Method for evaluating heat treatment environment and silicon carbide substrate

Abstract

The present invention provides a new technique for evaluating a heat treatment environment. The present invention is a method for evaluating a heat treatment environment, comprising: an image acquisition step (S20) of acquiring an image (I) by irradiating an electron beam (PE) at an incident angle (θ) inclined with respect to a normal line (N) of a {0001} plane of a SiC substrate (10) after heat treatment; and an environment evaluation step (S30) of evaluating a heat treatment environment (HE) of the SiC substrate (10) based on contrast information (C) of the image (I).

Description

Technical Field

[0001] This invention relates to a method for evaluating the heat treatment environment and a silicon carbide substrate. Background Technology

[0002] Compared to silicon (Si) or gallium arsenide (GaAs) semiconductor devices, silicon carbide (SiC) semiconductor devices can achieve higher voltage withstand, higher efficiency, and higher temperature operation. Therefore, development towards industrialization is underway.

[0003] To improve the yield or quality of SiC semiconductor devices, a method for controlling the step-plateau structure of SiC substrates has been proposed (see Patent Document 1 and Patent Document 2).

[0004] For example, Patent Document 1 describes a method for manufacturing SiC epitaxial wafers by controlling the surface shape of the SiC substrate using the concentration ratio C / Si of SiH4 gas and C3H8 gas simultaneously supplied to the SiC substrate.

[0005] Furthermore, Patent Document 2 describes a surface treatment method for SiC substrates that controls the surface shape of the SiC substrate after etching by controlling the etching mode and etching depth determined at least based on the etching rate.

[0006] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2011-49496 Patent Document 2: Japanese Re-evaluation No. 2016 / 079984 Summary of the Invention

[0007] The problem the invention aims to solve However, the step-plateau structure of the heat-treated SiC substrate is determined by the heat treatment environment (hereinafter referred to as the heat treatment environment). Therefore, whether the desired step-plateau structure can be reproduced depends on whether the desired heat treatment environment can be reproduced.

[0008] Since semiconductor substrates are heat-treated at temperatures exceeding several thousand degrees Celsius, it is difficult to directly evaluate the heat treatment environment. Therefore, the approach is to indirectly evaluate the heat treatment environment by making the heat treatment conditions (concentration ratio of raw material gases, heating temperature, growth rate, etching rate, etc.) correspond to the heat-treated step-plateau structure (AFM image, etc.). (Refer to Patent Document 1 or Patent Document 2)

[0009] However, it is known that the stepped-plateau structure after heat treatment can be affected by inherent crystal defects in the SiC substrate or by processing-induced altered layers introduced during substrate fabrication. Therefore, a problem exists: it is difficult to properly evaluate the heat treatment environment.

[0010] In view of the above problems, the problem to be solved by the present invention is to provide a new technology for evaluating the heat treatment environment.

[0011] means for solving problems The present invention, which addresses the above problems, is a method for evaluating a heat treatment environment, comprising: The image acquisition step involves acquiring an image by incident an electron beam at an incident angle tilted relative to the normal of the {0001} plane of the heat-treated silicon carbide substrate; and The environmental assessment step evaluates the thermal processing environment of the silicon carbide substrate based on the contrast information of the image.

[0012] In this way, by evaluating the thermal processing environment based on the contrast information of the image obtained from the silicon carbide substrate, the thermal processing environment experienced by the silicon carbide substrate can be appropriately evaluated.

[0013] Additionally, in this specification, in the Miller index markings, "-" represents a horizontal bar, followed by the index.

[0014] In a preferred embodiment of the present invention, the environmental assessment step is a step of evaluating the contrast information displayed on the platform of the silicon carbide substrate.

[0015] In a preferred embodiment of the present invention, the environmental evaluation step is a step of evaluating the contrast information displayed along the <1-100> direction.

[0016] In a preferred embodiment of the present invention, the contrast information has multiple brightness information reflecting the stacking direction of atoms, and the environmental assessment step includes a brightness comparison step of comparing the multiple brightness information.

[0017] In a preferred embodiment of the present invention, the contrast information has first brightness information reflecting the stacking direction of atoms and second brightness information that can be compared with the first brightness information, and the environmental assessment step includes a brightness comparison step of comparing the first brightness information and the second brightness information.

[0018] In a preferred embodiment of the present invention, the image acquisition step is a step of incidenting an electron beam inclined in the <1-100> direction onto the silicon carbide substrate.

[0019] In a preferred embodiment of the present invention, the environmental assessment step is a step of evaluating whether the heat treatment environment is a Si-SiC equilibrium vapor pressure environment or a C-SiC equilibrium vapor pressure environment.

[0020] In a preferred embodiment of the present invention, the environmental evaluation step is a step of evaluating whether the heat treatment environment is a Si-rich environment or a C-rich environment.

[0021] In a preferred embodiment of the present invention, the silicon carbide substrate has a hexagonal crystal structure.

[0022] In a preferred embodiment of the present invention, a heat treatment step is included, wherein a step-plateau structure is formed by heat treating a silicon carbide substrate in a heat treatment environment.

