Manufacturing method for SiC ingots and SiC substrates

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 that is one order of magnitude larger and a bandgap that is three times larger than that of silicon (Si). In addition, silicon carbide (SiC) has properties such as a thermal conductivity that is 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, and the like. 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 one in which a SiC single crystal has grown 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 growing the 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 pattern from the other crystal growth surfaces that grow by step flow. The part that has grown in a different pattern 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

[0006] Facets have lower resistance than the step-flow grown regions. This is because the amount of nitrogen uptake increases relatively in facets. The difference in resistivity between facets and step-flow grown regions negatively impacts laser processing and electrical discharge machining. For example, when cracking a SiC ingot with a laser and cutting out a SiC substrate from the ingot, the laser output needs to be changed at the boundary between the facets and the step-flow grown regions. The more times the laser output needs to be changed, the lower the processing throughput becomes. On the other hand, if the facets become too small, especially in the early stages of growth, it becomes difficult to introduce enough through-helix dislocations (TSDs) into the facets, making it easier for heteromorphs to occur.

[0007] This invention has been made in view of the above problems, and aims to provide a SiC ingot that achieves both high crystal quality and ease of processing, and a method for manufacturing a SiC substrate using the SiC ingot. [Means for solving the problem]

[0008] To solve the above problems, the present invention provides the following means.

[0009] (1) A SiC ingot according to the first embodiment has a step flow growth region and a facet. In a cross-section of the SiC ingot passing through the center along the <11-20> direction, the inner boundary between the facet and the step flow growth region has a first slope inclined in the [-1-120] direction with respect to the crystal growth direction and a second slope inclined in the [11-20] direction with respect to the crystal growth direction. The inflection point between the first slope and the second slope is located on the 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 embodiment of (1) above, the inflection point between the first slope and the second slope may be located on the first end side of a position shifted by 40% of the ingot length from the first end in the crystal growth direction.

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

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

[0013] (5) In a SiC ingot according to any of the embodiments of (1) to (4) above, the first slope and the second slope may include portions in which the absolute value of the inclination angle with respect to the crystal growth direction is 5° or more.

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

[0015] (7) In a SiC ingot according to any of the embodiments of (1) to (6) above, the facets may be located in the [11-20] direction from a plane that passes through the center of the <11-20> direction and is perpendicular to the <11-20> direction.

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

[0017] (9) The SiC ingot according to any of the above embodiments (1) to (8) 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.

Effect of the Invention

[0020] The SiC ingot according to the above aspect is excellent in crystal quality and workability. Also, 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] It is a cross-sectional view of the SiC ingot according to the present embodiment. [Figure 2] It is a plan view of the SiC ingot according to the present embodiment. [Figure 3] It is a diagram for explaining the manufacturing method of the SiC ingot according to the present embodiment. [Figure 4] It is a diagram for explaining the manufacturing method of the SiC ingot according to the present embodiment.

Mode for Carrying Out the Invention

[0022] The SiC ingot and the like according to this embodiment will be described in detail below, with reference to the figures as appropriate. In the drawings used in the following description, characteristic parts may be enlarged for convenience in order to make the features of this embodiment easier to understand, and the dimensional ratios of each component may differ from those of the actual product. The materials, dimensions, etc. exemplified in the following description are examples only, and the present invention is not limited to them, and can be implemented with appropriate modifications without changing the gist (technical requirements).

[0023] In this specification, individual orientations are indicated by [], collective orientations by <>, individual planes by () and collective planes by {}. While crystallography dictates that negative exponents are represented by a "-" (bar) above the number, in this specification, the negative sign is placed before the number.

[0024] First, let's define the directions. 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 on a plane perpendicular 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, on a plane perpendicular to the Z direction, the direction perpendicular to the X direction is defined as the Y direction. The Y direction is, for example, the <1-100> direction.

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

[0026] The SiC ingot 10 is a columnar body consisting of a seed crystal and a crystal growth portion grown on the seed crystal. The SiC ingot 10 may be a cylindrical object or an object before being processed into a cylindrical shape. The SiC ingot 10 is a single crystal of SiC grown from a first end 1 to a second end 2. The first end 1 and the second end 2 are connected by a side wall 3. The SiC ingot 10 may increase in diameter from the first end 1 to the second end 2, or it may be a cylindrical object 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, but no 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 diameter of the obtainable SiC substrate. For example, if the SiC ingot 10 expands in diameter from the first end 1 to the second end 2, the diameter of the first end 1 corresponds to the diameter D of the SiC ingot 10. For example, if the SiC ingot 10 is cylindrical with a constant diameter, the diameter of any cross-section obtained by cutting the SiC ingot 10 with a plane perpendicular to the Z direction corresponds to the diameter D of the SiC ingot 10. The SiC ingot 10 may be capable of producing, for example, a 6-inch substrate or 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. The thicker the SiC ingot 10, the more SiC substrates can be obtained. The thickness of the SiC ingot 10 may be referred to as the ingot length below.

