Evaluation method for heat treatment environment and silicon carbide substrate

Abstract

The problem addressed by the present invention is to provide a novel feature of evaluating a heat treatment environment. The present invention is a heat treatment environment evaluation method that includes: an image acquisition step S20 for acquiring an image I by introducing electron beam PE at an incident angle θ inclined with respect to a normal vector N of a (0001) plane of a heat-treated SiC substrate 10; and an environment evaluation step S30 for evaluating a heat treatment environment HE of the SiC substrate 10 on the basis of contrast information C of the image I.

Description

Technical Field

[0001] The present invention relates to a method for evaluating a heat treatment environment and a silicon carbide substrate.

Background Art

[0002] Silicon carbide (SiC) semiconductor devices can withstand higher voltages, operate more efficiently, and at higher temperatures than silicon (Si) or gallium arsenide (GaAs) semiconductor devices. Therefore, development is underway towards industrialization.

[0003] Techniques for controlling the step-terrace structure of SiC substrates have been proposed to improve the yield and quality of SiC semiconductor devices (see Patent Document 1 and Patent Document 2).

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

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

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] Incidentally, the step-terrace structure of a heat-treated SiC substrate is determined by the heat treatment environment (hereinafter referred to as the heat treatment environment) that the SiC substrate experiences. Therefore, whether or not the desired step-terrace structure can be repeatedly reproduced depends on whether the desired heat treatment environment can be reproduced.

[0008] Because semiconductor substrates are heat-treated at high temperatures of over 1,000 degrees Celsius, it is difficult to directly evaluate this heat treatment environment. Therefore, the heat treatment environment has been indirectly evaluated by correlating heat treatment conditions (concentration ratio of raw material gas, heating temperature, growth rate, etching rate, etc.) with the step-terrace structure after heat treatment (AFM image, etc.) (see Patent Documents 1 and 2).

[0009] However, it is known that the step-terrace structure after heat treatment is affected by crystal defects inherent in the SiC substrate and the processing-altered layer introduced during substrate processing. Therefore, there has been a problem in that it is not easy to properly evaluate the heat treatment environment.

[0010] In view of the problems described above, the problem that the present invention aims to solve is to provide a novel technology for evaluating a heat treatment environment. [Means for solving the problem]

[0011] The present invention, which solves the above-mentioned problems, includes an image acquisition step of acquiring an image by incidenting an electron beam at an incident angle inclined with respect to the normal of the {0001} plane of a heat-treated silicon carbide substrate, A method for evaluating a heat treatment environment, comprising an environmental evaluation step of evaluating the heat treatment environment of the silicon carbide substrate based on the contrast information of the aforementioned image.

[0012] In this way, by evaluating the heat treatment environment based on the contrast information of the image obtained from the silicon carbide substrate, the heat treatment environment experienced by the silicon carbide substrate can be appropriately evaluated. In this specification, when Miller indices are notated, "-" represents a bar that precedes the index immediately following it.

[0013] In a preferred embodiment of the present invention, the environmental evaluation step is a step of evaluating contrast information appearing on the terraces of the silicon carbide substrate.

[0014] In a preferred embodiment of the present invention, the environmental evaluation step is a step of evaluating contrast information that appears along the <1-100> direction.

[0015] In a preferred embodiment of the present invention, the contrast information has a plurality of brightness information reflecting the stacking direction of atoms, and the environmental evaluation step includes a brightness comparison step of comparing the plurality of brightness information.

[0016] In a preferred embodiment of the present invention, the contrast information comprises a first brightness information reflecting the stacking direction of atoms and a second brightness information that can be compared with the first brightness information, and the environmental evaluation step includes a brightness comparison step of comparing the first brightness information and the second brightness information.

[0017] In a preferred embodiment of the present invention, the image acquisition step is a step of incidenting an electron beam tilted in the <1-100> direction onto the silicon carbide substrate.

[0018] 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-SiC equilibrium vapor pressure environment or a C-SiC equilibrium vapor pressure environment.

[0019] 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.

[0020] In a preferred embodiment of the present invention, the silicon carbide substrate has a hexagonal crystal structure.

[0021] In a preferred embodiment of the present invention, the invention includes a heat treatment step in which a silicon carbide substrate is heat-treated in a heat treatment environment to form a step-terrace structure.

[0022] In a preferred embodiment of the present invention, the silicon carbide substrate includes a step formation portion that serves as a source of steps during heat treatment, and an environmental evaluation region where a step-terrace structure is formed due to this step formation portion, and the environmental evaluation step is a step of evaluating the environmental evaluation region.

[0023] In a preferred embodiment of the present invention, the step formation portion is a through dislocation.