[0023] In a preferred embodiment of the present invention, the silicon carbide substrate includes: a step-forming portion that becomes a step generation source during heat treatment, and an environmental assessment region that forms a step-plateau structure caused by the step-forming portion, wherein the environmental assessment step is a step of evaluating the environmental assessment region.

[0024] In a preferred embodiment of the present invention, the step-forming portion is a through dislocation.

[0025] In a preferred embodiment of the present invention, the step forming portion is a machined hole.

[0026] In a preferred embodiment of the present invention, the environmental assessment area is a machined recess.

[0027] Furthermore, the present invention also relates to a silicon carbide substrate. Specifically, the present invention, which solves the above-mentioned problems, is a silicon carbide substrate comprising: a step-forming portion that becomes a source of step generation during heat treatment; and an environmental assessment region forming a step-plateau structure caused by the step-forming portion.

[0028] In a preferred embodiment of the present invention, the step-forming portion is a through dislocation.

[0029] In a preferred embodiment of the present invention, the step forming portion is a machined hole.

[0030] In a preferred embodiment of the present invention, the environmental assessment area is a machined recess.

[0031] The effects of the invention Based on the disclosed technology, new technologies for evaluating heat treatment environments can be provided.

[0032] Other technical problems to be solved, features and advantages will become apparent from reading the detailed embodiments described below in conjunction with the accompanying drawings and claims. Attached Figure Description

[0033] Figure 1 This is a schematic diagram illustrating the steps of the method for evaluating the heat treatment environment according to the embodiment.

[0034] Figure 2 This is a diagram illustrating the heat treatment steps according to the implementation method.

[0035] Figure 3 This is a diagram illustrating the heat treatment steps according to the implementation method.

[0036] Figure 4 This is a schematic diagram of the crystal structure of 4H-SiC.

[0037] Figure 5 This is a schematic diagram of the crystal structure of 4H-SiC.

[0038] Figure 6 This is a diagram illustrating the image acquisition steps according to the embodiment.

[0039] Figure 7 This is a diagram illustrating the image acquisition steps according to the embodiment.

[0040] Figure 8 This is a diagram illustrating the SiC substrate according to an embodiment.

[0041] Figure 9 This is a diagram illustrating the SiC substrate according to an embodiment.

[0042] Figure 10 This is a diagram illustrating the SiC substrate according to an embodiment. Detailed Implementation

[0043] Hereinafter, a preferred embodiment of the heat treatment environment evaluation method and the SiC substrate according to the present invention will be described in detail with reference to the accompanying drawings. The scope of the present invention is not limited to the embodiments shown in the drawings, and appropriate modifications can be made within the scope of the claims. Furthermore, in the following description of the embodiments and the accompanying drawings, the same reference numerals are used to denote the same structures, and repeated descriptions are omitted.

[0044] Evaluation Methods for Heat Treatment Environment Figure 1This is a schematic diagram illustrating the steps of the method for evaluating the heat treatment environment according to an embodiment. The method for evaluating the heat treatment environment according to this embodiment includes: a heat treatment step S10, in which a step-plateau structure is formed by heat treating a hexagonal SiC substrate 10 under a heat treatment environment HE; an image acquisition step S20, in which an electron beam is incident at an incident angle θ that is tilted relative to the normal N of the {0001} plane of the heat-treated SiC substrate 10 to acquire an image I; and an environment evaluation step S30, in which the heat treatment environment HE of the SiC substrate 10 is evaluated based on the contrast information C of the image I.

[0045] The method for evaluating the heat treatment environment according to the present invention is characterized in that the heat treatment environment HE of the heat treatment step S10 is evaluated based on the contrast information C of an image I obtained by using an electron beam PE incident from a direction inclined relative to the normal N of the SiC substrate 10.

[0046] Specifically, an image I containing multiple brightness information (contrast information C) reflecting the stacking direction of atoms on the surface of the SiC substrate 10 is obtained using electron beam PE, and the multiple brightness information appearing in the image I is compared, thereby determining the heat treatment environment HE experienced by the SiC substrate 10.

[0047] As a result, it can be evaluated whether the heat treatment environment HE experienced by the SiC substrate 10 is a Si-SiC equilibrium vapor pressure environment or a C-SiC equilibrium vapor pressure environment. Furthermore, it can be evaluated whether the heat treatment environment HE experienced by the SiC substrate 10 is a Si-rich environment or a C-rich environment.

[0048] The "SiC-Si vapor pressure environment" in this specification refers to the vapor pressure environment when SiC (solid phase) and Si (liquid phase) reach phase equilibrium through the gas phase. This SiC-Si equilibrium vapor pressure environment is formed, for example, by heat treatment of a quasi-enclosed space with a Si / C atomic ratio exceeding 1.

[0049] Specifically, when a SiC substrate and a Si vapor supply source (Si substrate or Si particles, etc.) with a stoichiometric ratio of 1:1 are arranged inside a SiC container, the Si / C atomic ratio inside the container exceeds 1. By heating such a container, a SiC-Si vapor pressure environment can be formed inside the container.

