Method for manufacturing semiconductor wafer, susceptor, component for vacuum device, and semiconductor wafer

Abstract

Provided is a semiconductor wafer in which the intrusion of B and Al into an epitaxial film is suppressed and the variation of impurity concentration is reduced. Such a semiconductor wafer is provided by means of a semiconductor wafer manufacturing method comprising a step in which a susceptor 3 for holding an SiC substrate 4 having a first conductivity type is placed and an epitaxial film is formed on the SiC substrate 4. Here, the susceptor 3 has a protruding portion 3a formed so as to surround the periphery of the SiC substrate 4 in plan view, and a coating film covering the surface of the protruding portion. The protruding portion is composed of a polycrystalline body containing B, Al and SiC, and the coating film is composed of a polycrystalline body containing B, Al and SiC. In the semiconductor wafer manufacturing method, the thickness of the coating film is 60 μm or more, the concentration of B in the coating film is lower than the concentration of B in the protruding portion, and the concentration of Al in the coating film is lower than the concentration of Al in the protruding portion.

Description

Method for manufacturing semiconductor wafers, susceptor, component for vacuum equipment, and semiconductor wafer

[0001] This disclosure relates to methods for manufacturing semiconductor wafers, susceptors, components for vacuum equipment, and semiconductor wafers, and more particularly to a technology for manufacturing epitaxial films on a substrate made of SiC (silicon carbide).

[0002] SiC single crystals possess excellent physical properties, including high thermal and chemical stability, superior mechanical strength, strong radiation resistance, and higher dielectric breakdown voltage and thermal conductivity compared to Si (silicon) single crystals. Semiconductor devices using SiC single crystals can achieve performance that is difficult to realize with semiconductor devices using existing semiconductor materials such as Si single crystals. For this reason, SiC single crystals are expected to be the next-generation semiconductor material in various fields.

[0003] In the process of forming an epitaxial film on the upper surface of a substrate made of SiC single crystal (hereinafter referred to as a SiC substrate), it is known that a susceptor is used to hold the SiC substrate. Patent document 1 (Japanese Patent Application Publication No. 2012-131692) describes the use of a susceptor made of polycrystalline SiC.

[0004] Japanese Patent Publication No. 2012-131692

[0005] One type of susceptor is made of SiC manufactured by the CVD (Chemical Vapor Deposition) method (hereinafter referred to as CVD-SiC susceptor). Another type of susceptor is made of SiC manufactured by the powder sintering method (hereinafter referred to as sintered SiC susceptor). The former is expensive, while the latter has the advantage of being inexpensive. However, sintered SiC susceptors may contain boron (B) or aluminum (Al). As a result, in the process of forming an epitaxial film on the upper surface of the SiC substrate, the B or Al in the sintered SiC susceptor is incorporated into the epitaxial film, making it impossible to form an epitaxial film with the desired impurity concentration.

[0006] In view of the above circumstances, this disclosure aims to realize a semiconductor wafer that suppresses the penetration of B and Al into the epitaxial film and reduces variations in impurity concentration.

[0007] A semiconductor wafer manufacturing method in one embodiment includes the step of arranging a susceptor around a SiC substrate having a first conductivity type, and forming an epitaxial film on the SiC substrate while the SiC substrate is held by the susceptor. Here, the susceptor has a convex portion formed to surround the SiC substrate in a plan view, and a coating film covering the surface of the convex portion. The convex portion is composed of a polycrystalline material containing B, Al, and SiC, and the coating film is composed of a polycrystalline material containing B, Al, and SiC. The thickness of the coating film is 60 μm or more, the concentration of B in the coating film is lower than the concentration of B in the convex portion, and the concentration of Al in the coating film is lower than the concentration of Al in the convex portion.

[0008] In one embodiment, the susceptor can hold the SiC substrate by surrounding it with protrusions whose surfaces are covered with a coating film. Here, the protrusions are made of a polycrystalline material containing B, Al, and SiC, and the coating film is made of a polycrystalline material containing B, Al, and SiC. The thickness of the coating film is 60 μm or more, the concentration of B in the coating film is lower than the concentration of B in the protrusions, and the concentration of Al in the coating film is lower than the concentration of Al in the protrusions.

[0009] In one embodiment, the component for a vacuum apparatus can hold a SiC substrate by surrounding it with protrusions whose surfaces are covered with a coating film. Here, the protrusions are made of a polycrystalline material containing B, Al, and SiC, and the coating film is made of a polycrystalline material containing B, Al, and SiC. The thickness of the coating film is 60 μm or more, the concentration of B in the coating film is lower than the concentration of B in the protrusions, and the concentration of Al in the coating film is lower than the concentration of Al in the protrusions.

[0010] In one embodiment, the semiconductor wafer comprises a SiC substrate having an upper surface and a lower surface opposite the upper surface, and an epitaxial film formed on the SiC substrate containing B, Al, and SiC. Here, the SiC substrate and the epitaxial film have a first conductivity type. Furthermore, the average concentration of B in the range from the upper surface of the epitaxial film to a depth of 2 μm, which overlaps with a position 5 mm radially away from the edge of the SiC substrate, is 1 × 10⁻¹⁴ １５ atoms / cm ３ It is less than . Furthermore, the average concentration of Al in the range from the top surface to a depth of 2 μm of the epitaxial film that overlaps with a position 5 mm radially away from the edge of the SiC substrate is 1 × 10 １４ atoms / cm ３ It is less than.

[0011] According to one embodiment, it is possible to suppress the penetration of B and Al into the epitaxial film and realize a semiconductor wafer with reduced variation in impurity concentration.

[0012] Figure 1 is a schematic cross-sectional view showing the film deposition apparatus. Figure 2 is a graph showing the n-type impurity concentration in the epitaxial film. Figure 3 is a graph showing the concentration of B in the cross-section of the epitaxial film. Figure 4 is a graph showing the concentration of B in the cross-section of the epitaxial film. Figure 5 is a graph showing the concentration of Al in the cross-section of the epitaxial film. Figure 6 is a graph showing the concentration of Al in the cross-section of the epitaxial film. Figure 7 is a schematic cross-sectional view showing the film deposition apparatus in Modification 1. Figure 8 is a schematic perspective view showing the film deposition apparatus in Modification 2. Figure 9 is a graph showing the n-type impurity concentration in the epitaxial film in Comparative Example 1. Figure 10 is a graph showing the n-type impurity concentration in the epitaxial film in Comparative Example 2. Figure 11 is a graph showing the concentration of B in the cross-section of the epitaxial film in Comparative Example 2. Figure 12 is a graph showing the concentration of B in the cross-section of the epitaxial film in Comparative Example 2. Figure 13 is a graph showing the n-type impurity concentration in the epitaxial film in Comparative Example 3. Figure 14 is a schematic diagram of the film deposition apparatus.

