputtering target, and In-Ga-Zn oxide particles 14 Zinc particles 143a and oxygen particles 143b reach and adhere to the surface of the substrate 7. As a result, as shown in FIG. As shown in FIG. 1B, a hexagonal zinc oxide film 151 is formed.

[0149] After this, as in Figure 14(B), sputtering particles are released from the sputtering target. As shown in FIG. 16(C), the In-Ga-Zn oxide film is formed on the hexagonal zinc oxide film 151. On the In-Ga-Zn oxide particles 153, another In-Ga a-Zn oxide particles are deposited.

[0150] The process of forming the hexagonal zinc oxide film 151 shown in FIG. 16(B) and the process of forming the hexagonal zinc oxide film 152 shown in FIG. 16(C) By repeating the process of depositing In-Ga-Zn oxide particles 153, oxide with high crystallinity is obtained. A film can be formed.

[0151] Formed by sputtering using the sputtering target of embodiment 1 The atomic ratio of Ga to In in In-Ga-Zn oxide (Ga / In), Z to In The atomic ratio of n (Zn / In) is smaller than the atomic ratio contained in the sputtering target. In addition, in the In-Ga-Zn oxide film, the atomic ratio of Zn to Ga (Zn / Ga) is 0.5 or more.

[0152] Note that the crystal orientation of the oxide film obtained in the film formation process of FIGS. 14 to 16 is random. However, the sputtering particles deposited during the film formation process Each molecule has a homologous structure. The oxide film thus obtained contains a region with a homologous structure and has high crystallinity.

[0153] By the above steps, a polycrystalline In-Ga-Zn oxide film can be formed. In the In-Ga-Zn oxide, Al, Ti, Y, Zr may be used instead of Ga. By using La, Cs, Nd, or Hf, polycrystalline In-M-Zn oxide ( M can be Al, Ti, Y, Zr, La, Cs, Nd, or Hf.

[0154] Here, the polycrystalline In-M-Zn oxide that is formed will be described. The In-M-Zn oxide with a polycrystalline structure is hereinafter referred to as a polycrystalline oxide semiconductor. The body contains a plurality of grains.

[0155] In the polycrystalline oxide semiconductor film, crystal grains can be confirmed in the TEM observation image. The crystal grains contained in the crystalline oxide semiconductor film are, for example, 2 nm or more in a TEM observation image. The particle size is 00 nm or less, 3 nm to 100 nm or 5 nm to 50 nm. In addition, in the polycrystalline oxide semiconductor film, the grain boundaries can be confirmed in the TEM observation image. This may be the case.

[0156] The polycrystalline oxide semiconductor film has, for example, a plurality of crystal grains, and the crystal grains are separated from each other. The crystal orientation may be different. When structural analysis is performed using this method, for example, a polycrystalline oxide semiconductor with InGaZnO4 crystals is obtained. In the out-of-plane analysis of the film, a peak at 2θ near 31° and a peak at 2θ near 3 A peak near 6° or other peaks may appear.

[0157] A polycrystalline oxide semiconductor film has high crystallinity and therefore high electron mobility. Therefore, a transistor using a polycrystalline oxide semiconductor film for a channel formation region may However, the polycrystalline oxide semiconductor film has impurities at the grain boundaries. In addition, the grain boundaries of the polycrystalline oxide semiconductor film become defect states. In oxide semiconductor films, grain boundaries can become carrier traps or carrier generation sources. In the transistor using a polycrystalline oxide semiconductor film for a channel formation region, Compared to transistors using SiO2 in the channel formation region, the fluctuation in electrical characteristics is large and reliability is low. This may result in a low-power transistor.

[0158] <Room temperature film formation (film formation temperature: 20℃ or higher and 150℃ or lower)> Next, a film formation method different from that shown in FIGS. 4 to 9 will be described with reference to FIGS. The film formation methods shown in FIGS. 17 and 18 have a lower film formation temperature than the film formation methods shown in FIGS.

[0159] As shown in FIG. 17(A), similarly to FIG. 4(A), the sputtering target 13 is The particles 15 collide with the sputtering target 13, causing sputtering particles to be ejected. Therefore, the plasma 17 contains ions, sputtering particles, electrons, and the like.

[0160] Sputtering particles include zinc particles, oxygen particles, zinc oxide particles, and In-Ga-Zn. The sputtering target manufactured in the first embodiment contains Z particles rather than Ga particles. Therefore, in this case, zinc particles, acid After the zinc particles, oxygen particles, zinc oxide particles, and zinc oxide particles are preferentially peeled off, This will be explained using a model in which In-Ga-Zn oxide particles are peeled off.

[0161] First, zinc particles 163a and oxygen particles 163b are sputtered as sputtering particles. The zinc particles 163a and the oxygen particles 16b are peeled off from the plating target 13 and deposited on the substrate 161. 3b arrives, and a zinc oxide film 165 is formed on the substrate 161 as shown in FIG. 17(B). do.

[0162] Here, since the substrate temperature is 20° C. or more and 150° C. or less, the zinc oxide film 165 Low crystallinity.

[0163] Next, sputtering particles are ejected from the sputtering target. As the sputtering particles, In-Ga-Zn oxide particles peeled off, as shown in Figure 17(C). In-Ga-Zn oxide particles 167 are deposited on the zinc oxide film 165, and the In-Ga-Zn A film 169 having oxide particles is formed. The In-Ga-Zn oxide particles 167 are In The structure of the -Ga-Zn oxide particles 127 is the same as that of the -Ga-Zn oxide particles 127. Zinc particles and oxygen particles are also exfoliated as tarring particles, but are omitted here.

[0164] In this case, since the zinc oxide film 165 has low crystallinity, the In deposited on the zinc oxide film 165 The crystal orientation of the -Ga-Zn oxide particles 167 is random.

[0165] After that, as shown in FIG. 18(A), zinc particles 163a and oxygen particles 163b are spat out. The zinc particles 16 are peeled off from the quenching target and deposited on the In-Ga-Zn oxide particles 167. As a result, a zinc oxide film with low crystallinity is formed. In addition, zinc particles 163a and oxygen particles 163b are simultaneously sputtered. The particles are deposited on the In-Ga-Zn oxide particles 167 or on the zinc oxide film with low crystallinity. As a result, as shown in FIG. 18(B), a zinc oxide film 169a with low crystallinity and an In-G a-Zn oxide particles 169b are mixed in.

[0166] As shown in FIG. 18(A), zinc particles 163a and an acid are formed on In-Ga-Zn oxide particles 167. The process in which the elementary particles 163b arrive and adhere, and the process in which the In-Ga-Zn oxide shown in FIG. By repeating the process of depositing particles 169b, a microcrystalline In-Ga-Zn oxide film is formed. A film can be formed.

[0167] Formed by sputtering using the sputtering target of embodiment 1 The atomic ratio of Ga to In in In-Ga-Zn oxide (Ga / In), Z to In The atomic ratio of n (Zn / In) is smaller than the atomic ratio contained in the sputtering target. In addition, in the In-Ga-Zn oxide film, the atomic ratio of Zn to Ga (Zn / Ga) is 0.5 or more.

[0168] The crystal orientation of the oxide film obtained in the film formation process of FIGS. 17 and 18 is random. Furthermore, since the film formation temperature is lower than that of the oxide film obtained by the film formation process shown in FIGS. However, the sputtering particles deposited during the film formation process have homologous structures. The oxide film has a higher crystallinity than an oxide film with an amorphous structure.

[0169] Through the above steps, an In-Ga-Zn oxide film having a microcrystalline structure can be formed. In the In-Ga-Zn oxide, Al, Ti, Y, Zr may be used instead of Ga. By using La, Cs, Nd, or Hf, a microcrystalline In-M-Zn oxide ( M can be Al, Ti, Y, Zr, La, Cs, Nd, or Hf.

[0170] The crystal structure of the formed oxide film having a microcrystalline structure will now be described. Hereinafter, the In-M-Zn oxide having a microcrystalline structure will be referred to as a microcrystalline oxide semiconductor.

[0171] It is difficult to clearly identify the crystal parts of a microcrystalline oxide semiconductor film in a TEM image. The crystal parts included in the microcrystalline oxide semiconductor film may have a size of, for example, 1 nm or more and 100 nm or less. The size is often less than 1 nm, or between 1 nm and 10 nm. Nanocrystals (nc: nanoc) are microcrystals of 10 nm or less, or 1 nm to 3 nm. The oxide semiconductor film having nanocrystalline silicon was The nc-OS film is also called an nc-OS film. For example, it may be difficult to clearly identify grain boundaries in TEM images.

[0172] The nc-OS film is a microscopic region (e.g., a region of 1 nm to 10 nm, especially a region of 1 nm or less). The nc-OS film has a periodic atomic arrangement in the region of 3 nm or less. There is no regularity in the crystal orientation between the crystals, so no orientation is observed throughout the film. Depending on the analysis method, the nc-OS film may be indistinguishable from an amorphous oxide semiconductor film. For example, an XRD device using X-rays with a diameter larger than that of the crystal part is used for the nc-OS film. When structural analysis is performed using the out-of-plane method, peaks indicating crystal planes are observed. In addition, for the nc-OS film, the probe diameter is larger than that of the crystalline part. Electron beam diffraction pattern (selected area electron beam diffraction) using an electron beam (e.g., 50 nmφ or larger) ) a halo-like diffraction pattern is observed. For the -OS film, the probe diameter is close to or smaller than the size of the crystal part (for example, 1 nm When electron diffraction is performed using an electron beam with a diameter of 30 nm or more, spots are observed. Nanobeam electron diffraction of the nc-OS film revealed multiple spots within the ring-shaped region. may be observed.

[0173] Figure 10(B) shows the nanobeam electrons at different measurement points on the sample with the nc-OS film. 1 shows an example of a X-ray diffraction pattern. Here, the sample is aligned in a direction perpendicular to the surface on which the nc-OS film is formed. The specimen is cut into thin slices with a thickness of 10 nm or less. An electron beam of 1 nm is incident from a direction perpendicular to the cut surface of the sample. When nanobeam electron diffraction is performed on a sample with an -OS film, a diffraction pattern showing the crystal planes is obtained. However, it was found that no orientation to a specific crystal plane was observed.

[0174] The nc-OS film is an oxide semiconductor film with higher order than an amorphous oxide semiconductor film. Therefore, the nc-OS film has a lower density of defect states than the amorphous oxide semiconductor film. The nc-OS film has no regularity in the crystal orientation between different crystal parts. , the defect density is higher than that of the CAAC-OS film.

[0175] Therefore, the nc-OS film may have a higher carrier density than the CAAC-OS film. An oxide semiconductor film with high carrier density may have high electron mobility. The transistor using the nc-OS film for the channel formation region has high field-effect mobility. In addition, the nc-OS film has a higher defect density than the CAAC-OS film. Therefore, the nc-OS film is used in the channel formation region. The transistors using a CAAC-OS film in the channel formation region are Compared to conventional transistors, the electrical characteristics may fluctuate more, resulting in a less reliable transistor. However, the nc-OS film can be formed even if it contains a relatively large amount of impurities. It is easier to form than the AAC-OS film and can be used preferably in some applications. Therefore, it is possible to manufacture a semiconductor device having a transistor using an nc-OS film with high productivity. It can be made.

[0176] (Embodiment 3) In this embodiment, a film forming apparatus for forming an oxide film with high crystallinity is described below. This will be explained using FIG. 19 and FIG. 20.

[0177] First, let us look at the structure of the film formation equipment that minimizes the amount of impurities mixed into the film during film formation. Explain using 0.

[0178] FIG. 19 is a schematic top view of a single-wafer multi-chamber film-forming apparatus 4000. The film forming apparatus 4000 includes a cassette port 4101 for accommodating a substrate and a substrate alignment unit. and an atmosphere-side substrate supply chamber 4001 having an alignment port 4102 for performing the alignment. The substrate supply chamber 4001 transports the substrate to the atmospheric substrate transport chamber 4002, and the substrate is transported into the atmospheric substrate transport chamber 4002. and a load lock chamber in which the pressure inside the chamber is switched from atmospheric pressure to reduced pressure or from reduced pressure to atmospheric pressure. 4003a, and the substrate is removed, and the pressure in the chamber is reduced to atmospheric pressure, or atmospheric pressure to atmospheric pressure. The unload lock chamber 4003b is switched to a reduced pressure, and the transfer chamber 4003b transfers the substrate in a vacuum. 004, a substrate heating chamber 4005 for heating the substrate, and a sputtering target The film forming chambers 4006a, 4006b, and 4006c are provided for film formation.

[0179] As shown in FIG. 19, the cassette port 4101 is provided in a plurality of positions (three positions in FIG. 19). ) may be present.

[0180] The atmospheric substrate transfer chamber 4002 is provided with a load lock chamber 4003a and an unload lock chamber 4003b. chamber 4003b, and the load lock chamber 4003a and unload lock chamber 4003b are connected to the The transfer chamber 4004 is connected to the substrate heating chamber 4005 and the film forming chamber 400. Connect to 6a, 4006b, and 4006c.

[0181] A gate valve 4104 is provided at the connection between the chambers, and the atmosphere-side substrate supply chamber 4 Except for the atmospheric side substrate transfer chamber 4001 and the atmospheric side substrate transfer chamber 4002, each chamber can be independently maintained in a vacuum state. The atmospheric side substrate transfer chamber 4002 and the transfer chamber 4004 are connected to the substrate transfer robot 41. 03, which can transport glass substrates.

[0182] The film forming apparatus 4000 can transport the substrate between processes without exposing it to the atmosphere. This prevents impurities from being adsorbed onto the substrate. The number of lock chambers, unload lock chambers and substrate heating chambers is not limited to the above, and may vary depending on the installation space. An optimum number can be set appropriately according to the process conditions.

[0183] Next, a cross section of the film forming apparatus 4000 shown in FIG. 19, which corresponds to the dashed line B1-B2, is shown in FIG. show.

[0184] The heating mechanism that can be used in the substrate heating chamber 4005 is, for example, a resistance heating mechanism. Alternatively, the heating mechanism may be a mechanism that uses a medium such as a heated gas to heat the object. For example, the heating mechanism may be a GRTA (G as Rapid Thermal Anneal), LRTA(Lamp Rapid RTA (Rapid Thermal Anneal) eal) can be used. LRTA can be used with halogen lamps, metal halide lamps, Xenon arc lamp, carbon arc lamp, high-pressure sodium lamp, high-pressure mercury lamp The object to be treated is heated by the radiation of light (electromagnetic waves) emitted from the lamps. Heat treatment is performed using high-temperature gas, which is an inert gas.

[0185] The transfer chamber 4004 includes a substrate transfer robot 4103. 3 has a plurality of movable parts and an arm for holding a substrate, and can transport the substrate to each chamber. The transfer chamber 4004 is connected to a vacuum pump 4200 and a cryopump 4200 via a valve. With this configuration, the transfer chamber 4004 is connected to the air Use the vacuum pump 4200 to go from high pressure to low or medium vacuum (0.1 to several hundred Pa). The vacuum is evacuated by switching the valve to change from medium vacuum to high vacuum or ultra-high vacuum (0.1 Pa to 1 x10 -7 The pressure is evacuated to a temperature of 1000 KPa using a cryopump 4201.

[0186] In addition, for example, two or more cryopumps 4201 are connected in parallel to the transfer chamber 4004. With this configuration, even if one cryopump is in the regeneration Even if the remaining cryopump is used, it is possible to pump the remaining cryopump. Cryopumping is the process of releasing molecules (or atoms) stored in the cryopump. If the Lyopump accumulates too many molecules (or atoms), its pumping capacity will decrease. It is periodically regenerated.

[0187] FIG. 20 shows cross sections of the film-forming chamber 4006b, the transfer chamber 4004, and the load-lock chamber 4003a. The load lock chamber 4003 a has a substrate transfer stage 4111 .

