n-type SiC single crystal substrates and SiC epitaxial wafers

Abstract

To provide a 8-inch n type SiC single crystal substrate having high dopant concentration and capable of suppressing a variation in concentration distribution.SOLUTION: A 8-inch n type SiC single crystal substrate 1 has a diameter of 195-205 mm and a dopant concentration of 2×1018 / cm3 or more and 6×1019 / cm3 or less; and the dopant concentrations of at least five points including points within 1 mm from the outermost circumference in the radial direction is within ±20% to a dopant concentration at the in-plane center in the same depth from a main surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an n-type SiC single crystal substrate, an SiC epitaxial wafer, and an n-type SiC single crystal ingot. [Background technology]

[0002] Silicon carbide (SiC) has a dielectric breakdown field that is one order of magnitude larger than that of silicon (Si) and a band gap that is three times larger. Silicon carbide (SiC) also 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 operating devices, etc. For this reason, SiC epitaxial wafers have recently come to be used in these types of semiconductor devices.

[0003] SiC epitaxial wafers are obtained by stacking a SiC epitaxial layer on the surface of a SiC single crystal substrate. Hereinafter, the substrate before the SiC epitaxial layer is stacked will be referred to as the SiC single crystal substrate, and the substrate after the SiC epitaxial layer is stacked will be referred to as the SiC epitaxial wafer. SiC single crystal substrates are sliced ​​from SiC single crystal ingots.

[0004] The current market mainstream for SiC single crystal substrates is 6-inch (150mm) in diameter, but development is also underway for the mass production of 8-inch (200mm) SiC single crystal substrates, and full-scale mass production is about to begin. With the improvement in production efficiency and cost reduction achieved by increasing the diameter from 6 inches to 8 inches, it is expected that SiC power devices will become even more widespread as a trump card in energy-saving technology.

[0005] When manufacturing the next generation of larger-diameter SiC single crystal substrates, applying the manufacturing conditions optimized for manufacturing SiC single crystal substrates of current diameters will not achieve the same level of quality. This is because new issues arise depending on the new size. For example, Patent Document 1 describes the problem that when manufacturing 6-inch SiC single crystal substrates using manufacturing techniques for 4-inch SiC single crystal substrates, thermal decomposition frequently occurs around the outer periphery of the seed crystal, which causes macro-defects, resulting in a low yield of single crystals with high crystal quality. Patent Document 1 also describes an invention that solves this problem by using a seed crystal of a specified thickness. As such, it is necessary to establish manufacturing conditions for SiC single crystal substrates of new sizes while resolving new issues that arise depending on the new sizes.

[0006] In SiC devices as power semiconductors, it is extremely important to increase the doping concentration to reduce resistance in order to reduce loss. Also, to reduce the characteristic variability between SiC devices, it is necessary to minimize the variability in dopant concentration. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6594146 [Patent Document 2] Patent No. 6598150 [Patent Document 3] Japanese Patent Publication No. 2020-17627 [Patent Document 4] Japanese Patent Application Publication No. 2019-189499 Summary of the Invention [Problem to be solved by the invention]

[0008] SiC single crystal substrates are obtained through a SiC single crystal ingot production process and a SiC single crystal substrate process in which SiC single crystal substrates are produced from those SiC single crystal ingots. Establishing the manufacturing technology for 8-inch SiC single crystal substrates requires solving new challenges unique to 8-inch substrates in both the SiC single crystal ingot production process and the SiC single crystal substrate process.

[0009] Here, new challenges unique to 8-inch substrates include, for example, obtaining 8-inch substrates with the same dislocation density as that of 6-inch substrates in the SiC single crystal ingot production process. If 8-inch substrates were produced by simply applying SiC single crystal substrate production technology optimized for 6-inch substrate production, the resulting 8-inch substrates would have a higher dislocation density than that of 6-inch substrates. This is because the hurdle to achieving the same quality increases significantly as the size increases. Therefore, when evaluating manufacturing technology for 8-inch SiC single crystal substrates, the starting point is the dislocation density of 8-inch substrates obtained by simply applying SiC single crystal substrate production technology optimized for 6-inch substrate production, and the technological value should be evaluated based on the degree of improvement relative to the starting dislocation density. On the other hand, the yield of 8-inch SiC single crystal substrates in mass production is determined by evaluation standards that are the same as or even stricter than those for 6-inch SiC single crystal substrates. Step-by-step improvements will lead to the establishment of manufacturing technology for 8-inch SiC single crystal substrates.

[0010] Furthermore, in order to meet the increasing demand for power semiconductors, it is essential to establish manufacturing technology for 8-inch SiC single crystal substrates, as well as technology that can achieve high dopant concentrations while suppressing concentration distribution variations.