[0013] In all the drawings illustrating the embodiments, the same reference numeral is used for identical components, and repeated explanations of the same components are omitted. Hatching may be used even in plan views to improve clarity.

[0014] In this specification, the radial direction refers to the direction along the diameter of the SiC substrate held by the susceptor 3.

[0015] Embodiment 1 Below, we will describe how to suppress the penetration of B or Al into an epitaxial film formed on a SiC substrate by covering the surface of a sintered SiC susceptor with a SiC film formed by the CVD method. Here, we will describe forming an epitaxial film with conductivity type n on the upper surface of a SiC substrate with conductivity type n. However, the conductivity types of the SiC substrate and the epitaxial film may each be p type. In other words, each of the SiC substrate and the epitaxial film has a first conductivity type, and the first conductivity type may be either n type or p type.

[0016] <Room for Improvement> As explained in "Problems the Invention Aims to Solve," in the process of forming an epitaxial film on a SiC substrate, there are two types of susceptors for holding the SiC substrate: CVD-SiC susceptors and sintered SiC susceptors. CVD-SiC susceptors are manufactured by forming a plate material made of SiC on a support substrate by the CVD method, and then removing the support substrate, for example, by cutting. Sintered SiC susceptors are manufactured by mixing a sintering aid such as a binder with SiC powder, forming a slurry, and sintering it at a high temperature. Both CVD-SiC susceptors and sintered SiC susceptors can be processed into a desired shape by cutting or polishing.

[0017] A susceptor has, for example, a circular recess on which a SiC substrate is placed. By placing the SiC substrate in this recess, the inner wall of the recess adjacent to the SiC substrate prevents the SiC substrate from moving, thereby holding the SiC substrate in place. When a film deposition process is performed to form an epitaxial film on the SiC substrate, a deposit film is formed on the surface of the susceptor. The deposit film can be removed by polishing or other processes, but even if such a process is performed, the susceptor needs to be replaced after multiple film deposition processes. Therefore, from the viewpoint of reducing the manufacturing cost of semiconductor wafers, it is important that the components constituting the susceptor are inexpensive.

[0018] CVD-SiC susceptors contain virtually no p-type impurities such as B or Al. Therefore, in the process of forming an epitaxial film on a SiC substrate, the problem of p-type impurities entering the epitaxial film from within the CVD-SiC susceptor does not occur. However, CVD-SiC susceptors are more expensive than sintered SiC susceptors.

[0019] Furthermore, CVD-SiC susceptors are manufactured using the CVD method, and because stress tends to remain inside, they have the problem of being more prone to cracking compared to sintered SiC susceptors.

[0020] Sintered SiC susceptors are less expensive than CVD-SiC susceptors and are less prone to cracking during machining. Therefore, from the perspective of reducing semiconductor wafer manufacturing costs, it is desirable to use sintered SiC susceptors as holding members for SiC substrates. However, sintered SiC susceptors contain large amounts of p-type impurities such as B or Al. This is because the sintering aids used in the production of sintered SiC susceptors contain B or Al.

[0021] In the process of forming an epitaxial film on a SiC substrate, the film is formed by blowing a raw material gas onto the SiC substrate, which is held by a sintered SiC susceptor, in a film deposition apparatus heated to approximately 1600°C. At this high temperature, the B or Al in the sintered SiC susceptor becomes more mobile. As a result, the B or Al in the sintered SiC susceptor may vaporize, mix with the raw material gas, and be incorporated into the growing epitaxial film. In addition, at the point where the SiC substrate and the sintered SiC susceptor are in contact, the B or Al in the sintered SiC susceptor may be incorporated into the growing epitaxial film. Furthermore, in the process of forming an epitaxial film, it is conceivable that the B or Al in the sintered SiC susceptor may adhere to the inner wall of the chamber (container) that constitutes the film deposition apparatus for forming the epitaxial film. As a result, B or Al adhering to the inner wall of the chamber may be incorporated into the epitaxial film during the subsequent process of forming the epitaxial film.

[0022] As described above, B or Al deposited from the sintered SiC susceptor is incorporated into the epitaxial film, particularly near the radial edges of the SiC substrate (the radial edges are called the peripheral edges). When a convex portion constituting the sintered SiC susceptor is adjacent to a side surface of the SiC substrate, a problem arises in which p-type impurities penetrate from within the sintered SiC susceptor into the epitaxial film, regardless of whether the convex portion and the side surface of the SiC substrate are in contact with each other.

[0023] When an n-type epitaxial film is formed on the upper surface of an n-type SiC substrate, nitrogen (N) is added to the epitaxial film as a donor, making the epitaxial film an electron-carrier film. Therefore, desired electrical properties can be obtained in semiconductor devices using the SiC substrate. However, if acceptors such as B or Al are unintentionally added to the epitaxial film, some of the electrons in the epitaxial film recombine with holes. As a result, desired electrical properties may not be obtained in semiconductor devices using the SiC substrate.

[0024] Furthermore, when a p-type epitaxial film is formed on the top surface of a p-type SiC substrate, B or Al is added as an acceptor to the epitaxial film, whereby holes are used as carriers in the epitaxial film. Accordingly, desired electrical characteristics can be obtained in a semiconductor device using the SiC substrate. However, if B or Al is unintentionally added to the epitaxial film, the p-type impurity concentration in the epitaxial film becomes partially excessively high. For this reason, there are cases where desired electrical characteristics cannot be obtained in a semiconductor device using the SiC substrate.

[0025] FIG. 9 is a graph showing the n-type impurity concentration in an epitaxial film of Comparative Example 1. FIG. 10 is a graph showing the n-type impurity concentration in an epitaxial film of Comparative Example 2. Each of FIGS. 9 and 10 shows the result of measuring the n-type impurity concentration in an epitaxial film formed on a separate SiC substrate. In FIGS. 9 and 10, the horizontal axis indicates the position in the radial direction of the SiC substrate, and the vertical axis indicates the n-type impurity concentration in the epitaxial film. The unit of the vertical axis is described as "atoms / cm ３ ", but this means "impurities contained per unit volume of cm ３ ".

[0026] The SiC substrate is a disc-shaped n-type semiconductor substrate. The diameter of each of the SiC substrates of Comparative Example 1 and Comparative Example 2 is 152 mm. That is, the SiC substrate has a diameter of 6 inches. Note that the SiC substrate may have a diameter of 8 inches. The diameter of a 6-inch SiC substrate is preferably 145 mm or more, more preferably 150 mm or more. The diameter of an 8-inch SiC substrate is preferably 195 mm or more, more preferably 200 mm or more.