[0024] In a preferred embodiment of the present invention, the step formation portion is a processing hole.

[0025] In a preferred embodiment of the present invention, the environmental evaluation region is a processing recess.

[0026] The present invention also relates to a silicon carbide substrate. That is, the present invention that solves the above-described problems is a silicon carbide substrate including a step formation portion that serves as a source of steps during heat treatment, and an environmental evaluation region where a step-terrace structure is formed due to this step formation portion.

[0027] In a preferred embodiment of the present invention, the step formation portion is a through dislocation.

[0028] In a preferred embodiment of the present invention, the step formation portion is a processing hole.

[0029] In a preferred embodiment of the present invention, the environmental evaluation region is a processing recess.

Advantages of the Invention

[0030] According to the disclosed technology, a novel technology for evaluating a heat treatment environment can be provided.

[0031] Other problems, features, and advantages will become apparent when reading the embodiments for carrying out the invention described below together with the drawings and the claims.

Brief Description of the Drawings

[0032] [Figure 1] This is a schematic diagram illustrating each step of the heat treatment environment evaluation method according to the embodiment. [Figure 2] This is a diagram illustrating the heat treatment process according to the embodiment. [Figure 3] This is a diagram illustrating the heat treatment process according to the embodiment. [Figure 4] This is a schematic diagram of the crystal structure of 4H-SiC. [Figure 5] This is a schematic diagram of the crystal structure of 4H-SiC. [Figure 6] This is a diagram illustrating the image acquisition process according to the embodiment. [Figure 7] This is a diagram illustrating the image acquisition process according to the embodiment. [Figure 8] This is a diagram illustrating a SiC substrate according to an embodiment. [Figure 9] This is a diagram illustrating a SiC substrate according to an embodiment. [Figure 10] This is a diagram illustrating a SiC substrate according to an embodiment. [Modes for carrying out the invention]

[0033] The following describes in detail a method for evaluating a heat treatment environment and a preferred embodiment of a SiC substrate according to the present invention, with reference to the attached drawings. The technical scope of the present invention is not limited to the embodiments shown in the attached drawings, and modifications can be made as appropriate within the scope described in the claims. In the following description of embodiments and in the attached drawings, the same reference numerals are used for similar components, and redundant explanations are omitted.

[0034] Evaluation Methods for Heat Treatment Environments Figure 1 is a schematic diagram illustrating the steps of a heat treatment environment evaluation method according to an embodiment of the present invention. The heat treatment environment evaluation method according to the embodiment includes a heat treatment step S10 in which a step-terrace structure is formed by heat treatment of a hexagonal SiC substrate 10 in a heat treatment environment HE; an image acquisition step S20 in which an electron beam PE is incident at an incident angle θ tilted with respect 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.

[0035] The present invention is characterized by evaluating the heat treatment environment HE of the heat treatment process S10 based on contrast information C of an image I acquired using an electron beam PE incident from a direction tilted with respect to the normal N of the SiC substrate 10.

[0036] 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 acquired using electron beam PE, and by comparing the multiple brightness information appearing in this image I, the heat treatment environment HE experienced by the SiC substrate 10 can be identified.

[0037] As a result, it is possible to evaluate 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 is possible to evaluate whether the heat treatment environment HE experienced by the SiC substrate 10 is a Si-rich environment or a C-rich environment.

[0038] In this specification, "SiC-Si vapor pressure environment" refers to the vapor pressure environment when SiC (solid phase) and Si (liquid phase) reach phase equilibrium via the gas phase. This SiC-Si equilibrium vapor pressure environment is formed, for example, by heat treatment of a quasi-closed space where the atomic ratio Si / C exceeds 1.

[0039] Specifically, when a SiC substrate with a stoichiometric ratio of 1:1 and a Si vapor source (such as a Si substrate or Si pellets) are placed inside a SiC container with a stoichiometric ratio of 1:1, the atomic ratio Si / C inside the container will exceed 1. By heating such a container, a SiC-Si vapor pressure environment can be formed inside the container.

[0040] In this specification, "SiC-C equilibrium vapor pressure environment" refers to the vapor pressure environment when SiC (solid phase) and C (solid phase) reach phase equilibrium via the gas phase. This SiC-C equilibrium vapor pressure environment is formed, for example, by heat treatment of a quasi-closed space where the atomic ratio Si / C is 1 or less.

[0041] Specifically, when a SiC substrate satisfying a stoichiometric ratio of 1:1 is placed inside a SiC container satisfying a stoichiometric ratio of 1:1, the atomic ratio Si / C inside the container becomes 1. Alternatively, a C vapor supply source (such as C pellets) can be placed to make the atomic ratio Si / C less than 1. By heating the container with this configuration, a SiC-C vapor pressure environment can be formed inside the container.