[0188] Here, the details of the film formation chamber will be described with reference to FIG. A film forming chamber, a plasma processing chamber, etc. can be used as appropriate. The deposition chamber corresponds to the deposition chamber described in the second embodiment. In the film formation chamber shown in the second embodiment, the sputtering target and the substrate are placed horizontally. In the film formation chamber shown in this embodiment, the sputtering target and The board is shown in a vertical position.

[0189] The film forming chamber 4006b shown in FIG. 20 includes a sputtering target 4106 and an adhesion prevention plate 41 4107 and a substrate stage 4108. The substrate stage 4108 is not shown, but the substrate 4109 is placed on the substrate stage 4108. The substrate 4109 is equipped with a substrate holding mechanism for holding the substrate 4109, and a backside heater for heating the substrate 4109 from the backside. It's fine.

[0190] A direct current (DC) power supply is used to apply voltage to the sputtering target. It is also possible to use a high frequency (RF) power source or an alternating current (AC) power source. However, in sputtering using an RF power source, it is difficult to generate uniform plasma over a large area. Therefore, sputtering using an RF power source is not suitable for forming on a large-area substrate. In addition, DC power is more suitable than AC power for the following reasons: C power supply may be preferred.

[0191] In the sputtering method using a DC power supply, for example, as shown in FIG. A DC voltage is applied between the target and the substrate. The potential difference between the sputtering target and the substrate during this time is kept constant as shown in Figure 21(B1). Thus, the sputtering method using a DC power supply maintains a continuous plasma discharge. It can be held.

[0192] On the other hand, in the sputtering method using an AC power supply, for example, as shown in FIG. 21(A2), , the cathode and anode in the adjacent sputtering targets in periods A and B. For example, in the period A shown in FIG. 21(B2), the sputtering The getter (1) acts as the cathode and the sputtering target (2) acts as the anode. In addition, for example, in the period B shown in FIG. 21(B2), the sputtering The target (1) acts as the anode and the sputtering target (2) acts as the cathode. The sum of period A and period B can be, for example, 20 microseconds to 50 microseconds. In this way, the sputtering method using an AC power supply has two periods, period A and period B. Plasma discharge occurs while alternately switching between these.

[0193] The substrate stage 4108 is held in a substantially vertical position relative to the floor during film formation. When transferring, the device is kept in a roughly horizontal position relative to the floor. The position indicated by is the position where the substrate stage 4108 is held when the substrate is delivered. By adopting such a structure, dust or particles that may be mixed in during film formation do not adhere to the substrate 4109. However, the probability of the substrate stage 41 being moved can be reduced compared to when the substrate stage 41 is held horizontally. If the 08 is held perpendicular (90°) to the floor, the board 4109 may fall. Therefore, it is preferable that the substrate stage 4108 be at least 80° but less than 90°.

[0194] The adhesion prevention plate 4107 is formed by sputtering from the sputtering target 4106. The anti-adhesion plate 4107 can prevent the accumulated particles from accumulating in unnecessary areas. It is desirable to process the surface so that the sputtered particles do not peel off. For example, It is also possible to perform blasting to increase the resistance, or to provide the surface of the adhesion prevention plate 4107 with irregularities.

[0195] The deposition chamber 4006b is connected to a mass flow controller 4006 via a gas heating mechanism 4302. 300, and the gas heating mechanism 4302 is precisely controlled via the mass flow controller 4300. The gas is introduced into the film-forming chamber 4006b by a gas heating mechanism 4302. The gas can be heated to 40°C or higher and 400°C or lower, or 50°C or higher and 200°C or lower. The gas heating mechanism 4302, the mass flow controller 4300, and the refiner 43 Although the number of gas types is equal to the number of gas types, only one gas type is shown for simplicity. The dew point of the introduced gas is -80°C or less, -100°C or less, or -120°C or less. For example, oxygen gas, nitrogen gas, and rare gas (argon gas) can be used. (such as a sachet) is used.

[0196] The film-forming chamber 4006b is connected to a turbo molecular pump 4202 and a vacuum pump 4203 via a valve. It is connected to P4200.

[0197] Furthermore, the film formation chamber 4006b is provided with a cryotrap 4110.

[0198] The Cryotrap 4110 adsorbs molecules (or atoms) with a relatively high melting point, such as water. The turbo molecular pump 4202 is a mechanism that can pump large molecules (or atoms). It has excellent productivity due to stable exhaust of hydrogen and hydrogen atoms and low maintenance frequency. Therefore, in order to improve the pumping capacity for water, etc., a cryotrap is used. The cryotrap 4110 is connected to the film forming chamber 4006b. The temperature of the cryo-refrigerator is set to 100K or less, or 80K or less. When 110 has multiple refrigerators, changing the temperature of each refrigerator can improve the efficiency of exhaust. For example, the temperature of the first stage refrigerator is set to 100 K or less, and the second stage The temperature of the first refrigerator should be set to 20K or less.

[0199] The method of exhausting the film forming chamber 4006b is not limited to this, and may be the same as that of the transfer chamber 4004. The same configuration as the exhaust method (exhaust method of a cryopump and a vacuum pump) may also be used. Of course, the exhaust method of the transfer chamber 4004 is the same as that of the film forming chamber 4006b (a turbo molecular pump and It may be configured in the same way as the exhaust method using a vacuum pump.

[0200] In addition, the back pressure ( The total pressure and the partial pressure of each gas molecule (atom) are preferably as follows. The back pressure of the film-forming chamber 4006b and the partial pressure of each gas molecule (atom) are mixed into the film to be formed. It is necessary to be careful because there is a possibility that

[0201] The back pressure (total pressure) of each chamber mentioned above is 1 x 10 -4 Pa or less, or 3 x 10 -5 Pa or less , or 1 × 10 -5 The mass-to-charge ratio (m / z) of each chamber is 18. The partial pressure of the gas molecules (atoms) is 3 x 10 -5 Pa or less, or 1×10 -5 Pa or less, or 3 x 10 -6 In addition, the gas molecules ( The partial pressure of the atom is 3×10 -5 Pa or less, or 1×10 -5 Pa or less, or 3 x 10 -6 In addition, the partial pressure of the gas molecules (atoms) with m / z of 44 in each of the above-mentioned chambers is is 3 x 10 -5 Pa or less, or 1×10 -5 Pa or less, or 3 x 10 -6 Pa or less is.

[0202] The total and partial pressures in the vacuum chamber can be measured using a mass spectrometer. For example, the quadrupole mass spectrometer (also called Q-mass) manufactured by ULVAC, Inc. lee CGM-051 can be used.

[0203] The transfer chamber 4004, the substrate heating chamber 4005, and the film forming chamber 4006b are externally It is desirable to have a configuration with little leakage or internal leakage.

[0204] For example, the above-mentioned transfer chamber 4004, substrate heating chamber 4005, and film forming chamber 4006b The crate is 3 x 10 -6 Pa·m 3 / s or less, or 1×10 -6 Pa·m 3 / s or less In addition, the leak rate of gas molecules (atoms) with m / z of 18 is 1×10 -7 Pa m 3 / s or less, or 3×10 -8 Pa·m 3 / s or less. If the leak rate of a gas molecule (atom) is 1×10 -5 Pa·m 3 / s or less, or 1 x 1 0 -6 Pa·m 3 / s or less. Also, the leak of gas molecules (atoms) with m / z of 44 The rate is 3x10 -6 Pa·m 3 / s or less, or 1×10 -6 Pa·m 3 / s or less do.

[0205] The leak rate was calculated from the total pressure and partial pressure measured using the mass spectrometer mentioned above. It can be derived from

[0206] By forming an oxide film using the above film forming equipment, the inclusion of impurities in the oxide film is suppressed. It can be controlled.

[0207] (Fourth embodiment) In this embodiment, a semiconductor device according to one embodiment of the present invention and a manufacturing method thereof will be described with reference to drawings. Please refer to the following for explanation.

[0208] In a transistor including an oxide semiconductor film, An example of such defects is oxygen vacancies. The threshold voltage of a transistor using a thin film is easily shifted in the negative direction, and the This is because charges are generated due to oxygen vacancies in the oxide semiconductor film. This is because the resistance is lowered when the transistor has normally-on characteristics. Various problems may occur, such as malfunctions becoming more likely to occur or power consumption increasing when not in operation. In addition, the electrical characteristics of transistors, typically There is a problem in that the amount of fluctuation in the threshold voltage increases.

[0209] One of the causes of oxygen vacancies is damage that occurs during the transistor manufacturing process. For example, an insulating film or a conductive film is formed on an oxide semiconductor film by plasma CVD or sputtering. When forming an oxide semiconductor film, the oxide semiconductor film may be damaged depending on the forming conditions. This sometimes happens.

[0210] One of the causes of oxygen vacancies is oxygen desorption from an oxide semiconductor film due to heat treatment. For example, in order to remove impurities such as hydrogen and water contained in the oxide semiconductor film, However, when heat treatment is performed in a state where the oxide semiconductor film is exposed, the oxide Oxygen is released from the semiconductor film, forming oxygen vacancies.

[0211] In addition to oxygen deficiency, impurities such as silicon and carbon, which are constituent elements of the insulating film, also affect the Therefore, the impurities are mixed into the oxide semiconductor film, which causes poor electrical characteristics of the transistor. As a result, the resistance of the oxide semiconductor film is reduced, and the oxide semiconductor film is susceptible to deterioration over time and stress testing. This leads to a problem of an increase in the amount of fluctuation in the electrical characteristics of the transistor, typically the threshold voltage. There is.

[0212] In view of this, in this embodiment, a semiconductor device including a transistor having an oxide semiconductor film In this case, oxygen vacancies in the oxide semiconductor film, which is the channel region, and impurities in the oxide semiconductor film are generated. One of the objectives is to reduce the concentration of substances.

[0213] On the other hand, display devices on the market are becoming larger, with screen sizes of 60 inches or more diagonally. Furthermore, development is being carried out with a view to screen sizes of 120 inches or more diagonally. For this reason, the glass substrates used in display devices are large, 8th generation and above. However, when using a large-area substrate, high-temperature processing, for example, 450 Heating at temperatures above 100°C requires large and expensive heating equipment, which increases production costs. Furthermore, high temperature processing can cause warping and shrinkage of the substrate, resulting in a lower yield. is reduced.

[0214] Therefore, in this embodiment, the number of heat treatment steps is small and it is possible to use a large-area substrate. An object of the present invention is to manufacture a semiconductor device by using heat treatment at a low temperature.

[0215] 22A to 22C are top views and diagrams of a transistor 250 included in a semiconductor device. The transistor 250 shown in FIG. 22 is a channel-etched transistor. 22(A) is a top view of the transistor 250, and FIG. 22(B) is a top view of the transistor 250. 22(A) is a cross-sectional view taken along the dashed line AB, and FIG. 22(C) is a cross-sectional view taken along the dashed line C- 22(A) is a cross-sectional view of the section D. In FIG. 22(A), for clarity, the substrate 211, the transistor Some of the components of the gate insulating film 217, the oxide insulating film 223, the oxide The insulating film 224, the nitride insulating film 225, etc. are omitted.

[0216] The transistor 250 shown in FIGS. 22B and 22C is provided on a substrate 211. The gate electrode 215 is formed on the substrate 211 and the gate electrode 215. and an oxide semiconductor layer overlapping the gate electrode 215 via the gate insulating layer 217. The semiconductor device includes a conductive film 218 and a pair of electrodes 221 and 222 in contact with the oxide semiconductor film 218 . Further, on the gate insulating film 217, the oxide semiconductor film 218, and the pair of electrodes 221 and 222, The insulating film 222 is made of an oxide insulating film 223, an oxide insulating film 224, and a nitride insulating film 225. A protective membrane 226 is formed.

[0217] The transistor 250 described in this embodiment includes an oxide semiconductor film 218. In addition, part of the oxide semiconductor film 218 functions as a channel region. The oxide insulating film 223 is formed in contact with the insulating film 218. An oxide insulating film 224 is formed so as to cover the insulating film 224 .

[0218] The oxide semiconductor film 218 is typically an In-M-Zn oxide (M is Al, Ti, Ga , Y, Zr, La, Cs, Nd, or Hf).

[0219] Metal elements of sputtering target used for forming In-M-Zn oxide film The atomic ratio preferably satisfies In≧M, Zn≧M. The atomic ratio of the target metal elements is In:M:Zn=1:1:1, In:M:Zn= 3:1:2 is preferred.

[0220] When the oxide semiconductor film 218 is an In-M-Zn oxide film, the sum of In and M is 10 When the atomic percentage is 0, the atomic ratio of In to M is also is In 25 atomic % or more, M less than 75 atomic %, or In 34 atomic % omic% or more, and M is less than 66 atomic%.

[0221] The oxide semiconductor film 218 has an energy gap of 2 eV or more, or 2.5 eV or more. In this way, oxide semiconductors with wide energy gaps are used. As a result, the off-state current of the transistor 250 can be reduced.

[0222] The thickness of the oxide semiconductor film 218 is greater than or equal to 3 nm and less than or equal to 200 nm, or greater than or equal to 3 nm and less than or equal to 100 nm. nm or less, or 3 nm to 50 nm.

[0223] The oxide semiconductor film 218 was formed using the sputtering target described in Embodiment 1. It is preferable to form a Zn-based alloy having an atomic ratio of In:M:Zn=1:1:1.05 or more. A sputtering target having a porosity of 1.5 or less can be used. In the oxide semiconductor film 218 formed using the sputtering target, The atomic ratio of M and the atomic ratio of Zn to In are compared with those of the sputtering target. and becomes smaller.

[0224] The In-Ga-Zn oxide film formed using such a sputtering target has the following properties: It has a homologous structure.

[0225] As the oxide semiconductor film 218, an oxide semiconductor film with low carrier density is used. For example, The oxide semiconductor film 218 has a carrier density of 1×1017 pieces / cm 3 or less, or 1×1 0 15 pieces / cm 3 or less, or 1 x 10 13 pieces / cm 3 or less, or 1 x 10 11 pcs / c m 3 The following oxide semiconductor film is used.

[0226] However, the semiconductor characteristics and electrical characteristics (field effect) of the required transistors are not limited to these. It is sufficient to use an appropriate composition depending on the required properties (e.g., the mobility, threshold voltage, etc.). In order to obtain semiconductor characteristics of a transistor, the carrier density and impurity of the oxide semiconductor film 218 are controlled. The material concentration, defect density, atomic ratio of metal elements to oxygen, interatomic distance, density, etc. are set appropriately. It is preferable.

[0227] Note that the oxide semiconductor film 218 is an oxide semiconductor having a low impurity concentration and a low density of defect states. By using a conductive film, it is possible to fabricate a transistor with even better electrical characteristics. In addition, a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film is preferably an oxide semiconductor film having an off-state property. The current is extremely small and the channel width is 1×10 6 The element has a channel length L of 10 μm. However, the voltage between the source and drain electrodes (drain voltage) is in the range of 1V to 10V. In this case, the off-state current is below the measurement limit of the semiconductor parameter analyzer, i.e., 1×10 - 13 Therefore, the oxide semiconductor film has a channel region of 0.25A or less. The transistors in which this is formed have small fluctuations in electrical characteristics and are highly reliable. This may be the case.

[0228] Hydrogen contained in the oxide semiconductor film reacts with oxygen that is bonded to metal atoms to form water. Oxygen vacancies are formed in the lattice from which oxygen has been desorbed (or in the part from which oxygen has been desorbed). When hydrogen enters the gap, electrons, which act as carriers, are generated. When bonded to oxygen, which bonds to metal atoms, electrons, which act as carriers, may be generated. Therefore, a transistor using an oxide semiconductor containing hydrogen has normally-on characteristics. It is easy to become.