[0027] The values ​​on the horizontal axis in Figures 9 and 10 represent the distance from the center of the top surface of the disc-shaped SiC substrate. In Figures 9 and 10, the diamond-shaped plots represent the n-type impurity concentrations measured at each of the multiple measurement points aligned in the X direction, which is the radial direction of the SiC substrate. In Figures 9 and 10, the square plots represent the n-type impurity concentrations measured at each of the multiple measurement points aligned in the Y direction, which is the radial direction of the SiC substrate. The X and Y directions are orthogonal to each other in a plan view. Note that "plan view" refers to, for example, viewing the top surface of the silicon carbide substrate along a direction perpendicular to the top surface of the silicon carbide substrate.

[0028] In Comparative Examples 1 and 2, an n-type epitaxial film was formed on an n-type SiC substrate held by a sintered SiC susceptor. As shown in Figures 9 and 10, the concentration of n-type impurities in the epitaxial film was almost constant within a 50 mm range from the center of the SiC substrate. In contrast, outside the 50 mm range from the center of the SiC substrate, the concentration of n-type impurities in the epitaxial film was significantly lower than within the 50 mm range. This is thought to be because B or Al was incorporated into the edges of the epitaxial film from the sintered SiC susceptor used to hold the SiC substrate. In other words, when acceptors are incorporated into the epitaxial film, donors and acceptors recombine, resulting in a reduction in donors.

[0029] Figures 11 and 12 are graphs showing the concentration of B in a cross-section of an epitaxial film in Comparative Example 2. Said cross-section is viewed in the depth direction. The horizontal axes in Figures 11 and 12 indicate the distance in the depth direction from the upper surface of the epitaxial film. The vertical axes in Figures 11 and 12 indicate the concentration of B in the epitaxial film. Figure 11 shows the concentration of B in the epitaxial film overlapping a position 35 mm away from the center of the SiC substrate in Comparative Example 2. The position where the B concentration shown in Figure 11 was measured is the position enclosed by the solid circle in Figure 10. Figure 12 shows the concentration of B in the epitaxial film overlapping a position 70 mm away from the center of the SiC substrate in Comparative Example 2. The position where the B concentration shown in Figure 12 was measured is located within the area enclosed by the broken-line circle in Figure 10. In other words, the position 70 mm away from the center of the SiC substrate is a position 5 mm away in the radial direction from the peripheral edge of the SiC substrate. Figures 11 and 12 show impurity concentrations measured using secondary ion mass spectrometry (SIMS: Secondary Ion Mass Spectrometry).

[0030] As shown in Figure 11, at a location closer to the center than the edge of the SiC substrate, the concentration of B in the epitaxial film is 1×10 １４ atoms / cm ３ or less. In contrast, as shown in Figure 12, the concentration of B in the epitaxial film at the edge of the SiC substrate is approximately 1×10 １５ atoms / cm ３ Thus, in Comparative Example 2, in which an epitaxial film is formed on a SiC substrate held by a sintered SiC susceptor, the concentration of B in the epitaxial film at the edge is higher than that on the center side of the SiC substrate. Further, although illustration of a graph is omitted, similarly, the concentration of Al in the epitaxial film at the edge of the SiC substrate of Comparative Example 2 is approximately 1×10 １４ atoms / cm ３ , which is higher than the concentration of Al in the epitaxial film on the center side of the SiC substrate.

[0031] Therefore, in the technique of forming an epitaxial film on a SiC substrate using a sintered SiC susceptor as a holding member, it is necessary to suppress the incorporation of B and Al from the sintered SiC susceptor into the epitaxial film. Therefore, Embodiment 1 incorporates a modification. The technical concept of Embodiment 1, which incorporates this modification, will be explained below.

[0032] The structure of the film deposition apparatus according to Embodiment 1 will be described using Figures 1 and 14 of the film deposition apparatus and susceptor structure diagrams. Figure 1 is a schematic cross-sectional view showing the film deposition apparatus including the susceptor. Figure 14 is a schematic diagram showing the film deposition apparatus. In Figure 1, the susceptor and SiC substrate shown in Figure 14 are specifically shown, and other structures are simplified.

[0033] Figure 14 shows a schematic configuration of the film deposition apparatus 1 in Embodiment 1. The film deposition apparatus 1 is a "vertical single-wafer film deposition apparatus". The film deposition apparatus 1 is a film deposition apparatus that flows the raw material gas in the vertical direction. The film deposition apparatus 1 is a film deposition apparatus that processes SiC substrates 4 one at a time. The film deposition apparatus 1 has a housing 2, a susceptor 3, a heater 52, and a fixed susceptor 53.

[0034] The housing 2 is cylindrical. The susceptor 3 is configured to hold the SiC substrate 4. The susceptor 3 is configured to rotate. When the susceptor 3 rotates, the SiC substrate 4 also rotates on its central axis. The heater 52 is embedded inside the fixed susceptor 53. The heater 52 is composed of a resistor and heats by resistance heating. The heater 52 heats the SiC substrate 4 using Joule heat generated by passing an electric current through the resistor. The heater 52 has an inner heater 52A and an outer heater 52B. The outer heater 52B has a concentric circular planar shape. The inner heater 52A is arranged within a concentric circle. The inner heater 52A and the outer heater 52B can each be controlled independently. Therefore, by appropriately controlling the inner heater 52A and the outer heater 52B, the in-plane temperature uniformity of the SiC substrate 4 can be improved. As a result, the uniformity of the "C / Si ratio" on the upper surface of the SiC substrate 4 can be improved.

[0035] The raw material gas flows along arrow GF1. Next, the raw material gas flows along arrow GF2, and then along arrow GF3. Arrow GF1 indicates a flow perpendicular to the top surface of the SiC substrate 4. Arrow GF1 indicates a flow descending toward the SiC substrate 4. Arrow GF2 indicates a flow parallel to the top surface of the SiC substrate 4. Arrow GF2 indicates a flow from the center of the SiC substrate 4 toward the outer edge. Arrow GF3 indicates a flow parallel to the side surface of the susceptor 3. Arrow GF3 indicates a downward flow along the side surface of the susceptor 3.

[0036] As shown in Figure 1, the film deposition apparatus (vacuum apparatus) 1 according to Embodiment 1 comprises a housing 2 which is a container capable of being evacuated, and a susceptor 3 disposed inside the housing 2. The upper surface of the susceptor 3 is provided with a recess 5 which has a circular shape in plan view. The upper surface of the susceptor 3, which is the bottom surface of the recess 5, is the area on which the SiC substrate 4 is placed, i.e., the mounting area.

[0037] There are various shapes for the susceptor 3. In addition, the structure of the susceptor 3 other than the protrusions adjacent to the SiC substrate 4 placed on the mounting section has little relation to the above-mentioned improvements. For this reason, the shape of the susceptor 3 other than the protrusions can be changed as appropriate. The susceptor 3 has at least a protrusion (annular portion) 3a that is positioned adjacent to the SiC substrate 4 placed on the mounting section in the radial direction of the SiC substrate 4.