[0050] The "SiC-C equilibrium vapor pressure environment" in this specification refers to the vapor pressure environment when SiC (solid phase) and C (solid phase) reach phase equilibrium through the gas phase. This SiC-C equilibrium vapor pressure environment is formed, for example, by heat treatment of a quasi-enclosed space with a Si / C atomic ratio of less than 1.

[0051] Specifically, when a SiC substrate with a stoichiometric ratio of 1:1 is placed inside a SiC container, the Si / C atomic ratio inside the container is 1. Alternatively, a C vapor supply source (C particles, etc.) can be configured to make the Si / C atomic ratio less than 1. By heating such a container, a SiC-C vapor pressure environment can be formed inside the container.

[0052] In addition, the SiC-Si equilibrium vapor pressure environment and SiC-C equilibrium vapor pressure environment mentioned in this specification include near-thermal equilibrium vapor pressure environments that satisfy the relationship between growth rate and growth temperature derived from the theoretical thermal equilibrium environment.

[0053] In this specification, "quasi-closed space" refers to a space capable of being evacuated within the container but capable of containing at least a portion of the vapor generated within the container. This quasi-closed space can be formed inside the container.

[0054] Furthermore, the method for evaluating the heat treatment environment according to the present invention can evaluate the heat treatment environment HE experienced by the SiC substrate 10 by evaluating the pre-heat-treated SiC substrate 10. Therefore, the method for evaluating the heat treatment environment according to the present invention only needs to include at least the image acquisition step S20 and the environment evaluation step S30.

[0055] The steps according to the preferred embodiments of the present invention will be described in detail below.

[0056] <Heat Treatment Steps> The heat treatment step S10 is a step of heat-treating the SiC substrate 10 in a heat treatment environment HE, which is the object of evaluation of the present invention. Specifically, the heat treatment step S10 is a step of forming a step-plateau structure that reflects the heat treatment environment HE by heat-treating the hexagonal SiC substrate 10 in a heat treatment environment HE.

[0057] Examples of methods for heat treatment step S10 include crystal growth method, which forms a growth layer on SiC substrate 10, and etching method, which etches the SiC substrate 10.

[0058] As crystal growth methods, for example, chemical vapor deposition (CVD), physical vapor transport (PVT), metastable solvent epitaxy (MSE), and CPVT (confined physical vapor transport) crystal growth methods (see below) can be employed. Figure 2 ).

[0059] As etching methods, for example, hydrogen etching using hydrogen as the etching gas, Si vapor pressure etching (SiVE) heated in a Si atmosphere, and CPVT etching (described later) can be employed. Figure 3 ).

[0060] The following is for reference Figure 2 and Figure 3 The method of heat treatment step S10 according to the preferred embodiment is described in detail.

[0061] According to the preferred embodiment, heat treatment step S10 involves housing the SiC substrate 10 and SiC material 20 inside the heat treatment container 30 and heating them to form a temperature gradient inside the heat treatment container 30. Furthermore, it is desirable that the heat treatment container 30 is housed within a high-melting-point container 40.

[0062] In this embodiment, there may be an embodiment in which crystal growth is performed on the SiC substrate 10 based on the positional relationship between the SiC substrate 10 and the SiC material 20 and the direction of the temperature gradient, and an embodiment in which etching is performed.

[0063] Figure 2 This is an explanatory diagram illustrating an embodiment of crystal growth on a SiC substrate 10 using the CPVT crystal growth method. In this crystal growth embodiment, the SiC substrate 10 and the SiC material 20 are arranged opposite each other, and a temperature gradient is applied to heat the substrate with the SiC substrate 10 as the low-temperature side and the SiC material 20 as the high-temperature side. Using this temperature gradient, Si and C elements are transported from the SiC material 20 to the SiC substrate 10, and a growth layer is grown on the SiC substrate 10.

[0064] Figure 3 This is an explanatory diagram illustrating an embodiment of etching a SiC substrate 10 using the CPVT etching method. In this etching embodiment, the SiC substrate 10 and the SiC material 20 are arranged opposite each other, and a temperature gradient is applied to heat the substrate by means of a low-temperature side (SiC material 20) and a high-temperature side (SiC substrate 10). Using this temperature gradient, Si and C elements are transported from the SiC substrate 10 to the SiC material 20, thereby etching the SiC substrate 10.

[0065] In addition, Figure 2 and Figure 3 In this case, the positions of the SiC substrate 10 and the SiC material 20 are swapped. Alternatively, the positions of the SiC substrate 10 and the SiC material 20 can be reversed while the direction of the temperature gradient is reversed, thereby reversing the transport direction of Si and C elements.

[0066] exist Figure 2 (a) and Figure 3In (a) of this paper, an embodiment is shown in which a SiC substrate 10 and a SiC material 20 are arranged in a quasi-closed space with a Si / C atomic ratio of more than 1 and subjected to heat treatment. In this way, by heat treating the SiC substrate 10 in a quasi-closed space with a Si / C atomic ratio of more than 1, a step-plateau structure corresponding to the Si-SiC equilibrium vapor pressure environment (heat treatment environment HE) is formed on the surface of the SiC substrate 10.

