Silicon carbide substrate manufacturing method

Abstract

To provide a silicon carbide substrate manufacturing method capable of restraining cracks on a silicon carbide substrate.SOLUTION: A silicon carbide substrate manufacturing method has the following steps. A silicon carbide single crystal having a poly-type of 4H is prepared. The silicon carbide single crystal has a first end face, a second end face, and an outer peripheral face. The second end face is opposite to the first end face. The outer peripheral face is communicated with the first and second end faces. The silicon carbide single crystal is ground on at least one of the first and second end faces. The silicon carbide single crystal is ground on the outer peripheral face. After the step of grinding the silicon carbide single crystal on at least one of the first and second end faces and the step of grinding the silicon carbide single crystal on the outer peripheral face, a silicon carbide wafer is formed by cutting the silicon carbide single crystal. A notch part is formed on the silicon carbide wafer using electric discharge wire processing.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a silicon carbide substrate.

Background Art

[0002] Japanese Patent Application Laid-Open No. 2000-331897 (Patent Document 1) describes a method for manufacturing a semiconductor wafer in which a notch is formed in the outer peripheral portion of a semiconductor wafer using a grindstone.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to the method for manufacturing a semiconductor wafer described in Patent Document 1, when forming a notch in the semiconductor wafer, the grindstone comes into contact with the semiconductor wafer. Therefore, when forming a notch in a semiconductor wafer made of silicon carbide, cracks may occur in the semiconductor wafer due to the fact that silicon carbide is a hard material.

[0005] An object of the present disclosure is to provide a method for manufacturing a silicon carbide substrate capable of suppressing the occurrence of cracks in the silicon carbide substrate.

Means for Solving the Problems

[0006] The method for manufacturing a silicon carbide substrate according to the present disclosure includes the following steps. A silicon carbide single crystal with a polytype of 4H is prepared. The silicon carbide single crystal has a first end face, a second end face, and an outer peripheral face. The second end face is opposite to the first end face. The outer peripheral face is continuous with each of the first end face and the second end face. The silicon carbide single crystal is ground on at least one of the first end face and the second end face. The silicon carbide single crystal is ground on the outer peripheral face. After the steps of grinding the silicon carbide single crystal on at least one of the first end face and the second end face and grinding the silicon carbide single crystal on the outer peripheral face, a silicon carbide wafer is formed by cutting the silicon carbide single crystal. A notch portion is formed in the silicon carbide wafer using wire electrical discharge machining.

Effect of the Invention

[0007] According to the present disclosure, it is possible to provide a method for manufacturing a silicon carbide substrate capable of suppressing the occurrence of cracks in the silicon carbide substrate.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

DETAILED DESCRIPTION OF THE INVENTION

[0009] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0010] (1) The method for manufacturing a silicon carbide substrate according to the present disclosure includes the following steps. A silicon carbide single crystal having a polytype of 4H is prepared. The silicon carbide single crystal has a first end face, a second end face, and an outer peripheral face. The second end face is opposite to the first end face. The outer peripheral face is continuous with each of the first end face and the second end face. The silicon carbide single crystal is ground on at least one of the first end face and the second end face. The silicon carbide single crystal is ground on the outer peripheral face. After the steps of grinding the silicon carbide single crystal on at least one of the first end face and the second end face and grinding the silicon carbide single crystal on the outer peripheral face, a silicon carbide wafer is formed by cutting the silicon carbide single crystal. A notch portion is formed in the silicon carbide wafer using wire electrical discharge machining. Thereby, generation of cracks in the silicon carbide substrate can be suppressed as compared with the case of forming the notch portion using a grinding wheel.

[0011] (2) The method for manufacturing a silicon carbide substrate according to (1) above may further include a step of chamfering the notch portion. Thereby, a processed and altered portion of the silicon carbide substrate formed when forming the notch portion can be removed.

[0012] (3) According to the method for manufacturing a silicon carbide substrate according to (2) above, in the chamfering process, the amount of cutting in the notch portion may be 0.1 mm or more. Therefore, the processed and altered portion of the silicon carbide substrate formed when forming the notch portion can be more reliably removed.

[0013] (4) The method for manufacturing a silicon carbide substrate according to the present disclosure has the following steps. A silicon carbide wafer with a polytype of 4H is prepared. A notch portion is formed in the silicon carbide wafer using wire electrical discharge machining. Thereby, the generation of cracks in the silicon carbide substrate can be suppressed as compared with the case of forming the notch portion using a grinding wheel.

[0014] (5) The method for manufacturing a silicon carbide substrate according to (4) above may further have a step of performing chamfering on the notch portion. Thereby, the processed and altered portion of the silicon carbide substrate formed when forming the notch portion can be removed.

[0015] (6) According to the method for manufacturing a silicon carbide substrate according to any one of (1) to (5) above, the applied voltage in the wire electrical discharge machining may be 100 V or more and 500 V or less. By the applied voltage being 500 V or less, it is possible to suppress the thickness of the processed and altered portion of the silicon carbide substrate from becoming excessively thick.

[0016] (7) According to the method for manufacturing a silicon carbide substrate according to any one of (1) to (6) above, the feed rate of the wire in the wire electrical discharge machining may be 100 m / min or more and 600 m / min or less. By the feed rate of the wire being 100 m / min or more, it is possible to suppress the wire from being melted. By the feed rate of the wire being 600 m / min or less, it is possible to reduce the consumption of the wire.