[0038] A film deposition apparatus is a type of vacuum apparatus. Other types of vacuum apparatus include heat treatment apparatuses, heating apparatuses, oxidation apparatuses, and ion implantation apparatuses. The susceptor 3 is a component for vacuum apparatuses and can be placed inside these vacuum apparatuses to hold the SiC substrate 4.

[0039] In plan view, the contour of the susceptor 3 is, for example, circular, and this contour and the recess 5 are concentric circles in plan view. For example, the susceptor 3 has a cylindrical or disc-like shape with a recess 5 on its upper surface. In plan view, the convex portion 3a has a shape that surrounds the SiC substrate 4 placed on the mounting portion. Here, the shape of the convex portion 3a in plan view is annular. In plan view, the side surface of the recess 5 constitutes the inner contour of the convex portion 3a.

[0040] The diameter (outer diameter) of the protrusion 3a is, for example, 100 mm or more and 250 mm or less. The diameter of the protrusion 3a may be greater than 250 mm. The difference between the inner diameter and outer diameter of the protrusion 3a, that is, the width of the protrusion 3a, is, for example, 30 mm or more and 50 mm or less. The diameter of the recess 5 is close in size to the diameter of the SiC substrate 4, but in order to place the SiC substrate 4 in the recess 5, the diameter of the recess 5 is slightly larger than the diameter of the SiC substrate 4. For example, the diameter of the recess 5 is about 1 to 5 mm larger than the diameter of the SiC substrate 4. Therefore, the SiC substrate 4 placed in the recess 5 and the side surface of the recess 5 may be in contact with each other, but they may also be separated by a small distance. The depth of the recess 5 is, for example, about the same as the thickness of the SiC substrate 4. The depth of the recess 5 may be, for example, greater than or less than the thickness of the SiC substrate 4, or the same as it. The thickness of the protrusion 3a is, for example, 0.8 mm or more and 2 mm or less. The thickness of the protrusion 3a may be 2 mm or more.

[0041] The susceptor 3 is mainly composed of a protrusion 3a and a base 3c made of sintered SiC, and the surface of the protrusion 3a is covered with a coating film 3f. The coating film 3f is a SiC film (CVD-SiC film) formed by the CVD method. The susceptor 3 contains the coating film 3f. The protrusion 3a is mainly composed of sintered SiC. The thickness of the coating film 3f formed on the surface of the protrusion 3a is 60 μm or more. The protrusion 3a is composed of a polycrystalline body of sintered SiC, more specifically, a polycrystalline body containing B, Al, and SiC. The coating film 3f is composed of a polycrystalline body containing SiC or an amorphous body containing SiC, more specifically, a polycrystalline body containing B, Al, and SiC or an amorphous body containing B, Al, and SiC. For example, the sides and bottom of the base 3c are covered with the coating film 3f. The diameter of the base 3c is, for example, 100 mm or more and 250 mm or less. The thickness of the base 3c is, for example, about 5 mm.

[0042] The housing 2 has, for example, a hollow cylindrical shape. Although not shown in the figures, the film deposition apparatus 1 is equipped with a heater for heating the inside of the housing 2. For example, the housing 2 has an inner wall and a side wall, and the heater is built between the inner wall and the outer wall. The heater may be located on the outside or inside of the housing 2. The heater may also be located below or above the mounting portion of the SiC substrate 4.

[0043] Although not shown in the diagram, for example, a gas supply section consisting of multiple holes is provided in the upper part (top surface) of the housing 2. Raw material gas is supplied into the housing 2 from the gas supply section. In addition to the raw material gas, a carrier gas may also be supplied from the gas supply section.

[0044] The susceptor according to the first embodiment of the susceptor manufacturing method is mainly composed of a protrusion 3a and a base 3c formed by powder sintering. In the susceptor formation process, first, a slurry is prepared by mixing a sintering aid such as a binder with powder made of SiC. The sintering aid contains B or Al. Next, the slurry is formed into, for example, a disc shape and sintered at, for example, 1600°C to form a protrusion 3a and a base 3c made of sintered SiC. The formed protrusion 3a is then processed into a desired shape by cutting or polishing to obtain a protrusion 3a that constitutes the susceptor. The protrusion 3a is composed of a polycrystalline body of sintered SiC.

[0045] Next, a coating film 3f is formed on the protrusion 3a. The coating film 3f is a SiC film formed by the CVD method. In this step, the thickness of the coating film 3f formed on the surface of the protrusion 3a is 60 μm or more. With this, the susceptor 3 is completed. The coating film 3f formed on the surface of the protrusion 3a contains almost no B or Al. In other words, the B content per unit volume of the coating film 3f covering the protrusion 3a is smaller than the B content per unit volume of the protrusion 3a made of sintered SiC. Also, the Al content per unit volume of the coating film 3f covering the protrusion 3a is smaller than the Al content per unit volume of the protrusion 3a made of sintered SiC. In other words, the concentration of B or Al in the coating film 3f covering the protrusion 3a is lower than the concentration of B or Al in the protrusion 3a.

[0046] Here, the upper surface of the susceptor 3, including the bottom surface of the recess 5, is covered by the coating film 3f. Also, the side surface of the recess 5 is covered by the coating film 3f. In other words, the upper and side surfaces of the protrusion 3a are covered by the coating film 3f. The side surfaces of the protrusion 3a referred to here are both the inner and outer circumferential surfaces of the protrusion 3a, and both of these surfaces are covered by the coating film 3f.

[0047] A method for manufacturing a semiconductor wafer will be described using Figure 1, which shows how to form an epitaxial film on a SiC substrate and thereby manufacture a semiconductor wafer.

[0048] The film deposition apparatus shown in Figure 1 is an apparatus for forming an epitaxial film on a SiC substrate by epitaxial growth. In Embodiment 1, the epitaxial film is formed using the CVD method, which is one of the epitaxial growth methods.

[0049] In the epitaxial film formation process, first, the SiC substrate 4 is placed in the recess 5 (mounting area) on the upper surface of the susceptor 3 within the housing 2. Here, a part of the susceptor 3 surrounds the SiC substrate 4. The SiC substrate 4 is fixed by being surrounded on its outer periphery by the susceptor 3. In other words, the SiC substrate 4 is held by the susceptor 3. The side surface of the SiC substrate 4 and the susceptor 3 may be in contact with each other or separated. A part of the bottom surface of the SiC substrate 4 and the susceptor 3 may be separated from each other.