[0011] The present invention has been made in view of the above circumstances, and has as its object to provide an 8-inch SiC single crystal substrate, an n-type SiC single crystal substrate having a high dopant concentration and suppressed variation in concentration distribution, and an SiC epitaxial wafer. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention provides the following means.

[0013] A first aspect of the present invention is an 8-inch n-type SiC single crystal substrate having a diameter in the range of 195 to 205 mm and a dopant concentration of 2×10 18 / cm 3 That's it, 6 x 10 19 / cm 3 or less, and the dopant concentration at at least five points in the radial direction, including points within 1 mm from the outermost periphery, is within ±20% of the dopant concentration at the in-plane center at the same depth from the main surface.

[0014] A second aspect of the present invention is an n-type SiC single crystal substrate according to the first aspect, wherein the dopant concentration at at least five points in the radial direction, including points within 1 mm from the outermost periphery, is within ±15% of the dopant concentration at the in-plane center at the same depth from the main surface.

[0015] A third aspect of the present invention is an n-type SiC single crystal substrate according to the first or second aspect, wherein the dopant concentration at at least five points in the radial direction, including points within 1 mm from the outermost periphery, is within ±10% of the dopant concentration at the in-plane center at the same depth from the main surface.

[0016] A fourth aspect of the present invention is an n-type SiC single crystal substrate according to any one of the first to third aspects, wherein the dopant is nitrogen.

[0017] A fifth aspect of the present invention is a SiC epitaxial wafer comprising an n-type SiC single crystal substrate according to any one of the first to fourth aspects, and an SiC epitaxial layer laminated on the surface of the n-type SiC single crystal substrate.

[0018] A sixth aspect of the present invention is an n-type SiC single crystal ingot, wherein substrates having a diameter in the range of 195 to 205 mm are cut out from the n-type SiC single crystal ingot, and when the dopant concentration of the cut out substrates is measured, the dopant concentration is 2×10 18 / cm3 That's it, 6 x 10 19 / cm 3 or less, and the dopant concentration at at least five points in the radial direction, including points within 1 mm from the outermost periphery, is within ±20% of the dopant concentration at the in-plane center at the same depth from the main surface of the sliced ​​substrate.

[0019] A seventh aspect of the present invention is an n-type SiC single crystal ingot according to the sixth aspect, wherein the dopant concentration at at least five radial points, including points within 1 mm from the outermost periphery, is within ±15% of the dopant concentration at the in-plane center at the same depth from the main surface of the sliced ​​substrate.

[0020] Aspect 8 of the present invention is an n-type SiC single crystal ingot according to aspect 6 or aspect 7, wherein the dopant concentration at at least five radial points, including points within 1 mm from the outermost periphery, is within ±10% of the dopant concentration at the in-plane center at the same depth from the main surface of the sliced ​​substrate.

[0021] A ninth aspect of the present invention is the n-type SiC single crystal ingot according to any one of the sixth to eighth aspects, wherein the dopant is nitrogen. [Effects of the Invention]

[0022] According to the n-type SiC single crystal substrate of the present invention, it is possible to provide an 8-inch SiC single crystal substrate having a high dopant concentration and suppressed variation in concentration distribution. [Brief explanation of the drawings]

[0023] [Figure 1] 1(a) is a cross-sectional view of a SiC single crystal substrate according to this embodiment, and FIG. 1(b) is a plan view thereof. [Figure 2] 1(a) is a cross-sectional view of a SiC single crystal substrate according to this embodiment, and FIG. 1(b) is a plan view thereof. [Figure 3] This is a conceptual diagram showing the definition of SORI. [Figure 4]1 is a conceptual diagram showing a process in which the depth of a work-affected layer is reduced by mechanical processing. [Figure 5] FIG. 1 is a cross-sectional schematic diagram of a SiC single crystal manufacturing apparatus. [Figure 6] FIG. 2 is a cross-sectional schematic view of another example of an SiC single crystal growing apparatus. [Figure 7] 1 is a cross-sectional schematic diagram of a driving means for moving a heat insulating material up and down in a SiC single crystal manufacturing apparatus. [Figure 8] The figure shows the positional relationship between the bottom surface of the heat insulating material and the surface of the single crystal, and the relationship with the isothermal surface near the single crystal. [Figure 9] FIG. 1 is a diagram showing a schematic view of the shape of an isothermal surface in the vicinity of a single crystal during crystal growth. [Figure 10] FIG. 1 is a plan view showing an example of a 10 mm square mesh. DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention will be described in detail below with reference to the drawings as appropriate. The drawings used in the following description may show characteristic portions enlarged for the sake of clarity, and the dimensional proportions of each component may differ from the actual proportions. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate modifications can be made within the scope of the effects of the present invention. Furthermore, in each drawing, components well known to those skilled in the art other than those illustrated in that drawing may be omitted.