[0017] (8) According to the method for manufacturing a silicon carbide substrate according to any one of (1) to (7) above, in wire electrical discharge machining, the silicon carbide substrate may be disposed on a stage configured to be movable. The feed rate of the stage in wire electrical discharge machining may be 0.5 mm / min or more and 10 mm / min or less. By the feed rate of the stage being 0.5 mm / min or more, the time required to form a notch portion in the silicon carbide wafer can be shortened.

[0018] (9) According to the method for manufacturing a silicon carbide substrate according to any one of (1) to (3) above, after the step of grinding the outer peripheral surface, the diameter of the silicon carbide single crystal may be 150 mm or more.

[0019] (10) According to the method for manufacturing a silicon carbide substrate according to (9) above, after the step of grinding the outer peripheral surface, the diameter of the silicon carbide single crystal may be 200 mm or more.

[0020] (11) According to the method for manufacturing a silicon carbide substrate according to any one of (1) to (10) above, the thickness of the silicon carbide wafer may be 1 mm or less.

[0021] [Details of Embodiments of the Present Disclosure] Next, details of an embodiment of the present disclosure (hereinafter also referred to as the present embodiment) will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated. In the crystallographic descriptions in this specification, individual orientations are indicated by [], collective orientations by <>, individual planes by (), and collective planes by {}. Also, for negative indices, in crystallography, a "-" (bar) is placed above the number, but in this specification, a negative sign is placed before the number.

[0022] (First Embodiment) <Silicon Carbide Substrate> First, the configuration of the silicon carbide substrate according to the first embodiment will be described.

[0023] FIG. 1 is a schematic plan view showing the configuration of a silicon carbide substrate according to the first embodiment. As shown in FIG. 1, the silicon carbide substrate 100 mainly has a first main surface 11 and a first outer peripheral surface 19. The first main surface 11 is, for example, planar. The first main surface 11 extends along each of a first direction 101 and a second direction 102. The first outer peripheral surface 19 is continuous with the first main surface 11. The shape of the first outer peripheral surface 19 is annular.

[0024] The first direction 101 is, for example, the <11-20> direction. The first direction 101 may be, for example, the [11-20] direction. The first direction 101 may be a direction obtained by projecting the <11-20> direction onto the first main surface 11. From another perspective, the first direction 101 may be, for example, a direction including a <11-20> direction component.

[0025] The second direction 102 is perpendicular to the first direction 101. The second direction 102 is, for example, the <1-100> direction. The second direction 102 may be, for example, the [1-100] direction. The second direction 102 may be a direction obtained by projecting the <1-100> direction onto the first main surface 11. From another perspective, the second direction 102 may be, for example, a direction including a <1-100> direction component.

[0026] The first main surface 11 is the {0001} plane or a plane inclined with respect to the {0001} plane. The inclination angle (off angle) of the first main surface 11 with respect to the {0001} plane is, for example, 0° or more and 8° or less. When the first main surface 11 is inclined with respect to the {0001} plane, the inclination direction (off direction) of the first main surface 11 may be, for example, the first direction 101 or the second direction 102.

[0027] In the silicon carbide substrate 100, a notch 14 is provided. The notch 14 is a notch provided in the silicon carbide substrate 100. The first outer peripheral surface 19 has an arc-shaped portion 18 and a notch portion 17. When viewed perpendicularly to the first main surface 11 (hereinafter also referred to as a plan view), the shape of the arc-shaped portion 18 is arc-shaped. In a plan view, the center A of the silicon carbide substrate 100 is the center of a circle including an arc along the arc-shaped portion 18.

[0028] The notch portion 17 is continuous with the arc-shaped portion 18. The notch portion 17 constitutes the notch 14. In a plan view, the notch portion 17 is concave, for example, along the second direction 102. From another perspective, in a plan view, the notch portion 17 is concave from the circle including the arc along the arc-shaped portion 18 toward the center A. In a plan view, the tangent line of the notch portion 17 is taken as the first virtual line 91.

[0029] The silicon carbide substrate 100 is made of, for example, hexagonal silicon carbide. The polytype of the hexagonal silicon carbide constituting the silicon carbide substrate 100 is 4H. The silicon carbide substrate 100 may be a conductive substrate or a semi-insulating substrate.

[0030] As shown in FIG. 1, the diameter of the silicon carbide substrate 100 is taken as the first diameter W1. The first diameter W1 may be, for example, 150 mm (6 inches) or more, or 200 mm (8 inches) or more, or 250 mm (10 inches) or more. The first diameter W1 may be, for example, 400 mm (16 inches) or less. In a plan view, the first diameter W1 is the longest straight-line distance between two different points on the first outer peripheral surface 19.

[0031] In this specification, 6 inches means 150 mm or 152.4 mm (6 inches × 25.4 mm / inch). 8 inches means 200 mm or 203.2 mm (8 inches × 25.4 mm / inch). 10 inches means 250 mm or 254 mm (10 inches × 25.4 mm / inch). 16 inches means 400 mm or 406.4 mm (16 inches × 25.4 mm / inch).

[0032] FIG. 2 is a schematic cross-sectional view taken along line II-II of FIG. 1. The cross-section shown in FIG. 2 is a cross-section perpendicular to the first main surface 11 and perpendicular to the first virtual line 91. As shown in FIG. 2, the silicon carbide substrate 100 has a second main surface 12. The second main surface 12 is opposite to the first main surface 11. The second main surface 12 is continuous with the first outer peripheral surface 19. The direction from the second main surface 12 toward the first main surface 11 is defined as the third direction 103. The thickness of the silicon carbide substrate 100 in the third direction 103 is, for example, 1 mm or less. The thickness of the silicon carbide substrate 100 in the third direction 103 may be, for example, 0.5 mm or less, or may be 0.35 mm or less. The thickness of the silicon carbide substrate 100 in the third direction 103 is, for example, 0.1 mm or more.