[0050] The diameter of the SiC substrate 4 to be deposited is, for example, 6 inches. The diameter of the SiC substrate 4 may also be, for example, 8 inches. In the epitaxial film formation process, it is necessary to use a susceptor 3 that is sized to match the diameter of the SiC substrate 4.

[0051] Next, the inside of the housing 2 is evacuated, and then the temperature inside the housing 2 is raised using a heater. This raises the temperature inside the housing 2 to, for example, 1500°C or higher. Specifically, for example, the temperature inside the housing 2 is raised to 1600°C. Next, the gas supply unit blows the raw material gas toward the SiC substrate 4. Here, for example, H ２ (Hydrogen), SiH ４ (Silan), C ３ H ８ (Propane) or the like is used as a raw material gas. This forms a deposit film, or epitaxial film, on the upper surface of the SiC substrate 4. The epitaxial film is made of SiC. Thus, a semiconductor wafer, or laminated substrate, can be formed from the SiC substrate 4 with an epitaxial film formed on its upper surface. In this way, the epitaxial film is formed on the SiC substrate 4 held by the susceptor 3 in an environment with a temperature of 1500°C or higher.

[0052] Effects of Embodiment 1 As explained in "Room for Improvement," sintered SiC susceptors have the advantage of being inexpensive. On the other hand, when a SiC substrate is held using a sintered SiC susceptor, there is a problem that B or Al contained in the sintered SiC susceptor is incorporated into the epitaxial film during the epitaxial film formation process.

[0053] Therefore, in Embodiment 1, a coating film 3f is formed to cover the surface of the sintered SiC susceptor. This has the effect of suppressing the incorporation of B and Al from the sintered SiC that mainly constitute the susceptor 3 into the epitaxial film during the process of forming the epitaxial film on the SiC substrate 4. To obtain this effect, in Embodiment 1, the surface of the portion of the susceptor 3 that is exposed when the SiC substrate 4 is placed on the susceptor 3 is covered with the coating film 3f. From the viewpoint of obtaining the above effect, it is particularly important to cover the surface of the convex portion 3a adjacent to the SiC substrate 4 in the radial direction of the SiC substrate with the coating film 3f when the SiC substrate 4 is placed on the susceptor 3.

[0054] Furthermore, compared to the case where the top, side, and bottom surfaces of the base 3c are exposed from the coating film 3f, covering the top, side, and bottom surfaces of the base 3c with the coating film 3f more effectively suppresses the incorporation of B and Al into the epitaxial film.

[0055] The following describes the measurement results showing improved n-type impurity concentration, B concentration, and Al concentration by using a sintered SiC susceptor covered with a CVD-SiC film, using Figures 2 to 6. Figure 2 is a graph showing the n-type impurity concentration in the epitaxial film in Embodiment 1. Figure 2 shows the results of measuring the n-type impurity concentration in the epitaxial film formed on a SiC substrate. Figure 2 shows the n-type impurity concentration in the epitaxial film formed using a susceptor made of sintered SiC with its surface covered with a CVD-SiC film. Figure 2 shows the n-type impurity concentration measured using the mercury probe (Hg-CV) method. Figures 9, 10, and 13 also show the n-type impurity concentration measured using the mercury probe method, similar to Figure 2. Figures 3 to 6 show the impurity concentration in the epitaxial film measured using secondary ion mass spectrometry (SIMS).

[0056] In Figure 2, the horizontal axis represents the position of the SiC substrate in the radial direction, and the vertical axis represents the n-type impurity concentration in the epitaxial film. The diameter of the SiC substrate is 150 mm. In other words, the SiC substrate is a wafer with a diameter of 6 inches. The values ​​on the horizontal axis in Figure 2 represent the distance from the center of the top surface in the radial direction of the disc-shaped SiC substrate. In Figure 2, the diamond-shaped plots represent the n-type impurity concentrations measured at each of several measurement points aligned in the X direction, which is the radial direction of the SiC substrate. In Figure 2, the square plots represent the n-type impurity concentrations measured at each of several measurement points aligned in the Y direction, which is the radial direction of the SiC substrate. An orientation flat is formed on the disc-shaped SiC substrate, although it is not shown in the figure. The X direction is the direction of extension of the orientation flat (the direction along the

[1120] direction), and the Y direction is the direction perpendicular to the direction of extension of the orientation flat in a plan view. Note that a notch may be provided instead of an orientation flat. In this case, the direction perpendicular to the line connecting the center of the disc and the notch in a plan view corresponds to the X direction.

[0057] In Embodiment 1, an n-type epitaxial film was formed on an n-type SiC substrate held by a sintered SiC susceptor covered with a CVD-SiC film. When the upper surface of the epitaxial film is divided into multiple regions, the maximum value of the concentration in each of these regions is denoted as Max, the minimum value as Min, and the average value as Ave. In this case, the concentration variation expressed by the formula 0.5 × (Max - Min) / Ave. is preferably 20% or less, and preferably 10% or less.

[0058] Next, the concentration of B in the epitaxial film of Embodiment 1 will be described. Figures 3 and 4 are graphs showing the concentration of B in the cross-section of the epitaxial film in Embodiment 1. In Figures 3 and 4, the horizontal axis represents the distance in the depth direction from the top surface of the epitaxial film, and the vertical axis represents the concentration of B in the epitaxial film. Figure 3 shows the concentration of B in the epitaxial film that coincides with the center of the SiC substrate used for measurement in the graph shown in Figure 2. The position where the concentration of B shown in Figure 3 was measured is the position enclosed by a solid line circle in Figure 2. Figure 4 shows the concentration of B in the epitaxial film that coincides with a position 70 mm radially away from the center of the SiC substrate used for measurement in the graph shown in Figure 2. The position where the concentration of B shown in Figure 4 was measured is the position enclosed by a dashed line circle in Figure 2. The position 70 mm radially away from the center of the SiC substrate is, in other words, a position 5 mm radially away from the periphery of the SiC substrate toward the center.

[0059] As shown in Figure 3, the concentration of B in the epitaxial film at the center of the SiC substrate is 1 × 10⁻¹⁰ １４ atoms / cm ３ It is less than . More specifically, the average concentration of B in the range from the top surface of the epitaxial film overlapping the center of the SiC substrate to a depth of 2 μm is 1 × 10⁻¹⁶. １４ atoms / cm ３ It is less than . Also, as shown in Figure 4, the concentration of B in the epitaxial film at the edge of the SiC substrate is 1 × 10 １５ atoms / cm ３It is less than . More specifically, the average concentration of B in the range from the top surface of the epitaxial film to a depth of 2 μm, which overlaps with a position 5 mm radially away from the periphery of the SiC substrate, is 1 × 10⁻⁶. １５ atoms / cm ３ It is less than [value missing]. In this way, by forming an epitaxial film on a SiC substrate held by a sintered SiC susceptor covered with a CVD-SiC film, the concentration of B in the epitaxial film at the edges of the SiC substrate can be reduced compared to Comparative Example 2.

