Sic ingot and sic substrate manufacturing method

Abstract

To provide an SiC ingot capable of realizing both of high quality and workability.SOLUTION: This SiC ingot has a step-flow growth region, and a facet. On a cross section passing through a center in a <11-20> direction, an inside boundary between the facet and the step flow growth region has: a first slope inclined in a [-1-120] direction with respect to a crystal growth direction; and a second slope inclined in a [11-20] direction with respect to the crystal growth direction. An inflection point between the first and second slopes is nearer a first end on a Si face side than a center position of ingot length.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a SiC ingot and a SiC substrate.

Background Art

[0002] Silicon carbide (SiC) has a breakdown electric field one order of magnitude larger and a bandgap three times larger than that of silicon (Si). In addition, silicon carbide (SiC) has properties such as a thermal conductivity about three times higher than that of silicon (Si). Therefore, silicon carbide (SiC) is expected to be applied to power devices, high-frequency devices, high-temperature operation devices, etc. For this reason, in recent years, SiC epitaxial wafers have been used for semiconductor devices as described above.

[0003] A SiC epitaxial wafer is obtained by laminating a SiC epitaxial layer on the surface of a SiC substrate. Hereinafter, the substrate before laminating the SiC epitaxial layer is referred to as a SiC substrate, and the substrate after laminating the SiC epitaxial layer is referred to as a SiC epitaxial wafer. The SiC substrate is cut out from a SiC ingot. The SiC ingot is obtained by crystal growth of a SiC single crystal on a seed crystal.

[0004] For example, as described in Patent Document 1, when manufacturing a SiC ingot, facets are formed on the SiC ingot. When crystal-growing a SiC ingot, a part of the crystal growth surface becomes parallel to the c-plane, and a plane parallel to the c-plane is exposed on the crystal growth surface. The plane parallel to the c-plane has a different crystal growth mode from the other crystal growth surfaces that grow by step flow. The part that has grown in a different mode from the part that has grown by step flow is a facet.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The facet has a lower resistance value than the step-flow grown portion. This is because the relative amount of nitrogen uptake increases in the facet. The difference in specific resistance between the facet and the step-flow growth region affects laser processing and electrical discharge machining adversely. For example, when a crack is introduced into a SiC ingot with a laser and a SiC substrate is cut out from the SiC ingot, it is necessary to change the laser output at the boundary between the facet and the step-flow growth region. The more the number of changes in the laser output increases, the lower the processing throughput becomes. On the other hand, if the facet becomes too small particularly in the initial stage of growth, it becomes impossible to sufficiently introduce threading screw dislocations (TSDs) inside the facet, and polytypes are likely to occur.

[0007] The present invention has been made in view of the above problems, and an object thereof is to provide a SiC ingot that achieves both crystal quality and ease of processing, and a method for manufacturing a SiC substrate using the SiC ingot.

Means for Solving the Problems

[0008] In order to solve the above problems, the present invention provides the following means.

[0009] (1) The SiC ingot according to the first aspect has a step-flow growth region and a facet. In a cross-sectional plane passing through the center and along the <11-20> direction, the inner boundary between the facet and the step-flow growth region has a first inclined surface inclined in the [-1-120] direction with respect to the crystal growth direction and a second inclined surface inclined in the [11-20] direction with respect to the crystal growth direction. The inflection point between the first inclined surface and the second inclined surface is on a first end side which is a Si plane or a plane inclined by an offset angle from the Si plane, from the center position of the ingot length.

[0010] (2) In the SiC ingot according to the aspect of (1) above, the inflection point between the first inclined surface and the second inclined surface may be on the first end side from a position shifted by 40% of the ingot length in the crystal growth direction from the first end.

[0011] (3) In the SiC ingot according to the aspect of (1) or (2) above, the first inclined surface may be closer to the first end than the second inclined surface.

[0012] (4) In the SiC ingot according to any one of the aspects of (1) to (3) above, the inclination angle of the first inclined surface with respect to the crystal growth direction may be smaller than the inclination angle of the second inclined surface with respect to the crystal growth direction.

[0013] (5) In the SiC ingot according to any one of the aspects of (1) to (4) above, the first inclined surface and the second inclined surface may include a portion where the absolute value of the inclination angle with respect to the crystal growth direction is 5° or more.

[0014] (6) In the SiC ingot according to any one of the aspects of (1) to (5) above, at least one of the first inclined surface and the second inclined surface may include a portion where the absolute value of the inclination angle with respect to the crystal growth direction is 15° or more.

[0015] (7) In the SiC ingot according to any one of the aspects of (1) to (6) above, the facet may be located in the [11-20] direction from a plane passing through the center in the <11-20> direction and orthogonal to the <11-20> direction.

[0016] (8) The SiC ingot according to any one of the aspects of (1) to (7) above may have an ingot length of 10 mm or more.

[0017] (9) The SiC ingot according to any one of the aspects of (1) to (8) above may have a diameter of 145 mm or more.

[0018] (10) The SiC ingot according to any one of the above aspects (1) to (8) may have a diameter of 195 mm or more.

[0019] (11) The method for manufacturing a SiC substrate according to the second aspect includes a step of producing a SiC ingot according to any one of the above aspects (1) to (10), and a step of slicing the SiC ingot. (12) The method for manufacturing a SiC substrate according to the third aspect has a step of preparing a SiC ingot according to any one of the above aspects (1) to (10), and a step of slicing the SiC ingot.