[0229] Therefore, it is preferable that the amount of hydrogen in the oxide semiconductor film 218 be reduced as much as possible. Specifically, the oxide semiconductor film 218 was analyzed by secondary ion mass spectrometry (SIMS). Hydrogen concentration obtained by Common Ion Mass Spectrometry , 5 × 10 19 atoms / cm 3 or less, or 1 x 10 19 atoms / cm 3 below , 5×10 18 atoms / cm 3 or less, or 1 x 10 18 atoms / cm 3 below, or 5×10 17 atoms / cm 3 or less, or 1 x 10 16 atoms / cm 3 Below Below.

[0230] The oxide semiconductor film 218 contains silicon or carbon, which is one of the Group 14 elements. As a result, oxygen vacancies increase in the oxide semiconductor film 218, causing the oxide semiconductor film 218 to become n-type. The silicon and carbon concentrations in the nitride semiconductor film 218 (obtained by secondary ion mass spectrometry) concentration) is 2 x 10 18 atoms / cm3 or less, or 2 x 10 17 atoms / c m 3 The following applies.

[0231] In addition, in the oxide semiconductor film 218, alkali metal ions obtained by secondary ion mass spectrometry The concentration of metal or alkaline earth metal is 1×10 18 atoms / cm 3 Less than or equal to 2 x10 16 atoms / cm 3 The alkali metals and alkaline earth metals are oxidized When they bond with semiconductors, they can generate carriers, which increases the off-state current of the transistor. For this reason, the alkali metal or alkaline earth metal in the oxide semiconductor film 218 may It is preferable to reduce the concentration of metalloids.

[0232] When nitrogen is contained in the oxide semiconductor film 218, electrons serving as carriers are generated, and As a result, the carrier density increases and it becomes easier to make the semiconductor n-type. Therefore, the transistor having the oxide semiconductor film tends to be normally on. In this case, it is preferable that nitrogen is reduced as much as possible. For example, in the case of secondary ion mass spectrometry, The nitrogen concentration obtained is 5×10 18 atoms / cm 3 It is preferable to do the following: .

[0233] The oxide semiconductor film 218 is formed using the film formation model described in Embodiment 2. The oxide semiconductor film 218 may have a non-single-crystal structure. CAAC-OS (C Axis Aligned Crystalline O oxide semiconductor), polycrystalline structure, microcrystalline structure, and amorphous structure Among non-single-crystal structures, the amorphous structure has the highest defect level density, and CAAC-OS Therefore, the oxide semiconductor film 218 is a CAAC-OS film. is preferred.

[0234] Note that the oxide semiconductor film 218 may have an amorphous structure, a microcrystalline structure, or a polycrystalline structure. The film may be a mixed film having two or more of the following: a CAAC-OS region, a CAAC-OS region, and a single crystal structure region. The mixed film may have, for example, an amorphous structure region, a microcrystalline structure region, a polycrystalline structure region, a CA In the case of a single-layer structure having two or more regions, either an AC-OS region or a single-crystal structure region The mixed film may have, for example, an amorphous structure region, a microcrystalline structure region, a polycrystalline structure region, and the like. A stacked structure of two or more regions of a single crystal structure region, a CAAC-OS region, or a single crystal structure region. There may be cases where this is the case.

[0235] In the transistor 250 described in this embodiment, The oxide insulating film 223 is formed as shown in FIG. A velum 224 is formed.

[0236] The oxide insulating film 223 is an oxygen-permeable oxide insulating film. 3 is a film thickness of the oxide semiconductor film 218. The film thickness of the oxide semiconductor film 218 is 1 / 2 mm. It also functions as a pressure relief film.

[0237] The oxide insulating film 223 has a thickness of 5 nm to 150 nm, or A silicon oxide film, a silicon oxynitride film, or the like having a thickness of 0 nm or less can be used. In the specification, a silicon oxynitride film is a film having a higher oxygen content than nitrogen content. A silicon nitride oxide film is a film that contains more nitrogen than oxygen. It refers to a thin membrane.

[0238] The oxide insulating film 223 preferably has few defects. The signal at g = 2.001 originating from the silicon dangling bond is The density is 3×10 17 spins / cm 3 This is because the oxide insulating If the insulating film 223 contains a large number of defects, oxygen will bond to the defects, resulting in an oxide insulating film. This is because the amount of oxygen permeating through the film 223 decreases.

[0239] In addition, the number of defects at the interface between the oxide insulating film 223 and the oxide semiconductor film 218 is small. It is preferable that the oxide semiconductor film 218 has a defect-causing property, and typically, the defect-causing property is detected by ESR measurement. The spin density of the signal appearing at g=1.93 is 1×10 17 spins / cm 3 Further details are as follows: is preferably below the lower limit of detection.

[0240] An oxide insulating film 224 is formed in contact with the oxide insulating film 223. The film 224 is formed by using an oxide insulating film containing more oxygen than the oxygen required for the stoichiometric composition. The oxide insulating film containing more oxygen than the stoichiometric composition is formed by heating. Oxides containing more oxygen than the stoichiometric composition are The insulating film was analyzed by TDS and found to have an oxygen desorption of 1.0 x 10 18 at oms / cm 3 or more, or 3.0 x 1020 atoms / cm 3 More than oxide insulation It is a membrane.

[0241] The oxide insulating film 224 has a thickness of 30 nm to 500 nm, or Silicon oxide, silicon oxynitride, etc., up to 400 nm or less can be used.

[0242] The oxide insulating film 224 preferably has few defects. The signal at g = 2.001 originating from the silicon dangling bond is The density is 1.5 x 10 18 spins / cm 3 Less than or even 1×10 18 spins / c m 3 Note that the oxide insulating film 224 is preferably Since the oxide insulating film 223 is located farther away from the oxide semiconductor film 218, the defect density is lower than that of the oxide insulating film 223. More is better.

[0243] Other configuration details of transistor 250 are described below.

[0244] There is no particular restriction on the material of the substrate 211, but it should be strong enough to withstand the subsequent heat treatment. For example, glass substrates, ceramic substrates, quartz substrates, and A fire substrate or the like may be used as the substrate 211. Also, silicon, silicon carbide, etc. single crystal semiconductor substrates, polycrystalline semiconductor substrates, compound semiconductor substrates such as silicon germanium, It is also possible to use an SOI substrate, etc., and a semiconductor element is provided on such a substrate. The substrate 211 may be a glass substrate. In this case, 6th generation (1500mm x 1850mm), 7th generation (1870mm x 2200mm) ), 8th generation (2200mm x 2400mm), 9th generation (2400mm x 2800mm ), 10th generation (2950mm x 3400mm) and other large area substrates, A display device can be fabricated.

[0245] In addition, a flexible substrate is used as the substrate 211, and the transistor 25 is directly formed on the flexible substrate. Alternatively, a peeling layer may be provided between the substrate 211 and the transistor 250. The release layer is preferably removed from the substrate 211 after a semiconductor device is partially or entirely completed thereon. The transistor 250 can be separated and transferred to another substrate. It can also be transferred to substrates with poor thermal properties or flexible substrates.

[0246] The gate electrode 215 may be made of aluminum, chromium, copper, tantalum, titanium, molybdenum, or titanium. or an alloy containing the above-mentioned metal elements, or It can be formed by using an alloy or the like that combines metal elements such as manganese, zinc, etc. Alternatively, one or more metal elements selected from the group consisting of ruthenium, arsenic, and chromium may be used. The electrode 215 may have a single layer structure or a laminated structure of two or more layers. a single layer structure of aluminum film containing titanium, a two-layer structure of titanium film laminated on aluminum film, and titanium nitride Two-layer structure with titanium film stacked on titanium film, two-layer structure with tungsten film stacked on titanium nitride film Two-layer structure in which a tungsten film is laminated on a tantalum nitride film or a tungsten nitride film The structure is a titanium film, an aluminum film is laminated on the titanium film, and a titanium film is laminated on top of that. There are also three-layer structures that can be formed using aluminum, titanium, tantalum, tungsten, A combination of one or more elements selected from molybdenum, chromium, neodymium, and scandium Alternatively, an alloy film or a nitride film may be used.

[0247] The gate electrode 215 may be made of indium tin oxide, indium containing tungsten oxide, or the like. oxide, indium zinc oxide with tungsten oxide, indium oxide with titanium oxide oxide, indium tin oxide containing titanium oxide, indium zinc oxide, silicon oxide A light-transmitting conductive material such as indium tin oxide may also be used. Alternatively, the light-transmitting conductive material and the metal element may be laminated together.

[0248] The gate insulating film 217 is made of, for example, silicon oxide, silicon oxynitride, silicon nitride oxide, Silicon nitride, aluminum oxide, hafnium oxide, gallium oxide or Ga-Zn based gold Metal oxides or the like may be used, and the layer may be formed as a laminate or a single layer.

[0249] The gate insulating film 217 is made of hafnium silicate (HfSiO x ), nitrogen is added Added hafnium silicate (HfSi x O y N z ), nitrogen-doped hafnium Luminate (HfAl x O y N z ), hafnium oxide, yttrium oxide, etc. The use of -k materials can reduce gate leakage of transistors.

[0250] The thickness of the gate insulating film 217 is 5 nm or more and 400 nm or less, or 10 nm or more and 300 It is preferable to set the thickness to 50 nm or less, or 50 nm or more and 250 nm or less.

[0251] The pair of electrodes 221 and 222 are made of a conductive material such as aluminum, titanium, chromium, or nickel. copper, yttrium, zirconium, molybdenum, silver, tantalum, or tungsten The metal is used as a single layer or a laminated structure. For example, a single layer structure of aluminum film containing silicon, a titanium film on an aluminum film, Two-layer structure with a titanium film laminated on a tungsten film, two-layer structure with a copper-magnesium film laminated on a tungsten film, A two-layer structure in which a copper film is laminated on a titanium-aluminum alloy film, a titanium film or a titanium nitride film, An aluminum film or a copper film is laminated on the titanium film or the titanium nitride film, and A three-layer structure in which a titanium film or titanium nitride film is formed on top of the molybdenum film or molybdenum nitride film a molybdenum film and an aluminum film or A three-layer structure in which a copper film is laminated and a molybdenum film or molybdenum nitride film is formed on top of that It should be noted that transparent conductive materials containing indium oxide, tin oxide, or zinc oxide may also be used. good.

[0252] Further, oxygen, hydrogen, water, an alkali metal, an alkaline earth metal, or the like is added to the oxide insulating film 224. By providing the nitride insulating film 225 having a blocking effect such as Diffusion of oxygen from the oxide semiconductor film 218 to the outside and penetration of hydrogen, water, etc. from the outside into the oxide semiconductor film 218 The nitride insulating film can be made of silicon nitride, silicon nitride oxide, aluminum nitride, etc. Aluminum, aluminum nitride oxide, etc. In addition, oxygen, hydrogen, water, alkali metals, aluminum Instead of a nitride insulating film with a blocking effect such as potassium earth metal, oxygen, hydrogen, water, etc. An oxide insulating film having a blocking effect against oxygen, hydrogen, water, etc. may be provided. Examples of oxide insulating films having a blocking effect include aluminum oxide, aluminum oxynitride, and oxide. Gallium oxide, gallium oxynitride, yttrium oxide, yttrium oxynitride, hafnium oxide Examples include hafnium oxide nitride and hafnium oxynitride.

[0253] Next, a manufacturing method of the transistor 250 shown in FIGS. 22A and 22B will be described with reference to FIGS. 23A and 23B. .

[0254] As shown in FIG. 23(A), a gate electrode 215 is formed on a substrate 211. A gate insulating film 217 is formed on the substrate 15 .

[0255] Here, a glass substrate is used as the substrate 211.

[0256] The gate electrode 215 is formed by the following methods. First, the sputtering method, the CVD method, A conductive film is formed by evaporation or the like, and a mask is formed on the conductive film by photolithography. Next, a part of the conductive film is etched using the mask to form a gate electrode 215. After this, the mask is removed.

[0257] The gate electrode 215 may be formed by electrolytic plating, printing, ink jet printing, or the like instead of the above-mentioned method. It may also be formed by a jet method or the like.

[0258] Here, a tungsten film having a thickness of 100 nm is formed by sputtering. A mask is formed by a photolithography process, and a tungsten film is formed using the mask. A gate electrode 215 is formed by dry etching.

[0259] The gate insulating film 217 is formed by sputtering, CVD, vapor deposition, or the like.

[0260] When a gallium oxide film is formed as the gate insulating film 217, MOCVD (Me Organic Chemical Vapor Deposition (OCCVD) method was used. It can be formed by

[0261] Here, the gate insulating film 217 is a silicon nitride film having a thickness of 400 nm and a silicon nitride film having a thickness of 50 A silicon oxynitride film with a thickness of nm is formed by laminating it using the plasma CVD method.

[0262] Next, as shown in FIG. 23B, an oxide semiconductor film 218 is formed on the gate insulating film 217. Complete.

[0263] A method for forming the oxide semiconductor film 218 will be described below. Then, an oxide semiconductor film to be the oxide semiconductor film 218 is formed. After a mask is formed by a photolithography process, a part of the oxide semiconductor film is By etching the portion, as shown in FIG. 23(B), The oxide semiconductor film 218 is formed so as to overlap with a part of the gate electrode 215. After this, the mask is removed.

[0264] The oxide semiconductor film that will become the oxide semiconductor film 218 later can be formed by a sputtering method, a coating method, a pulsation method, or the like. The layer can be formed by using a laser deposition method, a laser ablation method, or the like.

[0265] Here, the film formation apparatus shown in the third embodiment has a sputtering chamber as a film formation chamber. The oxide semiconductor film is formed by a sputtering method using a deposition apparatus. The sputtering chamber is equipped with a sputtering target manufactured using the method of the first embodiment. It is being done.

[0266] The sputtering gas is a rare gas (typically argon), oxygen, or a mixture of rare gas and oxygen. In the case of a mixture of rare gas and oxygen, the ratio of the oxygen gas to the rare gas is A higher ratio is preferred.

[0267] In order to obtain a highly pure intrinsic or substantially highly pure intrinsic oxide semiconductor film, a chamber It is necessary not only to evacuate the inside of the chamber to a high vacuum, but also to highly purify the sputtering gas. The oxygen gas and argon gas used must have a dew point of -40°C or less, or -80°C or less, By using gases that have been highly purified to temperatures below -100°C or -120°C, oxides can be This can prevent moisture and the like from being absorbed into the semiconductor film as much as possible.

[0268] Here, the atomic ratio of In:Ga:Zn is 1:1:1.05. A 35-nm-thick In-G oxide semiconductor film was deposited by sputtering using a target. Next, a mask is formed on the oxide semiconductor film, and the oxide semiconductor The oxide semiconductor film 218 is formed by selectively etching part of the film.

[0269] Next, as shown in FIG. 23(C), a pair of electrodes 221 and 222 are formed.

[0270] The method for forming the pair of electrodes 221 and 222 will be described below. First, a sputtering method, C A conductive film is formed by a VD method, a vapor deposition method, or the like. Next, a photolithography process is performed on the conductive film. Next, the conductive film is etched using the mask to form a pair of electrodes 22. 1, 222 are formed. After this, the mask is removed.

[0271] Here, a tungsten film with a thickness of 50 nm, an aluminum film with a thickness of 400 nm, and a A titanium film having a thickness of 100 nm is then laminated on the titanium film by sputtering. A mask is formed by a photolithography process, and a tungsten film and an aluminum film are formed using the mask. The aluminum film and the titanium film are dry-etched to form a pair of electrodes 221 and 222. do.

[0272] Next, as shown in FIG. 23D, the oxide semiconductor film 218 and the pair of electrodes 221 and 222 are The oxide insulating film 223 is formed over the oxide insulating film 223. Form 24.