[0042] In this specification, the SiC-Si equilibrium vapor pressure environment and the SiC-C equilibrium vapor pressure environment include a near-thermal equilibrium vapor pressure environment that satisfies the relationship between growth rate and growth temperature derived from a theoretical thermal equilibrium environment.

[0043] In this specification, a "semi-closed space" refers to a space in a container that can be vacuumed but can contain at least a portion of the vapor generated inside the container. This semi-closed space can be formed inside the container.

[0044] Furthermore, the heat treatment environment evaluation method according to the present invention makes it possible to evaluate the heat treatment environment HE experienced by the SiC substrate 10 by evaluating the SiC substrate 10 that has been heat-treated in advance. For this reason, the heat treatment environment evaluation method according to the present invention only needs to include at least an image acquisition step S20 and an environmental evaluation step S30. The following describes in detail the steps of a preferred embodiment of the present invention.

[0045] <Heat treatment process> The heat treatment step S10 is a step in which the SiC substrate 10 is heat-treated in the heat treatment environment HE, which is the subject of evaluation in the present invention. Specifically, it is a step in which a hexagonal SiC substrate 10 is heat-treated in the heat treatment environment HE to form a step-terrace structure that reflects the heat treatment environment HE.

[0046] Examples of methods for the heat treatment process S10 include a crystal growth method for forming a growth layer on the SiC substrate 10, and an etching method for etching the SiC substrate 10.

[0047] Examples of crystal growth methods that can be employed include chemical vapor deposition (CVD), physical vapor transport (PVT), metastable solvent epitaxy (MSE), and the confined physical vapor transport (CPVT) crystal growth method (see Figure 2), which will be described later.

[0048] Examples of etching methods that can be employed include hydrogen etching, which uses hydrogen gas as the etching gas; Si vapor pressure etching (SiVE), which involves heating under a Si atmosphere; and CPVT etching, which will be described later (see Figure 3).

[0049] The method of the heat treatment process S10 according to a preferred embodiment will be described in detail below with reference to Figures 2 and 3.

[0050] In a preferred embodiment, the heat treatment step S10 involves placing the SiC substrate 10 and the SiC material 20 inside a heat treatment container 30 and heating the container 30 so that a temperature gradient is formed inside it. Furthermore, it is desirable that the heat treatment container 30 is housed in a high-melting-point container 40.

[0051] In this embodiment, depending on the positional relationship between the SiC substrate 10 and the SiC material 20 and the direction of the temperature gradient, the SiC substrate 10 may be subjected to crystal growth or etching.

[0052] Figure 2 is an explanatory diagram showing a configuration for growing crystals on a SiC substrate 10 using the CPVT crystal growth method. In this crystal growth configuration, the SiC substrate 10 and the SiC material 20 are placed opposite each other, and a temperature gradient is applied so that the SiC substrate 10 is on the lower temperature side and the SiC material 20 is on the higher temperature side. This temperature gradient transports Si and C elements from the SiC material 20 to the SiC substrate 10, thereby growing a growth layer on the SiC substrate 10.

[0053] Figure 3 is an explanatory diagram showing an etching method for a SiC substrate 10 using the CPVT etching method. In this etching method, the SiC substrate 10 and the SiC material 20 are placed opposite each other, and a temperature gradient is applied so that the SiC material 20 is on the lower temperature side and the SiC substrate 10 is on the higher temperature side. This temperature gradient transports Si and C elements from the SiC substrate 10 to the SiC material 20, thereby etching the SiC substrate 10.

[0054] Note that in Figures 2 and 3, the positions of the SiC substrate 10 and the SiC material 20 are swapped. Alternatively, the transport direction of Si and C elements can be reversed by reversing the direction of the temperature gradient without swapping the positions of the SiC substrate 10 and the SiC material 20.

[0055] Figures 2(a) and 3(a) show a configuration in which a SiC substrate 10 and a SiC material 20 are placed in a quasi-closed space where the atomic ratio of Si / C exceeds 1 and then heat-treated. In this way, by heat-treating the SiC substrate 10 in a quasi-closed space where the atomic ratio of Si / C exceeds 1, a step-terrace structure corresponding to the Si-SiC equilibrium vapor pressure environment (heat treatment environment HE) is formed on the surface of the SiC substrate 10.