Advantages of the Invention

[0020] The SiC ingot according to the above aspect is excellent in crystal quality and workability. Further, the method for manufacturing a SiC substrate according to the above aspect is excellent in production efficiency.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0022] Hereinafter, the SiC ingot and the like according to this embodiment will be described in detail with appropriate reference to the drawings. The drawings used in the following description may show, for the sake of convenience, the characteristic parts enlarged in order to make the characteristics of this embodiment easier to understand, and the dimensional ratios of each component may be different from the actual ones. The materials, dimensions, etc. exemplified in the following description are just examples, and the present invention is not limited thereto, and it can be appropriately changed and implemented within the range without changing the gist (technical requirements).

[0023] In this specification, the individual orientation is indicated by [], the collective orientation by <>, the individual plane by (), and the collective plane by {}. Regarding negative indices, in crystallography, a "-" (bar) is to be attached above the number, but in this specification, a negative sign is attached in front of the number.

[0024] First, the directions are defined. The crystal growth direction of the SiC ingot 10 is defined as the Z direction. The Z direction is the height direction of the cylindrical SiC ingot 10. One direction of the plane orthogonal to the Z direction is defined as the X direction. The X direction is, for example, the <11-20> direction. For example, the +X direction is the [11-20] direction, and the -X direction is the [-1-120] direction. Also, in the plane orthogonal to the Z direction, the direction orthogonal to the X direction is defined as the Y direction. The Y direction is, for example, the <1-100> direction.

[0025] "SiC ingot" FIG. 1 is a cross-sectional view of the SiC ingot 10 according to this embodiment. FIG. 2 is a plan view of the SiC ingot 10 according to this embodiment as viewed from the Z direction.

[0026] The SiC ingot 10 is a columnar body composed of a seed crystal and a crystal growth portion that has grown on the seed crystal. The SiC ingot 10 may be in the state after being processed into a cylindrical shape or in the state before being processed into a cylindrical shape. The SiC ingot 10 is a single crystal of SiC that has grown from the first end 1 toward the second end 2. The first end 1 and the second end 2 are connected by a side wall 3. The SiC ingot 10 may have a diameter that expands from the first end 1 toward the second end 2, or may be a cylindrical shape with a constant diameter. The first end 1 is, for example, a (0001) plane (Si plane), or a plane inclined by an offset angle from the (0001) plane. The second end 2 is, for example, a (000-1) plane (C plane) or a plane inclined by an offset angle from the (000-1) plane. The second end 2 faces the first end 1. For example, the first end 1 and the second end 2 may have an offset angle of 0.1 degrees or more and 8 degrees or less in the <11-20> direction and may not have an offset angle in the <1-100> direction. Note that the offset angle of the SiC ingot 10 is not limited to this example.

[0027] The diameter D of the SiC ingot 10 is, for example, 145 mm or more, preferably 149 mm or more, more preferably 155 mm or less, and even more preferably 151 mm or less. The diameter D of the SiC ingot 10 is, for example, 195 mm or more, preferably 199 mm or more, more preferably 205 mm or less, and even more preferably 201 mm or less. The diameter D of the SiC ingot 10 is, for example, 305 mm or less. Here, the diameter D of the SiC ingot 10 is the minimum diameter of the SiC ingot 10 and corresponds to the minimum value of the diameter of the obtainable SiC substrate. For example, when the SiC ingot 10 expands in diameter from the first end 1 toward the second end 2, the diameter of the first end 1 corresponds to the diameter D of the SiC ingot 10. For example, when the SiC ingot 10 is a cylindrical shape with a constant diameter, the diameter of any cross section obtained by cutting the SiC ingot 10 in a plane orthogonal to the Z direction corresponds to the diameter D of the SiC ingot 10. The SiC ingot 10 may be, for example, one that can obtain a 6-inch substrate or one that can obtain an 8-inch substrate.

[0028] The thickness (ingot length) of the SiC ingot 10 is, for example, 10 mm or more, preferably 20 mm or more, more preferably 30 mm or more, even more preferably 40 mm or more, and particularly preferably 50 mm or more. The thickness of the SiC ingot 10 is preferably 300 mm or less, for example. The thicker the SiC ingot 10, the more SiC substrates can be obtained. The thickness of the SiC ingot 10 may hereinafter be referred to as the ingot length in some cases.

[0029] The SiC ingot 10 has a facet 4 and a step-flow growth region 5.

[0030] The SiC ingot 10 grows crystals on a SiC seed crystal. In order to suppress the generation of polytypes, seed crystals having an offset angle with respect to the {0001} plane are often used. The offset angle is, for example, 3.5° or more and 4.5° or less, preferably 4°. By step-flow growth of SiC on the seed crystal, the generation of polytypes can be suppressed. Even when the SiC ingot 10 grows by step-flow growth, a part of the crystal growth surface becomes parallel to the (0001) plane, and a plane parallel to the (0001) plane is exposed on the crystal growth surface. Since the crystal grows perpendicular to the (0001) plane on this plane parallel to the (0001) plane, step-flow growth does not occur. The facet 4 is a region where the crystal grows perpendicular to the (0001) plane. The step-flow growth region 5 is a region where the crystal grows by step-flow growth. The step-flow growth region 5 has an offset angle with respect to the {0001} plane of, for example, 3.5° or more and 4.5° or less.