[0033] As shown in FIG. 2, the silicon carbide substrate 100 has a first machined altered layer 15, a second machined altered layer 16, and a main body portion 10. The first machined altered layer 15 constitutes a notch portion 17. The first machined altered layer 15 is a portion that has received machining damage by wire electrical discharge machining. Specifically, the first machined altered layer 15 is composed of silicon carbide crystals that have been amorphized due to heat generated in wire electrical discharge machining.

[0034] In a cross-section perpendicular to the first main surface 11 and perpendicular to the first virtual line 91, the thickness of the first machined altered layer 15 in a direction perpendicular to the notch portion 17 is defined as the first thickness H1. The first thickness H1 is, for example, 0.05 mm or less.

[0035] The second machined altered layer 16 constitutes an arc-shaped portion 18. The second machined altered layer 16 is a portion that has received machining damage by grinding the silicon carbide single crystal on the outer peripheral surface described later. Specifically, the second machined altered layer 16 is composed of silicon carbide crystals that have been distorted due to grinding of the silicon carbide single crystal on the outer peripheral surface.

[0036] As shown in FIG. 2, the thickness of the second machined and altered portion 16 is the second thickness H2. The second thickness H2 is the thickness of the second machined and altered portion 16 in the direction from the arcuate portion 18 toward the center A (see FIG. 1) in a plan view. The second thickness H2 is, for example, thicker than the first thickness H1. The second thickness H2 is, for example, 0.1 mm or less.

[0037] The main body portion 10 is a portion that has not received machining damage due to wire electrical discharge machining and machining damage due to grinding of the single-crystalline silicon carbide on the outer peripheral surface. The main body portion 10 is composed of a single-crystalline silicon carbide having a normal crystal lattice.

[0038] In a cross section perpendicular to the first main surface 11 and perpendicular to the first virtual line 91, the main body portion 10 is between the first machined and altered portion 15 and the second machined and altered portion 16. The main body portion 10 is in contact with each of the first machined and altered portion 15 and the second machined and altered portion 16. The main body portion 10 is surrounded by the first machined and altered portion 15 and the second machined and altered portion 16.

[0039] (Second Embodiment) Next, the configuration of the silicon carbide substrate 100 according to the second embodiment will be described. The silicon carbide substrate 100 according to the second embodiment is different from the silicon carbide substrate 100 according to the first embodiment mainly in that the silicon carbide substrate 100 is chamfered at each of the notch portion 17 and the arcuate portion 18, and in other respects, is substantially the same as the silicon carbide substrate 100 according to the first embodiment. Hereinafter, the description will focus on the differences from the silicon carbide substrate 100 according to the first embodiment.

[0040] FIG. 3 is a schematic cross-sectional view showing the configuration of the silicon carbide substrate 100 according to the second embodiment. The cross section shown in FIG. 3 corresponds to the cross section shown in FIG. 2. As shown in FIG. 3, in a cross section perpendicular to the first main surface 11 and perpendicular to the first virtual line 91 (see FIG. 1), the notch portion 17 is convex in the direction from the arcuate portion 18 toward the notch portion 17. In a cross section perpendicular to the first main surface 11 and perpendicular to the first virtual line 91, the arcuate portion 18 is convex in the direction from the notch portion 17 toward the arcuate portion 18.

[0041] In FIG. 3, the dashed line indicates a portion removed from the silicon carbide substrate 100 (see FIG. 2) according to the first embodiment. As shown in FIG. 3, in the silicon carbide substrate 100 according to the second embodiment, each of the first processed altered portion 15 and the second processed altered portion 16 has been removed. From another perspective, the silicon carbide substrate 100 is constituted by, for example, the main body portion 10.

[0042] By performing chamfering on the notch portion 17, the first processed altered portion 15 has been removed. The amount of cutting in the notch portion 17 is taken as the first cutting amount T1. The first cutting amount T1 is the amount of cutting of the silicon carbide substrate 100 in the direction perpendicular to the notch portion 17 in a cross section perpendicular to the first main surface 11 and perpendicular to the first virtual line 91. The first cutting amount T1 is, for example, 0.1 mm or more.

[0043] By performing chamfering on the arc-shaped portion 18, the second processed altered portion 16 has been removed. The amount of cutting in the arc-shaped portion 18 is taken as the second cutting amount T2. The second cutting amount T2 is the amount of cutting of the silicon carbide substrate 100 in the direction from the arc-shaped portion 18 toward the center A (see FIG. 1) in a plan view. The second cutting amount T2 may be substantially the same as the first cutting amount T1, or may be larger than the first cutting amount T1. The second cutting amount T2 is, for example, 0.1 mm or more.

[0044] Note that the silicon carbide substrate 100 may have a portion that has received processing damage due to chamfering. The portion may constitute the first outer peripheral surface 19. The portion may surround the main body portion 10.