[0029] The SiC ingot 10 has facets 4 and step flow growth regions 5.

[0030] SiC ingot 10 is grown on a SiC seed crystal. To suppress the occurrence of heteromorphism, a seed crystal having an offset angle with respect to the {0001} plane is often used. The offset angle is, for example, 3.5° to 4.5°, preferably 4°. By having SiC grow in step flow on the seed crystal, the occurrence of heteromorphism can be suppressed. Even when SiC ingot 10 undergoes 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, it does not undergo step flow growth. Facet 4 is a region where the crystal grew perpendicular to the (0001) plane. Step flow growth region 5 is a region where the crystal underwent step flow growth. Step flow growth region 5 has, for example, an offset angle with respect to the {0001} plane of 3.5° to 4.5°.

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

[0032] The boundary between facet 4 and step flow growth region 5 can be determined visually, but it can also be determined using the following procedure. First, an image of the cross-section to be measured is acquired. The image can be acquired, for example, by polishing both sides of the substrate and using a scanner. For example, a Canon flatbed scanner can be used. Next, the acquired image is converted to the HLS color space consisting of hue, luminance, and saturation, and the luminance is determined. Then, in the image converted to a luminance distribution, a circle with radius X pixels is drawn with an arbitrary pixel as the center. If there is a pixel in this circle whose luminance difference from the center pixel is Y or greater, the pixel at the center of the circle becomes a facet candidate pixel. If there is no pixel in this circle whose luminance difference from the center pixel is Y or greater, the pixel at the center of the circle becomes a non-facet candidate pixel. Next, the same process is performed on all pixels in the image, and each pixel is classified as either a facet candidate pixel or a non-facet candidate pixel. Then, the boundary between facet candidate pixels and non-facet candidate pixels is detected, and the area inside this boundary can be designated as a facet. Furthermore, pixels that are isolated from other facet candidate pixels can be determined not to be facet candidates. The radius X and brightness difference Y of the circle are set according to the image size and number of pixels. These settings should be set to values ​​that do not cause a large discrepancy between the visual result and the judgment result. For example, when using a 640 pixels x 480 pixels image including a 150 mm wafer, set the radius X to 9 pixels and the brightness difference Y to 4 W·sr. -1 ·m -2 Set it as follows.

[0033] Even in the XZ cross-section, the boundary between facet 4 and the step-flow growth region 5 can be visually determined. Hereinafter, the boundary between facet 4 and the step-flow growth region 5 located towards the center of the SiC ingot 10 will be referred to as the inner boundary 6, and the boundary outside the inner boundary will be referred to as the outer boundary 7.

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

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

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

[0037] The further the inflection point 8 is from the first end 1, the further facet 4 moves downstream of the offset (-X direction: [-1-120] direction). In other words, the further the inflection point 8 is from the first end 1, the further facet 4 penetrates inside the SiC ingot 10. The further facet 4 penetrates inside the SiC ingot 10, the higher the probability that the planar coordinates of facet 4 viewed from the Z direction at the height of the inflection point 8 will differ from the planar coordinates of facet 4 observed at the second end 2.

[0038] In the actual SiC ingot 10, only the planar coordinates of facet 4 at the first end 1 or the second end 2 can be confirmed, and the planar coordinates of facet 4 inside can only be estimated. Facet 4 has a lower resistance value than the step flow growth region 5, and the light absorption coefficient also changes. Therefore, when laser processing, it is necessary to adjust conditions such as laser output and cutting speed. For example, if facet 4 is located in a position where it is estimated that there would be no facet 4 inside based on the planar coordinates of facet 4 at the second end 2, the laser output may be insufficient during laser processing. As described above, the further facet 4 extends into the SiC ingot 10, the higher the possibility that the height position of the inflection point 8 and the planar position of facet 4 at the second end 2 will differ, increasing the risk of errors during processing. Therefore, if the inflection point 8 is located on the first end 1 side, the processing stability of the SiC ingot 10 increases. Furthermore, the closer the inflection point 8 is to the first end 1 side, the higher the processing stability of the SiC ingot 10.