[0273] The oxide insulating film 223 is made of a silicon dioxide film placed in a vacuum-evacuated processing chamber of a plasma CVD apparatus. The substrate is maintained at a temperature of 280°C or higher and 400°C or lower, and raw material gas is introduced into the processing chamber. The pressure in the chamber must be between 20 Pa and 250 Pa, or between 100 Pa and 250 Pa. Depending on the conditions for supplying high frequency power to an electrode provided in the processing chamber, the oxide insulating film 223 is formed. A silicon oxide film or a silicon oxynitride film can be formed by this method.

[0274] The source gas of the oxide insulating film 223 is a deposition gas containing silicon and an oxidizing gas. Representative examples of deposition gases containing silicon include silane and disilane. , trisilane, fluorinated silane, etc. Oxidizing gases include oxygen, ozone, and dinitrogen monoxide. Examples include nitrogen dioxide and chlorine.

[0275] By using the above conditions, an oxide insulating film that allows oxygen to permeate is formed as the oxide insulating film 223. Furthermore, by providing the oxide insulating film 223, the oxide insulating film 223 can be formed later. In the step of forming the insulating film 224, damage to the oxide semiconductor film 218 can be reduced. As a result, the amount of oxygen vacancies in the oxide semiconductor film can be reduced.

[0276] Under the above film formation conditions, by setting the substrate temperature at the above temperature, the bonding strength of silicon and oxygen As a result, the oxide insulating film 223 becomes oxygen-permeable, dense, and hard. Etching of thin oxide insulating films, typically in 0.5 wt % hydrofluoric acid at 25°C Silicon oxide or silicon oxynitride films with a deposition rate of 10 nm / min or less, or 8 nm / min or less A silicon film can be formed.

[0277] Here, the oxide insulating film 223 is formed by silane at a flow rate of 30 sccm and silane at a flow rate of 4000 s ccm of dinitrogen monoxide was used as the source gas, the pressure in the processing chamber was 200 Pa, and the substrate temperature was 220°C. A 27.12 MHz high-frequency power source was used to supply 150 W of high-frequency power to the parallel plate electrodes. A silicon oxynitride film having a thickness of 50 nm is formed by the plasma CVD method using the supplied gas. In this case, a silicon oxynitride film that is permeable to oxygen can be formed.

[0278] The oxide insulating film 224 is made of a silicon dioxide film placed in a processing chamber of a plasma CVD apparatus that has been evacuated. The substrate is then heated to a temperature between 180°C and 280°C, or between 200°C and 240°C. A raw material gas is introduced into the chamber to set the pressure in the processing chamber at 100 Pa or more and 250 Pa or less, or The pressure is between 100 Pa and 200 Pa, and the electrode installed in the processing chamber is set to 0.17 W / cm 2 Below Upper 0.5W / cm 2 or less than 0.25W / cm2 More than 0.35W / cm 2 High frequency Depending on the conditions for supplying the wave power, a silicon oxide film or a silicon oxynitride film is formed.

[0279] The source gas of the oxide insulating film 224 is a deposition gas containing silicon and an oxidizing gas. Representative examples of deposition gases containing silicon include silane and disilane. , trisilane, fluorinated silane, etc. Oxidizing gases include oxygen, ozone, and dinitrogen monoxide. Examples include nitrogen dioxide and chlorine.

[0280] Here, the oxide insulating film 224 is formed by using silane at a flow rate of 200 sccm and SiO 2 at a flow rate of 4000 sccm. The source gas was dinitrogen monoxide at 200 sccm, the pressure in the processing chamber was 200 Pa, and the substrate temperature was 220 ℃, and a 27.12MHz high frequency power supply was used to apply 1500W of high frequency power to parallel plate electrodes. A silicon oxynitride film having a thickness of 400 nm is formed by plasma CVD using a gas supplied to the substrate. The plasma CVD device has an electrode area of ​​6000 cm 2 Parallel plate plasma CV D equipment, and the supplied power is converted to power per unit area (power density) of 0.25 W / cm 2 is.

[0281] Next, a heat treatment is carried out. The temperature of the heat treatment is typically 250° C. or higher but not higher than the substrate distortion point. or 300°C or higher and 550°C or lower, or 350°C or higher and 510°C or lower.

[0282] The heat treatment can be carried out using an electric furnace, an RTA device, or the like. Therefore, heat treatment can be performed at a temperature above the strain point of the substrate for a short period of time. The processing time can be reduced.

[0283] Heat treatment is carried out in nitrogen, oxygen, or ultra-dry air (water content less than 20 ppm or less than 1 ppm) or less, or 10 ppb or less air), or rare gas (argon, helium, etc.) atmosphere It should be noted that if the above nitrogen, oxygen, ultra-dry air, or rare gas contains hydrogen, water, etc. It is preferable that this is not the case.

[0284] The heat treatment apparatus used in the heat treatment is the substrate heating chamber 400 shown in the third embodiment. The heating mechanism provided in 5 can be used as appropriate.

[0285] By this heat treatment, part of oxygen contained in the oxide insulating film 224 is oxidized to the oxide semiconductor film 21 8, the amount of oxygen vacancies in the oxide semiconductor film 218 can be further reduced. do.

[0286] When the oxide insulating film 223 and the oxide insulating film 224 contain water, hydrogen, or the like, A nitride insulating film 225 having a function of blocking elements is formed later, and a heat treatment is performed. The water, hydrogen, and the like contained in the oxide insulating film 223 and the oxide insulating film 224 are absorbed by the oxide semiconductor. The oxide semiconductor film 218 is then transferred to the oxide semiconductor film 218, causing defects in the oxide semiconductor film 218. Water, hydrogen, and the like contained in the oxide insulating films 223 and 224 are released by heat. This reduces the variation in the electrical characteristics of the transistor 250 and also reduces the threshold. This makes it possible to suppress fluctuations in the low voltage.

[0287] Note that by forming the oxide insulating film 224 over the oxide insulating film 223 under heating, Since oxygen can be transferred to the oxide semiconductor film 218, the heat treatment is not required. It's good to

[0288] Here, heat treatment is performed in a nitrogen and oxygen atmosphere at 350° C. for 1 hour.

[0289] Next, a nitride insulating film 225 is formed by sputtering, CVD, or the like.

[0290] When the nitride insulating film 225 is formed by the plasma CVD method, The substrate placed in the evacuated processing chamber is heated to 300°C or higher and 400°C or lower, or 320°C or lower. A temperature of 370° C. or higher is preferable because a dense nitride insulating film can be formed.

[0291] Here, silane at a flow rate of 50 sccm and HCl at a flow rate of 5000 The source gases were nitrogen at a flow rate of 100 sccm and ammonia at a flow rate of 100 sccm. The pressure in the processing chamber was The substrate temperature was set at 350°C under 100 Pa, and a 27.12 MHz high frequency power supply was used for 1000 A 50 nm thick nitride film was formed by plasma CVD using a 1000 W high frequency power supplied to parallel plate electrodes. A silicon film is formed. The plasma CVD device has an electrode area of ​​6000 cm. 2 It is flat It is a horizontal and flat type plasma CVD device, and the supplied power is measured as the power per unit area (power density ) is converted to 1.7 × 10 -1 W / cm 2 is.

[0292] Through the above steps, the oxide insulating film 223, the oxide insulating film 224, and the nitride insulating film 22 5, a protective film 226 can be formed.

[0293] Next, a heat treatment may be performed. The temperature of the heat treatment is typically 300° C. or higher and 40° C. or lower. The temperature must be below 0°C, or between 320°C and 370°C.

[0294] Through the above steps, the transistor 250 can be manufactured.

[0295] As described above, in a semiconductor device using an oxide semiconductor film, the amount of defects is reduced. Furthermore, the electrical characteristics of a semiconductor device using an oxide semiconductor film can be improved. The above semiconductor device can be obtained.

[0296] <Modification 1, Regarding the Undercoat Insulating Film> In the transistor 250 described in this embodiment, the substrate 211 and the gate electrode 212 may be formed as needed. An insulating base layer can be provided between the gate electrode 215. The insulating base layer can be made of an oxide. Silicon, silicon oxynitride, silicon nitride, silicon nitride oxide, gallium oxide, gallium oxide Examples include fluorine, yttrium oxide, aluminum oxide, and aluminum oxynitride. The materials for the underlying insulating film include silicon nitride, gallium oxide, hafnium oxide, and yttrium oxide. By using sodium, aluminum oxide, etc., impurities, typically alkali, are removed from the substrate 211. Diffusion of silicon metals, water, hydrogen, and the like into the oxide semiconductor film 218 can be suppressed.

[0297] The base insulating film can be formed by a sputtering method, a CVD method, or the like.

[0298] <Modification 2: Gate insulating film> In the transistor 250 described in this embodiment, the gate insulating film 217 may be formed as needed. can be made into a laminated structure.

[0299] The gate insulating film 217 is made of a nitride insulating film and an oxide insulating film, which are stacked in this order from the gate electrode 215 side. The nitride insulating film is provided on the gate electrode 215 side. As a result, impurities from the gate electrode 215, typically hydrogen, nitrogen, alkali metals, or This can prevent the alkaline earth metal and the like from moving to the oxide semiconductor film 218.

[0300] In addition, by providing an oxide insulating film on the oxide semiconductor film 218 side, the gate insulating film 217 and The defect state density at the interface between the oxide semiconductor film 218 and the silicon dioxide film 219 can be reduced. As a result, a transistor with little deterioration in electrical characteristics can be obtained. As in the oxide insulating film 224, the oxide insulating film 224 contains more oxygen than the stoichiometric composition. When the oxide insulating film is used, a gate insulating film 217 is formed at the interface between the gate insulating film 217 and the oxide semiconductor film 218. This is more preferable because it is possible to further reduce the defect state density in the silicon dioxide.

[0301] The gate insulating film 217 is made of a nitride insulating film with few defects and a high hydrogen blocking property. A laminated structure in which a thin nitride insulating film and an oxide insulating film are laminated in this order from the gate electrode 215 side. The gate insulating film 217 can be formed of a nitride insulating film with few defects. This can improve the dielectric strength of the gate insulating film 217. By providing a nitride insulating film with high durability, the gate electrode 215 and the nitride insulating film with few defects can be formed. Hydrogen from the film can be prevented from moving to the oxide semiconductor film 218.

[0302] The gate insulating film 217 is made of a nitride insulating film having high impurity blocking properties and a gate insulating film having high defect blocking properties. a nitride insulating film with low hydrogen blocking properties, a nitride insulating film with high hydrogen blocking properties, and an oxide insulating film; The gate insulating film 21 may have a laminated structure in which the layers are stacked in order from the gate electrode 215 side. By providing a nitride insulating film having high impurity blocking properties as the gate electrode 21 Impurities from 5, typically hydrogen, nitrogen, alkali metals, alkaline earth metals, etc. The transfer to the oxide semiconductor film 218 can be prevented.

[0303] <Modification 3, Pair of Electrodes> The pair of electrodes 221 and 222 provided in the transistor 250 in this embodiment , tungsten, titanium, aluminum, copper, molybdenum, chromium, or tantalum element It is preferable to use a conductive material that easily bonds with oxygen, such as an alloy. The oxygen contained in the compound semiconductor film 218 is bonded to the conductive material contained in the pair of electrodes 221 and 222. When the oxide semiconductor film 218 is mixed with the oxide semiconductor film 218, an oxygen vacancy region is formed. When a part of the constituent elements of the conductive material forming the pair of electrodes 221 and 222 is mixed into the film 218, As a result, as shown in FIG. 24, a pair of Low resistance regions 220a and 220b are formed near the regions in contact with the electrodes 221 and 222. The low resistance regions 220a and 220b are in contact with a pair of electrodes 221 and 222, and are formed on the gate insulating film. 217 and a pair of electrodes 221 and 222. Since the oxide semiconductor film 218 has high conductivity, the contact resistance between the oxide semiconductor film 218 and the pair of electrodes 221 and 222 is small. It is possible to reduce the ON current of the transistor and increase the ON current of the transistor.

[0304] <Modification 4: Oxide Semiconductor Film> In the method for manufacturing the transistor 250 described in this embodiment, After forming the oxide semiconductor film 218, the oxide semiconductor film 218 is exposed to plasma generated in an oxygen atmosphere to be oxidized. Oxygen can be supplied to the compound semiconductor film 218. The oxidizing atmosphere can be oxygen, ozone, In the plasma treatment, the substrate is subjected to an atmosphere of nitrous oxide, nitrogen dioxide, etc. The oxide semiconductor film 218 is exposed to plasma generated without applying a bias to the 211 side. As a result, the oxide semiconductor film 218 is not damaged and oxygen is supplied. Therefore, the amount of oxygen vacancies in the oxide semiconductor film 218 can be reduced. Furthermore, impurities, such as For example, halogens such as fluorine and chlorine can be removed.

[0305] The configurations and methods shown in this embodiment may be applied to other embodiments and their modifications, as well as The present invention can be used in appropriate combination with the configurations and methods shown in the examples.

[0306] (Embodiment 5) In this embodiment, the number of defects in the oxide semiconductor film is further reduced compared to that in Embodiment 4. A semiconductor device having a transistor capable of performing this function will be described with reference to the drawings. The transistor described in this embodiment has a structure in which an oxide semiconductor film and an oxide semiconductor film are formed, as compared with that in Embodiment 4. The difference is that it has a multilayer film having an oxide in contact with an oxide semiconductor film.

[0307] 25A and 25B are a top view and a cross-sectional view of a transistor 260 included in the semiconductor device. 25(A) is a top view of the transistor 260, and FIG. 25(B) is a diagram showing the transistor 260 in the dashed line of FIG. 25(A). FIG. 25(C) is a cross-sectional view between dashed lines CD in FIG. 25(A). In FIG. 25(A), for clarity, the configuration of the substrate 211 and the transistor 260 is shown. A part of the element (for example, the gate insulating film 217), the oxide insulating film 223, and the oxide insulating film 224 , the nitride insulating film 225, etc. are omitted.

[0308] The transistor 260 shown in FIGS. 25A to 25C has a gate insulating film 217 interposed therebetween. The multilayer film 220 overlaps the gate electrode 215, and the pair of electrodes 22 contact the multilayer film 220. 1, 222. Also, the gate insulating film 217, the multilayer film 220, and the pair of electrodes 22 An oxide insulating film 223, an oxide insulating film 224, and a nitride insulating film 225 are formed over the insulating films 1 and 222. A protective film 226 made of the above is formed.

[0309] In the transistor 260 described in this embodiment, the multilayer film 220 includes an oxide semiconductor film 2 18 and an oxide film 219. That is, the multilayer film 220 has a two-layer structure. A part of the semiconductor film 218 functions as a channel region. The oxide insulating film 223 is formed on the insulating film 224. That is, an insulating film 224 is formed between the oxide semiconductor film 218 and the oxide insulating film 223. An oxide film 219 is provided on the surface.

[0310] The oxide film 219 is an oxide film formed of one or more of the elements constituting the oxide semiconductor film 218. The oxide film 219 is a oxide film containing at least one of the elements forming the oxide semiconductor film 218. Since the oxide semiconductor film 218 and the oxide film 219 are formed from above, the interface Therefore, the movement of carriers is not hindered at the interface, and The field effect mobility of the transistor is increased.

[0311] The oxide film 219 is typically an In-Ga oxide, an In-Zn oxide, or an In-MnO n oxides (M is Al, Ti, Ga, Y, Zr, La, Cs, Nd or Hf), and The energy of the bottom of the conduction band is closer to the vacuum level than that of the oxide semiconductor film 218. , the energy of the bottom of the conduction band of the oxide film 219 and the energy of the bottom of the conduction band of the oxide semiconductor film 218 The difference in energy between the 0.15 eV or more and 2 eV or less, 1 eV or less, 0.5 eV or less, or 0.4 eV or more That is, the electron affinity of the oxide film 219 and the electron affinity of the oxide semiconductor film 218 are The difference is 0.05 eV or more, 0.07 eV or more, 0.1 eV or more, or 0.15 eV or more. and 2 eV or less, 1 eV or less, 0.5 eV or less, or 0.4 eV or less.