[0045] <Method for manufacturing a silicon carbide substrate> Next, a method for manufacturing the silicon carbide substrate 100 according to the present embodiment will be described. FIG. 4 is a flowchart schematically showing the method for manufacturing the silicon carbide substrate 100 according to the present embodiment. As shown in FIG. 4, the method for manufacturing the silicon carbide substrate 100 according to the present embodiment mainly includes a step of preparing a silicon carbide single crystal (S10), a step of grinding the silicon carbide single crystal at an end face (S20), a step of grinding the silicon carbide single crystal at an outer peripheral surface (S30), a step of forming a silicon carbide wafer by cutting the silicon carbide single crystal (S40), a step of forming a notch portion in the silicon carbide wafer using wire electrical discharge machining (S50), a step of chamfering an arcuate portion (S60), and a step of chamfering the notch portion (S70).

[0046] First, the step of preparing a silicon carbide single crystal (S10) is carried out. FIG. 5 is a cross-sectional schematic view showing the step of preparing a silicon carbide single crystal (S10). As shown in FIG. 5, a silicon carbide single crystal 200 is prepared. Specifically, for example, a polytype 4H silicon carbide single crystal 200 is manufactured by the sublimation method. The growth direction of the silicon carbide single crystal 200 is the same as, for example, the third direction 103. The thickness of the silicon carbide single crystal 200 in the third direction 103 is, for example, 10 mm or more. The silicon carbide single crystal 200 has a first end face 21, a second end face 22, and a second outer peripheral surface 29.

[0047] The first end face 21 is convex, for example, in the third direction 103. The second end face 22 is opposite to the first end face 21. The second end face 22 is, for example, planar. The first end face 21 is in the third direction 103 with respect to the second end face 22. The second outer peripheral surface 29 is continuous with each of the first end face 21 and the second end face 22. The second outer peripheral surface 29 is annular. As it separates from the second end face 22 along the third direction 103, for example, the diameter of the second outer peripheral surface 29 increases.

[0048] Next, a step (S20) of grinding the silicon carbide single crystal on the end face is performed. For example, using a grinding wheel (not shown), the silicon carbide single crystal 200 is ground on at least one of the first end face 21 and the second end face 22. Specifically, for example, the silicon carbide single crystal 200 is ground on the first end face 21 so that the first end face 21 becomes flat. On the second end face 22, the silicon carbide single crystal 200 may not be ground.

[0049] In the step (S20) of grinding the silicon carbide single crystal on the end face, the abrasive grains of the grinding wheel are composed of, for example, diamond. The bonding material of the grinding wheel is, for example, a vitrified bond. When the bonding material of the grinding wheel is a vitrified bond as compared with the case where the bonding material is a metal bond, the self-generation action of the grinding wheel is promoted. In the step (S20) of grinding the silicon carbide single crystal on the end face, the grit size of the grinding wheel is, for example, #140 or #170.

[0050] Next, a step (S30) of grinding the silicon carbide single crystal on the outer peripheral surface is performed. For example, using a grinding wheel (not shown), the silicon carbide single crystal 200 is ground on the second outer peripheral surface 29. Specifically, when viewed in the third direction 103, the silicon carbide single crystal 200 is ground on the second outer peripheral surface 29 so that the silicon carbide single crystal 200 has a cylindrical shape.

[0051] In the step (S30) of grinding the silicon carbide single crystal on the outer peripheral surface, the abrasive grains of the grinding wheel are composed of, for example, diamond. The bonding material of the grinding wheel is, for example, a vitrified bond. In the step (S30) of grinding the silicon carbide single crystal on the outer peripheral surface, the grit size of the grinding wheel is, for example, #140 or #170. Note that the step (S30) of grinding the silicon carbide single crystal on the outer peripheral surface may be performed before the step (S20) of grinding the silicon carbide single crystal on the end face.

[0052] In FIG. 5, the dashed line 99 indicates the outer shape of the silicon carbide single crystal 200 after the step (S20) of grinding the silicon carbide single crystal on the end face and the step (S30) of grinding the silicon carbide single crystal on the outer peripheral face. The diameter of the silicon carbide single crystal 200 after the step (S20) of grinding the silicon carbide single crystal on the end face and the step (S30) of grinding the silicon carbide single crystal on the outer peripheral face is the second diameter W2. The second diameter W2 may be, for example, 150 mm (6 inches) or more, or 200 mm (8 inches) or more, or 250 mm (10 inches) or more. The second diameter W2 may be, for example, 400 mm (16 inches) or less.

[0053] Next, the step (S40) of cutting the silicon carbide single crystal is performed. For example, by slicing the silicon carbide single crystal 200 using a wire saw, a silicon carbide wafer 300 is formed. Thus, the silicon carbide wafer 300 is prepared. The configuration of the silicon carbide wafer 300 will be described later.

[0054] Next, the step (S50) of forming a notch portion in the silicon carbide wafer using wire electrical discharge machining is performed. FIG. 6 is a schematic diagram showing the step (S50) of forming a notch portion in the silicon carbide wafer using wire electrical discharge machining. As shown in FIG. 6, a wire electrical discharge machining apparatus 500 is prepared. The wire electrical discharge machining apparatus 500 mainly includes a wire 51, a wire supply unit 52, a stage 53, a power supply 54, and a machining fluid supply unit (not shown).

[0055] The wire 51 is, for example, a brass-plated wire. Specifically, the wire 51 is, for example, an iron wire plated with brass. The wire supply unit 52 feeds out the wire 51. The wire supply unit 52 controls the feeding speed of the wire 51.

[0056] Stage 53 is a part that supports the silicon carbide wafer 300. Stage 53 is composed of a conductive material. Stage 53 moves, for example, along a horizontal plane. Power supply 54 applies a pulsed voltage between wire 51 and stage 53. Power supply 54 controls the magnitude of the voltage (applied voltage) applied between wire 51 and stage 53. Power supply 54 controls the interval of the pulsed voltage (discharge interval) applied between wire 51 and stage 53.