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

[0040] The first slope 61 is inclined in the -X direction with an angle of inclination θ1 with respect to the Z direction. The second slope 62 is inclined in the +X direction with an angle of inclination θ2 with respect to the Z direction. The angle of inclination θ1 is the absolute value of the interior angle between the first slope 61 and the Z direction. The angle of inclination θ2 is the absolute value of the interior angle between the second slope 62 and the Z direction. It is preferable that the angle of inclination θ1 is smaller than the angle of inclination θ2. By making the angle of inclination θ1 smaller than the angle of inclination θ2, it is possible to avoid the facet 4 extending far inside the SiC ingot 10. Also, if the angle of inclination θ2 is larger than the angle of inclination θ1, the planar coordinates of facet 4 will shift far outside the SiC ingot 10 at height positions after the inflection point 8. The area outside the SiC ingot 10 is often outside the acquisition area of ​​the SiC substrate, and by making the angle of inclination θ2 larger than the angle of inclination θ1, facet 4 can be excluded from the acquisition area of ​​the SiC substrate.

[0041] Figure 1 illustrates the case where the inclination angle θ1 of the first slope 61 and the inclination angle θ2 of the second slope 62 are constant. However, the inclination angle θ1 of the first slope 61 and the inclination angle θ2 of the second slope 62 may change depending on the position in the Z direction. In this case, the average inclination angle of the first slope 61 and the second slope 62 is treated as inclination angle θ1 and 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 slope 61 preferably includes a portion with an inclination angle θ1 of 5° or more, and more preferably includes a portion with an inclination angle θ1 of 15° or more. Similarly, the second slope 62 preferably includes a portion with an inclination angle θ2 of 5° or more, and more preferably includes a portion with an inclination angle θ2 of 15° or more. Both the first slope 61 and the second slope 62 are more preferably included in portions where the inclination angles θ1 and θ2 are 5° or more. Furthermore, at least one of the first slope 61 and the second slope 62 is more preferably included in portions where the inclination angles θ1 and θ2 are 15° or more.

[0043] Furthermore, it is preferable that the area of ​​facet 4 at the first end 1 is larger than the area of ​​facet 4 at the second end 2. The first end 1 corresponds to the part of the SiC ingot 10 that has grown crystallized earlier than the second end 2. In the early stages of SiC single crystal growth, crystal growth is unstable. By providing facet 4 with a sufficient area on the first end 1 side, the occurrence of different polymorphs can be further suppressed. Also, if the area of ​​facet 4 at the second end 2, which corresponds to the later stages of crystal growth, is small, the SiC ingot 10 becomes easier to process.

[0044] "Method for manufacturing SiC ingots" Next, a method for manufacturing the SiC ingot 10 according to this embodiment will be described. Figures 3 and 4 are diagrams illustrating the method for manufacturing the SiC ingot 10 according to this embodiment.

[0045] The SiC ingot manufacturing apparatus 10 comprises 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. A seed crystal S and SiC raw material M are placed inside the growth space A of the crucible 20. The heating coil 21 surrounds the outer circumference 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, causing the SiC ingot 10 to grow.

[0047] The atmospheric pressure during crystal growth in growth space A is greater than 0.3 Torr and less than 50 Torr. For example, the atmospheric pressure during crystal growth in growth space A is 10 Torr. If the pressure in growth space A is too low, the dopant elements cannot be sufficiently incorporated into the crystal, resulting in a high resistivity of the SiC ingot 10. The resistivity of the SiC ingot 10 is a parameter that affects electrical discharge machining. Also, if the pressure in growth space A is too high, insufficient sublimation gas is generated from the SiC raw material M, leading to decreased productivity.