[0031] In a plan view from the Z direction, the facet 4 and the step-flow growth region 5 have different colors and the boundary can be visually observed. This is because the crystal growth modes of the facet 4 and the step-flow growth region 5 are different. The facet 4 is observed visually as a region with a darker color than the step-flow growth region 5.

[0032] The boundary between the facet 4 and the step flow growth region 5 can be visually determined, or it can also be determined by the following procedure. First, an image of the cross-section to be measured is acquired. The image is obtained, for example, by double-side polishing the substrate and using a scanner. The scanner can be, for example, a flatbed scanner made by Canon. Next, the acquired image is converted into the HLS color space consisting of hue, luminance, and saturation, and the luminance is obtained. Then, in the image converted into the luminance distribution, a circle with a radius of X pixels is drawn centering on an arbitrary pixel. If there is a pixel in this circle whose luminance difference from the central pixel is Y or more, the pixel at the center of the circle becomes a pixel of the facet candidate. If there is no pixel in this circle whose luminance difference from the central pixel is Y or more, the pixel at the center of the circle is not a pixel of the facet candidate. Next, the same process is performed on all the pixels of the image, and each pixel is classified as a pixel of the facet candidate or a pixel that is not a facet candidate. Then, the boundary between the pixels of the facet candidate and the pixels that are not facet candidates is detected, and the inside of this region can be set as the facet. Among the pixels of the facet candidate, a pixel that is an outlier separated from the pixels of other facet candidates can be determined not to be a facet candidate. The radius X of the circle and the luminance difference Y are set according to the size of the image and the number of pixels. These settings are set to values such that the visual result and the determination result do not deviate significantly. For example, when using an image of 640 pixels × 480 pixels including a 150 mm wafer, the radius X is set to 9 pixels and the luminance difference Y is set to 4 W·sr -1 ·m -2 and set to.

[0033] Also in the XZ cross-section, the boundary between the facet 4 and the step flow growth region 5 can be visually determined. Hereinafter, the boundary located on the central side of the SiC ingot 10 among the boundaries between the facet 4 and the step flow growth region 5 is referred to as the inner boundary 6, and the boundary outside the inner boundary is referred to as the outer boundary 7.

[0034] The inner boundary 6 has a first inclined surface 61 and a second inclined surface 62. The first inclined surface 61 is an inclined surface that slopes in the -X direction with respect to the Z direction. The second inclined surface 62 is an inclined surface that slopes in the +X direction with respect to the Z direction. The first inclined surface 61 is, for example, closer to the first end 1 than the second inclined surface 62.

[0035] Similarly, the outer boundary 7 has a first inclined surface 71 and a second inclined surface 72. The first inclined surface 71 is an inclined surface that slopes in the -X direction with respect to the Z direction. The second inclined surface 72 is an inclined surface that slopes in the +X direction with respect to the Z direction. The first inclined surface 71 is, for example, closer to the first end 1 than the second inclined surface 72.

[0036] At the boundary between the first inclined surface 61 and the second inclined surface 62, there is an inflection point 8 where the inclination angle with respect to the Z direction changes discontinuously. The inflection point 8 preferably passes through the center of the SiC ingot 10 in the Z direction (the center position of the ingot length) and is on the first end 1 side of the plane H1 parallel to the XY plane. Furthermore, the inflection point 8 preferably passes through a position shifted by 40% of the ingot length in the Z direction from the first end 1 and is on the first end 1 side of the plane H2 parallel to the XY plane. More preferably, the inflection point 8 passes through a position shifted by 30% of the ingot length in the Z direction from the first end 1 and is on the first end 1 side of a plane parallel to the XY plane, more preferably through a position shifted by 20% and on the first end 1 side of a plane parallel to the XY plane, and even more preferably through a position shifted by 10% and on the first end 1 side of a plane parallel to the XY plane.

[0037] The farther the inflection point 8 is from the first end 1, the more the facet 4 moves to the offset downstream side (-X direction: [-1 - 120] direction). That is, the farther the inflection point 8 is from the first end 1, the more the facet 4 penetrates deeply into the SiC ingot 10. The more the facet 4 penetrates deeply into the SiC ingot 10, the higher the likelihood that the planar coordinates of the facet 4 when viewed from the Z direction at the height position of the inflection point 8 and the planar coordinates of the facet 4 confirmed at the second end 2 will deviate significantly.

[0038] Here, in the actual SiC ingot 10, only the planar coordinates of the facet 4 at the first end 1 or the second end 2 can be confirmed, and the planar coordinates of the facet 4 inside can only be estimated. The facet 4 has a lower resistance value and a changing light absorption coefficient than the step flow growth region 5. Therefore, when performing laser processing, it is necessary to adjust conditions such as the laser output and cutting speed. For example, if it is estimated that there is no facet 4 inside from the planar coordinates of the facet 4 at the second end 2 but there is a facet 4 at the estimated position, the laser output may be insufficient during laser processing. As described above, the more the facet 4 enters deeply into the SiC ingot 10, the higher the possibility that the height position of the inflection point 8 and the planar position of the facet 4 at the second end 2 will deviate greatly, and the risk of errors occurring during processing increases. Therefore, when the inflection point 8 is on the first end 1 side, the processing stability of the SiC ingot 10 is enhanced. Also, the more the inflection point 8 is on the first end 1 side, the higher the processing stability of the SiC ingot 10.