[0312] The oxide film 219 contains In, which increases carrier mobility (electron mobility). preferable.

[0313] The oxide film 219 is made of Al, Ti, Ga, Y, Zr, La, Cs, Nd or Hf. Having a higher atomic ratio than In may have the following effects: (1) Oxide film (2) Enlarge the energy gap of the oxide film 219. (3) It blocks impurities from the outside. (4) It has higher insulation properties than the oxide semiconductor film 218. (5) Al, Ti, Ga, Y, Zr, La, Cs, Nd, or Hf is an acid. Because they are metallic elements with strong bonding strength with elements, Al, Ti, Ga, Y, Zr, La, Cs, N By having d or Hf in a higher atomic ratio than In, oxygen vacancies are less likely to occur.

[0314] The oxide film 219 is an In-M-Zn oxide film (M is Al, Ti, Ga, Y, Zr, La, In the case of Cs, Nd or Hf, the sputtering agent used to deposit the In-M-Zn oxide film The atomic ratio of the metal elements in the deposition target preferably satisfies M>In and Zn>M. The atomic ratio of the metal elements in such a sputtering target is In:Ga:Z. n=1:3:4, In:Ga:Zn=1:3:5, In:Ga:Zn=1:3:6, In :Ga:Zn=1:3:7, In:Ga:Zn=1:3:8, In:Ga:Zn=1:3 :9, In:Ga:Zn=1:3:10, In:Ga:Zn=1:4:5, In:Ga: Zn=1:4:6, In:Ga:Zn=1:4:7, In:Ga:Zn=1:4:8, I n:Ga:Zn=1:4:9, In:Ga:Zn=1:4:10, In:Ga:Zn=1 :5:6, In:Ga:Zn=1:5:7, In:Ga:Zn=1:5:8, In:Ga :Zn=1:5:9, In:Ga:Zn=1:5:10, In:Ga:Zn=1:6:7 , In:Ga:Zn=1:6:8, In:Ga:Zn=1:6:9, In:Ga:Zn= 1:6:10 is preferred.

[0315] When the oxide film 219 is an In-M-Zn oxide film, the sum of In and M is 10 When the atomic percentage of In and M is 0, the atomic percentage of In is 50. c% or less, M is 50 atomic % or more, or In is less than 25 atomic %, M is Must be 75 atomic % or more.

[0316] The oxide semiconductor film 218 and the oxide film 219 are In-M-Zn oxide films (M is A). In the case of (I, Ti, Ga, Y, Zr, La, Cs, Nd or Hf), the oxide semiconductor film 21 Compared with 8, the M (Al, Ti, Ga, Y, Zr, La, Cs) contained in the oxide film 219 , Nd, or Hf) is present in a large atomic ratio, and is typically contained in the oxide semiconductor film 218. The atomic ratio is 1.5 times or more, 2 times or more, or 3 times or more higher than the above atoms. be.

[0317] The oxide semiconductor film 218 and the oxide film 219 are In-M-Zn oxide films (M is A). In the case of Zn, Ti, Ga, Y, Zr, La, Cs, Nd or Hf, the oxide film 219 is n:M:Zn=x1:y1:z1 [atomic ratio], and the oxide semiconductor film 218 was In:M:Zn =x2:y2:z2 [atomic ratio], y1 / x1 is greater than y2 / x2, and is y1 / x1 is 1.5 times or more than y2 / x2. Or, y1 / x1 is y2 / x 2 or y1 / x1 is more than three times greater than y2 / x2. In this case, when y2 is equal to or greater than x2 in the oxide semiconductor film, This is preferable because it can provide stable electrical characteristics to the transistor. However, if y2 is three times larger than x2, If the temperature exceeds this value, the field-effect mobility of a transistor including the oxide semiconductor film decreases. Therefore, it is preferable that y2 is less than three times x2.

[0318] The oxide semiconductor film 218 was formed by a formation process similar to that of the oxide semiconductor film described in Embodiment 4. It can be used as appropriate.

[0319] The oxide film 219 was formed using the sputtering target described in Embodiment 1. It is preferable to form a Zn-based alloy having an atomic ratio of In:M:Zn=1:3:(3.05 or a sputtering target having an atomic ratio of In:M:Zn=1 :6: (6.05 or more and 10 or less) can be used. The oxide film 219 formed using such a sputtering target contains The atomic ratios of M / In and Zn / In are determined based on the atomic ratios contained in the sputtering target. In addition, in the In-Ga-Zn oxide film, the atomic ratio of Zn to M (Z n / M) is 0.5 or more.

[0320] By using such a sputtering target, a homologous structure It is possible to form an In-Ga-Zn oxide film having a structure and CAAC-OS. .

[0321] The oxide film 219 is a film formed by forming an oxide semiconductor film when forming an oxide insulating film 224 later. As a result, the oxide semiconductor film 218 also functions as a damage mitigating film. Furthermore, by forming the oxide film 219, the amount of oxygen vacancies can be reduced. The insulating film to be formed over the oxide semiconductor film 218, for example, the oxide insulating film, contains an element selected from the group consisting of the oxide, Therefore, the inclusion of the fluorine atoms in the compound semiconductor film 218 can be suppressed.

[0322] The thickness of the oxide film 219 is set to 3 nm or more and 100 nm or less, or 3 nm or more and 50 nm or less. do.

[0323] Similarly to the oxide semiconductor film 218, the oxide film 219 may have a non-single-crystal structure, for example. The non-single-crystal structure may be, for example, the CAAC-OS described in Embodiment 2, a polycrystalline structure, or a microcrystalline structure. Among non-single crystalline structures, the amorphous structure has the lowest density of defect levels. The oxide film 219 has the highest defect density, and the CAAC-OS has the lowest defect density. Preferably it is AC-OS.

[0324] Note that the oxide semiconductor film 218 and the oxide film 219 are amorphous and microcrystalline regions, respectively. Two or more of the following: a crystal structure region, a polycrystalline structure region, a CAAC-OS region, and a single crystal structure region The mixed film may have, for example, an amorphous structure region, a microcrystalline structure region, and the like. two or more of the following: a region of a polycrystalline structure, a region of a CAAC-OS structure, and a region of a single crystal structure The mixed film may have a single layer structure with regions, for example, an amorphous structure region, a finely crystalline structure region, or a mixed film with a single layer structure. A region of crystalline structure, a region of polycrystalline structure, a region of CAAC-OS, or a region of single crystal structure The oxide semiconductor film 218 and the oxide semiconductor film 219 may have a stacked structure of two or more regions. The oxide film 219 may have a stacked structure of a microcrystalline structure and a CAAC-OS structure in this order. The oxide semiconductor film 218 has a stacked structure of a microcrystalline structure and a CAAC-OS structure, and the oxide film 21 9 may be CAAC-OS.

[0325] When the oxide semiconductor film 218 and the oxide film 219 are both CAAC-OS, It is possible to improve the crystallinity at the interface between the solid film 218 and the oxide film 219, which is preferable. .

[0326] In the multilayer film 220, the gate electrode 215 is overlapped and a pair of electrodes 221 and 222 are formed. The region sandwiched between 22 is called a channel formation region. The region where carriers mainly flow is called the channel region. The oxide semiconductor film 218 provided between the pair of electrodes 221 is a channel region. , 222 is called the channel length.

[0327] Here, the oxide film 219 is provided between the oxide semiconductor film 218 and the oxide insulating film 223. Therefore, impurities and Even if trap states are formed due to defects, the trap states and the oxide semiconductor film 218 As a result, electrons flowing through the oxide semiconductor film 218 are trapped in the trap states. It is difficult to be trapped, and it is possible to increase the on-current of the transistor. In addition, when an electron is captured in the trap level, the electron As a result, the threshold voltage of the transistor fluctuates. However, since there is a gap between the oxide semiconductor film 218 and the trap states, It is possible to reduce the capture of electrons in the trap level, and the fluctuation of the threshold voltage is reduced. It can be reduced.

[0328] In addition, the oxide film 219 can block impurities from the outside. The amount of impurities that move from the oxide semiconductor film 218 to the oxide semiconductor film 218 can be reduced. Therefore, oxygen vacancies in the oxide semiconductor film 218 are not easily formed. It is possible to reduce the concentration of impurities and the amount of oxygen vacancies.

[0329] Note that the oxide semiconductor film 218 and the oxide film 219 are not simply stacked but are formed continuously. The structure in which the energy of the bottom of the conduction band changes continuously between the layers is called the "junction." In other words, trap centers and recombination centers are formed at the interfaces of each film. The stacked structure is such that there are no impurities that would form defect levels. When impurities are present between the oxide semiconductor film 218 and the oxide film 219, The continuity of the energy band is lost, and carriers are trapped or recombined at the interface, It will disappear.

[0330] In order to form continuous junctions, a multi-chamber equipped with a load lock chamber as shown in the third embodiment is used. Using a multi-layer film-forming device, each film can be stacked continuously without being exposed to the atmosphere. It is necessary.

[0331] As in the case of a transistor 265 shown in FIG. 25(D), a gate insulating film 217 is formed between the gate electrode 211 and the gate electrode 212. A multilayer film 234 overlapping the electrode 215 and a pair of electrodes 221 and 222 in contact with the multilayer film 234 and

[0332] The multilayer film 234 includes an oxide film 231, an oxide semiconductor film 218, and an oxide film 219. That is, the multilayer film 234 has a three-layer structure. It functions as:

[0333] In addition, the gate insulating film 217 and the oxide film 231 are in contact with each other. An oxide film 231 is provided between the oxide semiconductor film 218 and the oxide semiconductor film 218 .

[0334] The multilayer film 234 and the oxide insulating film 223 are in contact with each other. The oxide insulating film 224 is in contact with the oxide semiconductor film 218. An oxide film 219 is provided on the surface.

[0335] The oxide film 231 is formed using a material and a method similar to those of the oxide film 219 described in Embodiment 4. It can be used as appropriate.

[0336] The oxide film 231 is thinner than the oxide semiconductor film 218, so that the transistor It is possible to reduce the amount of variation in the threshold voltage.

[0337] The transistor described in this embodiment has a gate insulating film 217 and an oxide semiconductor film 218. The oxide film 231 is provided between the oxide semiconductor film 218 and the oxide insulating film 223. Since the oxide film 219 is provided between the oxide film 231 and the oxide semiconductor film 218 the concentration of silicon or carbon in the oxide semiconductor film 218 near the interface with the oxide semiconductor film 218; The concentration of carbon or the concentration of silicon in the vicinity of the interface between the oxide film 219 and the oxide semiconductor film 218 The concentration of fluorine and carbon can be reduced.

[0338] The transistor 265 having such a structure includes a multilayer film 2 including an oxide semiconductor film 218. 34 has very few defects, which can improve the electrical characteristics of transistors Typically, it is possible to increase the on-current and improve the field effect mobility. The threshold voltage in the BT stress test and the light BT stress test, which are examples of stress tests, The fluctuation is small and the reliability is high.

[0339] The configurations and methods shown in this embodiment may be applied to other embodiments and their modifications, as well as The present invention can be used in appropriate combination with the configurations and methods shown in the examples.

[0340] (Sixth embodiment) In this embodiment, a transistor having a structure different from those in the fourth and fifth embodiments is described. 26. The transistor 280 described in this embodiment is made of an oxide semiconductor It is characterized by having a plurality of gate electrodes that face each other via a film.

[0341] The transistor 280 shown in FIG. 26 has a gate electrode 215 provided on a substrate 211. In addition, a gate insulating film 217 formed on the substrate 211 and the gate electrode 215 and a gate insulating film 218 formed on the gate electrode 215 are an oxide semiconductor film 218 overlapping the gate electrode 215 with the gate insulating film 217 interposed therebetween; A pair of electrodes 221 and 222 are in contact with the semiconductor film 218. 17, an oxide insulating film 22 is formed over the oxide semiconductor film 218 and the pair of electrodes 221 and 222. 3. A protective film 226 consisting of an oxide insulating film 224 and a nitride insulating film 225 is formed. In addition, a gate electrode 281 overlapping with the oxide semiconductor film 218 with the protective film 226 interposed therebetween is provided. do.

[0342] The gate electrode 281 can be formed in the same manner as the gate electrode 215 shown in the fourth embodiment. Cut.

[0343] The transistor 280 described in this embodiment has a gate electrode facing the gate insulating film 218 with the oxide semiconductor film 218 interposed therebetween. The gate electrode 215 and the gate electrode 281 are By applying different potentials, the threshold voltage of the transistor 280 can be controlled. do.

[0344] Furthermore, by using the oxide semiconductor film 218 in which the amount of oxygen vacancies is reduced, It is possible to improve electrical characteristics. In addition, the fluctuation of threshold voltage is small, and reliability is high. This results in a high-performance transistor.

[0345] The configurations and methods shown in this embodiment may be applied to other embodiments and their modifications, as well as The present invention can be used in appropriate combination with the configurations and methods shown in the examples.

[0346] (Embodiment 7) In this embodiment, a transistor having a structure different from those in Embodiments 4 to 6 will be described. This will be explained with reference to FIG.

[0347] In this embodiment, compared with Embodiments 4 to 6, defects in an oxide semiconductor film are A semiconductor device having a transistor capable of further reducing the amount of The transistor described in this embodiment is the same as that described in Embodiments 4 to 6. In contrast, the back channel side of the oxide semiconductor film 218 is covered with a protective film, and The difference is that it is not exposed to the plasma generated in the etching process for forming the poles.

[0348] 27A and 27B are a top view and a cross-sectional view of a transistor 290 included in the semiconductor device. 27(A) is a top view of the transistor 290, and FIG. 27(B) is a diagram showing the transistor 290 shown in FIG. 27(A) along the dashed line. FIG. 27(C) is a cross-sectional view taken along the dashed line CD in FIG. 27(A). In FIG. 27(A), for clarity, the structure of the substrate 211 and the transistor 290 is shown. A part of the element (for example, the gate insulating film 217), the oxide insulating film 223, and the oxide insulating film 224 , the nitride insulating film 225, etc. are omitted.

[0349] The transistor 290 shown in FIG. 27 has a gate electrode 215 provided on a substrate 211. In addition, a gate insulating film 217 formed on the substrate 211 and the gate electrode 215 and a gate insulating film 218 formed on the gate electrode 215 are The gate electrode 215 includes an oxide semiconductor film 218 overlapping with the gate electrode 215 with the gate insulating film 217 interposed therebetween. Further, an oxide insulating film 223 and an oxide semiconductor film 218 are formed over the gate insulating film 217 and the oxide semiconductor film 218. A protective film 226 is formed by an insulating film 224 and a nitride insulating film 225. A pair of electrodes 22 are formed and connected to the oxide semiconductor film 218 through the openings in the protective film 226. 1b, 222b.

[0350] Next, a method for manufacturing the transistor 290 will be described.

[0351] As in the fourth embodiment, a gate electrode 215 is formed on a substrate 211. A gate insulating film 217 is formed on the gate electrode 215. Next, an oxide film is formed on the gate insulating film 217. A compound semiconductor film 218 is formed.

[0352] Next, in a manner similar to that of Embodiment 4, a 2 The oxide insulating film 223 is formed by heating at a temperature higher than or equal to 20° C. and lower than or equal to 400° C., and then the oxide insulating film After the oxide insulating film 224 is formed, a nitride insulating film 225 is formed. Heat treatment is performed to supply part of oxygen contained in the oxide insulating film 224 to the oxide semiconductor film 218. Provide.