[0057] The machining fluid supply unit supplies machining fluid (not shown) to the position where wire 51 and silicon carbide wafer 300 come into contact. The machining fluid is, for example, deionized water. The machining fluid cools each of wire 51 and the silicon carbide single crystal. The machining fluid removes the machining debris generated by wire electrical discharge machining.

[0058] As shown in FIG. 6, in the step (S50) of forming a notch portion in the silicon carbide wafer using wire electrical discharge machining, the silicon carbide wafer 300 is placed on stage 53. The silicon carbide wafer 300 is the workpiece. The silicon carbide wafer 300 has a third main surface 31 and a third outer peripheral surface 39. When viewed in the direction perpendicular to the third main surface 31, the shape of the third main surface 31 is circular. The third outer peripheral surface 39 is continuous with the third main surface 31. The shape of the third outer peripheral surface 39 is cylindrical. The silicon carbide wafer 300 is electrically connected to the power supply 54 via the stage 53.

[0059] The thickness of the silicon carbide wafer 300 in the direction perpendicular to the third main surface 31 is, for example, 1 mm or less. The thickness of the silicon carbide wafer 300 in the direction perpendicular to the third main surface 31 may be, for example, 0.5 mm or less, or may be 0.35 mm or less. The thickness of the silicon carbide wafer 300 in the direction perpendicular to the third main surface 31 is, for example, 0.1 mm or more.

[0060] Wire 51 is supplied from wire supply unit 52. Wire 51 is supplied along the first arrow B1. The feed speed of wire 51 is, for example, 100 m / min or more and 600 m / min or less. The feed speed of wire 51 may be, for example, 150 m / min or more, or 200 m / min or more. The feed speed of wire 51 may be, for example, 500 m / min or less, or 400 m / min or less.

[0061] Using power supply 54, a pulse voltage is applied between wire 51 and stage 53. As a result, a pulse voltage is applied between wire 51 and silicon carbide wafer 300. The applied voltage is, for example, 100 V or more and 500 V or less. The applied voltage may be, for example, 180 V or more, or 250 V or more. The applied voltage may be, for example, 420 V or less, or 350 V or less. The discharge interval is, for example, 5 μs.

[0062] When stage 53 moves, silicon carbide wafer 300 is moved. The feed speed of stage 53 is, for example, 0.5 mm / min or more and 10 mm / min or less. The feed speed of stage 53 may be, for example, 2 mm / min or more, or 4 mm / min or more. The feed speed of stage 53 may be, for example, 8 mm / min or less, or 6 mm / min or less.

[0063] FIG. 7 is a schematic plan view showing the step (S50) of forming a notch portion in a silicon carbide wafer using electrical discharge wire machining. In FIG. 7, the cross section of wire 51 is shown. In FIG. 7, the second virtual line 92 indicates the path of wire 51. The length of the second virtual line 92 when viewed perpendicular to the third main surface 31 is the machining length in electrical discharge wire machining. The machining length is, for example, about 5 mm. As shown in FIG. 7, the portion of silicon carbide wafer 300 surrounded by the third outer peripheral surface 39 and the second virtual line 92 is defined as the removed portion 68.

[0064] The silicon carbide wafer 300 is moved using the stage 53 so that the wire 51 passes through the second virtual line 92. The silicon carbide wafer 300 moves along the second arrow B2. A pulsed voltage is applied between the silicon carbide wafer 300 and the wire 51 in a state where the silicon carbide wafer 300 approaches the wire 51, causing a discharge to occur between the silicon carbide wafer 300 and the wire 51. Due to the heat generated by the discharge, the portion of the silicon carbide wafer 300 around the wire 51 melts. For this reason, the silicon carbide wafer 300 is cut without the wire 51 and the silicon carbide wafer 300 substantially contacting each other.

[0065] By applying a pulsed voltage between the silicon carbide wafer 300 and the wire 51 while moving the silicon carbide wafer 300, the silicon carbide wafer 300 is cut along the second virtual line 92. Due to the heat generated by the discharge, the portion of the silicon carbide wafer 300 around the second virtual line 92 becomes amorphous. From another perspective, due to the heat generated by the discharge, the first processed altered layer 15 (see FIG. 2) is formed.

[0066] The removed portion 68 is separated from the silicon carbide wafer 300. By removing the removed portion 68, the notch 14 and the notch portion 17 (see FIG. 1) are formed. Thus, the silicon carbide substrate 100 according to the above-described first embodiment is manufactured. From another perspective, the step of preparing a silicon carbide single crystal (S10), the step of grinding the silicon carbide single crystal at the end face (S20), the step of grinding the silicon carbide single crystal at the outer peripheral surface (S30), the step of forming a silicon carbide wafer by cutting the silicon carbide single crystal (S40), and the step of forming a notch portion in the silicon carbide wafer using wire electrical discharge machining (S50) constitute the manufacturing method of the silicon carbide substrate 100 according to the first embodiment.

[0067] Next, a chamfering process (S60) for the arcuate portion is performed. FIG. 8 is a schematic diagram showing the chamfering process (S60) for the arcuate portion. As shown in FIG. 8, the silicon carbide substrate 100 is disposed on the support base 86. The support base 86 rotates the silicon carbide substrate 100. The support base 86 is movable along a plane perpendicular to the central axis (first central axis C1) of the silicon carbide substrate 100.