[0060] From the perspective of preventing a decrease in the n-type impurity concentration within the epitaxial film, it is important that the concentration difference of B between the center of the epitaxial film and the peripheral edge of the epitaxial film is sufficiently lower than the N concentration of the epitaxial film. For this reason, the concentration difference of B within the plane of the upper surface of the epitaxial film should be at most 1 × 10⁻⁶. １５ atoms / cm ３ It is preferable that it be less than [a certain value].

[0061] Next, the concentration of Al in the epitaxial film of Embodiment 1 will be described. Figures 5 and 6 are graphs showing the concentration of Al in the cross-section of the epitaxial film in Embodiment 1. In Figures 5 and 6, the horizontal axis represents the distance in the depth direction from the top surface of the epitaxial film, and the vertical axis represents the concentration of Al in the epitaxial film. Figure 5 shows the concentration of Al in the epitaxial film that coincides with the center of the SiC substrate used for measurement in the graph shown in Figure 2. The position where the Al concentration shown in Figure 5 was measured is the position enclosed by the solid line circle in Figure 2. Figure 6 shows the concentration of Al in the epitaxial film that coincides with a position 70 mm radially away from the center of the SiC substrate used for measurement in the graph shown in Figure 2. The position where the Al concentration shown in Figure 6 was measured is the position enclosed by the dashed line circle in Figure 2.

[0062] As shown in Figure 5, the concentration of Al in the epitaxial film at the center of the SiC substrate is approximately 1 × 10⁻⁶. １４ atoms / cm ３ It is less than 1 × 10⁻¹⁰. Specifically, at the center of the SiC substrate, the concentration of Al is 1 × 10⁻¹⁰. １４ atoms / cm ３It is less than . More specifically, the average concentration of Al in the range from the top surface of the epitaxial film overlapping the center of the SiC substrate to a depth of 2 μm is 1 × 10⁻¹⁶. １４ atoms / cm ３ It is less than . Also, as shown in Figure 6, the concentration of Al in the epitaxial film at the edge of the SiC substrate is approximately 1 × 10⁻⁶. １４ atoms / cm ３ It is less than 1 × 10⁻¹⁰. Specifically, at a position 5 mm radially from the periphery of the SiC substrate toward the center of the SiC substrate, the Al concentration is 1 × 10⁻¹⁰. １４ atoms / cm ３ It is less than . More specifically, the average concentration of Al in the range from the top surface of the epitaxial film to a depth of 2 μm, which overlaps with a position 5 mm radially toward the center of the SiC substrate from the peripheral edge of the SiC substrate, is 1 × 10⁻¹⁶. １４ atoms / cm ３ It is less than [value missing]. In this way, by forming an epitaxial film on a SiC substrate held by a sintered SiC susceptor covered with a CVD-SiC film, the concentration of Al in the epitaxial film at the edges of the SiC substrate can be reduced compared to Comparative Example 2.

[0063] Next, the thickness of the CVD-SiC film covering the sintered SiC susceptor of Embodiment 1 will be explained using Figures 2, 9, and 13. Figure 13 is a graph showing the n-type impurity concentration in the epitaxial film in Comparative Example 3. Similar to Figure 9, the horizontal axis of Figure 13 indicates the position in the radial direction of the SiC substrate, and the vertical axis indicates the n-type impurity concentration in the epitaxial film.

[0064] As explained using Figure 9, when a sintered SiC susceptor not covered with a CVD-SiC film, that is, a sintered SiC susceptor with a CVD-SiC film thickness of 0 mm, is used, the n-type impurity concentration of the epitaxial film formed on the SiC substrate decreases significantly at the edges. Therefore, in Comparative Example 3 shown in Figure 13, an epitaxial film was formed on the SiC substrate using a sintered SiC susceptor with a CVD-SiC film thickness of 42 μm covering the surface.

[0065] As shown in Figure 13, when the thickness of the CVD-SiC film is 42 μm, the concentration of n-type impurities in the epitaxial film is significantly lower outside the 50 mm radius from the center of the SiC substrate compared to within the 50 mm radius from the center of the SiC substrate. This is because the relatively thin thickness of the CVD-SiC film prevents sufficient suppression of the deposition of B or Al within the sintered SiC susceptor.

[0066] In contrast, in Embodiment 1 shown in Figure 2, an epitaxial film is formed on a SiC substrate using a sintered SiC susceptor with a CVD-SiC film having a thickness of 60 μm. As a result, as shown in Figure 2, excessive reduction in the n-type impurity concentration in the epitaxial film outside the 50 mm radius from the center of the SiC substrate, i.e., at the edges, is prevented. Thus, by making the thickness of the CVD-SiC film covering the sintered SiC susceptor 60 μm or more, excessive reduction in the n-type impurity concentration in the epitaxial film at the edges of the SiC substrate can be prevented.

[0067] Based on the above, in Embodiment 1, as a result of forming an epitaxial film on a SiC substrate held by a sintered SiC susceptor covered with a CVD-SiC film, it is possible to suppress the incorporation of B and Al into the epitaxial film on the edge side of the SiC substrate. Therefore, Embodiment 1 can eliminate the above-mentioned room for improvement. In other words, it is possible to suppress the intrusion of B and Al into the epitaxial film and realize a semiconductor wafer with reduced variation in impurity concentration. Furthermore, compared to forming an epitaxial film on a SiC substrate using a CVD-SiC susceptor, an epitaxial film can be formed at a lower cost.

[0068] In this embodiment, the case where the shape of the protrusion 3a in plan view, as shown in Figure 1, is annular has been described. In this case, the protrusion 3a continuously surrounds the outer periphery of the mounting portion of the SiC substrate 4 in plan view. In contrast, the protrusion 3a may discontinuously surround the outer periphery of the mounting portion of the SiC substrate 4 in plan view. In that case, the protrusion 3a may be composed of multiple parts that surround the outer periphery of the mounting portion of the SiC substrate 4 in plan view.

[0069] Modification 1 Figure 7 is a schematic cross-sectional view showing a film deposition apparatus in Modification 1 of Embodiment 1.

[0070] As shown in Figure 7, the film deposition apparatus 1a in the modified example 1 is equipped with a susceptor 3 inside. Here, the susceptor 3 is composed of a base 3c having a mounting portion on its upper surface for placing the SiC substrate, and an annular component 3b positioned on the base 3c to hold the SiC substrate so that it does not move laterally. In other words, the susceptor 3 may be composed of separate components for the portion adjacent to the SiC substrate 4 in the radial direction and the portion located below the SiC substrate 4. The annular component 3b corresponds to the convex portion 3a shown in Figure 1, and makes the convex portion 3a separable from the base 3c below the convex portion 3a. Note that only the annular component 3b may be called the susceptor. Thus, the susceptor 3 has at least a portion (convex portion) that is positioned radially adjacent to the side surface of the SiC substrate 4 placed on the mounting portion.