[0067] exist Figure 2 (b) and Figure 3 In (b) of the diagram, an embodiment is shown in which a SiC substrate 10 and a SiC material 20 are arranged in a quasi-closed space with a Si / C atomic ratio of 1 or less and then subjected to heat treatment. In this way, by heat treating the SiC substrate 10 in a quasi-closed space with a Si / C atomic ratio of 1 or less, a step-plateau structure corresponding to the C-SiC equilibrium vapor pressure environment (heat treatment environment HE) is formed on the surface of the SiC substrate 10.

[0068] Hereinafter, the SiC substrate 10, SiC material 20, heat treatment container 30, and high melting point container 40 of the heat treatment step S10 according to the preferred embodiment will be described in detail.

[0069] (SiC substrate) The SiC substrate 10 can be exemplified as a substrate formed by processing single-crystal SiC into a thin plate shape. Specifically, it can be exemplified as a SiC wafer formed by slicing a SiC ingot produced by methods such as sublimation into a disk shape. In addition, more than 200 polytypes of single-crystal SiC have been identified. Among the polytypes of the hexagonal crystal system, which have a high probability of occurrence and are important in applications, 4H-SiC and 6H-SiC are known.

[0070] Figure 4 A schematic diagram of the crystal structure of 4H-SiC is shown. Figure 4 (a) shows the crystal structure of 4H-SiC as observed from the <11-20> direction. Figure 4 (b) shows the crystal structure of 4H-SiC as viewed from the

[0001] direction.

[0071] Furthermore, the markings "A, B, C" in the figure represent the occupancy positions of the three types of atoms in the hexagonal close-packed structure (equivalent to Si-C pairs). The crystal structure of 4H-SiC is shown in the figure. Figure 4 In (a), the stacking of atoms at positions A and C corresponds to a zinc-blend structure, and the stacking of atoms at position B corresponds to a wurtzite structure.

[0072] Figure 5A schematic diagram of a step-plateau structure formed on the surface of a SiC substrate 10 is shown. This step-plateau structure is a stepped structure consisting of alternating steps 101 (as steps above 1 molecular layer) and platforms 102 (as flat areas exposed on the {0001} surface). In step 101, a 1 molecular layer (0.25 nm) is the minimum height (smallest unit), and multiple layers are overlapped from this 1 molecular layer to form various step heights. Figure 5 The image shows a step 101 consisting of two molecular layers (0.5 nm: half cell) of 4H-SiC.

[0073] (SiC material) The SiC material 20 is composed of SiC, which, by being heated relative to the SiC substrate 10, can receive or exchange Si and C elements with the SiC substrate 10. In an embodiment, as... Figure 2 and Figure 3 As shown, the SiC substrate 10 and the SiC material 20 made of SiC substrate are positioned opposite each other by the retainer 34. Alternatively, a container made of SiC (heat treatment container 30) or a container in which a portion of the container is made of SiC may be used as the SiC material 20. Furthermore, any polymorph of the SiC material 20 may be used, including polycrystalline SiC.

[0074] (Heat treatment container) The heat treatment container 30 can be constructed as long as it generates vapor pressures of gaseous species containing Si and gaseous species containing C within its internal space during heat treatment. For example, structures with SiC exposed inside the container or structures where SiC material (such as a SiC substrate) is separately disposed within the heat treatment container 30 can be shown. Furthermore, embodiments using a heat treatment container 30 made of materials other than SiC, where the material generating Si and C elements is housed inside the container, are also possible.

[0075] In a preferred embodiment, the entire heat treatment container 30 is made of polycrystalline SiC. By heating the heat treatment container 30 made of polycrystalline SiC in this way, an atmosphere containing Si and C elements can be generated inside the container (a quasi-enclosed space).

[0076] Ideally, the environment within the heat treatment vessel 30 after heat treatment should be a vapor pressure environment of a mixture of gaseous species containing Si and gaseous species containing C. Examples of gaseous species containing Si include Si, Si2, Si3, Si2C, SiC2, and SiC. Examples of gaseous species containing C include Si2C, SiC2, SiC, and C. That is, the heat treatment vessel 30 should be in a state where SiC-based gases exist.

[0077] like Figure 2 and Figure 3 As shown, the heat treatment container 30 is a fitted container comprising an upper container 31 and a lower container 32 that can be fitted together. A small gap 33 is formed at the fitting portion of the upper container 31 and the lower container 32, which allows for venting (vacuuming) of the heat treatment container 30 through the gap 33. That is, the interior of the heat treatment container 30 becomes a quasi-closed space.

[0078] Furthermore, the heat treatment container 30 may also have a retaining member 34 that holds the SiC substrate 10 or SiC material 20 in a hollow state. The retaining member 34 can be any structure capable of holding at least a portion of the SiC substrate 10 in the hollow state of the heat treatment container 30. For example, conventional support methods such as one-point support, three-point support, structures supporting the outer periphery, or structures clamping a portion can certainly be used. A high-melting-point material can be used as the material for the retaining member 34.