[0353] Next, the oxide insulating film 223, the oxide insulating film 224, and the nitride insulating film 225 were A part of the oxide semiconductor film 218 is etched to form an opening that exposes a part of the oxide semiconductor film 218. Thereafter, the pair of electrodes 221b and 222b in contact with the oxide semiconductor film 218 are formed in the same manner as in the fourth embodiment. Formed in the same way.

[0354] In this embodiment, when etching the pair of electrodes 221b and 222b, oxide Since the semiconductor film 218 is covered with the protective film 226, a pair of electrodes 221b and 222b are formed. The oxide semiconductor film 218, particularly the back surface of the oxide semiconductor film 218, is etched by the etching. The channel region is not damaged. Furthermore, the oxide insulating film 224 has a stoichiometric composition. The oxide insulating film contains more oxygen than the oxygen that fills the gap. Part of the oxygen contained in the oxide semiconductor film 224 is transferred to the oxide semiconductor film 218. The amount of oxygen vacancies contained in the silicon dioxide can be reduced.

[0355] Through the above steps, defects in the oxide semiconductor film 218 can be reduced. , the reliability of the transistor 290 can be improved.

[0356] The configurations and methods shown in this embodiment may be applied to other embodiments and their modifications, as well as The present invention can be used in appropriate combination with the configurations and methods shown in the examples.

[0357] (Embodiment 8) In this embodiment, a transistor having a structure different from those in Embodiments 4 to 7 will be described. This will be explained with reference to FIG.

[0358] In this embodiment, compared with Embodiments 4 to 7, defects in an oxide semiconductor film are A semiconductor device having a transistor capable of further reducing the amount of The transistor described in this embodiment is a transistor formed of an oxide semiconductor, similar to that in Embodiment 5. The back channel side of the conductive film 218 is covered with a protective film, and a pair of electrodes is formed. The point that the semiconductor device is not exposed to the plasma generated in the etching process is different from that of the fourth to seventh embodiments. is different from.

[0359] 28A and 28B are a top view and a cross-sectional view of a transistor 295 included in the semiconductor device. The transistor 295 shown in FIG. 28A is a channel-protective transistor. 28(B) is a top view of the transistor 295, and FIG. 28(B) is a view of the transistor 295 between the dashed line AB in FIG. 28(A). 28(C) is a cross-sectional view taken along the dashed line CD in FIG. 28(A), for clarity, the substrate 211 and some of the components of the transistor 295 are shown. (For example, gate insulating film 217, etc.) are omitted.

[0360] The transistor 295 shown in FIG. 28 has a gate electrode 215 provided on a substrate 211. In addition, a gate insulating film 217 formed on the substrate 211 and the gate electrode 215 and a gate insulating film 218 formed on the gate electrode 215 are and an oxide semiconductor film 218 overlapping the gate electrode 215 with a gate insulating film 217 interposed therebetween. Further, an oxide insulating film 223a, an oxide semiconductor film 218, and a a protective film 226a formed of a nitride insulating film 224a and a nitride insulating film 225a; A pair of electrodes 2 formed on the insulating film 217, the oxide semiconductor film 218, and the protective film 226a. 21c, 222c.

[0361] Next, a method for manufacturing the transistor 295 will be described.

[0362] As in the fourth embodiment, a gate electrode 215 is formed on a substrate 211. A gate insulating film 217 is formed on the gate electrode 215. Next, an oxide film is formed on the gate insulating film 217. A compound semiconductor film 218 is formed.

[0363] Next, in a manner similar to that of Embodiment 4, a 2 The oxide insulating film 223 is formed by heating at a temperature higher than or equal to 20° C. and lower than or equal to 400° C., and then the oxide insulating film After the oxide insulating film 224 is formed, a nitride insulating film 225 is formed. Heat treatment is performed to supply part of oxygen contained in the oxide insulating film 224 to the oxide semiconductor film 218. Provide.

[0364] Next, the oxide insulating film 223, the oxide insulating film 224, and the nitride insulating film 225 were The oxide insulating film 223a, the oxide insulating film 224a, and the nitride insulating film 224b are partially etched. A protective film 226a is formed from the film 225a.

[0365] Next, the pair of electrodes 221c and 222c in contact with the oxide semiconductor film 218 are formed by the method described in Embodiment 4. Formed in the same manner as above.

[0366] In this embodiment, when etching the pair of electrodes 221c and 222c, oxide Since the semiconductor film 218 is covered with the protective film 226a, the pair of electrodes 221c and 222c The oxide semiconductor film 218 is not damaged by the etching. The oxide insulating film 224a is an oxide insulating film containing more oxygen than the oxygen required for the stoichiometric composition. Therefore, part of the oxygen contained in the oxide insulating film 224a is converted into the oxide semiconductor The amount of oxygen vacancies in the oxide semiconductor film 218 can be reduced by transferring oxygen to the oxide semiconductor film 218. do.

[0367] In FIG. 28, a nitride insulating film 225a is formed as the protective film 226a. Alternatively, the oxide insulating film 223a and the oxide insulating film 224a may have a stacked-layer structure. In this case, after forming the pair of electrodes 221c and 222c, the nitride insulating film 225a is formed. As a result, it is possible to prevent hydrogen, water, and the like from entering the oxide semiconductor film 218 from the outside. can be done.

[0368] Through the above steps, defects in the oxide semiconductor film 218 can be reduced. , the reliability of the transistor 295 can be improved.

[0369] (Embodiment 9) In this embodiment, a top-gate transistor and a manufacturing method thereof will be described. do.

[0370] 29A to 29C are top views and diagrams of a transistor 400 included in a semiconductor device. 29A is a top view of the transistor 400, and FIG. 29(A) is a cross-sectional view taken along the dashed line AB in FIG. 29(A), and FIG. 29(C) is a cross-sectional view taken along the dashed line AB in FIG. 29A is a cross-sectional view taken along the dashed line CD. For clarity, in FIG. 29A, the substrate 401, the acid The oxide insulating film 413, some of the components of the transistor 400 (for example, the oxide film 423, the gate insulating film 413, the gate insulating film 42 ... The gate insulating film 425, the insulating film 427, the insulating film 429, etc. are omitted.

[0371] The transistor 400 shown in FIG. 29 is formed on an oxide insulating film 413 provided over a substrate 401. an oxide film 409, an oxide semiconductor film 411 provided over the oxide film 409, and an oxide semiconductor film A pair of electrodes 415 and 416 in contact with the conductive film 411, an oxide insulating film 413, an oxide semiconductor The oxide film 423 is in contact with the film 411 and the pair of electrodes 415 and 416. The gate insulating film 425 is in contact with the oxide semiconductor film 411 and overlaps the oxide semiconductor film 411 with the gate insulating film 425 interposed therebetween. The oxide film 409, the oxide semiconductor film 411, and the oxide semiconductor film 412 are The oxide film 423 is called a multilayer film 424. The gate insulating film 425 and the gate electrode 421 are The gate insulating film 427 may cover the gate electrode 421 and the insulating film 429 may cover the gate electrode 421. A pair of electrodes is formed in openings 433 and 434 of the insulating films 425, 427, and 429. There may be wires 431 and 432 in contact with the poles 415 and 416 .

[0372] Each component of the transistor 400 will be described below.

[0373] The substrate 401 can be the substrate 211 described in Embodiment 4 as appropriate.

[0374] The oxide insulating film 413 serving as a base insulating film can be made of silicon oxide, silicon oxynitride, or the like. silicon nitride, silicon oxide nitride, gallium oxide, hafnium oxide, yttrium oxide Aluminum oxide, aluminum oxynitride, etc. are used as the base insulating film. The insulating film 413 may be made of silicon nitride, gallium oxide, hafnium oxide, or yttrium oxide. By using aluminum oxide or the like, impurities, typically aluminum, are removed from the substrate 401. The diffusion of potassium metal, water, hydrogen, and the like into the oxide semiconductor film can be suppressed.

[0375] The oxide insulating film 413 contains more oxygen than the stoichiometric composition. That is, the insulating film can be formed using an oxide insulating film in which part of oxygen is released by heating. In this way, the oxide insulating film 413 can be formed. The oxygen contained in the oxide semiconductor film 411 is transferred to the oxide insulating film 413. The defect states at the interface of the oxide semiconductor film 409 can be reduced, and the defect states at the interface of the oxide semiconductor film 411 can be reduced. By filling the oxygen vacancies, it is possible to further reduce the oxygen vacancies.

[0376] The oxide film 409 and the oxide film 423 constituting the multilayer film 424 are formed by the oxide film 409 and the oxide film 423 of the oxide film 409 shown in Embodiment 5. The oxide semiconductor film 411 can be made of a material selected from the group consisting of the oxide semiconductor films 219 and 231, The material of the oxide semiconductor film 218 described in Embodiment 5 can be used as appropriate.

[0377] The thickness of the oxide semiconductor film 411 is greater than or equal to 3 nm and less than or equal to 200 nm, or greater than or equal to 3 nm and less than or equal to 100 nm. nm or less, or 3 nm to 50 nm.

[0378] The thickness of the oxide film 409 and the oxide film 423 is 0.3 nm or more and 200 nm or less, and 3 nm or less The thickness of the oxide film 409 is set to 100 nm or more, or 3 nm or more and 50 nm or less. The thickness of the oxide film 423 is preferably thicker than that of the oxide semiconductor film 411. It is preferably thinner than the oxide semiconductor film 411.

[0379] When the oxide film 409 is too thin, the interface between the oxide film 409 and the oxide semiconductor film 411 On the other hand, the oxide film 4 If the thickness of O9 is too thick, oxygen moves from the oxide insulating film 413 to the oxide semiconductor film 411. As a result, it becomes difficult to reduce the amount of oxygen vacancies in the oxide semiconductor film 411. For this reason, the thickness of the oxide film 409 is set to be thicker than that of the oxide semiconductor film 411 and to be 20 nm or more. The thickness of the oxide film 423 is preferably 200 nm or less. The thickness of the oxide film 409 is made thinner than that of the oxide semiconductor film 411. This is preferable because it allows the manufacture of a transistor with a small amount of fluctuation in threshold voltage.

[0380] If the oxide film 423 is a semiconductor, a large number of electrons are induced in the oxide film 423 . The oxide film 423 in which electrons are induced shields the electric field of the gate electrode 421, and the oxide semiconductor film 4 The electric field applied to 11 is weakened, resulting in a decrease in the on-state current of the transistor. Therefore, the thickness of the oxide film 423 is set to be thinner than that of the oxide semiconductor film 411 and to be 0.3 nm or more. It is preferable to set it to 10 nm or less.

[0381] The oxide films 409 and 423 and the oxide semiconductor film 411 were formed by the deposition model described in Embodiment 2. The oxide films 409 and 423 and the oxide semiconductor film 411 are non-single-crystal films. The non-single crystal structure may be, for example, the CAAC-OS shown in Embodiment 2 or a polycrystalline structure. Among non-single crystal structures, the amorphous structure is the most The defect density of the oxide film 4 is high, and the defect density of the CAAC-OS is the lowest. The oxide semiconductor film 411 and the oxide semiconductor film 423 are preferably CAAC-OS.

[0382] Note that the oxide films 409 and 423 and the oxide semiconductor film 411 each have an amorphous structure. region, microcrystalline structure region, polycrystalline structure region, CAAC-OS region, single crystal structure region The mixed film may have two or more kinds of materials. The mixed film may have, for example, an amorphous structure region, a microcrystalline structure region, or the like. The structure region, the polycrystalline structure region, the CAAC-OS region, and the single-crystal structure region are either two or more of the following: In some cases, the mixed film has a single layer structure with more than one type of region. region, microcrystalline structure region, polycrystalline structure region, CAAC-OS region, single crystal structure region The oxide film 409 and the oxide film 408 may have a stacked structure of two or more of these regions. The oxide semiconductor film 411 and the oxide film 423 have a microcrystalline structure, a CAAC-OS structure, and a CA Alternatively, the oxide film 409 may have a microcrystalline structure and a CAA layer structure. The oxide semiconductor film 411 and the oxide film 423 are stacked layers of the CAAC-OS. may be.

[0383] The pair of electrodes 415 and 416 may be the pair of electrodes 221 and 222 shown in the fourth embodiment. You can be there.

[0384] The gate insulating film 425 can be formed using the gate insulating film 217 described in Embodiment 4 as appropriate. Cut.

[0385] The gate electrode 421 can be formed using the gate electrode 215 described in Embodiment 4 as appropriate. .

[0386] The insulating films 427 and 429 are the oxide insulating film 223 and the oxide insulating film 222 described in Embodiment 4. 4 can be used as appropriate for the insulating film 427. Aluminum oxide film, hafnium oxide, yttrium oxide, etc. can be used. It is possible.

[0387] The oxide film 423, the gate insulating film 425, and the gate electrode 421 are arranged so that their side surfaces are substantially aligned. The insulating film 427 covers the surfaces of the pair of electrodes 415 and 416, the oxide film 423, and the gate electrode 424. When the multilayer film 4 is in contact with the gate insulating film 425 and the gate electrode 421, the multilayer film 4 This reduces the desorption of oxygen from 24, thereby reducing the variation in the electrical characteristics of transistors. At the same time, fluctuations in the threshold voltage can be suppressed.

[0388] Although the insulating films 427 and 429 have a stacked structure here, they may have a single layer structure.

[0389] The wirings 431 and 432 can be made of the same material as the pair of electrodes 415 and 416. Cut.

[0390] In the transistor described in this embodiment, the oxide film 423 and the gate insulating film 425 are formed at the edge portions thereof. The oxide film 423 is characterized by being substantially aligned with the edge of the gate electrode 421. The gate insulating film 425 is formed by forming the gate electrode 421 in FIG. 31(A) and then by etching with an acid. By etching the oxide film 417 and the gate insulating film 419, the number of photomasks can be increased. Therefore, the oxide film 423 and the gate insulating film 425 can be formed without heating.

[0391] In the transistor 400, etching residues from the formation of the gate electrode 421 are oxidized. Since it can be removed during the process of forming the gate insulating film 423 and the gate insulating film 425, It is possible to reduce the leakage current occurring between the port electrode 421 and the wiring 431, 432. is.

[0392] Next, a manufacturing method of the semiconductor device will be described with reference to FIGS.

[0393] As shown in FIG. 30(A), an oxide insulating film 403 serving as a base insulating film is formed on a substrate 401. An oxide film 405 and an oxide semiconductor film 407 are formed over the oxide insulating film 403.

[0394] Here, a glass substrate is used as the substrate 401 .

[0395] The oxide insulating film 403 can be formed by a sputtering method or a CVD method. do.

[0396] In addition, the oxide insulating film 403 was formed using a compound similar to the oxide insulating film 224 described in Embodiment 4. When forming an oxide insulating film containing more oxygen than the oxygen that satisfies the stoichiometric composition, the CVD method Alternatively, the film can be formed by a CVD method or a sputtering method. After forming an oxide insulating film by the ring method, etc., ion implantation, ion doping, plasma Oxygen may be added to the oxide insulating film by ionization treatment or the like.

[0397] Here, the oxide insulating film 403 is formed by sputtering an oxide insulating film having a thickness of 300 nm. A silicon membrane is used.

[0398] The oxide film 405 and the oxide semiconductor film 407 can be formed by a sputtering method, a coating method, a pulse laser deposition method, or the like. The layer can be formed by using a laser deposition method, a laser ablation method, or the like.

[0399] Here, the sputtering target has an atomic ratio of In:Ga:Zn=1:3:4. The oxide film 405 was formed by sputtering using In-Ga- A Zn oxide film is formed.

[0400] Next, heat treatment is performed to remove the oxide insulating film 403, the oxide film 405, and the oxide semiconductor film It is preferable that oxygen be transferred to the oxide film 405 and the oxide semiconductor film 407. It is preferable to remove impurities contained in 07.