[0039] The facet 4 is preferably located on the offset upstream side of the SiC ingot 10. That is, the facet 4 is preferably located in the +X direction ([11-20] direction) from the plane (YZ plane) passing through the center in the X direction and perpendicular to the X direction. As described above, by preventing the facet 4 from entering too deeply into the SiC ingot 10, the processing stability of the SiC ingot 10 is enhanced.

[0040] The first inclined surface 61 is inclined in the -X direction at an inclination angle θ1 with respect to the Z direction, for example. The second inclined surface 62 is inclined in the +X direction at an inclination angle θ2 with respect to the Z direction, for example. The inclination angle θ1 is the absolute value of the interior angle formed by the first inclined surface 61 and the Z direction. The inclination angle θ2 is the absolute value of the interior angle formed by the second inclined surface 62 and the Z direction. It is preferable that the inclination angle θ1 is smaller than the inclination angle θ2. By the inclination angle θ1 being smaller than the inclination angle θ2, it is possible to avoid the facet 4 from largely entering the inside of the SiC ingot 10. Further, if the inclination angle θ2 is larger than the inclination angle θ1, at the height position after the inflection point 8, the planar coordinates of the facet 4 largely shift outside the SiC ingot 10. The outside of the SiC ingot 10 often falls outside the acquisition region of the SiC substrate, and by making the inclination angle θ2 larger than the inclination angle θ1, the facet 4 can be excluded from the acquisition region of the SiC substrate.

[0041] In FIG. 1, the case where the inclination angle θ1 of the first inclined surface 61 and the inclination angle θ2 of the second inclined surface 62 are constant is illustrated, but the inclination angle θ1 of the first inclined surface 61 and the inclination angle θ2 of the second inclined surface 62 may vary depending on the position in the Z direction. In this case, the average inclination angles of the first inclined surface 61 and the second inclined surface 62 are treated as the inclination angle θ1 and the inclination angle θ2. The average inclination angle is the average value of the inclination angles measured at five different positions in the Z direction.

[0042] The first inclined surface 61 preferably includes a portion where the inclination angle θ1 is 5° or more, and more preferably includes a portion where the inclination angle θ1 is 15° or more. Similarly, the second inclined surface 62 preferably includes a portion where the inclination angle θ2 is 5° or more, and more preferably includes a portion where the inclination angle θ2 is 15° or more. It is more preferable that both the first inclined surface 61 and the second inclined surface 62 include portions where the inclination angle θ1 and the inclination angle θ2 are 5° or more. Further, it is more preferable that at least one of the first inclined surface 61 and the second inclined surface 62 includes a portion where the inclination angle θ1 and the inclination angle θ2 are 15° or more.

[0043] Also, it is preferable that the area of the facet 4 at the first end 1 is larger than the area of the facet 4 at the second end 2. The first end 1 corresponds to the portion where crystal growth occurred earlier in the crystal growth of the SiC ingot 10 than the second end 2. In the initial stage of crystal growth of the SiC single crystal, crystal growth is unstable. By providing a facet 4 with a sufficient area on the first end 1 side, the generation of different polytypes can be further suppressed. Also, if the area of the facet 4 at the second end 2 corresponding to the later stage of crystal growth is small, it becomes easier to process the SiC ingot 10.

[0044] "Method for manufacturing SiC ingot" Next, the method for manufacturing the SiC ingot 10 according to the present embodiment will be described. FIGS. 3 and 4 are diagrams for explaining the method for manufacturing the SiC ingot 10 according to the present embodiment.

[0045] The manufacturing apparatus for the SiC ingot 10 includes a crucible 20, a heating coil 21, a heat insulating member 22, a guide member 23, and a shielding member 24.

[0046] The crucible 20 is made of, for example, graphite. The crucible 20 surrounds the growth space A. In the growth space A of the crucible 20, a seed crystal S and a SiC raw material M are arranged. The heating coil 21 surrounds the outer periphery of the crucible 20. The heating coil 21 heats the SiC raw material M. The heated SiC raw material M sublimes. The gas sublimated from the SiC raw material M recrystallizes on the surface of the seed crystal S, and the SiC ingot 10 grows crystallographically.

[0047] The atmospheric pressure during crystal growth in the growth space A is more than 0.3 Torr and less than 50 Torr. The atmospheric pressure during crystal growth in the growth space A is, for example, 10 Torr. If the pressure in the growth space A is too low, the dopant element cannot be sufficiently included in the crystal, and the resistivity of the SiC ingot 10 increases. The resistivity of the SiC ingot 10 is a parameter that affects electrical discharge machining. Also, if the pressure in the growth space A is too high, sufficient sublimated gas does not occur from the SiC raw material M, and productivity decreases.

[0048] The growth space A is, for example, an argon and nitrogen gas atmosphere. The crucible 20 is heated while rotating at a constant speed. The rotation speed of the crucible is, for example, 5 rpm. The temperature of the crucible 20 is, for example, 2300 °C at the bottom and 2000 °C at the top.