[0068] The first grindstone 81 is prepared. The first grindstone 81 is attached to the first shaft portion 83. The abrasive grains of the first grindstone 81 are composed of, for example, diamond. The binder of the first grindstone 81 is, for example, a metal bond. When the binder of the first grindstone 81 is a metal bond as compared with the case where the binder is a vitrified bond, the shape accuracy of the silicon carbide substrate 100 can be improved. The mesh number of the first grindstone 81 is, for example, #400 or #600. The first shaft portion 83 rotates the first grindstone 81.

[0069] FIG. 9 is a partial cross-sectional schematic diagram showing the chamfering process (S60) for the arcuate portion. As shown in FIGS. 8 and 9, the first grindstone 81 has a first concave surface 71. The first concave surface 71 is a surface that contacts the silicon carbide substrate 100. The first concave surface 71 is concave in a direction from the silicon carbide substrate 100 toward the central axis (second central axis C2) of the first grindstone 81. When viewed along the direction in which the second central axis C2 extends, the shape of the first concave surface 71 is annular. The minimum diameter of the first grindstone 81 is defined as the first minimum diameter D1. The first minimum diameter D1 is the diameter of the portion of the first concave surface 71 that is closest to the second central axis C2.

[0070] As shown in FIGS. 8 and 9, when the support base 86 rotates, the silicon carbide substrate 100 rotates about the first central axis C1. When the first shaft portion 83 rotates, the first grindstone 81 rotates about the second central axis C2. When viewed along the direction in which the first central axis C1 extends, the rotation direction of the silicon carbide substrate 100 and the rotation direction of the first grindstone 81 are, for example, the same.

[0071] As shown in FIGS. 8 and 9, when the support base 86 moves, the silicon carbide substrate 100 moves. As a result, while each of the first grinding wheel 81 and the silicon carbide substrate 100 rotates, the first concave surface 71 and the arc-shaped portion 18 come into contact. In the arc-shaped portion 18, the silicon carbide substrate 100 is ground. The amount of material removed from the silicon carbide substrate 100 in the arc-shaped portion 18 (second amount of material removed T2, see FIG. 3) is, for example, 0.1 mm or more. By the above, the second heat-affected layer 16 is removed.

[0072] Next, a chamfering process (S70) for the notch portion is performed. FIG. 10 is an enlarged plan schematic view showing the chamfering process (S70) for the notch portion. FIG. 11 is a partial cross-sectional schematic view showing the chamfering process (S70) for the notch portion.

[0073] As shown in FIGS. 10 and 11, a second grinding wheel 82 is prepared. The second grinding wheel 82 is attached to the second shaft portion 84. The abrasive grains of the second grinding wheel 82 are composed of, for example, diamond. The bonding material of the second grinding wheel 82 is, for example, a metal bond. Therefore, as described above, the shape accuracy of the silicon carbide substrate 100 can be improved. The grit size of the second grinding wheel 82 is, for example, #400 or #600.

[0074] The second shaft portion 84 rotates the second grinding wheel 82. The second grinding wheel 82 has a second concave surface 72. The second concave surface 72 is a surface that contacts the silicon carbide substrate 100. The second concave surface 72 is concave in a direction from the silicon carbide substrate 100 toward the central axis (third central axis C3) of the second grinding wheel 82.

[0075] The minimum diameter of the second grinding wheel 82 is defined as the second minimum diameter D2. The second minimum diameter D2 is the diameter at the portion of the second concave surface 72 that is closest to the third central axis C3. The second minimum diameter D2 is smaller than the first minimum diameter D1 (see FIG. 9).

[0076] As shown in FIG. 10, the maximum width E of the notch portion 17 before chamfering is performed on the notch portion is larger than the second minimum diameter D2 (see FIG. 11) and smaller than the first minimum diameter D1 (see FIG. 9). The maximum width E is the distance between two connection points of the notch portion 17 and the arc-shaped portion 18 in a plan view.

[0077] When the second shaft portion 84 rotates, the second grindstone 82 rotates about the third central axis C3. In the step (S70) of performing chamfering on the notch portion, the silicon carbide substrate 100 is disposed on the support base 86. In the step (S70) of performing chamfering on the notch portion, the silicon carbide substrate 100 does not rotate.

[0078] As shown in FIG. 10, when the silicon carbide substrate 100 moves, the second grindstone 82 moves relative to the silicon carbide substrate 100 along the third arrow B3. Specifically, the second grindstone 82 moves along the notch portion 17. As shown in FIG. 11, while the second grindstone 82 rotates, the second concave surface 72 and the notch portion 17 come into contact with each other. Thereby, the silicon carbide substrate 100 is ground at the notch portion 17. Note that the step (S70) of performing chamfering on the notch portion may be performed before the step (S60) of performing chamfering on the arc-shaped portion.

[0079] The amount of material removed from the silicon carbide substrate 100 at the notch portion 17 (the first amount of material removed T1, see FIG. 3) is, for example, 0.1 mm or more. Thereby, the first processed altered layer 15 is removed. Thus, the silicon carbide substrate 100 (see FIG. 3) according to the second embodiment described above is manufactured.

[0080] Next, the effects of the method for manufacturing a silicon carbide substrate according to the present embodiment will be described. As a method of forming a notch portion in a substrate composed of silicon or the like, there is a method of forming a notch portion using a grinding wheel. In this method, the grinding wheel and the substrate come into contact when forming the notch portion. Compared with a substrate composed of silicon or the like, a substrate composed of silicon carbide (silicon carbide substrate) is likely to crack, chip, and develop cracks because silicon carbide is a hard material. In particular, as the thickness of the silicon carbide substrate decreases, cracking, chipping, and cracking are more likely to occur. Therefore, when forming a notch portion using a grinding wheel, cracks, chips, and cracks may occur in the silicon carbide substrate.