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

[0049] The thermal insulation member 22 is movable in the Z direction. The position of the thermal insulation member 22 in the Z direction changes as the SiC ingot 10 undergoes crystal growth. The growth process of the SiC ingot 10 is divided into two stages, a first growth stage and a second growth stage, and the position of the thermal insulation member 22 in the Z direction is adjusted in each of the two stages. The first growth stage includes the beginning of growth, and the second growth stage includes the end of growth. The position of the thermal insulation member 22 in the Z direction is 5 mm above the center of the crystal growth surface of the SiC ingot 10 during the first growth stage, and 5 mm below the center of the crystal growth surface of the SiC ingot 10 during the second growth stage. The boundary point between the first and second growth stages is 10% to 55% of the final growth amount. For example, if the boundary point is at 30% of the final growth amount, the first growth process is the process of SiC ingot 10 growing to 30% of the final growth amount, and the second growth process is the process of SiC ingot 10 growing from 30% of the final growth amount to the end. Also, "5 mm above the center of the crystal growth surface" means "a position 5 mm closer to the seed crystal S than the center of the crystal growth surface in the Z direction," and "5 mm below the center of the crystal growth surface" means "a position 5 mm away from the seed crystal S than the center 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 differs, for example, on the upstream side of the offset (+X direction) and the downstream side of the offset (-X direction). The inner surface of the guide member 23 located on the upstream side of the offset has a different inclination angle φ with respect to the horizontal direction (direction perpendicular to the Z direction) depending on its position in the Z direction. In the range of positions in the Z direction of the crystal growth surface during the first growth process, the inclination angle φ is 50° to 85°, and in the range of positions in the Z direction of the crystal growth surface during the second growth process, the inclination angle φ is 80° to 90°. For example, if the boundary point between the first and second growth processes is 30% of the final growth amount, the inclination angle φ is 50° to 85° up to 30% of the final growth amount of the SiC ingot 10, and 80° to 90° from 30% to 100% of the final growth amount of the SiC ingot 10. Furthermore, the inner surface of the guide member 23 located downstream of the offset has an inclination angle of 80° to 90° with respect to the horizontal direction (direction perpendicular to the Z direction), regardless of its position in the Z direction.

[0051] The shielding member 24 is located between the seed crystal S or the SiC ingot 10 undergoing crystal growth and the SiC raw material M. The shielding member 24 is positioned at a distance of 20 mm or more from the surface of the SiC ingot 10 after crystal growth. The shape of the shielding member 24 is not specified, but its thickness is, for example, 5 mm or more. The shielding member 24 covers only the upstream offset side of the SiC ingot 10 when viewed from the Z direction. For example, the shielding member 24 covers only the upstream offset side of the SiC ingot 10 in a fan shape when viewed from the Z direction.

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

[0053] Furthermore, by processing the fabricated SiC ingot 10 into a cylindrical shape and slicing it, a SiC substrate can be manufactured.

[0054] In this embodiment, the SiC ingot 10 has high crystal quality and is easy to process because the shape of the facets 4 is controlled. In the initial stages of crystal growth, the facets 4 move downstream of the offset, and a first slope 61 is formed. By growing the facets 4 toward the downstream of the offset during the initial stages of crystal growth when crystal growth is unstable, the generation of different polymorphs within the SiC ingot 10 is suppressed. Furthermore, in the later stages of crystal growth, the facets 4 move upstream of the offset, and a second slope 62 is formed. By moving the position of the facets 4 to the outside of the SiC ingot 10, the proportion of the facets 4 that occupy within the SiC substrate acquisition area can be reduced, making the SiC ingot 10 easier to process.

[0055] "Method for manufacturing SiC substrates" The method for manufacturing a SiC substrate according to the first embodiment comprises the steps of: producing the SiC ingot 10 according to the above embodiment using the method described above; and slicing the SiC ingot 10. As a process for slicing the SiC ingot 10, for example, a method can be used in which cracks are made in the SiC ingot 10 by processing it with a laser and then the SiC substrate is cut out. The SiC ingot 10 may also be processed into a cylindrical shape before slicing it.

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

[0057] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to any particular embodiment, and various modifications and changes are possible within the scope of the gist of the present invention (technical requirements) as described in the claims. [Examples]

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

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

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

[0061] Under the above conditions, a SiC ingot of Example 1 was fabricated. The cross-section of the fabricated SiC ingot was then examined, and the shape of the inner boundary between the facets and the step-flow growth region was confirmed. The ingot had a first end opposite the growth plane of the seed crystal and a second end on the growth plane, and the inner boundary of the facet had a first slope and a second slope. The first slope was closer to the first end than the second slope, and the inclination angle of the first slope with respect to the crystal growth direction was smaller than the inclination angle of the second slope with respect to the crystal growth direction. The first slope 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 slope 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 and second slopes was located at a position shifted by 20% of the ingot length in the Z direction from the first end. The facets were located in the [11-20] direction from a plane passing through the center of the <11-20> direction and perpendicular to the <11-20> direction.