[0049] The heat insulation member 22 is movable in the Z direction. The Z-direction position of the heat insulation member 22 changes as the SiC ingot 10 grows. The growth process of the SiC ingot 10 is divided into two processes, a first growth process and a second growth process, and in the two processes, the Z-direction position of the heat insulation member 22 is adjusted. The first growth process includes the start of growth, and the second growth process includes the end of growth. The Z-direction position of the heat insulation member 22 is set 5 mm above the center position of the crystal growth surface of the SiC ingot 10 in the first growth process, and 5 mm below the center position of the crystal growth surface of the SiC ingot 10 in the second growth process. The boundary point between the first growth process and the second growth process is 10% - 55% of the final growth amount. For example, when the boundary point is 30% of the final growth amount, the first growth process is the process until the SiC ingot 10 grows to 30% of the final growth amount, and the second growth process is the process in which the SiC ingot 10 grows from 30% of the final growth amount to the end. Also, "5 mm above the center position of the crystal growth surface" means "a position 5 mm closer to the seed crystal S than the center position of the crystal growth surface in the Z direction", and "5 mm below the center position of the crystal growth surface" means "a position 5 mm away from the seed crystal S from the center position of the crystal growth surface in the Z direction".

[0050] The guide member 23 is made of, for example, graphite or a high melting point ceramic. The shape of the guide member 23 is different, for example, between the offset upstream side (+X direction) and the offset downstream side (-X direction). The inner surface of the guide member 23 located on the offset upstream side has a different inclination angle φ with respect to the horizontal direction (a direction perpendicular to the Z direction) depending on the position in the Z direction. In the range of the position in the Z direction of the crystal growth surface in the first growth process, the inclination angle φ is 50° or more and 85° or less, and in the range of the position in the Z direction of the crystal growth surface in the second growth process, the inclination angle φ is 80° or more and 90° or less. For example, when the boundary point between the first growth process and the second growth process is 30% of the final growth amount, the inclination angle φ is 50° or more and 85° or less at the position up to 30% of the final growth amount of the SiC ingot 10, and 80° or more and 90° or less at the position from 30% to 100% of the final growth amount of the SiC ingot 10. Further, the inner surface of the guide member 23 located on the offset downstream side has an inclination angle with respect to the horizontal direction (a direction perpendicular to the Z direction) of 80° or more and 90° or less regardless of the position in the Z direction.

[0051] The shielding member 24 is located between the seed crystal S or the SiC ingot 10 during crystal growth and the SiC raw material M. The shielding member 24 is disposed at a position where the distance from the surface of the SiC ingot 10 after crystal growth is 20 mm or more. Regardless of the shape of the shielding member 24, the thickness is, for example, 5 mm or more. The shielding member 24 covers only the offset upstream side of the SiC ingot 10 when viewed from the Z direction. For example, the shielding member 24 covers only the offset upstream side of the SiC ingot 10 in a fan shape when viewed from the Z direction.

[0052] The heat insulating member 22, the guide member 23, and the shielding member 24 are arranged at the above-described positions, and the SiC ingot 10 is crystal-grown on the seed crystal S. By arranging the heat insulating member 22, the guide member 23, and the shielding member 24 at predetermined positions, the temperature distribution in the growth space A can be controlled, and a SiC ingot 10 having a desired facet 4 can be produced.

[0053] Further, the produced SiC ingot 10 can be processed into a columnar shape and sliced to produce a SiC substrate.

[0054] Since the shape of the facet 4 of the SiC ingot 10 according to this embodiment is controlled, the crystal quality is high and it is easy to process. In the SiC ingot 10 according to this embodiment, at the initial stage of crystal growth, the facet 4 moves to the offset downstream side and the first inclined surface 61 is formed. By growing the facet 4 toward the offset downstream side at the initial stage of crystal growth where crystal growth is unstable, the generation of different polymorphs in the SiC ingot 10 is suppressed. Further, in the SiC ingot 10 according to this embodiment, at the later stage of crystal growth, the facet 4 moves to the offset upstream side and the second inclined surface 62 is formed. By moving the position of the facet 4 to the outside of the SiC ingot 10, the ratio of the facet 4 in the SiC substrate acquisition region can be reduced, and the SiC ingot 10 can be easily processed.

[0055] "Method for manufacturing SiC substrate" The method for manufacturing the SiC substrate according to the first embodiment includes a step of manufacturing the SiC ingot 10 of the above-described embodiment by the above-described method, and a step of slicing the SiC ingot 10. As the step of slicing the SiC ingot 10, for example, a method of making a crack by processing the SiC ingot 10 with a laser and cutting out the SiC substrate can be used. The SiC ingot 10 may be processed into a columnar shape before slicing the SiC ingot 10.

[0056] The method for manufacturing the SiC substrate according to the second embodiment includes a step of preparing the SiC ingot 10 of the above-described embodiment, and a step of slicing the SiC ingot 10. The step of preparing the SiC ingot 10 may include obtaining the SiC ingot 10 of the above-described embodiment from another company. The SiC ingot 10 may be a boule as long as it satisfies the requirements of the above-described embodiment. The step of slicing the SiC ingot 10 is the same as that of the first embodiment. Also, the SiC ingot 10 may be processed into a columnar shape before slicing the SiC ingot 10.

[0057] As described above, the preferred embodiments of the present invention have been described in detail. However, the present invention is not limited to specific embodiments, and various modifications and changes are possible within the scope of the gist (technical requirements) of the present invention described in the claims.