[0025] (SiC single crystal substrate) FIG. 1(a) is a schematic cross-sectional view of a SiC single crystal substrate according to this embodiment, and (b) is a schematic plan view. The SiC single crystal substrate 1 shown in FIG. 1 is an 8-inch n-type SiC single crystal substrate, with a diameter in the range of 195 to 205 mm, a thickness in the range of 300 to 650 μm, a process-affected layer thickness on both the front and back surfaces of 0.1 nm or less, and a dopant concentration of 2×10 18 / cm 3 That's it, 6 x 10 19 / cm 3The following is the result.

[0026] There are no particular limitations on the external shape of the SiC single crystal substrate 1, and various flat plate shapes and thicknesses can be used, but a disk shape is typical. The thickness of the SiC single crystal substrate can be in the range of 300 to 650 μm, for example.

[0027] The SiC single crystal substrate 1 is preferably 4H—SiC, because although there are various polytypes of SiC, 4H—SiC is the one that is primarily used to fabricate practical SiC devices.

[0028] One surface of the SiC single crystal substrate 1 is the surface (main surface) on which the SiC epitaxial layer is formed, and it is preferable that the main surface be the c-plane (the (0001) plane of the 4H-SiC crystal) or a plane inclined from the c-plane at an inclination angle (off-angle) of more than 0 degrees and less than 10 degrees. This is a 4H-SiC type single crystal wafer. The off-angle is preferably more than 0 degrees and less than 10 degrees, with the c-plane tilted in the <11-20> direction. Since the larger the off-angle, the fewer wafers can be obtained from a SiC single crystal ingot, a small off-angle is preferable from the viewpoint of cost reduction. SiC single crystal substrates with an off-angle of, for example, 0.4° to 5° can be used. 0.4° can be said to be the lower limit of the off-angle at which step-flow growth is possible.

[0029] The n-type dopant may be, but is not limited to, nitrogen, which is a common n-type dopant.

[0030] The dopant concentration of the SiC single crystal substrate 1 is 2 × 10 18 / cm 3 That's it, 6 x 10 19 / cm 3 The following is the result. The dopant concentration of the SiC single crystal substrate is 2×10 18 / cm 3 If the dopant concentration is less than 6×10, the resistivity of the SiC single crystal substrate becomes too high. 19 / cm 3If the dopant concentration of the SiC single crystal substrate exceeds 2×10, it becomes difficult to suppress stacking faults in the SiC single crystal substrate. 18 / cm 3 That's it, 6 x 10 19 / cm 3 By setting the thickness within the following range, it is possible to reduce the resistivity while suppressing stacking faults in the SiC single crystal substrate. The dopant concentration can be adjusted by a known method, for example, by adjusting the amount of dopant gas introduced into the crucible (see reference numeral 10 in FIG. 5) during crystal growth by adjusting the introduction time, partial pressure, etc.

[0031] In the surface 1A of the SiC single crystal substrate 1, which is within 5% of the thickness in the depth direction from the main surface 1a, at least five arbitrarily selected points are selected to have a dopant concentration of 2×10 18 / cm 3 That's it, 6 x 10 19 / cm 3 It is preferable that: FIG. 1 shows nine points, including the in-plane center O, as measurement points for the dopant concentration in the surface 1A.

[0032] In the SiC single crystal substrate 1, the dopant concentration at at least five points in the radial direction, including point p1 within 1 mm from the outermost periphery 1b, is preferably within ±20%, more preferably ±15%, and even more preferably ±10%, of the dopant concentration at the in-plane center at the same depth from the main surface 1a. In FIG. 1, reference numeral 1bb denotes a circle 1 mm from the outermost periphery 1b.

[0033] The in-plane distribution of the dopant concentration can be adjusted by a known method. For example, to make the amount of dopant supplied to the outer periphery higher than the amount of dopant supplied to the inner periphery, a dopant gas flow path can be provided in the crucible (see reference numeral 10 in FIG. 5) and the gas permeability of the crucible can be adjusted to make the amount of dopant supplied to the outer periphery higher than the amount of dopant supplied to the inner periphery. Furthermore, the amount of dopant supplied to the outer periphery can be adjusted by providing an opening in a guide member (see reference numeral 20 in FIG. 5 and reference numeral 25 in FIG. 6) or adjusting the thickness of the guide member.

[0034] FIG. 2(a) is a schematic cross-sectional view of the SiC single crystal substrate according to this embodiment, and (b) is a schematic plan view. In SiC single crystal substrate 1 shown in FIG. 2, when surface 1AA at the same depth from main surface 1a is divided into 10 mm square meshes M, and the dopant concentration at any point within each mesh is defined as the dopant concentration of that mesh, it is preferable that the proportion of meshes whose dopant concentration is within ±20% of the dopant concentration of mesh M0 including the in-plane center be 80% or more.