[0081] According to the method for manufacturing the silicon carbide substrate 100 according to the present embodiment, a notch portion is formed in the silicon carbide wafer 300 using wire electrical discharge machining. In wire electrical discharge machining, the silicon carbide wafer 300 and the wire 51 do not substantially come into contact. For this reason, generation of cracks in the silicon carbide substrate 100 can be suppressed as compared with the case of forming a notch portion using a grinding wheel.

[0082] Since the silicon carbide wafer 300 and the wire 51 do not substantially come into contact in wire electrical discharge machining, generation of each of cracking and chipping in the silicon carbide substrate 100 can be suppressed as compared with the case of forming a notch portion using a grinding wheel.

[0083] As a binder for the grinding wheel used when forming the notch portion, a metal bond may be used. When the binder is a vitrified bond, the accuracy of the shape of the notch portion can be improved compared to the case where the binder is a metal bond. However, the frequency of replacing the grinding wheel increases due to wear of the abrasive grains. In particular, when forming a notch portion in a silicon carbide wafer, wear of the abrasive grains becomes excessively fast because silicon carbide is a hard material. Therefore, the consumption of relatively expensive grinding wheels increases excessively. As a result, the cost required to manufacture the silicon carbide substrate 100 increases.

[0084] According to the method for manufacturing the silicon carbide substrate 100 according to this embodiment, the wire 51 is used when forming the notch portion. Compared with the price of the grinding wheel, the price of the wire 51 is low. Therefore, the cost required to manufacture the silicon carbide substrate 100 can be reduced as compared with the case of forming the notch portion in the silicon carbide wafer 300 using a grinding wheel.

[0085] The method for manufacturing the silicon carbide substrate 100 according to this embodiment has a step (S30) of grinding the silicon carbide single crystal on the outer peripheral surface. Therefore, in the method for manufacturing the silicon carbide substrate 100 according to this embodiment, the outer peripheral surface of the silicon carbide single crystal 200 is ground, and a notch portion is formed in the silicon carbide wafer 300 using wire electrical discharge machining. For this reason, when forming the shape of the outer peripheral surface into a columnar shape, the machining can be facilitated by using grinding, and when forming the notch portion, the occurrence of cracks in the silicon carbide substrate 100 can be suppressed by using wire electrical discharge machining.

[0086] When machining the outer peripheral surface of the silicon carbide single crystal 200 using wire electrical discharge machining, amorphous silicon carbide is formed in the portion of the silicon carbide single crystal 200 close to the second outer peripheral surface 29. For example, when slicing the silicon carbide single crystal 200 using a wire saw, it is considered that the load applied to the wire saw differs between when cutting the portion composed of amorphous silicon carbide and when cutting the portion composed of non-amorphous silicon carbide. In this case, the shape accuracy of the silicon carbide wafer 300 formed by slicing deteriorates. As a result, the shape accuracy of the silicon carbide substrate 100 deteriorates. According to the method for manufacturing the silicon carbide substrate 100 according to this embodiment, silicon carbide does not become amorphous in the portion of the silicon carbide single crystal 200 close to the second outer peripheral surface 29. Thereby, it is possible to suppress deterioration of the shape accuracy of the silicon carbide substrate 100.

[0087] When forming a notch using a grinding stone, the grinding stone comes into contact with the silicon carbide wafer 300. In this case, due to the silicon carbide wafer 300 being pulled by the grinding stone along the moving direction and the rotational direction of the grinding stone, processing strain occurs in the silicon carbide wafer 300. The portion of the silicon carbide wafer 300 where processing strain has occurred may remain in the silicon carbide substrate 100 manufactured using the silicon carbide wafer 300. Specifically, even after chamfering the first outer peripheral surface 19 of the silicon carbide substrate 100, the portion where processing strain has occurred may remain. When an epitaxial layer is formed on the silicon carbide substrate 100, it is considered that defects in the epitaxial layer increase due to the processing strain remaining in the silicon carbide substrate 100.

[0088] According to the method for manufacturing the silicon carbide substrate 100 according to this embodiment, a notch is formed in the silicon carbide wafer 300 using a discharge wire. Therefore, it is possible to suppress the remaining of processing strain in the manufactured silicon carbide substrate 100. As a result, it is considered that an increase in defects in the epitaxial layer formed on the silicon carbide substrate 100 can be suppressed.

[0089] The method for manufacturing the silicon carbide substrate 100 according to this embodiment includes a step (S70) of chamfering the notch. Therefore, the first processed altered portion 15 formed by the formation of the notch can be removed. As a result, when an epitaxial layer is formed on the silicon carbide substrate 100, an increase in defects in the epitaxial layer due to the first processed altered portion 15 can be suppressed.

[0090] According to the method for manufacturing the silicon carbide substrate 100 according to this embodiment, in the chamfering process, the amount of material removed at the notch 17 is 0.1 mm or more. Therefore, the first processed altered portion 15 can be more reliably removed.

[0091] When the applied voltage in wire electrical discharge machining is excessively large, the thickness of the first heat-affected zone 15 in the silicon carbide substrate 100 becomes excessively thick. In this case, when manufacturing the silicon carbide substrate 100, the time required to remove the first heat-affected zone 15 increases. According to the manufacturing method of the silicon carbide substrate 100 according to the present embodiment, the applied voltage in wire electrical discharge machining is 500 V or less. Therefore, it is possible to suppress the thickness of the first heat-affected zone 15 from becoming excessively thick. As a result, the time required to remove the first heat-affected zone 15 can be reduced.