Example

[0058] 「Example 1」 A seed crystal with a diameter of 8 inches (200 mm) was prepared. Then, using the manufacturing apparatus shown in FIGS. 3 and 4, a SiC ingot was grown by 30 mm on the seed crystal.

[0059] The inside of the growth space A was set to an Ar and N2 gas atmosphere with a pressure of 10 Torr. The temperature of the crucible 20 was 2300°C at the bottom and 2000°C at the top. The rotation speed of the crucible 20 was 5 rpm. The inclination angle φ of the inner surface of the guide member 23 located on the offset upstream side was set to 70° at the position up to 30% of the final growth amount of the SiC ingot (the Z-direction position of the crystal growth surface in the first growth process described later), and 85° at the position from 30% to 100% of the final growth amount of the SiC ingot (the Z-direction position of the crystal growth surface in the second growth process described later). Also, the inclination angle of the inner surface of the guide member 23 located on the offset downstream side was set to 90° regardless of the Z-direction position. The shielding member 24 was arranged to cover only the offset upstream side in a fan shape.

[0060] Then, as the crystal growth progressed, the position of the heat insulating member 22 was changed. The process until the SiC ingot 10 grew to 30% of the final growth amount was defined as the first growth process, and the process from 30% to the end of the final growth amount of the SiC ingot 10 was defined as the second growth process. The Z-direction position of the heat insulating member 22 was set 5 mm above the center position of the crystal growth surface of the SiC ingot 10 in the first growth process, and 5 mm below the center position of the crystal growth surface of the SiC ingot 10 in the second growth process.

[0061] Under the above conditions, a SiC ingot of Example 1 was fabricated. Then, the cross-section of the fabricated SiC ingot was examined, and the shape of the inner boundary between the facet and the step-flow growth region was confirmed. The SiC ingot had a first end corresponding to the side opposite to the growth surface of the seed crystal and a second end corresponding to the growth surface. The inner boundary of the facet had a first inclined surface and a second inclined surface. The first inclined surface was closer to the first end than the second inclined surface, and the inclination angle of the first inclined surface with respect to the crystal growth direction was smaller than that of the second inclined surface with respect to the crystal growth direction. The first inclined surface included a portion where the absolute value of the inclination angle with respect to the crystal growth direction was 5° or more, and the second inclined surface included a portion where the absolute value of the inclination angle with respect to the crystal growth direction was 15° or more. The inflection point between the first inclined surface and the second inclined surface was located at a position shifted by 20% of the ingot length in the Z direction from the first end. The facet was located in the [11-20] direction with respect to the plane passing through the center of the <11-20> direction and perpendicular to the <11-20> direction.

[0062] Also under the same conditions, 20 SiC ingots of Example 1 were fabricated and evaluated. Specifically, the quality yield of the SiC ingots and the average time required for processing the SiC ingots were determined.

[0063] The quality yield of the SiC ingots was evaluated by assessing the presence or absence of polytypes. Specifically, the SiC ingots were cut with a wire saw at positions shifted 2 mm from each of the first end and the second end of the SiC ingots to obtain substrates for evaluation. The thickness of the substrates was 0.5 mm. After polishing both sides of the substrates, X-ray topograph (XRT) (diffraction vector g: 1-100) transmission images were acquired to confirm the presence or absence of polytypes and micropipes caused thereby.

[0064] As the time required for processing the SiC ingot, the time required to obtain SiC wafers from a cylindrically processed SiC ingot was measured. When obtaining SiC wafers from the SiC ingot, laser processing was used. The laser scan pitch was 200 μm, the feed rate of the laser scan was 200 mm / sec, the number of scans was 1 time, the acceleration / deceleration time was 0.1 second, and the inter-line movement time was 0.1 second. The acceleration / deceleration time is the time required for acceleration / deceleration when scanning the laser in the opposite direction after scanning the laser in one direction. The inter-line movement time indicates the time related to the movement in the second direction in the process of repeating the laser scanning in the first direction and the movement in the second direction orthogonal to the first direction.

[0065] Among the 20 SiC ingots of Example 1, 19 did not contain polytypes of different kinds, and the quality yield was 95%. Also, the time required to slice the SiC ingot of Example 1 into wafers was 18.2 minutes per sheet.

[0066] "Example 2" A seed crystal with a diameter of 8 inches (200 mm) was prepared. Then, using the manufacturing apparatus shown in FIGS. 3 and 4, a SiC ingot was grown by 30 mm on the seed crystal. The process until the SiC ingot grew to 50% of the final growth amount was defined as the first growth process, and the process from 50% of the final growth amount to the end of the SiC ingot growth was defined as the second growth process. Then, in the first growth process, the position of the heat insulating member 22 in the Z direction was set 5 mm above the center position of the crystal growth surface of the SiC ingot. In the second growth process, the position of the heat insulating member 22 in the Z direction was set 5 mm below the center position of the crystal growth surface of the SiC ingot. The inclination angle φ of the inner surface of the guide member 23 located on the offset upstream side was 70° at the position up to 50% of the final growth amount of the SiC ingot (the position in the Z direction of the crystal growth surface in the first growth process), and 85° at the position from 50% to 100% of the final growth amount of the SiC ingot (the position in the Z direction of the crystal growth surface in the second growth process). Other conditions were the same as those in Example 1, and the SiC ingot of Example 2 was produced.