[0071] The annular component 3b is separable from the base 3c. The annular component 3b is mainly composed of protrusions made of sintered SiC, and the surface of the protrusions is covered with a coating film 3f, which is a CVD-SiC film. Specifically, the top surface, bottom surface, and both sides (inner and outer surfaces) of the ring-shaped annular component 3b are continuously covered with the coating film 3f. This makes it possible to suppress the incorporation of B and Al into the epitaxial film on the end side of the SiC substrate 4 when an epitaxial film is formed on the top surface of the SiC substrate 4 held by the susceptor 3. The annular component 3b can be formed, for example, by cutting or polishing a plate made of sintered SiC, and then covering the surface of the protrusions with the coating film 3f. It is desirable that the amount of warpage of the annular component 3b before being covered with the coating film 3f be less than 1 mm. The amount of warping is the distance in a direction perpendicular to the upper surface of the plane on which the annular component 3b is placed (for example, the base 3c), and is the distance between the center of the lower surface of the disc and the plane, assuming that the annular component 3b is disc-shaped. The base 3c can be formed, for example, by cutting or polishing a heat-resistant plate. For example, the sides and bottom surface of the base 3c are exposed from the coating film 3f. Also, the upper surface of the base 3c is exposed from the coating film 3f, except for the area on which the annular component 3b is placed.

[0072] In the process of forming an epitaxial film on a SiC substrate, first, the SiC substrate 4 is placed on the upper surface of the base 3c, which is the mounting portion inside the annular component 3b, within the housing 2. In this case, the annular component 3b surrounds the SiC substrate 4. The SiC substrate 4 is fixed by being surrounded on its outer periphery by the annular component 3b. In other words, the SiC substrate 4 is held by the annular component 3b. In this state, an epitaxial film is formed by blowing a raw material gas toward the SiC substrate 4.

[0073] In the above film deposition process, the base 3c, the annular component 3b, and the SiC substrate 4 are rotated while the raw material gas is blown toward the SiC substrate 4. To prevent the annular component 3b from detaching due to centrifugal force caused by this rotation, it is desirable that the center of the circumscribed circle on the outer circumference of the annular component 3b and the center of the inscribed circle on the inner circumference overlap each other. The distance (amount of misalignment) between these centers in a plan view is preferably 1.5 mm or less.

[0074] In the process of forming an epitaxial film on the SiC substrate 4, the annular component 3b suppresses the formation of a deposit film on the surface of the base 3c. This makes it possible to reuse the base 3c repeatedly. In other words, the number of uses of the base 3c can be increased. Therefore, the manufacturing cost of semiconductor wafers can be reduced.

[0075] The annular component 3b is covered with a coating film 3f on its inner circumferential surface, outer circumferential surface, top surface, and bottom surface. When the concentration of n-type impurities in the epitaxial film formed by the epitaxial growth method decreases, the concentration of n-type impurities at the edges of the epitaxial film tends to decrease. Therefore, from the viewpoint of suppressing the decrease in the concentration of n-type impurities at the edges of the epitaxial film, it is desirable that both the top and bottom surfaces of the annular component 3b constituting the susceptor 3 be covered with a coating film 3f.

[0076] The thickness of the annular component 3b is, for example, 0.8 mm or more and 2 mm or less. The thicker the annular component 3b, the less likely it is to warp. Therefore, from the viewpoint of suppressing warping of the annular component 3b, it is desirable that the thickness of the annular component 3b be 1 mm or more. The thickness of the annular component 3b may also be 2 mm or more. The difference between the inner diameter and outer diameter of the annular component 3b, that is, the width of the annular component 3b, is, for example, 30 mm or more and 50 mm or less. If the width of the annular component 3b is excessively large, the area subjected to stress increases due to the difference in thermal expansion coefficient between the annular component 3b and the SiC film deposited on the annular component 3b during the film formation process, making the annular component 3b more prone to warping. Therefore, from the viewpoint of suppressing warping of the annular component 3b, it is desirable that the width of the annular component 3b be 50 mm or less.

[0077] In this case, CVD-SiC is prone to internal stress due to its manufacturing process. Therefore, when a SiC film (deposit film, epitaxial film) is deposited on the annular component 3b during the film deposition process, there is a risk that the annular component 3b will warp. For example, if the annular component 3b is made of C (carbon), the thermal expansion coefficient α is different between C and SiC, so when a SiC film is deposited during the film deposition process, the annular component 3b will warp. If the amount of warping of the annular component 3b becomes large, the annular component 3b will no longer be able to hold the SiC substrate 4. This problem is particularly pronounced when the width of the annular component 3b is 30 mm or more.

[0078] For example, if the outer diameter of the annular component 3b is 187 mm, the inner diameter is 153 mm, the thickness of the coating film 3f is 60 μm, and the annular component 3b is made of carbon, then the amount of warpage of the annular component 3b is likely to be around 0.29 mm. If the thickness of the SiC substrate 4 is around 0.35 mm and the amount of warpage of the annular component 3b is around 0.29 mm, then it will be difficult for the annular component 3b to hold the SiC substrate 4.

[0079] Furthermore, if the annular component 3b warps, the SiC film will accumulate between the annular component 3b and the base 3c during the film deposition process, causing the surface of the substrate on which the annular component 3b is placed to deform. As a result, the annular component 3b cannot be placed stably.

[0080] In contrast, the annular component 3b of the modified example 1 is made of sintered SiC formed by sintering SiC powder with a binder. Therefore, internal stress is less likely to occur in the annular component 3b compared to CVD-SiC. Also, the coating film 3f is made of SiC. Therefore, compared to the case where the annular component 3b is made of C, the thermal expansion coefficient of the annular component 3b can be brought closer to the thermal expansion coefficient of the SiC film deposited on the coating film 3f. Thus, even if an SiC film is deposited on the coating film 3f, the occurrence of warping of the annular component 3b can be suppressed. This effect is particularly noticeable when the width of the annular component 3b is 30 mm or more. Furthermore, by suppressing the warping of the annular component 3b, the deposition of the SiC film between the annular component 3b and the base 3c can be suppressed during the film formation process.

[0081] Modification 2 Figure 8 is a schematic perspective view showing a film deposition apparatus including a susceptor in Modification 2 of Embodiment 1.