[0079] Alternatively, the retainer 34 may not be configured according to the shape of the SiC material 20. That is, if the heat treatment container 30 itself is made of SiC material 20, the SiC substrate 10 may be disposed on the bottom surface of the lower container 32 (without the retainer 34).

[0080] Moreover, such as Figure 2 (a) and Figure 3 As shown in (a), the heat treatment container 30 may also have a Si vapor supply source 35. The Si vapor supply source 35 can be any structure that generates Si vapor within the heat treatment container 30 during heating, for example, solid Si (Si particles such as single-crystal Si wafers or Si powder) or Si compounds.

[0081] (High melting point container) The high-melting-point container 40 can be any structure that houses the heat treatment container 30 and generates a vapor pressure (a Si-containing atmosphere) of gaseous species containing Si in the internal space during heat treatment. According to the embodiment, the Si-containing atmosphere within the high-melting-point container 40 is formed using a Si vapor supply source 44. Furthermore, any method capable of forming a Si-containing atmosphere around the heat treatment container 30 can naturally be used.

[0082] The high-melting-point container 40 is configured to contain a high-melting-point material. Examples include C as a general heat-resistant component, W, Re, Os, Ta, Mo as high-melting-point metals, Ta9C8, HfC, TaC, NbC, ZrC, Ta2C, TiC, WC, MoC as carbides, HfN, TaN, BN, Ta2N, ZrN, TiN as nitrides, HfB2, TaB2, ZrB2, NB2, TiB2 as borides, and polycrystalline SiC.

[0083] The high-melting-point container 40, like the heat treatment container 30, is a fitted container comprising an upper container 41 and a lower container 42 that can fit together, configured to house the heat treatment container 30. A small gap 43 is formed at the fitting portion of the upper container 41 and the lower container 42, configured to allow venting (vacuuming) of the high-melting-point container 40 through the gap 43.

[0084] Preferably, the high-melting-point container 40 has a Si vapor supply source 44 capable of supplying a vapor pressure of a gaseous species containing Si to the high-melting-point container 40. The Si vapor supply source 44 can be any structure that generates Si vapor within the high-melting-point container 40 upon heating. Examples of the Si vapor supply source 44 include solid Si (Si particles such as single-crystal Si wafers or Si powder) or Si compounds.

[0085] According to the embodiment, heat treatment step S10 uses TaC as the material of the high-melting-point container 40 and tantalum silicide as the Si vapor supply source 44. Figure 2 and Figure 3 As shown, a tantalum silicide layer is formed on the inner side of the high-melting-point container 40. The container is configured such that a Si vapor pressure environment is created by supplying Si vapor from the tantalum silicide layer into the container during heating.

[0086] <Image Acquisition Steps> like Figure 5 As shown, the image acquisition step S20 is a step of acquiring an image I containing contrast information C of a platform 102 that reflects the atomic stacking direction of the surface of the SiC substrate 10 by incident electron beams PE onto the SiC substrate 10 at an incident angle θ that is tilted relative to the normal N of the {0001} plane of the SiC substrate 10.

[0087] The image acquisition step S20 includes: a setting step S21, in which a SiC substrate 10 is set on the stage of a scanning electron microscope; a tilting step S22, in which the stage is tilted such that the electron beam PE is incident on the SiC substrate 10 at an incident angle θ that is tilted relative to the normal N of the {0001} surface of the SiC substrate 10; and an electron beam irradiation step S23, in which the electron beam PE is irradiated onto the SiC substrate 10 and an image I is obtained.

[0088] Preferably, in the tilting step S22, the stage is tilted in such a way that the electron beam PE is tilted relative to the normal N of the SiC substrate 10 in the <1-100> direction.

[0089] The tilt angle of the stage in tilting step S22 The electron beam PE is tilted such that the incident angle θ is preferably in the range of 22° or more and 42° or less, more preferably in the range of 27° or more and 37° or less, and even more preferably in the range of 30° or more and 31° or less.

[0090] In addition, the tilt angle of the stage in tilting step S22 The incident angle θ of the electron beam PE is preferably in the range of 5° or more and 10° or less, more preferably in the range of 7° or more and 9° or less, and even more preferably in the manner of 8°.

[0091] In the electron beam irradiation step S23, it is preferable to perform irradiation under conditions where the accelerating voltage of the electron beam PE is 1.0 kV or less. By incident the electron beam PE onto the SiC substrate 10 with such an accelerating voltage, an image I reflecting the contrast information C can be obtained.

[0092] Image I is generated based on electron beams PE (primary electrons) irradiated by the electron emission section of a scanning electron microscope, which bounce off the surface of the SiC substrate 10 to form electrons, or electrons emitted after interacting with the SiC substrate 10 (reflected electrons), or electrons generated during the interaction process (secondary electrons).