[0062] Furthermore, under the same conditions, 20 SiC ingots of Example 1 were produced 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 SiC ingots was evaluated by assessing the presence or absence of heteromorphisms. Specifically, SiC ingots were cut with a wire saw at positions 2 mm away from both the first and second ends, and evaluation substrates were obtained. The thickness of the substrates was 0.5 mm. After polishing both sides of these substrates, X-ray topography (XRT) (diffraction vector g: 1-100) transmission images were obtained to confirm the presence or absence of heteromorphisms and the resulting micropipes.

[0064] The time required for processing SiC ingots was measured by determining the time required to obtain SiC wafers from cylindrical SiC ingots. Laser processing was used to obtain SiC wafers from SiC ingots. The laser scan pitch was set to 200 μm, the laser scan feed rate to 200 mm / sec, the number of scans to 1, the acceleration / deceleration time to 0.1 seconds, and the inter-line travel time to 0.1 seconds. The acceleration / deceleration time is the time required to accelerate and decelerate when scanning the laser in the opposite direction after scanning in one direction. The inter-line travel time represents the time required for movement in the second direction in a process that repeatedly involves laser scanning in the first direction and movement in the second direction perpendicular to the first direction.

[0065] Of the 20 SiC ingots in Example 1, 19 were free of heteromorphisms, and the quality yield was 95%. The time required to slice the SiC ingots in Example 1 onto wafers was 18.2 minutes per wafer.

[0066] Example 2 A seed crystal with a diameter of 8 inches (200 mm) was prepared. Then, using the manufacturing apparatus shown in Figures 3 and 4, a SiC ingot was grown on the seed crystal to a thickness of 30 mm. The process of growing the SiC ingot to 50% of its final growth amount was defined as the first growth process, and the process of growing the SiC ingot from 50% to the end 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 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 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 upstream side of the offset was set to 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 to 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 in Example 1, and the SiC ingot of Example 2 was fabricated.

[0067] The cross-section of the fabricated SiC ingot was examined, and the shape of the inner boundary between the facets and the step flow region was confirmed. It had a first end opposite the growth plane of the seed crystal and a second end on the growth plane, and the inner boundary of the facet had a first slope and a second slope. The first slope was closer to the first end than the second slope, and the inclination angle of the first slope with respect to the crystal growth direction was smaller than the inclination angle of the second slope with respect to the crystal growth direction. The first slope 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 slope 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 and second slopes was located at a position shifted by 40% of the ingot length in the Z direction from the first end. The facets were located in the [11-20] direction from a 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 evaluated. Of the 20 SiC ingots of Example 2, 19 did not contain heteromorphs, and the quality yield was 95%. The time required to obtain a SiC wafer from a SiC ingot was measured under the same conditions as in Example 1. The time required to slice the SiC ingot into wafers was 18.6 minutes per wafer.

[0069] "Comparative Example 1" Comparative Example 1 differs from Example 1 in that it manufactured a SiC ingot using a SiC ingot manufacturing apparatus that does not have a guide member 23 and a shielding member 24. In addition, during the manufacturing process of the SiC ingot in 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 to the end of the growth process.

[0070] Under the above conditions, a SiC ingot of Comparative Example 1 was fabricated. The cross-section of the fabricated SiC ingot was then examined to confirm the shape of the inner boundary between the facets and the step-flow growth region. The inner boundary consisted only of a first slope 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 ingot in Comparative Example 1 was 95%. The time required to slice the SiC ingot in Comparative Example 1 onto wafers was 20.4 minutes per wafer.

[0073] "Comparative Example 2" Comparative Example 2 differs from Example 1 in that it manufactured a SiC ingot using a SiC ingot manufacturing apparatus that does not have a guide member 23 and a shielding member 24. In addition, during the manufacturing process of the SiC ingot in Comparative Example 2, the position of the heat insulating member 22 in the Z direction was always 5 mm below the center position of the crystal growth surface of the SiC ingot from the initial to the end of the growth process.

[0074] Under the above conditions, a SiC ingot of Comparative Example 2 was fabricated. The cross-section of the fabricated SiC ingot was then examined to confirm the shape of the inner boundary between the facets and the step-flow growth region. The inner boundary consisted only of a second slope 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 ingot in Comparative Example 2 was 70%. The time required to slice the SiC ingot of Comparative Example 2 onto wafers was 17.8 minutes per wafer.