[0067] The cross-section of the produced SiC ingot was examined, and the shape of the inner boundary between the facet and the step-flow region was confirmed. The SiC ingot had a first end corresponding to the side opposite to the growth surface of the seed crystal and a second end corresponding to the growth surface. The inner boundary of the facet had a first inclined surface and a second inclined surface. The first inclined surface was closer to the first end than the second inclined surface, and the inclination angle of the first inclined surface with respect to the crystal growth direction was smaller than that of the second inclined surface with respect to the crystal growth direction. The first inclined surface included a portion where the absolute value of the inclination angle with respect to the crystal growth direction was 5° or more, and the second inclined surface included a portion where the absolute value of the inclination angle with respect to the crystal growth direction was 15° or more. The inflection point between the first inclined surface and the second inclined surface was located at a position shifted by 40% of the ingot length in the Z direction from the first end. The facet was located in the [11-20] direction with respect to the plane passing through the center of the <11-20> direction and perpendicular to the <11-20> direction.

[0068] Under the same conditions, 20 SiC ingots of Example 2 were produced, and the SiC ingots were evaluated. Among the 20 SiC ingots of Example 2, 19 did not contain polytypes, and the quality yield was 95%. The time required to obtain SiC wafers from SiC ingots under the same conditions as in Example 1 was measured. The time required to slice the SiC ingot into wafers was 18.6 minutes per wafer.

[0069] "Comparative Example 1" Comparative Example 1 is different from Example 1 in that a SiC ingot was produced using a manufacturing apparatus for SiC ingots that does not have a guide member 23 and a shielding member 24. Further, in the manufacturing process of the SiC ingot of Comparative Example 1, the position of the heat insulating member 22 in the Z direction was always 5 mm above the center position of the crystal growth surface of the SiC ingot from the initial stage to the end of growth.

[0070] Under the above conditions, a SiC ingot of Comparative Example 1 was produced. Then, the cross-section of the produced SiC ingot was examined, and the shape of the inner boundary between the facet and the step-flow growth region was confirmed. The inner boundary consisted only of a first inclined surface inclined in the [-1-120] direction with respect to the crystal growth direction.

[0071] Under the same conditions, 20 SiC ingots of Comparative Example 1 were produced, and the quality yield of the SiC ingots and the average time required for processing the SiC ingots were determined.

[0072] The quality yield of the SiC ingots of Comparative Example 1 was 95%. Also, the time required to slice the SiC ingots of Comparative Example 1 into wafers was 20.4 minutes per sheet.

[0073] "Comparative Example 2" Comparative Example 2 is different from Example 1 in that a SiC ingot manufacturing apparatus having no guide member 23 and shielding member 24 was used to manufacture the SiC ingot. Further, in the manufacturing process of the SiC ingot of Comparative Example 2, the Z-direction position of the heat insulating member 22 was always 5 mm below the center position of the crystal growth surface of the SiC ingot from the initial stage to the end of growth.

[0074] Under the above conditions, SiC ingots of Comparative Example 2 were produced. Then, the cross section of the produced SiC ingot was confirmed, and the shape of the inner boundary between the facet and the step flow growth region was confirmed. The inner boundary consisted only of a second inclined surface inclined in the [11-20] direction with respect to the crystal growth direction.

[0075] Under the same conditions, 20 SiC ingots of Comparative Example 2 were produced, and the quality yield of the SiC ingots and the average time required for processing the SiC ingots were determined.

[0076] The quality yield of the SiC ingots of Comparative Example 2 was 70%. Also, the time required to slice the SiC ingots of Comparative Example 2 into wafers was 17.8 minutes per sheet.

[0077] "Comparative Example 3" In Comparative Example 3, the position of the heat insulating member 22 during crystal growth was changed from that in Example 1. In Comparative Example 3, the process until the SiC ingot grew to 60% of the final growth amount was defined as the first growth process, and the process from 60% to the end of the final growth amount of the SiC ingot was defined as the second growth process. In the first growth process, the position of the heat insulating member 22 in the Z direction was set 5 mm above the center position of the crystal growth surface of the SiC ingot. In the second growth process, the position of the heat insulating member 22 in the Z direction was set 5 mm below the center position of the crystal growth surface of the SiC ingot. The inclination angle φ of the inner surface of the guide member 23 located on the offset upstream side was set to 70° at the position up to 70% of the final growth amount of the SiC ingot, and 85° at the position from 70% to 100% of the final growth amount of the SiC ingot.

[0078] Under the above conditions, a SiC ingot of Comparative Example 3 was fabricated. Then, the cross-section of the fabricated SiC ingot was examined, and the shape of the inner boundary between the facet and the step flow growth region was examined. The inner boundary had a first slope and a second slope. The inflection point between the first slope and the second slope was at a position shifted in the Z direction by 80% of the ingot length from the first end.

[0079] Also under the same conditions, 20 SiC ingots of Comparative Example 3 were fabricated, and the quality yield of the SiC ingots and the average time required for processing the SiC ingots were determined.

[0080] The quality yield of the SiC ingots of Comparative Example 3 was 95%. Also, the time required to slice a SiC ingot of Comparative Example 3 into wafers was 19.5 minutes per sheet.