[0401] The temperature of the heat treatment is typically 250°C or higher and lower than the substrate distortion point, or 300°C or higher and lower than 5°C. 50°C or less, or further, 350°C or more and 510°C or less.

[0402] The heat treatment can be carried out using an electric furnace, an RTA device, or the like. Therefore, heat treatment can be performed at a temperature above the strain point of the substrate for a short period of time. The processing time can be reduced.

[0403] Heat treatment is carried out in nitrogen, oxygen, or ultra-dry air (water content less than 20 ppm or less than 1 ppm) or less, or 10 ppb or less air), or rare gas (argon, helium, etc.) atmosphere It should be noted that if the above nitrogen, oxygen, ultra-dry air, or rare gas contains hydrogen, water, etc. It is preferable that this is not the case.

[0404] Here, after heat treatment at 450°C for 1 hour in a nitrogen atmosphere, Then, heat treatment is carried out at 450°C for 1 hour.

[0405] By this heat treatment, the oxide insulating film 403 serving as a base insulating film and the oxide film to which oxygen is added are A part of the oxygen contained in the oxide semiconductor film 409 is transferred to the oxide semiconductor film 407. The amount of oxygen vacancies in the oxide film 409 is reduced by the heat treatment. This process reduces the oxygen content.

[0406] Through the above steps, oxygen vacancies in the oxide semiconductor film can be reduced.

[0407] The heat treatment may be performed in a later step rather than in this step. By another heat treatment, part of the oxygen contained in the oxide insulating film 403 is converted into an oxide semiconductor. It may be moved to the conductive film 407. As a result, the number of heating steps can be reduced.

[0408] Next, a mask is formed over the oxide semiconductor film 407 by a photolithography process. Using the mask, the oxide film 409 and the oxide semiconductor film 407 are partly etched. As a result, the oxide film 409 and the oxide semiconductor film 411 were After this, the mask is removed. Note that in this etching process, the oxide insulating A portion of the film 403 may be etched. The oxide insulating film 403 is referred to as an oxide insulating film 413 .

[0409] Next, as shown in FIG. 30C, a pair of electrodes 415 and 416 are formed over the oxide semiconductor film 411. Form 6.

[0410] The method for forming the pair of electrodes 415 and 416 will be described below. First, a sputtering method, C A conductive film is formed by a VD method, a vapor deposition method, or the like. Next, a photolithography process is performed on the conductive film. Next, the conductive film is etched using the mask to form a pair of electrodes 41. 5, 416. After this, the mask is removed.

[0411] Here, a titanium film with a thickness of 50 nm, an aluminum film with a thickness of 400 nm, and a 10 Then, a 0 nm titanium film is deposited on the titanium film by sputtering. A mask is formed by a lithography process, and the titanium film, the aluminum film, The titanium film is then dry-etched to form a pair of electrodes 415 and 416 .

[0412] After forming the pair of electrodes 415 and 416, the substrate is washed to remove etching residues. By this cleaning treatment, the pair of electrodes 415 and 416 can be shortened. This cleaning process can prevent the tangles from forming. Alkaline solutions such as dilute hydrofluoric acid, oxalic acid, This can be done using an acidic solution such as phosphoric acid.

[0413] Next, as shown in FIG. 30(D), the oxide semiconductor film 411 and the pair of electrodes 415 and 41 An oxide film 417 is formed on the insulating film 6, and a gate insulating film 419 is formed on the oxide film 417.

[0414] The oxide film 417 can be formed in the same manner as the oxide film 409. The film 419 can be formed by sputtering, CVD, or the like.

[0415] Here, the sputtering target has an atomic ratio of In:Ga:Zn=1:3:4. The oxide film 417 was formed by sputtering using In-Ga-Z n-oxide film is formed.

[0416] Next, as shown in FIG. 31A, an oxide semiconductor film A gate electrode 421 is formed in the region overlapping with 411 .

[0417] The gate electrode 421 is formed by the following methods. First, sputtering, CVD, A conductive film is formed by evaporation or the like, and a mask is formed on the conductive film by photolithography. Next, the conductive film is partially etched using the mask to form a gate electrode 421. After this, the mask is removed.

[0418] The gate electrode 421 may be formed by electrolytic plating, printing, ink jet printing, or the like instead of the above-mentioned method. It may also be formed by a jet method or the like.

[0419] Here, a tantalum nitride film with a thickness of 15 nm and a tungsten film with a thickness of 135 nm are used. Next, a mask is formed by a photolithography process. The tantalum nitride film and the tungsten film are dry-etched using the mask to form a gate. A ground electrode 421 is formed.

[0420] Next, as shown in FIG. 31(B), the oxide film 417 is removed using the gate electrode 421 as a mask. The gate insulating film 419 is etched to form an oxide film 423 and a gate insulating film 425. Therefore, the oxide film 423 and the gate insulating film 424 can be formed without increasing the number of photomasks. In addition, the oxide film 423 and the gate insulating film 425 can be formed. The end portion substantially coincides with the end portion of the gate electrode 421 .

[0421] In the transistor 450, etching residues from the formation of the gate electrode 421 This can be removed during the process of forming the oxide film 423 and the gate insulating film 425. Therefore, a leakage current occurs between the gate electrode 421 and the wirings 431 and 432 to be formed later. It is possible to reduce

[0422] Next, as shown in FIG. 31(C), the pair of electrodes 415 and 416 and the gate electrode 421 are An insulating film 427 and an insulating film 429 are stacked in this order on the insulating film 427. Next, heat treatment is performed. After openings are formed in the insulating film 427 and the insulating film 429, wirings 431 and 432 are formed.

[0423] The insulating films 427 and 429 can be formed by a sputtering method, a CVD method, or the like as appropriate. By using an oxygen-blocking film as the insulating film 427, Since the desorption of oxygen from the multilayer film 424 can be reduced, the variations in the electrical characteristics of the transistors can be reduced. This can reduce adhesion and suppress fluctuations in threshold voltage.

[0424] Here, the insulating film 427 is an oxynitride silicon film having a thickness of 300 nm formed by plasma CVD. A silicon film is formed, and a 50 nm thick nitride silicon film is formed as an insulating film 429 by a sputtering method. Form a polymer membrane.

[0425] The heat treatment is typically performed at a temperature of 150°C or higher but lower than the substrate strain point, or 250°C or higher but lower than 500°C. Here, the temperature is set to 300°C or higher and 450°C or lower. Heat treatment is carried out at 350°C for 1 hour.

[0426] The wirings 431 and 432 can be formed in the same manner as the pair of electrodes 415 and 416. Alternatively, it can be formed by a damascene method.

[0427] By the above process, the multilayer film including the oxide semiconductor film has a low density of localized states and excellent electrical properties. It is possible to manufacture a transistor with the characteristics described above. Therefore, a highly reliable transistor with little fluctuation in electrical characteristics can be manufactured.

[0428] The configurations and methods shown in this embodiment may be applied to other embodiments and their modifications, as well as The present invention can be used in appropriate combination with the configurations and methods shown in the examples.

[0429] (Embodiment 10) Various films such as metal films, oxide semiconductor films, and inorganic insulating films disclosed in the above embodiments are and plasma CVD (Chemical Vapor Deposition) methods. However, it may be formed by other methods, for example, thermal CVD. As an example of CVD, MOCVD (Metal Organic Chemical Vapor Deposition) por Deposition) method and ALD (Atomic Layer Deposition) You can also use the tion method.

[0430] The thermal CVD method is a film formation method that does not use plasma, so defects can occur due to plasma damage. This has the advantage that no further processing is required.

[0431] In the thermal CVD method, the source gas and oxidant are simultaneously fed into a chamber, and the chamber is heated to atmospheric pressure. Alternatively, a film is formed by reacting the material near or on the substrate under reduced pressure and depositing the material on the substrate. You may go.

[0432] In addition, in the ALD method, the pressure inside the chamber is atmospheric or reduced, and the source gas for the reaction is The gases may be introduced into the chamber in sequence, and the film may be formed by repeating this gas introduction sequence. For example, by switching each switching valve (also called high-speed valve), two or more types of The above source gases are supplied to the chamber in order, and the first An inert gas (argon, nitrogen, etc.) is introduced simultaneously with or after the raw material gas. The second source gas is introduced. When an inert gas is introduced at the same time, the inert gas is It acts as a carrier gas, and even if an inert gas is introduced at the same time as the second source gas is introduced, Alternatively, instead of introducing an inert gas, the first source gas may be discharged by vacuum evacuation. After that, a second source gas may be introduced. The first source gas is adsorbed on the surface of the substrate to form a first layer. The first layer is deposited on the second layer by reacting with the second source gas introduced later. This process is repeated several times while controlling the gas introduction order until the desired thickness is achieved. By doing so, a thin film with excellent step coverage can be formed. The thickness can be precisely adjusted by changing the number of times the sequence is repeated. It is suitable for fabricating miniaturized FETs.

[0433] Thermal CVD methods such as MOCVD and ALD are disclosed in the embodiments described above. It is possible to form various films such as metal films, oxide semiconductor films, and inorganic insulating films. When forming an nGaZnO film, trimethylindium, trimethylgallium, and Dimethyl zinc is used. The chemical formula of trimethyl indium is In(CH3)3. The chemical formula of trimethylgallium is Ga(CH3)3. The chemical formula for lead is Zn(CH3)2. Using triethylgallium (chemical formula Ga(C2H5)3) instead of methylgallium It is also possible to use diethylzinc (chemical formula Zn(C2H5)2) instead of dimethylzinc. It is also possible.

[0434] For example, when forming a hafnium oxide film using a film forming apparatus that uses ALD, the solvent and a liquid containing a hafnium precursor compound (hafnium alkoxide solution, typically tetra The raw material gas is vaporized tetrachlorodibenzofuran (TDMAH) and the oxidizing agent is Two types of gases are used: tetrakisdimethylamidohafnium (Tetrakisdimethylamidohafnium) and ozone (O3). The chemical formula is Hf[N(CH3)2]4. Other material liquids include tetrakis(ethoxylated (ethylmethylamido) hafnium.

[0435] For example, when forming an aluminum oxide film using an ALD film forming device, A liquid containing a catalyst and an aluminum precursor compound (e.g., trimethylaluminum (TMA)) is added. Two types of gases are used: vaporized source gas and H2O as an oxidizing agent. The chemical formula for aluminum is Al(CH3)3. Other liquid materials include Tris( dimethylamido)aluminum, triisobutylaluminum, aluminum tris(2 ,2,6,6-tetramethyl-3,5-heptanedionate).

[0436] For example, when forming a silicon oxide film using a film forming device that uses ALD, Chlorodisilane is adsorbed onto the surface to be coated, removing the chlorine contained in the adsorbed material, and the oxidizing gas (O 2. Nitrous oxide (NO) radicals are supplied to react with the adsorbed material.

[0437] For example, when forming a tungsten film using an ALD deposition system, WF6 The initial tungsten film was formed by sequentially introducing BH gas and BH gas. The tungsten film is formed by simultaneously introducing B2H6 gas and H2 gas. Alternatively, SiH4 gas may be used.

[0438] For example, an oxide semiconductor film, such as In-Ga-Zn- When forming an O film, In(CH3)3 gas and O3 gas are introduced in sequence. Then, Ga(CH3)3 gas and O3 gas are introduced simultaneously to form a GaO layer. Then, Zn(CH3)2 and O3 gases are introduced simultaneously to form a ZnO layer. The order of these layers is not limited to this example. Alternatively, a mixed compound layer such as an O layer, an In-Zn-O layer, or a Ga-Zn-O layer may be formed. Instead of O gas, H2O gas obtained by bubbling with an inert gas such as Ar can be used. However, it is preferable to use O3 gas that does not contain H. Also, In(CH3)3 gas In addition, In(C2H5)3 gas may be used. Ga(C2H5)3 gas may be used. Also, instead of In(CH3)3 gas, In( C2H5)3 gas may be used, or Zn(CH3)2 gas may be used.

[0439] The configurations and methods shown in this embodiment may be applied to other embodiments and their modifications, as well as The present invention can be used in appropriate combination with the configurations and methods shown in the examples. [Example]

[0440] In this example, a sputtering target having an In-Ga-Zn oxide was used. In-Ga-Zn oxide film was formed. Atomic ratio of sputtering target and formed film and the crystal structure.

[0441] <Sample structure> First, the method for preparing the sample will be described.

[0442] In this example, a 100 nm thick In-Ga-Zn oxide film was formed on a quartz substrate. The material was prepared.

[0443] Here, a sputtering target having In-Ga-Zn oxide is used, and the flow rate is A mixed gas of oxygen and argon (1:2) was supplied into the deposition chamber as a sputtering gas. The pressure in the chamber was controlled to 0.4 Pa, and 200 W of DC power was supplied to the In-Ga-Zn oxide. A nitride film was formed.

[0444] The atomic ratio of metal elements contained in In-Ga-Zn oxide is In:Ga:Zn=1. In-Ga-Zn oxide films were deposited using a sputtering target with a ZnO / GaAs / ZnO ... The sample was designated as Sample 1. The substrate temperature was set to 200°C.

[0445] In addition, the atomic ratio of metal elements contained in In-Ga-Zn oxide is In:Ga:Zn=1 In-Ga-Zn oxide films were deposited using a sputtering target with a ZnO / GaAs / ZnO ... The sample was designated as Sample 2. The substrate temperature was set to 200°C.

[0446] The atomic ratio of metal elements contained in In-Ga-Zn oxide is In:Ga:Zn=1. In-Ga-Zn oxide films were deposited using a sputtering target with a ZnO / GaAs / ZnO ... The sample was designated as Sample 3. The substrate temperature was set to 200°C.

[0447] The atomic ratio of metal elements contained in In-Ga-Zn oxide is In:Ga:Zn=1. In-Ga-Zn oxide films were deposited using a sputtering target with a ZnO / GaAs / ZnO ... The sample was designated as Sample 4. The substrate temperature was set to 200°C.

[0448] The atomic ratio of metal elements contained in In-Ga-Zn oxide is In:Ga:Zn=1. In-Ga-Zn oxide films were deposited using a sputtering target with a ZnO / GaAs / ZnO ... The sample was designated as Sample 5. The substrate temperature was set to 200°C.

[0449] The atomic ratio of metal elements contained in In-Ga-Zn oxide is In:Ga:Zn=1. In-Ga-Zn oxide films were deposited using a sputtering target with a ZnO / GaAs / ZnO ... The sample was designated as Sample 6. The substrate temperature was set to 200°C.

[0450] The atomic ratio of metal elements contained in In-Ga-Zn oxide is In:Ga:Zn=1. In-Ga-Zn oxide films were formed using a sputtering target with a ratio of ZnO to Ga and ZnO to ZnO. The sample obtained is designated as Sample 7. The substrate temperature was set to 200°C.

[0451] The atomic ratio of metal elements contained in In-Ga-Zn oxide is In:Ga:Zn=0. In-Ga-Zn oxide films were deposited using a sputtering target with a ZnO / GaAs / ZnO ... The sample was designated as Sample 8. The substrate temperature was set to 200°C.

[0452] The atomic ratio of metal elements contained in In-Ga-Zn oxide is In:Ga:Zn=3. In-Ga-Zn oxide films were deposited using a sputtering target with a ZnO / GaAs / ZnO ... The sample was designated as Sample 9. The substrate temperature was set to 200°C.

[0453] The atomic ratio of metal elements contained in In-Ga-Zn oxide is In:Ga:Zn=1. In-Ga-Zn oxide films were deposited using a sputtering target with a ZnO / GaAs / ZnO ... The sample was designated as Sample 10. The substrate temperature was set to 300°C.