[0077] "Comparative Example 3" Comparative Example 3 differs from Example 1 in that the position of the heat insulating member 22 during crystal growth is changed. In Comparative Example 3, the process until the SiC ingot grows to 60% of its final growth amount is defined as the first growth process, and the process from 60% of the final growth amount to the end of growth is defined as the second growth process. In the first growth process, the position of the heat insulating member 22 in the Z direction is 5 mm above the center 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 is 5 mm below the center 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 upstream side of the offset is 70° up to 70% of the final growth amount of the SiC ingot, and 85° 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. The cross-section of the fabricated SiC ingot was then examined, and the shape of the inner boundary between the facets and the step-flow growth region was confirmed. The inner boundary had a first slope and a second slope. The inflection point between the first and second slopes was located at a position shifted by 80% of the ingot length in the Z direction from the first end.

[0079] Under the same conditions, 20 SiC ingots of Comparative Example 3 were produced, 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 ingot in Comparative Example 3 was 95%. The time required to slice the SiC ingot in Comparative Example 3 onto wafers was 19.5 minutes per wafer.

[0081] "Comparative Example 4" A seed crystal with a diameter of 8 inches (200 mm) was prepared. Then, using the manufacturing apparatus shown in Figures 3 and 4, a SiC ingot was grown on the seed crystal to a thickness of 30 mm. The process of growing the SiC ingot to 70% of its final growth amount was defined as the first growth process, and the process of growing the SiC ingot from 70% to the end 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 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 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 upstream side of the offset was set to 70° at the position up to 70% 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 to 85° at the position from 70% 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). All other conditions were the same as in Example 1, and the SiC ingot of Comparative Example 4 was fabricated.

[0082] The cross-section of the fabricated SiC ingot was examined, and the shape of the inner boundary between the facets and the step flow region was confirmed. It had a first end opposite the growth plane of the seed crystal and a second end on the growth plane, and the inner boundary of the facet had a first slope and a second slope. The first slope was closer to the first end than the second slope, but the inclination angle of the first slope with respect to the crystal growth direction was greater than the inclination angle of the second slope with respect to the crystal growth direction. The first slope contained a portion where the absolute value of the inclination angle with respect to the crystal growth direction was 5° or more, but the second slope did not contain 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 and second slopes was located at a position shifted by 60% of the ingot length in the Z direction from the first end. The facets were located in the [11-20] direction from a 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. Of the 20 SiC ingots of Comparative Example 4, 19 did not contain heteromorphs, and the quality yield was 95%. The time required to obtain a SiC wafer from a SiC ingot 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 1st end 2 2nd end 3 side wall 4 Facets 5-Step Flow Growth Area 6. Inner boundary 7 outer boundary 8 Inflection points 10 SiC ingots 20 Crucible 21 Heating coil 22 Insulation material 23 Guide member 24 Shielding member 61, 71 First Slope 62, 72 Second Slope A growth space H1, H2 side M SiC raw material S seed crystal θ1, θ2, φ Tilt angle

Claims

1. It has a step flow growth region and facets, In a cross-section 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 slope inclined in the [-1-120] direction with respect to the crystal growth direction, and a second slope inclined in the [11-20] direction with respect to the crystal growth direction. The inflection point between the first and second slopes is located on the first end side, which is the Si surface or a surface inclined by an offset angle from the Si surface, from the center position of the ingot length. The first slope is closer to the first end than the second slope. The aforementioned facet is located in the [11-20] direction from a plane that passes through the center in the <11-20> direction and is perpendicular to the <11-20> direction, in a SiC ingot.

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

3. The SiC ingot according to claim 1, wherein the area of ​​the facets at the first end is greater than the area of ​​the facets at the second end facing the first end.

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

5. The SiC ingot according to claim 1, wherein the first and second slopes include portions where the absolute value of the 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 slope and the second slope includes a portion in which the absolute value of the inclination angle with respect to the crystal growth direction is 15° or more.

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

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

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

10. A step of producing a SiC ingot according to any one of claims 1 to 9, A method for manufacturing a SiC substrate, comprising the step of slicing the SiC ingot.

11. The method for manufacturing a SiC substrate according to claim 10, wherein the step of slicing the SiC ingot is performed by laser processing.

12. A step of preparing a SiC ingot according to any one of claims 1 to 9, A method for manufacturing a SiC substrate, comprising the step of slicing the SiC ingot.

13. The method for manufacturing a SiC substrate according to claim 12, wherein the step of slicing the SiC ingot is performed by laser processing.

Images