[0093] That is, a detector configured in a scanning electron microscope detects reflected electrons and / or secondary electrons, and generates image I based on the position information of the SiC substrate 10 and the detection results of each electron.

[0094] Figure 6 This is an explanatory diagram illustrating image I obtained in image acquisition step S20 for a SiC substrate 10 that has been heat-treated in a Si-SiC equilibrium vapor pressure environment (heat treatment environment HE) in heat treatment step S10. Figure 6 Image (a) is an image of SiC substrate 10 after heat treatment under Si-SiC equilibrium vapor pressure environment. Figure 6 (b) is a schematic diagram of the crystal structure of the SiC substrate 10 after heat treatment under Si-SiC equilibrium vapor pressure environment.

[0095] Figure 7 This is an explanatory diagram illustrating image I obtained in image acquisition step S20 for a SiC substrate 10 that has been heat-treated in a C-SiC equilibrium vapor pressure environment (heat treatment environment HE) in heat treatment step S10. Figure 7 Image (a) is an image of SiC substrate 10 after heat treatment under C-SiC equilibrium vapor pressure environment. Figure 7 (b) is a schematic diagram of the crystal structure of the SiC substrate 10 after heat treatment under C-SiC equilibrium vapor pressure environment.

[0096] <Environmental Assessment Steps> The environmental evaluation step S30 is a step of evaluating the thermal processing environment HE of the SiC substrate 10 based on the contrast information C of image I. This environmental evaluation step S30 evaluates the contrast information C manifested on the platform 102 of the SiC substrate 10. Specifically, the environmental evaluation step S30 evaluates the contrast information C manifested along the <1-100> direction.

[0097] The contrast information C has multiple brightness information that reflects the stacking direction of atoms on the surface of the SiC substrate 10. Specifically, it has a first brightness information C1 that is expressed along the <1-100> direction and a second brightness information C2 that can be compared with the first brightness information C1.

[0098] The environmental assessment step S30 includes: a brightness comparison step S31, which compares multiple brightness information; and a crystal structure determination step S32, which determines the crystal structure of the outermost surface (platform 102) of the SiC substrate 10 based on the multiple brightness information.

[0099] The brightness comparison step S31 is a step of comparing multiple brightness information. Specifically, it is a step of evaluating whether the first brightness information C1, which appears white or black along the <1-100> direction, is compared with the brightness of the second brightness information C2. That is, it is a step of evaluating whether the platform 102 area used for evaluation is relatively black or white by comparing multiple brightness information.

[0100] The crystal structure determination step S32 is a step of obtaining information about the crystal structure of the outermost surface (platform 102) of the SiC substrate 10 based on the relationship between the first brightness information C1 obtained in the brightness comparison step S31 and the tilt direction of the electron ray PE relative to the incident angle θ of the SiC substrate 10 (the incident direction of the electron ray PE).

[0101] For example, in Figure 5 In the case where electron beam PE is incident on platform 102 where atoms are stacked along the first stacking direction D1 (the direction in which Si atoms are stacked in C→B→A), black contrast information C is obtained. When electron beam PE is incident on platform 102 where atoms are stacked along the second stacking direction D2 (the direction in which Si atoms are stacked in A→B→C), white contrast information C is obtained.

[0102] That is, if the relationship between the contrast information C of image I and the incident direction of electron beam PE relative to SiC substrate 10 is known, it is possible to determine whether the stacking direction of the atoms of platform 102 is the first stacking direction D1 or the second stacking direction D2.

[0103] The following is for reference Figure 6 and Figure 7 The brightness comparison step S31 and the crystal structure determination step S32 are described in detail.

[0104] Figure 6 The SiC substrate 10 after heat treatment under Si-SiC equilibrium vapor pressure environment is viewed from the [-1100] direction ( Figure 6 Image I was obtained by irradiating the left side of the image with electron beams PE.

[0105] At this time, the first brightness information C1 displayed on platform 102 in the [1-100] direction of image I can be determined to be black by comparing it with the second brightness information C2 (brightness comparison step S31). The second brightness information C2 compared with the first brightness information C1 is displayed as white, for example, in the area between the [10-10] direction and the [2-1-10] direction.

[0106] exist Figure 6 In the process of irradiating electron beams PE from the [-1100] direction, in order to make the area corresponding to the first brightness information C1 black, it is necessary to stack the crystal structure of the outermost surface of the SiC substrate 10 on the first stacking direction D1 (crystal structure determination step S32).

[0107] That is, for the Figure 6 The SiC substrate 10 shown, after heat treatment under Si-SiC equilibrium vapor pressure environment, has a black first brightness information C1, therefore it can be evaluated that the atomic stacking direction of the platform 102 in the [1-100] direction is the first stacking direction D1. Furthermore, as... Figure 6 As shown in (b), for the platform 102 of the SiC substrate 10 after heat treatment in the Si-SiC equilibrium vapor pressure environment, it can be evaluated as a surface with two C elements forming at the end of the step 101 in the <1-100> direction.