[0092] According to the manufacturing method of the silicon carbide substrate 100 according to the present embodiment, the feed rate of the wire 51 in wire electrical discharge machining is 100 m / min or more and 600 m / min or less. By the feed rate of the wire 51 being 100 m / min or more, it is possible to suppress the wire 51 from being melted. By the feed rate of the wire 51 being 600 m / min or less, it is possible to suppress the consumption of the wire 51 from increasing excessively.

[0093] According to the manufacturing method of the silicon carbide substrate 100 according to the present embodiment, the feed rate of the stage 53 in wire electrical discharge machining is 0.5 mm / min or more. As a result, the time required to form a notch in the silicon carbide substrate 100 can be shortened.

[0094] In addition, in the above, the configuration of the manufacturing method of the silicon carbide substrate 100 in which each of the first heat-affected zone 15 and the second heat-affected zone 16 is completely removed has been described. However, the configuration of the manufacturing method of the silicon carbide substrate 100 according to the present disclosure is not limited to the above configuration. Specifically, a part of each of the first heat-affected zone 15 and the second heat-affected zone 16 may remain without being removed. The first cutting amount T1 may be smaller than the first thickness H1, for example. The second cutting amount T2 may be smaller than the second thickness H2, for example.

[0095] The embodiments disclosed this time should be considered illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above-described embodiments but by the claims, and it is intended that all meanings equivalent to the claims and all modifications within the scope be included.

Explanation of Reference Numerals

[0096] 10 Main body 11 First main surface 12 Second main surface 14 Notch 15 First heat-affected zone 16 Second heat-affected zone 17 Notch portion 18 Arc-shaped portion 19 First outer peripheral surface 21 First end surface 22 Second end surface 29 Second outer peripheral surface 31 Third main surface 39 Third outer peripheral surface 51 Wire 52 Wire supply unit 53 Stage 54 Power supply 68 Portion to be removed 71 First concave surface 72 Second concave surface 81 First grinding wheel 82 Second grinding wheel 83 First shaft portion 84 Second shaft portion 86 Support base 91 First virtual line 92 Second virtual line 99 Dashed line 100 Silicon carbide substrate 101 First direction 102 Second direction 103 Third direction 200 Silicon carbide single crystal 300 Silicon carbide wafer 500 Electric discharge wire cutting machine A Center B1 First arrow B2 Second arrow Arrow 3 of B3 Central axis 1 of C1 Central axis 2 of C2 Central axis 3 of C3 Minimum diameter 1 of D1 Minimum diameter 2 of D2 Maximum width of E Thickness 1 of H1 Thickness 2 of H2 Amount of cutting 1 of T1 Amount of cutting 2 of T2 Diameter 1 of W1 Diameter 2 of W2

Claims

1. A step of preparing a silicon carbide single crystal with a polytype of 4H is provided, The silicon carbide single crystal has a first end face, a second end face opposite to the first end face, and an outer peripheral surface continuous with each of the first end face and the second end face, A step of grinding the silicon carbide single crystal on at least one of the first end face and the second end face; A step of grinding the silicon carbide single crystal on the outer peripheral surface; After the step of grinding the silicon carbide single crystal on at least one of the first end face and the second end face and the step of grinding the silicon carbide single crystal on the outer peripheral surface, a step of forming a silicon carbide wafer by cutting the silicon carbide single crystal; A method for manufacturing a silicon carbide substrate, further comprising a step of forming a notch portion in the silicon carbide wafer using wire electrical discharge machining.

2. The method for manufacturing a silicon carbide substrate according to claim 1, further comprising a step of chamfering the notch portion.

3. In the chamfering process, the amount of material removed at the notch portion is 0.1 mm or more. The method for manufacturing a silicon carbide substrate according to claim 2.

4. A step of preparing a silicon carbide wafer with a polytype of 4H; A method for manufacturing a silicon carbide substrate, comprising a step of forming a notch portion in the silicon carbide wafer using wire electrical discharge machining.

5. The method for manufacturing a silicon carbide substrate according to claim 4, further comprising a step of chamfering the notch portion.

6. The applied voltage in the wire electrical discharge machining is 100 V or more and 500 V or less. The method for manufacturing a silicon carbide substrate according to any one of claims 1 to 5.

7. The feed rate of the wire in the wire electrical discharge machining is 100 m / min or more and 600 m / min or less. The method for manufacturing a silicon carbide substrate according to any one of claims 1 to 5.

8. In the wire electrical discharge machining, the silicon carbide substrate is disposed on a stage configured to be movable, The feed rate of the stage in the wire electrical discharge machining is 0.5 mm / min or more and 10 mm / min or less. The method for manufacturing a silicon carbide substrate according to any one of claims 1 to 5.

9. After the step of grinding the outer peripheral surface, the diameter of the silicon carbide single crystal is 150 mm or more. The method for manufacturing a silicon carbide substrate according to any one of claims 1 to 3.

10. After the step of grinding the outer peripheral surface, the diameter of the silicon carbide single crystal is 200 mm or more. The method for manufacturing a silicon carbide substrate according to claim 9.

11. The thickness of the silicon carbide wafer is 1 mm or less. The method for manufacturing a silicon carbide substrate according to any one of claims 1 to 5.

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