[0082] As shown in Figure 8, the susceptor 3d placed in the film deposition apparatus 1b may have multiple mounting sections on its upper surface for placing the SiC substrate 4. Multiple recesses 5 are provided on the upper surface of the susceptor 3d. Here, five recesses 5 are provided on the upper surface of the susceptor 3d, and the SiC substrate 4 can be placed inside each of the recesses 5. That is, the susceptor 3d has multiple protrusions surrounding the mounting section in a plan view. The susceptor 3d may be similar to the susceptor 3 shown in Figure 1, with the protrusions adjacent to the SiC substrate 4 and the portion located below the SiC substrate 4 (base) being integrated. Alternatively, the susceptor 3d may be similar to the susceptor 3 shown in Figure 7, with the protrusions adjacent to the SiC substrate 4 and the portion located below the SiC substrate 4 being composed of separate parts.

[0083] Inside the film deposition apparatus 1b, a heater 6 is arranged in a spiral shape in a plan view. The heater 6 extends in a spiral shape on the surface facing the upper surface of the susceptor 3, that is, on the surface facing the upper surface of the SiC substrate 4 placed on each of the multiple mounting sections. In Figure 8, one coil constitutes the heater 6, but two or more coils arranged in a spiral shape may constitute the heater 6. The heater 6 is heated by an induction heating method using coils.

[0084] The film deposition apparatus 1b of the modified example 2 is a batch-type film deposition apparatus that can deposit films on multiple SiC substrates 4 simultaneously. In this configuration, when epitaxial films are formed on the upper surfaces of each of the multiple SiC substrates 4 held by the susceptor 3d, it is possible to suppress the incorporation of B and Al into the epitaxial films on the edge sides of each SiC substrate 4.

[0085] Although the present inventors have described the invention in detail based on its embodiments, it goes without saying that the present invention is not limited to the embodiments described above and can be modified without departing from the spirit of the invention.

[0086] For example, Embodiment 1 described a case where a SiC substrate with a diameter of 6 inches is used, but the diameter of the SiC substrate may be smaller or larger than 6 inches. The diameter of the SiC substrate may be, for example, 8 inches.

[0087] 1, 1a, 1b Film deposition apparatus 2 Housing 3, 3d Susceptor 3a Protrusion 3b Annular part 3c Base 3f Coating film 4 SiC substrate 5 Recess 6, 52 Heater 52A Inner heater 52B Outer heater 53 Fixed susceptor GF1-GF3 Arrow

Claims

1. A method for manufacturing a semiconductor wafer, comprising the steps of (a) forming an epitaxial film on a SiC substrate having a first conductivity type while the SiC substrate is held by a susceptor, wherein the susceptor has a convex portion formed so as to surround the periphery of the SiC substrate in a plan view, and a coating film covering the surface of the convex portion, the convex portion is composed of a polycrystalline material containing B, Al, and SiC, the coating film is composed of a polycrystalline material containing B, Al, and SiC, the concentration of B in the coating film is lower than the concentration of B in the convex portion, and the concentration of Al in the coating film is lower than the concentration of Al in the convex portion.

2. A method for manufacturing a semiconductor wafer according to claim 1, wherein the thickness of the coating film is 60 μm or more.

3. A method for manufacturing a semiconductor wafer according to claim 1, wherein the upper surface and side surface of the protrusions are each covered with the coating film.

4. A method for manufacturing a semiconductor wafer according to claim 1, wherein in step (a), the SiC substrate is placed on the upper surface of a base, the SiC substrate is held by the protrusions positioned on the base, and the epitaxial film is formed on the SiC substrate, the base and the protrusions constitute the susceptor, and the protrusions are separable from the base.

5. A method for manufacturing a semiconductor wafer according to claim 4, wherein the lower surface of the protrusion is covered with the coating film.

6. A method for manufacturing a semiconductor wafer according to claim 1, wherein the shape of the convex portion in a plan view is annular.

7. A method for manufacturing a semiconductor wafer according to claim 1, wherein the susceptor has a plurality of protrusions.

8. A method for manufacturing a semiconductor wafer according to claim 1, wherein in step (a), the epitaxial film is formed simultaneously on each of the plurality of SiC substrates.

9. A method for manufacturing a semiconductor wafer according to claim 1, wherein the protrusions are made of sintered SiC.

10. A method for manufacturing a semiconductor wafer according to claim 1, wherein the coating film is a CVD-SiC film.

11. A method for manufacturing a semiconductor wafer according to claim 1, wherein in step (a), the epitaxial film is formed at a temperature of 1500°C or higher.

12. A susceptor capable of holding a SiC substrate by surrounding the SiC substrate with protrusions whose surface is covered with a coating film, wherein the protrusions are composed of a polycrystalline material containing B, Al, and SiC, the coating film is composed of a polycrystalline material containing B, Al, and SiC, the concentration of B in the coating film is lower than the concentration of B in the protrusions, and the concentration of Al in the coating film is lower than the concentration of Al in the protrusions.

13. A susceptor according to claim 12, wherein the thickness of the coating film is 60 μm or more.

14. A susceptor according to claim 12, wherein the upper surface and side surface of the protrusion are each covered by the coating film.

15. A susceptor according to claim 14, wherein the lower surface of the protrusion is covered with the coating film.

16. A susceptor according to claim 12, wherein the shape of the protrusion in plan view is annular.

17. A susceptor according to claim 12, wherein it has a plurality of protrusions and is capable of holding a plurality of SiC substrates.

18. A susceptor according to claim 11, wherein the susceptor is used at a temperature of 1500°C or higher.

19. A vacuum device component capable of holding a SiC substrate by surrounding the SiC substrate with protrusions whose surfaces are covered with a coating film, wherein the protrusions are made of a polycrystalline material containing B, Al, and SiC, the coating film is made of a polycrystalline material containing B, Al, and SiC, the concentration of B in the coating film is lower than the concentration of B in the protrusions, and the concentration of Al in the coating film is lower than the concentration of Al in the protrusions.

20. A vacuum device component according to claim 19, wherein the thickness of the coating film is 60 μm or more.

21. A vacuum device component according to claim 19, which is used at a temperature of 1500°C or higher.

22. A SiC substrate having an upper surface and a lower surface opposite to the upper surface, and an epitaxial film formed on the upper surface of the SiC substrate and containing B, Al, and SiC, wherein the SiC substrate and the epitaxial film have a first conductivity type, and the average concentration of B in the range from the upper surface of the epitaxial film to a depth of 2 μm, which overlaps with a position 5 mm radially toward the center of the SiC substrate from the edge of the SiC substrate, is 1 × 10⁻¹⁴ １５ atoms / cm ３ The average concentration of Al in the range from the top surface to a depth of 2 μm of the epitaxial film, which overlaps with a position 5 mm radially away from the edge of the SiC substrate toward the center of the SiC substrate, is less than 1 × 10⁻¹⁰. １４ atoms / cm ３ A semiconductor wafer that is less than [a certain value].

Images