[0454] <xps> Next, in Samples 1 to 10, the In-Ga-Zn oxide film and Samples 1 to 10 The atomic ratio of the metal elements contained in the sputtering target used to form the 0 film was measured using X-ray photoelectron Spectroscopy (X-ray Photoelectron Spectroscopy:) Analysis Next, the atomic ratio of Ga to In and the atomic ratio of Zn to In were calculated. The numerical ratios are shown in FIG. 32. In FIG. 32, the parentheses indicate the spatula used for film formation. 4 shows the atomic ratio of In:Ga:Zn contained in the quenching target.

[0455] From Figure 32, the atomic ratio of Ga to In in the sputtering target and I Compared with the atomic ratio of Zn to n, the ratio of In to In in the deposited In-Ga-Zn oxide film is It can be seen that the atomic ratio of Ga to In and the atomic ratio of Zn to In are smaller.

[0456] <xrd> Next, the crystal structures of the In—Ga—Zn oxide films included in Samples 1 to 10 will be described. X-ray diffraction (XRD) measurements were carried out. In Sample 10, sputtering gas for forming the In-Ga-Zn oxide film Using two conditions, a mixed gas with a flow rate ratio of oxygen:argon = 1:2, or oxygen only, A sample was prepared.

[0457] Next, the results of X-ray diffraction measurement of the formed In-Ga-Zn oxide film are shown in Figs. 33 to 35. As representative examples, the X-ray diffraction measurement results of Sample 1, Sample 2, and Sample 3 are shown below. 33 to 35. In Samples 1, 2, and 3, the sputtering The In-Ga-Zn oxide film deposited using only oxygen as the annealing gas was measured.

[0458] In Fig. 33 to Fig. 35, (A) shows the XRD scan using the out-of-plane method. The results of measuring the spectrum are shown, with the vertical axis representing the X-ray diffraction intensity (arbitrary units) and the horizontal axis representing the diffraction angle. (B) The XRD spectrum was measured using the in-plane method. The vertical axis shows the X-ray diffraction intensity (arbitrary unit) and the horizontal axis shows the diffraction angle 2θ (deg .) is taken.

[0459] In Figures 33 to 35, h indicates a homologous structure, and s indicates a spinel structure. In addition, ( ) indicates the plane orientation of the crystal structure.

[0460] In Sample 1 shown in FIG. 33, the In—Ga—Zn oxide film has a spinel structure. On the other hand, Sample 2 shown in Figure 34 has a spinel structure and a homologous structure. 3. The In-Ga-Zn oxide film has a homologous structure.

[0461] 33 to 35, when a sputtering target with a larger Zn content than Ga was used, By forming the film using this method, it is possible to form an In-Ga-Zn oxide film with a homologous structure. be.

[0462] Next, based on the XPS measurement results shown in FIG. 32 and the X-ray diffraction measurement results shown in FIGS. 33 to 35, The In-Ga-Zn oxide film of each sample and the sputtering temperature used to prepare each sample are shown in Fig. A ternary phase diagram plotting the In, Ga, and Zn compositions of the get is shown in Figure 36. In the table, the numbers in parentheses indicate the compositions of In, Ga, and Zn contained in the sputtering target. Also, in Figure 36, the amount of oxygen is not taken into consideration.

[0463] In Figure 36, diamond markers indicate homologous structures, and square markers indicate spinel structures. The white markers indicate the composition of the sputtering target. The black markers indicate the In-Ga-Zn oxide films. Markers plotted according to film composition.

[0464] As can be seen from Figure 36, the In-Ga-Zn oxide film formed is It can be seen that this is different from the previous example.

[0465] The dashed line L1 indicates the composition of the metal elements Ga:Zn=2:1. The dashed line L2 indicates the composition of the trivalent gold. Group ions (M 3+ ) and divalent metal ions (M 2+ ) composition is M 3+ :M 2 +=2:1 do.

[0466] From Figure 36, in the region to the right of the dashed line L1, that is, the region where the amount of Ga increases relative to Zn, On the other hand, the dashed line L shows that an In-Ga-Zn oxide film with a spinel structure is formed. In the region to the left of 1, that is, the region where the amount of Zn increases relative to Ga, the homologous structure It can be seen that an In-Ga-Zn oxide film is formed.

[0467] Next, the composition of In, Ga, and Zn in the In-Ga-Zn oxide films included in Samples 1 to 9 was examined. The composition, atomic ratio of Zn to Ga (Zn / Ga), crystal structure, and the The composition of the sputtering target is shown in Table 2. The oxide film was formed using a deposition gas of 33 vol% oxygen (diluted with argon). The crystal structure of the film is measured using 33 vol% oxygen (diluted with argon) or The graph shows the measurement results for a film formed using 100 vol% oxygen as the film formation gas.

[0468] [Table 2]

[0469] From Table 2, in the sputtering target, the sputtering target having more Zn than Ga The In-Ga-Zn oxide film formed using the target has a homologous structure. It can be seen that...

[0470] In addition, from Table 2, the ratio of Zn to Ga in the formed In-Ga-Zn oxide film was It is found that films with a ratio (Zn / Ga) greater than 0.5 have a homologous structure.

[0471] From the above, it is considered that the film is formed using a sputtering target with a larger Zn content than Ga. By doing so, it is possible to form an In-Ga-Zn oxide film with a homologous structure.

[0472] <tem> Next, the atomic arrangement of the cross sections of Sample 2 and Sample 3 was observed using a transmission electron microscope. Observed using a TEM (Electron Microscope) A cross-sectional observation image (bright field image) is shown in Figure 37. Here, the accelerating voltage was 300 kV and the magnification was 8. The vicinity of the surface of the In-Ga-Zn oxide film of each sample was observed at a magnification of 100,000 times. In Figure 37, the values ​​in parentheses indicate the amounts of In, Ga, and Zn contained in the sputtering target. Represents the composition.

[0473] FIG. 37(A) is a cross-sectional observation image of sample 2, and is an enlarged cross-sectional observation image of a part of FIG. 37(A). FIG. 37(B) shows the cross-sectional observation image of sample 3. An enlarged cross-sectional observation image of a portion of the sample is shown in FIG. 37(D).

[0474] As shown in Figure 37, Sample 2 and Sample 3 have a regular atomic arrangement parallel to the top surface. This indicates that the In-Ga-Zn oxide formed in Samples 2 and 3 The oxide film was found to be a CAAC-OS film.

[0475] <haadf-stem> Next, the atomic arrangement of the cross sections of Sample 2 and Sample 3 was examined using a high-angle scattering annular dark-field scanning transmission electron microscope ( HAADF-STEM:High-Angle Annular Dark Field Scanning Transmission Electron Microscope The cross-sectional image obtained by observation using an accelerating voltage of 200 py is shown in Figure 38. The In-Ga-Zn oxide film on each sample was observed at a voltage of 100 kV and a magnification of 8 million times. Ta.

[0476] FIG. 38(A) is a cross-sectional observation image obtained by observing sample 2, and FIG. 38(B) is a cross-sectional observation image obtained by observing sample 2. This is a cross-sectional image obtained by observing 3.

[0477] In HAADF-STEM images, contrast proportional to the square of the atomic number is obtained. Therefore, brighter points indicate heavier atoms. The bright points indicated by the arrows are In, and the dark points between them are Ga or Zn. Since Zn and Zn have almost the same mass, it is difficult to distinguish them. No element is observed.

[0478] In FIG. 38(A), In, Ga, and Zn are arranged in parallel. In addition, two or three layers of Ga or Zn exist between the In indicated by the arrows. .

[0479] In FIG. 38(B), In, Ga, and Zn are arranged in parallel. In addition, three or four layers of Ga or Zn exist between the In indicated by the arrows. .

[0480] As can be seen from Figure 38, layers containing In are periodically arranged with multiple layers containing Ga or Zn between them. Therefore, the In-Ga-Zn oxide films of Sample 2 and Sample 3 have a homologous structure. That is, the results are obtained by using a sputtering target with a larger Zn content than Ga. By using this method, it is possible to form an In-Ga-Zn oxide film with a homologous structure. . [Example]

[0481] In this example, sputtering targets having In-Ga-Zn oxides of different compositions were used. Using a ZnO film, we formed stacked films of In-Ga-Zn oxides with different compositions. The bond diagram and crystal structure are explained.

[0482] Here, Samples 1 to 4, Sample 6, Sample 7, and Sample 10 shown in Example 1 were used. In Samples 1 to 4, 6, 7, and 10, silicon was used as the substrate. A silicon wafer was used.

[0483] In addition, the In-Ga-Zn oxide film (thickness 20 nm), an In-Ga-Zn oxide film (thickness 15 nm) formed on sample 10, and a A sample was prepared by laminating an In-Ga-Zn oxide film (5 nm thick) formed on the substrate. This sample is designated as Sample 11.

[0484] In addition, the In-Ga-Zn oxide film (thickness 20 nm), the In-Ga-Zn oxide film (thickness 15 nm) formed on sample 10, and sample 2 A sample was prepared by laminating an In-Ga-Zn oxide film (thickness 10 nm) formed on the substrate. This sample was designated as Sample 12.

[0485] In addition, the In-Ga-Zn oxide film (thickness 20 nm), the In-Ga-Zn oxide film (thickness 10 nm) formed on sample 10, and sample 3 A sample was prepared by laminating an In-Ga-Zn oxide film (15 nm thick) on the substrate. This sample was designated as Sample 13.

[0486] <Band diagram> Next, the layers formed on Samples 1 to 4, 6, 7, and 10 prepared in Example 1 were The energy difference between the conduction band edge Ec and the valence band edge Ev of the In-Ga-Zn oxide film is That is, the energy gap Eg was measured using a spectroscopic ellipsometer. Ultraviolet Photoelectron Spectrometry (UPS) spectroscopy) to determine the energy difference between the vacuum level Evac and the top of the valence band Ev, That is, the ionization potential Ip was measured. Next, the ionization potential Ip and the energy By calculating the difference between the vacuum level Evac and the conduction band edge Ec, The energy difference, i.e., the electron affinity χ, was calculated. The resulting band diagram is shown in Figure 39. Shown below.

[0487] As shown in FIG. 39, Samples 1 to 4, Sample 6, and Sample 7 are superior to Sample 10. The electron affinity χ is small, and the energy difference is between 0.2 eV and 0.4 eV. .

[0488] Next, the band diagrams of Samples 12 and 13 will be explained with reference to FIG. .

[0489] The ionization potential Ip and energy gap Eg of sample 12 were measured. The band diagram is shown in FIG. 40(A). The ionization potential Ip and energy The band diagram obtained by measuring the energy gap Eg is shown in Figure 40(B). In 40, the horizontal axis represents the sputtering time, and the vertical axis represents the valence band upper limit Ev and the vacuum level. The energy difference between Evac (Ev-Evac), and the electric band edge Ec and the vacuum level Evac The energy difference (Ec-Evac) is shown.

[0490] Here, an In-Ga-Zn oxide film is formed on the surface by sputtering with argon ions. UV photoelectron spectroscopy was performed to determine the In-Ga-Zn content of Samples 12 and 13. The energy difference between the vacuum level Evac and the top of the valence band Ev of the oxide film, i.e., the ionization potential The electrical charge Ip was measured and plotted. The energy difference between the lower end of the conduction band Ec and the upper end of the valence band Ev was also measured. The energy difference, i.e., the energy gap Eg, was measured using a spectroscopic ellipsometer. By calculating the difference between the ionization potential Ip and the energy gap Eg, the vacuum level Ev The energy difference between ac and the bottom edge of the conduction band Ec, that is, the electron affinity χ, was calculated. The upper edge Ev and the lower edge Ec of the conduction band are plotted.

[0491] As shown in FIG. 40(A), the In-Ga-Zn oxide film formed on Sample 2 and the In-Ga-Zn oxide film formed on Sample 10 The difference in energy between the conduction band minimum Ec and the In-Ga-Zn oxide film is 0.2 eV. In addition, the In-Ga-Zn oxide film formed in sample 10 was interposed between the In-Ga-Zn oxide films formed in sample 2. By providing the n-Ga-Zn oxide film, the In-Ga-Zn oxide formed on the sample 10 It can be seen that the membrane forms wells.

[0492] As shown in FIG. 40(B), the In-Ga-Zn oxide film formed on Sample 3 and the In-Ga-Zn oxide film formed on Sample 10 The difference in energy between the conduction band minimum Ec and the In-Ga-Zn oxide film is 0.2 eV. In addition, the In-Ga-Zn oxide film formed in sample 10 was interposed between the In-Ga-Zn oxide films formed in sample 3. By providing the n-Ga-Zn oxide film, the In-Ga-Zn oxide formed on the sample 10 It can be seen that the membrane forms wells.

[0493] <tem> Next, the atomic arrangement of the cross sections of Samples 11 to 13 was observed using a transmission electron microscope. Observation using a Transmission Electron Microscope (TEM) The cross-sectional observation images (bright field images) are shown in Figures 41 to 43. Here, the accelerating voltage was 300 kV. The In-Ga-Zn oxide film on each sample was photographed at a magnification of 2 million and 4 million times. was observed.

[0494] Figure 41 shows cross-sectional observation images of Samples 11 to 13 at a magnification of 2,000,000 times, and Figure 42 shows cross-sectional observation images of Samples 11 to 13 at a magnification of 2,000,000 times. 43 shows cross-sectional observation images of Samples 11 to 13 at a magnification of 4,000,000 times. 41 to 43 are enlarged cross-sectional observation images of the In- The Ga-Zn oxide films are designated S1, S2, and S3 in this order. indicates the vicinity of the interface between S1 and S2.

[0495] As shown in FIG. 41, in Samples 12 and 13, different sputtering targets were used. The crystallinity is uniform in the films S1 to S3 formed using the SiO2 solution.

[0496] As shown in FIG. 42, in Sample 11, no crystallinity was confirmed in S1, and only S2 On the other hand, in Samples 12 and 13, crystallinity was confirmed in S1 to S3. Crystallinity was confirmed.

[0497] As shown in FIG. 43, the In-Ga-Zn oxide films of Samples 12 and 13 have a flat top surface. It was found that the atomic arrangement is regular in the row. This indicates that the In formed in Samples 12 and 13 is a regular atomic arrangement. It was found that S1 and S2 contained in the Ga-Zn oxide film were CAAC-OS films. It is also clear that there is little crystal distortion at the interface between S1 and S2.

[0498] By using a sputtering target with a larger Zn content than Ga, It is possible to form an In-Ga-Zn oxide film with a logarithmic structure. By using a sputtering target with a large n composition, the CAAC-OS film It is also possible to deposit multiple films using sputtering targets with different compositions. In the In-Ga-Zn oxide film with several layers stacked, the crystal structure throughout the film is uniform. and there is little crystal distortion at the interface between the layers.

[0499] Therefore, the In-Ga-Zn oxide film fabricated in this example can reduce the number of defects. It is possible to reduce the fluctuation of the electrical characteristics of semiconductor devices fabricated using In-Ga-Zn oxide films. This can reduce the load and improve reliability.< / tem> < / tem> < / xrd> < / xps>

Claims

1. a first conductive layer having a region that functions as a gate electrode; a first insulating layer having a region functioning as a gate insulating film located above the first conductive layer; a first oxide layer having a region overlying the first insulating layer; a second oxide layer having a region located above the first oxide layer; a first electrode layer and a second electrode layer having regions located above the second oxide layer; an insulating layer having a region located above the second oxide layer; the first oxide layer and the second oxide layer contain In, Ga, and Zn; The semiconductor device, wherein the atomic ratio of Ga to In in the second oxide layer satisfies Ga>In, and the atomic ratio of Zn to Ga satisfies Zn>Ga.

2. In claim 1, the first oxide layer has a microcrystalline structure; Semiconductor device.

3. In claim 1, When the second oxide layer is analyzed by an out-of-plain method using an X-ray diffractometer, a peak is detected. Semiconductor device.

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