[0081] "Comparative Example 4" A seed crystal with a diameter of 8 inches (200 mm) was prepared. Then, using the manufacturing apparatus shown in FIGS. 3 and 4, a SiC ingot was grown on the seed crystal by 30 mm. The process until the SiC ingot grows to 70% of the final growth amount was defined as the first growth process, and the process from 70% to the end of the final growth amount of the SiC ingot was defined as the second growth process. In the first growth process, the position of the heat insulating member 22 in the Z direction was set 5 mm above the center position of the crystal growth surface of the SiC ingot. In the second growth process, the position of the heat insulating member 22 in the Z direction was set 5 mm below the center position of the crystal growth surface of the SiC ingot. The inclination angle φ of the inner surface of the guide member 23 located on the offset upstream side was set to 70° at the position up to 70% of the final growth amount of the SiC ingot (the Z-direction position of the crystal growth surface in the first growth process), and 85° at the position from 70% to 100% of the final growth amount of the SiC ingot (the Z-direction position of the crystal growth surface in the second growth process). Other conditions were the same as in Example 1, and a SiC ingot of Comparative Example 4 was produced.

[0082] The cross-section of the produced SiC ingot was observed, and the shape of the inner boundary between the facet and the step flow region was observed. It had a first end corresponding to the side opposite to the growth surface of the seed crystal and a second end corresponding to the growth surface, and the inner boundary of the facet had a first inclined surface and a second inclined surface. The first inclined surface was closer to the first end than the second inclined surface, but the inclination angle of the first inclined surface with respect to the crystal growth direction was larger than the inclination angle of the second inclined surface with respect to the crystal growth direction. The first inclined surface included a portion where the absolute value of the inclination angle with respect to the crystal growth direction was 5° or more, but the second inclined surface did not include a portion where the absolute value of the inclination angle with respect to the crystal growth direction was 15° or more. The inflection point between the first inclined surface and the second inclined surface was at a position shifted 60% of the ingot length in the Z direction from the first end. The facet was located in the [11-20] direction from the plane passing through the center of the <11-20> direction and perpendicular to the <11-20> direction.

[0083] Under the same conditions, 20 SiC ingots of Comparative Example 4 were produced and evaluated. Among the 20 SiC ingots of Comparative Example 4, 19 did not contain polytypes, and the yield was 95%. The time required to obtain SiC wafers from SiC ingots was measured under the same conditions as in Example 1. The time required to slice the SiC ingot into wafers was 19.1 minutes per wafer.

[0084]

Table 1

Explanation of symbols

[0085] 1 First end 2 Second end 3 Side wall 4 Facet 5 Step flow growth region 6 Inner boundary 7 Outer boundary 8 Inflection point 10 SiC ingot 20 Crucible 21 Heating coil 22 Heat insulating member 23 Guide member 24 Shielding member 61, 71 First inclined plane 62, 72 Second inclined plane A Growth space H1, H2 Plane M SiC raw material S Seed crystal θ1, θ2, φ Inclination angle

Claims

1. having a step-flow growth region and a facet, in a cross-sectional plane passing through the center and along the <11-20> direction, an inner boundary between the facet and the step-flow growth region has a first inclined surface inclined in the [-1-120] direction with respect to the crystal growth direction and a second inclined surface inclined in the [11-20] direction with respect to the crystal growth direction, a SiC ingot, wherein an inflection point between the first inclined surface and the second inclined surface is on a first end side which is a Si plane or a plane inclined by an offset angle from the Si plane, and is closer to the first end than the center position of the ingot length.

2. The SiC ingot according to claim 1, wherein an inflection point between the first inclined surface and the second inclined surface is on the first end side and is closer to the first end than a position shifted by 40% of the ingot length in the crystal growth direction from the first end.

3. The SiC ingot according to claim 1, wherein the first inclined surface is closer to the first end than the second inclined surface.

4. The SiC ingot according to claim 1, wherein an inclination angle of the first inclined surface with respect to the crystal growth direction is smaller than an inclination angle of the second inclined surface with respect to the crystal growth direction.

5. The SiC ingot according to claim 1, wherein the first inclined surface and the second inclined surface include a portion where an absolute value of an inclination angle with respect to the crystal growth direction is 5° or more.

6. The SiC ingot according to claim 1, wherein at least one of the first inclined surface and the second inclined surface includes a portion where an absolute value of an inclination angle with respect to the crystal growth direction is 15° or more.

7. The SiC ingot according to claim 1, wherein the facet is located in the [11-20] direction from a plane passing through the center in the <11-20> direction and perpendicular to the <11-20> direction.

8. The SiC ingot according to claim 1, wherein the ingot length is 10 mm or more.

9. The SiC ingot according to claim 1, wherein the diameter is 145 mm or more.

10. The SiC ingot according to claim 1, wherein the diameter is 195 mm or more.

11. A method for manufacturing a SiC substrate, comprising: a step of manufacturing a SiC ingot according to any one of claims 1 to 10; and a step of slicing the SiC ingot.

12. A method for manufacturing a SiC substrate, comprising: a step of preparing a SiC ingot according to any one of claims 1 to 10; and a step of slicing the SiC ingot.

13. A method for manufacturing a SiC substrate, having: a step of preparing a SiC ingot according to any one of claims 1 to 10; and a step of slicing the SiC ingot.

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