[0056] Figures 2(b) and 3(b) show a configuration in which a SiC substrate 10 and a SiC material 20 are placed in a quasi-closed space with an atomic ratio of Si / C of 1 or less and subjected to heat treatment. By heat-treating the SiC substrate 10 in this quasi-closed space with an atomic ratio of Si / C of 1 or less, a step-terrace structure corresponding to the C-SiC equilibrium vapor pressure environment (heat treatment environment HE) is formed on the surface of the SiC substrate 10.

[0057] The SiC substrate 10, SiC material 20, heat treatment container 30, and high melting point container 40 of the heat treatment process S10 according to a preferred embodiment will be described in detail below.

[0058] (SiC substrate) The SiC substrate 10 can be exemplified by a single-crystal SiC processed into a thin plate. Specifically, examples include SiC wafers sliced ​​into a disc shape from a SiC ingot fabricated by sublimation or the like. More than 200 polytypes of single-crystal SiC have been identified, and 4H-SiC and 6H-SiC are known as hexagonal polytypes that have a high probability of occurrence and are important for applications.

[0059] Figure 4 shows a schematic diagram of the crystal structure of 4H-SiC. Figure 4(a) shows the crystal structure of 4H-SiC viewed from the <11-20> direction. Figure 4(b) shows the crystal structure of 4H-SiC viewed from the

[0001] direction.

[0060] Furthermore, the notations “A, B, C” in the figure represent the three types of atomic occupancy positions (corresponding to Si-C pairs) in the hexagonal close-packed structure. In Figure 4(a), which shows the crystal structure of 4H-SiC, the stacking of atoms at positions A and C corresponds to the zinc-blend structure, and the stacking of atoms at position B corresponds to the wurtzite structure.

[0061] Figure 5 shows a schematic diagram of the step-terrace structure formed on the surface of the SiC substrate 10. This step-terrace structure is a staircase structure in which steps 101, which are stepped areas of one or more molecular layers, and terraces 102, which are flat areas where the {0001} plane is exposed, are arranged alternately. The minimum height (minimum unit) of a step 101 is one molecular layer (0.25 nm), and various step heights are formed by stacking multiple such single molecular layers. In Figure 5, a step 101 consisting of two molecular layers of 4H-SiC (0.5 nm: half-unit cell) is shown.

[0062] (SiC material) The SiC material 20 is composed of SiC that allows for the exchange of Si and C elements between it and the SiC substrate 10 by heating it in opposition to the SiC substrate 10. In this embodiment, as shown in Figures 2 and 3, the SiC substrate 10 and the SiC material 20 made of SiC are placed in opposition to each other via a holder 34. In addition, for example, a SiC container (heat treatment container 30) or a container in which a part of the container is made of SiC may be used as the SiC material 20. Any polytype can be used as the crystalline polymorph of this SiC material 20, and polycrystalline SiC may also be used.

[0063] (Heat treatment container) The heat treatment container 30 can be configured in any way that generates vapor pressure of gaseous species containing Si and C elements in its internal space during heat treatment. For example, it can be configured in which SiC is exposed on the inside of the container, or in which a separate SiC material (such as a SiC substrate) is placed inside the heat treatment container 30. It can also be configured in which a heat treatment container 30 made of a material other than SiC is used, and the material that generates Si and C elements is contained inside the container.

[0064] 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 semi-closed space).

[0065] The environment inside the heat-treated heat treatment container 30 is preferably a vapor pressure environment of a mixed gaseous system containing Si and C. Examples of gaseous systems containing Si include Si, Si2, Si3, Si2C, SiC2, and SiC. Examples of gaseous systems containing C include Si2C, SiC2, SiC, and C. In other words, a SiC-based gas is present inside the heat treatment container 30.

[0066] As shown in Figures 2 and 3, 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 in the fitting portion between the upper container 31 and the lower container 32, and the container is configured to allow exhaust (vacuuming) of the heat treatment container 30 through this gap 33. In other words, the inside of the heat treatment container 30 is a semi-closed space.

[0067] Furthermore, the heat treatment container 30 may have a holder 34 for holding the SiC substrate 10 or SiC material 20 in a hollow space. The holder 34 only needs to be configured to hold at least a portion of the SiC substrate 10 in the hollow space of the heat treatment container 30. For example, any conventional support means such as single-point support, three-point support, a configuration that supports the outer edge, or a configuration that clamps a portion can be used. A high-melting-point material can be used as the material for this holder 34.

[0068] The holder 34 may not be provided depending on the form 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 placed on the bottom surface of the lower container 32 (without providing the holder 34).

[0069] Furthermore, the heat treatment vessel 30 may have a Si vapor supply source 35, as shown in Figures 2(a) and 3(a). The Si vapor supply source 35 only needs to be configured to generate Si vapor inside the heat treatment vessel 30 when heated, and examples include solid Si (Si pellets such as single-crystal Si pieces or Si powder) or Si compounds.