[0108] In other words, in the crystal structure determination step S32, if the SiC substrate 10 has a surface with two C elements having dangling bonds at the end of the step 101 in the <1-100> direction, it can be evaluated that the heat treatment environment experienced by the SiC substrate 10 is a Si-SiC equilibrium vapor pressure environment.

[0109] In addition, Figure 6In the case of electron beam PE irradiation from the [1-100] direction (right side of the figure) under the same substrate and the same tilt angle, the contrast information C is reversed. That is, the first brightness information C1 reflecting the crystal structure in the first stacking direction D1 is white, and the second brightness information C2 reflecting the crystal structure in the second stacking direction D2 is black.

[0110] Thus, the contrast information C (first brightness information C1 and second brightness information C2) is determined by the relationship between the irradiation direction of the electron beam PE and the stacking direction of the SiC substrate 10. Therefore, in the crystal structure determination step S32, it is necessary to evaluate the stacking direction of the region containing the first brightness information C1 based on the crystal structure of the SiC substrate 10 and the direction of the irradiation of the electron beam PE.

[0111] Figure 7 Image I is obtained by irradiating a SiC substrate 10, which has been heat-treated under C-SiC equilibrium vapor pressure conditions, with electron beams PE from the [-1100] direction (the left direction of the figure).

[0112] At this time, the first brightness information C1 displayed on the platform 102 in the [1-100] direction of image I can be determined to be white by comparing it with the second brightness information C2 (brightness comparison step S31). The second brightness information C2 compared with the first brightness information C1 is, for example, displayed as black in the area between the [10-10] direction and the [2-1-10] direction.

[0113] exist Figure 7 In the process of irradiating electron beams PE from the [-1100] direction, in order to make the area corresponding to the first brightness information C1 white, it is necessary to stack the crystal structure of the outermost surface of the SiC substrate 10 on the second stacking direction D2 (crystal structure determination step S32).

[0114] That is, for the Figure 7 The SiC substrate 10 shown, after heat treatment under C-SiC equilibrium vapor pressure, is white in the first brightness information C1, therefore it can be evaluated that the atomic stacking direction of the platform 102 in the [1-100] direction is the second stacking direction D2. Furthermore, as... Figure 7 As shown in (b), for the platform 102 of the SiC substrate 10 after heat treatment under C-SiC equilibrium vapor pressure environment, it can be evaluated as a surface with a C element having a dangling bond of 1 at the end of the step 101 in the <1-100> direction.

[0115] In other words, in the crystal structure determination step S32, if the SiC substrate 10 has a surface with a C element having one dangling bond at the end of the step 101 in the <1-100> direction, it can be evaluated that the heat treatment environment experienced by the SiC substrate 10 is a C-SiC equilibrium vapor pressure environment.

[0116] In addition, Figure 7 In the case of electron beam PE irradiated from the [1-100] direction (the direction to the right of the figure) under the same substrate and the same tilt angle, the first brightness information C1 is black and the second brightness information C2 is white.

[0117] The method for evaluating the heat treatment environment according to the present invention includes: an image acquisition step S20, acquiring an image I by incident electron beam PE at an incident angle θ inclined relative to the normal N of the {0001} surface of the heat-treated SiC substrate 10; and an environment evaluation step S30, evaluating the heat treatment environment HE of the SiC substrate 10 based on the contrast information C of the image I.

[0118] The method for evaluating the heat treatment environment according to the present invention evaluates the atomic stacking orientation of the platform 102, which reflects the heat treatment environment HE. Therefore, the heat treatment environment HE can be evaluated without being affected by localized influences such as crystal defects or processing-modified layers in the SiC substrate 10.

[0119] Furthermore, the method for evaluating the heat treatment environment according to the present invention can easily evaluate the heat treatment environment HE using only an image I of the SiC substrate 10 obtained by scanning electron microscopy. That is, as... Figure 6 and Figure 7 As shown, the contrast information C of image I can be used to evaluate whether the heat treatment environment HE is a Si-SiC equilibrium vapor pressure environment or a C-SiC equilibrium vapor pressure environment.

[0120] SiC Substrates Next, a preferred embodiment of the SiC substrate used in the above-described method for evaluating the heat treatment environment will be described.

[0121] like Figure 8 As shown, the SiC substrate 50 has an evaluation pattern 60 for evaluating the heat treatment environment HE. The evaluation pattern 60 has a step-forming portion 61 that becomes the source of step 101 during heat treatment and an environmental evaluation region 62 that forms a step-plateau structure caused by the step-forming portion 61.

[0122] exist Figure 8 The example shown is an example of forming multiple evaluation patterns 60 on a SiC wafer. In this way, by distributing the evaluation patterns 60 on the SiC wafer, the heat treatment environment HE of each part can be evaluated.

[0123] However, there are no restrictions on the size, shape, or number of evaluation patterns 60 of the SiC substrate 50. For example, a single piece forming an evaluation pattern 60 can also be used as an evaluation sample for the heat treatment environment HE.

[0124] Figure 9 An example of the evaluation pattern 60 (601) has a machining hole 611 that becomes a step forming part 61 and a machining recess 621 that becomes an environmental evaluation area 62.