[0070] (High melting point container) The high-melting-point container 40 can be configured to house the heat treatment container 30 and generate a vapor pressure of a gaseous species containing Si (an atmosphere containing Si) in its internal space during the heat treatment. In this embodiment, the atmosphere containing Si inside the high-melting-point container 40 is formed using a Si vapor supply source 44. Naturally, any method capable of forming an atmosphere containing Si around the heat treatment container 30 can be adopted.

[0071] The high-melting-point container 40 is composed of a high-melting-point material. Examples include C, a general-purpose heat-resistant material; W, Re, Os, Ta, Mo, carbides such as Ta9C8, HfC, TaC, NbC, ZrC, Ta2C, TiC, WC, MoC; nitrides such as HfN, TaN, BN, Ta2N, ZrN, TiN; borides such as HfB2, TaB2, ZrB2, NB2, TiB2; and polycrystalline SiC.

[0072] 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 be fitted together, and is configured to accommodate the heat treatment container 30. A small gap 43 is formed in the fitting portion between the upper container 41 and the lower container 42, and the container is configured to allow exhaust (vacuuming) of the inside of the high-melting-point container 40 through this gap 43.

[0073] The high-melting-point container 40 preferably has a Si vapor supply source 44 capable of supplying the vapor pressure of a gaseous species containing Si element into the high-melting-point container 40. The Si vapor supply source 44 should be configured to generate Si vapor into the high-melting-point container 40 when heated. Examples of this Si vapor supply source 44 include solid Si (Si pellets such as single-crystal Si pieces or Si powder) and Si compounds.

[0074] In the heat treatment step S10 according to this embodiment, TaC is used as the material for the high-melting-point container 40, and tantalum silicide is used as the Si vapor supply source 44. As shown in Figures 2 and 3, a tantalum silicide layer is formed on the inside of the high-melting-point container 40. When heated, Si vapor is supplied into the container from the tantalum silicide layer, creating a Si vapor pressure environment.

[0075] <Image acquisition process> Image acquisition step S20 is a step in which an electron beam PE is incident on the SiC substrate 10 at an incident angle θ tilted with respect to the normal N of the {0001} plane of the SiC substrate 10, as shown in Figure 5, to acquire an image I that includes contrast information C of terraces 102 that reflect the stacking direction of atoms on the surface of the SiC substrate 10.

[0076] The image acquisition process S20 includes a setup process S21 in which the SiC substrate 10 is placed on the stage of the scanning electron microscope, a tilting process S22 in which the stage is tilted so that the electron beam PE is incident on the SiC substrate 10 at an incident angle θ tilted with respect to the normal N of the {0001} plane of the SiC substrate 10, and an electron beam irradiation process S23 in which the electron beam PE is irradiated onto the SiC substrate 10 to obtain an image I.

[0077] In the tilting process S22, it is preferable to tilt the stage so that the electron beam PE is tilted in the <1-100> direction with respect to the normal N of the SiC substrate 10.

[0078] In the inclination process S22, the inclination angle φ of the stage is set such that the incident angle θ of the electron beam PE is preferably in the range of 22° to 42°, more preferably in the range of 27° to 37°, and even more preferably in the range of 30° to 31°.

[0079] Furthermore, the inclination angle φ of the stage in the inclination process S22 is set such that the incident angle θ of the electron beam PE is preferably in the range of 5° to 10°, more preferably in the range of 7° to 9°, and even more preferably 8°.

[0080] In the electron beam irradiation step S23, it is preferable to irradiate with an acceleration voltage of 1.0 kV or less for the electron beam PE. By injecting the electron beam PE onto the SiC substrate 10 with such an acceleration voltage, an image I reflecting contrast information C can be obtained.

[0081] Image I is created based on electrons reflected from the surface of the SiC substrate 10 by the electron emission unit of a scanning electron microscope (primary electrons), electrons emitted after interacting with the SiC substrate 10 (backscattered electrons), and electrons generated during the interaction process (secondary electrons).

[0082] In other words, a detector placed inside the scanning electron microscope detects backscattered electrons and / or secondary electrons, and an image I is created based on the positional information of the SiC substrate 10 and the detection results of each electron.

[0083] Figure 6 is an explanatory diagram illustrating image I obtained in image acquisition step S20 for a SiC substrate 10 that was heat-treated in a Si-SiC equilibrium vapor pressure environment (heat treatment environment HE) in heat treatment step S10. Figure 6(a) is image I of the SiC substrate 10 heat-treated in a Si-SiC equilibrium vapor pressure environment. Figure 6(b) is a schematic diagram of the crystal structure of the SiC substrate 10 heat-treated in a Si-SiC equilibrium vapor pressure environment.

[0084] Figure 7 is an explanatory diagram illustrating the image I obtained in the image acquisition step S20 for a SiC substrate 10 that was heat-treated in a C-SiC equilibrium vapor pressure environment (heat treatment environment HE) in the heat treatment step S10. Figure 7(a) is image I of the SiC substrate 10 heat-treated in a C-SiC equilibrium vapor pressure environment. Figure 7(b) is a schematic diagram of the crystal structure of the SiC substrate 10 heat-treated in a C-SiC equilibrium vapor pressure environment.

[0085] <Environmental Assessment Process> The environmental evaluation step S30 is a step in which the heat treatment environment HE of the SiC substrate 10 is evaluated based on the contrast information C of image I. This environmental evaluation step S30 is a step in which the contrast information C that appears on the terraces 102 of the SiC substrate 10 is evaluated. In particular, the environmental evaluation step S30 is a step in which the contrast information C that appears along the <1-100> direction is evaluated.

[0086] 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 appears along the <1-100> direction, and a second brightness information C2 that can be compared with this first brightness information C1.

[0087] The environmental evaluation process S30 includes a brightness comparison process S31 that compares multiple brightness information, and a crystal structure identification process S32 that identifies the crystal structure of the outermost surface (terrace 102) of the SiC substrate 10 based on this multiple brightness information.

[0088] The brightness comparison step S31 is a step that compares multiple brightness information. Specifically, it is a step that evaluates whether the first brightness information C1, which appears along the <1-100> direction, is white or black by comparing the brightness of the first brightness information C1 with the brightness of the second brightness information C2. In other words, it is a step that evaluates whether the terrace 102 region used for evaluation is relatively black or white by comparing multiple brightness information.

[0089] The crystal structure identification step S32 is a step in which information about the crystal structure of the outermost surface (terrace 102) of the SiC substrate 10 is obtained from the relationship between the first brightness information C1 obtained in the brightness comparison step S31 and the tilt direction of the incident angle θ of the electron beam PE to the SiC substrate 10 (incident direction of the electron beam PE).

[0090] For example, in Figure 5, when the electron beam PE is incident on terrace 102 where atoms are stacked in the first stacking direction D1 (the direction in which Si atoms are stacked C→B→A), black contrast information C is obtained, and when the electron beam PE is incident on terrace 102 where atoms are stacked in the second stacking direction D2 (the direction in which Si atoms are stacked A→B→C), white contrast information C is obtained.

[0091] In other words, if the relationship between the contrast information C of image I and the incident direction of the electron beam PE on the SiC substrate 10 is known, it is possible to determine whether the stacking direction of the atoms of the terrace 102 is the first stacking direction D1 or the second stacking direction D2.

[0092] The brightness comparison step S31 and the crystal structure identification step S32 will be described in detail below with reference to Figures 6 and 7.

[0093] Figure 6 shows image I, obtained by irradiating a SiC substrate 10, which has been heat-treated in a Si-SiC equilibrium vapor pressure environment, with an electron beam PE from the [-1100] direction (left side in Figure 6). At this time, the first brightness information C1 appearing on the terrace 102 in the [1-100] direction of image I can be identified as black by comparing it with the second brightness information C2 (brightness comparison step S31). The second brightness information C2, which is compared with the first brightness information C1, appears as white, for example, in the region between the [10-10] direction and the [2-1-10] direction.

[0094] In Figure 6, when the electron beam PE is irradiated from the [-1100] direction, for the region corresponding to the first brightness information C1 to become black, the crystal structure of the outermost surface of the SiC substrate 10 must be stacked in the first stacking direction D1 (crystal structure identification step S32).

[0095] In other words, the SiC substrate 10 heat-treated in the Si-SiC equilibrium vapor pressure environment shown in Figure 6 has a first brightness information C1 that is black, so it can be evaluated that the stacking direction of atoms on the terrace 102 in the [1-100] direction is the first stacking direction D1. Furthermore, as shown in Figure 6(b), the terrace 102 of the SiC substrate 10 heat-treated in the Si-SiC equilibrium vapor pressure environment can be evaluated as forming a surface in which C elements with two dangling bonds exist at the end of the step 101 in the <1-100> direction.

[0096] In other words, if, in the crystal structure identification step S32, the SiC substrate 10 has a surface where two dangling bonds of element C exist at the step 101 end in the <1-100> direction, then the heat treatment environment experienced by this SiC substrate 10 can be evaluated as a Si-SiC equilibrium vapor pressure environment.