[0125] The machining hole 611 is formed deeper than the machining recess 621, thereby forming a cliff 63 between the machining hole 611 and the machining recess 621. When heat treatment is performed in a heat treatment environment HE, etching is preferentially performed from the cliff 63. Therefore, a platform 102 reflecting the heat treatment environment HE is formed in the region within the machining recess 621.

[0126] Figure 10 An example of the evaluation pattern 60 (602) has a through dislocation 612 that forms a step forming portion 61 and a processed recess 622 that forms an environmental evaluation area 62.

[0127] When a through-edge dislocation or through-spiral dislocation, which is a through dislocation 612, is heat-treated in a heat treatment environment HE, it is preferentially grown or etched. Therefore, a platform 102 reflecting the heat treatment environment HE is formed in the region within the machined recess 622.

[0128] The SiC substrate 50 according to the present invention includes: a step-forming portion 61 that becomes the source of step 101 during heat treatment, and an environmental evaluation region 62 that forms a step-plateau structure caused by the step-forming portion 61.

[0129] By heat-treating the SiC substrate 10, including the step formation portion 61 and the environmental evaluation region 62, in a heat treatment environment HE, a platform 102 reflecting the heat treatment environment HE can be obtained. Furthermore, by evaluating the SiC substrate 50 using the aforementioned heat treatment environment evaluation method, the heat treatment environment HE can be appropriately evaluated.

[0130] Explanation of reference numerals in the attached figures 10,50 SiC substrate 101 Steps 102 Platform 20 SiC material 30 Heat treatment containers 31 Upper container 32 Lower container 33 Clearance 34 Retaining element 35 Si vapor supply source 40 High melting point containers 41 Upper container 42 Lower container 43 Gap 44 Si vapor supply source 60 Evaluation Patterns 61 Step Formation Section 611 Machined hole; 612 Through dislocation 62 Environmental Assessment Area 621 Processing concave parts 622 Processing concave parts S10 Heat treatment step; S20 Image acquisition step S30 Environmental Assessment Steps C Contrast Information C1 First brightness information C2 Second brightness information HE heat treatment environment PE electron beam

Claims

1. A method for evaluating a heat treatment environment, comprising: The image acquisition step involves irradiating an electron beam at an incident angle tilted relative to the normal of the {0001} plane of the heat-treated silicon carbide substrate to acquire an image. as well as The environmental assessment step evaluates the thermal processing environment of the silicon carbide substrate based on the contrast information of the image. The contrast information includes multiple brightness information that reflects the stacking direction of atoms. The environmental assessment steps include: A brightness comparison step that compares the multiple brightness information; as well as The step of evaluating the heat treatment environment as a Si-SiC equilibrium vapor pressure environment or a C-SiC equilibrium vapor pressure environment.

2. The method for evaluating the heat treatment environment according to claim 1, wherein, The environmental assessment step is a step of evaluating the contrast information displayed on the platform.

3. The method for evaluating the heat treatment environment according to claim 1, wherein, The environmental assessment step is a step of evaluating the contrast information displayed along the <1-100> direction.

4. The method for evaluating the heat treatment environment according to claim 1, wherein, The contrast information includes first brightness information reflecting the stacking direction of atoms and second brightness information that can be compared with the first brightness information. The environmental assessment steps include a brightness comparison step that compares the first brightness information and the second brightness information.

5. The method for evaluating the heat treatment environment according to claim 1, wherein, The image acquisition step is a step of incidenting an electron beam inclined in the <1-100> direction onto the silicon carbide substrate.

6. The method for evaluating the heat treatment environment according to claim 1, wherein, The environmental assessment step is a step of evaluating whether the heat treatment environment is a Si-rich environment or a C-rich environment.

7. The method for evaluating the heat treatment environment according to claim 1, wherein, The silicon carbide substrate has a hexagonal crystal structure.

8. The method for evaluating the heat treatment environment according to claim 1, wherein, include: The heat treatment step involves heat-treating the silicon carbide substrate in a heat treatment environment to form a step-plateau structure.

9. The method for evaluating the heat treatment environment according to any one of claims 1 to 8, wherein, The silicon carbide substrate includes: a step-forming portion that becomes a step source during heat treatment, and an environmental assessment region that forms a step-plateau structure caused by the step-forming portion. The environmental assessment step is the step of evaluating the environmental assessment area.

10. The method for evaluating the heat treatment environment according to claim 9, wherein, The step-forming part is a through dislocation.

11. The method for evaluating the heat treatment environment according to claim 9, wherein, The step-forming part is a machining hole.

12. The method for evaluating the heat treatment environment according to claim 11, wherein, The environmental assessment area is the processed recess.

13. A silicon carbide substrate, comprising: The step-forming part that becomes the source of step formation during heat treatment; as well as The environmental assessment area for the step-platform structure formed by this step-forming part is established. The environmental assessment area is a machined recess, and the step forming part is a machined hole that is formed deeper than the machined recess.

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