[0097] In Figure 6, under the same substrate and the same tilt angle conditions, if the electron beam PE is irradiated from the [1-100] direction (right side of the figure), the contrast information C is inverted. That is, the first brightness information C1, which reflects the crystal structure of the first stacking direction D1, becomes white, and the second brightness information C2, which reflects the crystal structure of the second stacking direction D2, becomes black.

[0098] 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 identification step S32, it is necessary to evaluate the stacking direction of the region of the first brightness information C1 based on the crystal structure of the SiC substrate 10 and the direction in which the electron beam PE is irradiated.

[0099] Figure 7 shows image I, obtained by irradiating a SiC substrate 10, which has been heat-treated in a C-SiC equilibrium vapor pressure environment, with an electron beam PE from the [-1100] direction (left side of the figure). At this time, the first brightness information C1 appearing on the terrace 102 in the [1-100] direction of image I can be identified as white by comparing it with the second brightness information C2 (brightness comparison step S31). The second brightness information C2, which is compared with the first brightness information C1, appears as black in the region between the [10-10] direction and the [2-1-10] direction, for example.

[0100] In Figure 7, when the electron beam PE is irradiated from the [-1100] direction, for the region corresponding to the first brightness information C1 to appear white, the crystal structure of the outermost surface of the SiC substrate 10 must be stacked in the second stacking direction D2 (crystal structure identification step S32).

[0101] In other words, the SiC substrate 10 heat-treated in the C-SiC equilibrium vapor pressure environment shown in Figure 7 has a first brightness information C1 of white, so it can be evaluated that the stacking direction of atoms on the terrace 102 in the [1-100] direction is the second stacking direction D2. Furthermore, as shown in Figure 7(b), the terrace 102 of the SiC substrate 10 heat-treated in the C-SiC equilibrium vapor pressure environment can be evaluated as forming a surface in which a single dangling bond of C element exists at the end of the step 101 in the <1-100> direction.

[0102] In other words, if, in the crystal structure identification step S32, the SiC substrate 10 has a surface where a single dangling bond of C element exists at the step 101 end in the <1-100> direction, then the heat treatment environment experienced by this SiC substrate 10 can be evaluated as a C-SiC equilibrium vapor pressure environment.

[0103] In Figure 7, under the same substrate and the same tilt angle conditions, when the electron beam PE is irradiated from the [1-100] direction (right side of the figure), the first brightness information C1 becomes black and the second brightness information C2 becomes white.

[0104] The present invention provides a method for evaluating a heat treatment environment, which includes an image acquisition step S20 in which an electron beam PE is incident at an incident angle θ tilted with respect to the normal N of the {0001} plane of a 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.

[0105] The heat treatment environment evaluation method according to the present invention evaluates the stacking direction of atoms on terrace 102 that reflects the heat treatment environment HE. Therefore, the heat treatment environment HE can be evaluated without being affected by local influences such as crystal defects or processed altered layers of the SiC substrate 10.

[0106] Furthermore, the heat treatment environment evaluation method according to the present invention allows for easy evaluation of the heat treatment environment HE simply by acquiring an image I of the SiC substrate 10 using a scanning electron microscope. That is, as shown in Figures 6 and 7, it is possible to evaluate whether the heat treatment environment HE is a Si-SiC equilibrium vapor pressure environment or a C-SiC equilibrium vapor pressure environment based on the contrast information C of the image I.

[0107] SiC substrate Next, a preferred embodiment of the SiC substrate used in the heat treatment environment evaluation method described above will be explained.

[0108] As shown in Figure 8, the SiC substrate 50 has an evaluation pattern 60 for evaluating the heat treatment environment HE. The evaluation pattern 60 has a step-forming section 61 which is the source of step 101 during heat treatment, and an environmental evaluation region 62 in which a step-terrace structure resulting from this step-forming section 61 is formed.

[0109] Figure 8 shows an example in which multiple evaluation patterns 60 are formed on a SiC wafer. By distributing evaluation patterns 60 on the SiC wafer in this way, the heat treatment environment HE at each location can be evaluated. However, there are no restrictions on the size or shape of the SiC substrate 50 or the number of evaluation patterns 60. For example, a single piece with one evaluation pattern 60 formed on it may be used as an evaluation sample for the heat treatment environment HE.

[0110] Figure 9 shows an example of an evaluation pattern 60, which has a machined hole 611 that forms a step-forming area 61 and a machined recess 621 that forms an environmental evaluation area 62. Because the machined hole 611 is formed deeper than the machined recess 621, a cliff portion 63 is formed between the machined hole 611 and the machined recess 621. When heat treatment is performed in the heat treatment environment HE, etching preferentially proceeds from the cliff portion 63. As a result, a terrace 102 reflecting the heat treatment environment HE is formed in the region within the machined recess 621.

[0111] Figure 10 shows an example of an evaluation pattern 60, which has through dislocations 612 that form a step-forming area 61 and processed recesses 622 that form an environmental evaluation area 62. Through-hole dislocations 612, such as through-edge dislocations and through-helical dislocations, preferentially grow or are etched during heat treatment in the heat treatment environment HE. As a result, terraces 102 reflecting the heat treatment environment HE are formed in the region within the processed recess 622.

[0112] The SiC substrate 50 according to the present invention includes a step-forming portion 61 which is the source of step 101 during heat treatment, and an environmental evaluation region 62 in which a step-terrace structure resulting from the step-forming portion 61 is formed.

[0113] By heat-treating the SiC substrate 10, which includes the step forming section 61 and the environmental evaluation area 62, in the heat treatment environment HE, a terrace 102 reflecting the heat treatment environment HE can be obtained. Then, by evaluating the SiC substrate 50 using the heat treatment environment evaluation method described above, the heat treatment environment HE can be appropriately evaluated. [Explanation of Symbols]

[0114] 10,50 SiC substrate 101 Steps 102 Terrace 20 SiC material 30 Heat treatment containers 31 Upper container 32 Lower container 33 Gap 34 Holder 35 Si steam source 40 High melting point containers 41 Upper container 42 Lower container 43 Gap 44 Si vapor supply source 60 evaluation patterns 61 Step forming section 611 Machining hole 612 Penetrating Dislocation 62 Environmental Assessment Areas 621 Machined recess 622 Machined recess S10 Heat treatment process S20 Image acquisition process S30 Environmental Assessment Process C Contrast Information C1 First brightness information C2 Second brightness information HE Heat Treatment Environment PE electron beam

Claims

1. An image acquisition step involves irradiating a heat-treated silicon carbide substrate with an electron beam at an incident angle inclined with respect to the normal to the {0001} plane to acquire an image, The process includes an environmental evaluation step of evaluating the heat treatment environment of the silicon carbide substrate based on the contrast information of the aforementioned image, A method for evaluating a heat treatment environment, wherein the environmental evaluation 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.

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

3. The method for evaluating a heat treatment environment according to claim 1 or claim 2, wherein the environmental evaluation step is a step of evaluating contrast information that appears along the <1-100> direction.

4. The contrast information includes a plurality of brightness information reflecting the stacking direction of atoms. The method for evaluating a heat treatment environment according to any one of claims 1 to 3, wherein the environmental evaluation step includes a brightness comparison step for comparing the plurality of brightness information.

5. The contrast information comprises a first brightness information that reflects the stacking direction of atoms, and a second brightness information that can be compared with this first brightness information. The method for evaluating a heat treatment environment according to any one of claims 1 to 4, wherein the environmental evaluation step includes a brightness comparison step of comparing the first brightness information with the second brightness information.

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

7. The method for evaluating a heat treatment environment according to any one of claims 1 to 6, wherein the environmental evaluation step is a step of evaluating whether the heat treatment environment is a Si-rich environment or a C-rich environment.

8. The method for evaluating a heat treatment environment according to any one of claims 1 to 7, wherein the silicon carbide substrate has a hexagonal crystal structure.

9. A method for evaluating a heat treatment environment according to any one of claims 1 to 8, comprising a heat treatment step of forming a step-terrace structure by heat treatment of a silicon carbide substrate in a heat treatment environment.

10. The silicon carbide substrate comprises a step-forming portion that serves as a step source during heat treatment, and an environmental evaluation region in which a step-terrace structure resulting from the step-forming portion is formed. The method for evaluating a heat treatment environment according to any one of claims 1 to 9, wherein the environmental evaluation step is a step of evaluating the environmental evaluation area.

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

12. The method for evaluating a heat treatment environment according to claim 10, wherein the step forming portion is a processed hole.

13. The method for evaluating a heat treatment environment according to any one of claims 10 to 12, wherein the environmental evaluation area is a processed recess.

14. A step-forming section that is the source of steps during heat treatment, This includes an environmental evaluation region in which a step-terrace structure is formed due to the step-forming portion, The aforementioned environmental evaluation area is a processed recess, The step forming portion is a silicon carbide substrate, wherein the step forming portion is (a) or (b) below. (a) Penetrating dislocation (b) Machined hole formed deeper than the machined recess

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