[0035] The dopant concentration can be measured by secondary ion mass spectrometry (SIMS).

[0036] The SiC single crystal substrate 1 has process-affected layers on both the front and back surfaces each having a thickness of 0.1 nm or less.

[0037] The main surface (hereinafter sometimes referred to as the "front surface") of the SiC single crystal substrate 1 is a mirror finish. This is because the front surface of the SiC single crystal substrate is required to form a SiC epitaxial layer by epitaxially growing a SiC single crystal in order to fabricate various SiC devices. Therefore, the front surface is formed by cutting the substrate (or a portion that will become the substrate) from a SiC single crystal ingot manufactured using a sublimation method or the like, and then mirror-finishing the surface of the cut substrate. The other surface (hereinafter sometimes referred to as the "rear surface") does not have to be a mirror surface, but SiC single crystal substrates with a mirror surface on the front and a non-mirror surface on the back face have a problem in that a difference in residual stress occurs between the front and back faces, causing the substrate to warp to compensate for the residual stress (the Twyman effect). By making the back face mirror-finished as well, it is possible to suppress the warpage of the substrate caused by the Twyman effect. A method has been developed for producing SiC single crystal substrates with little warpage, even when the front face is mirror-finished and the back face is not (see, for example, Patent Document 2).

[0038] The SiC single crystal substrate 1 has a notch 2 that serves as an indicator of the crystal orientation, but may have an orientation flat (OF) instead of the notch 2.

[0039] The SORI of the SiC single crystal substrate 1 is preferably 50 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less, and most preferably 20 μm or less.

[0040] SORI is one of the parameters that indicates the degree of warpage of a substrate, and is expressed as the sum of the normal distances from the least-squares plane, which is calculated by the least-squares method using all data on the substrate surface when the backside of the substrate is supported and measured without changing the original shape, to the highest and lowest points on the substrate surface. In other words, as shown in Figure 3, if the least-squares plane on the substrate surface is taken as the reference height (least-squares plane height), SORI represents the sum ((a) + (b)) of the distance (a) between the height of the highest point on the substrate surface and the reference height, and the distance (b) between the height of the lowest point and the reference height.

[0041] <Relationship between processing-affected layer and SORI> SiC single crystal substrates are made by slicing a SiC single crystal ingot and flattening the surface. This mechanical processing introduces processing strain into the surface of the substrate. The portion of the surface of the SiC single crystal substrate where processing strain occurs is called a processing-affected layer. When processing-affected layers are present on the front and back surfaces, differences in processing strain occur between the front and back surfaces, which also cause differences in residual stress, resulting in substrate warpage due to the Twyman effect. The shape (warpage) of the substrate is determined by the balance of stress states generated by the processing-affected layers on both surfaces of the substrate.

[0042] Figure 4 is a conceptual diagram showing the process by which the depth d (d1, d2, d3, d4) of the affected layer is reduced by mechanical processing. For example, (a) is a cross section near the surface after lapping, (b) is polishing, (c) is finish grinding, and (d) is CMP.

[0043] Figure 14 of Patent Document 3 shows the relationship between the depth of the process-affected layer and the SORI of a single crystal SiC wafer. According to this graph, the deeper the process-affected layer, the larger the SORI value. Furthermore, when comparing a 6-inch SiC single crystal substrate with a 4-inch SiC single crystal substrate, the 6-inch SiC single crystal substrate is more susceptible to the effects of the process-affected layer and has a larger SORI. From this, it is presumed that when comparing an 8-inch SiC single crystal substrate with a 6-inch SiC single crystal substrate, the 8-inch SiC single crystal substrate is even more susceptible to the effects of the process-affected layer and will have an even larger SORI. Therefore, removing the process-affected layer to reduce warpage is more important for an 8-inch SiC single crystal substrate than for a 6-inch SiC single crystal substrate.

[0044] The in-plane variation in thickness of the SiC single crystal substrate 1 is 2.0 μm or less, preferably 1.5 μm or less, and more preferably 1.0 μm or less. In the SiC single crystal substrate according to this embodiment, lapping is performed using a novel lapping slurry, thereby realizing a reduction in in-plane variations in thickness.

[0045] In this specification, "in-plane variation in substrate thickness" refers to the difference between the maximum and minimum values ​​measured using a dial gauge or similar to measure the thickness of a SiC single crystal substrate at five points (one point at the center and four points on a circle with a (1 / 2) radius (positions at the inclined angles of 0°, 90°, 180°, and 270°)

[0046] Figure 14 of Patent Document 3 shows the relationship between the depth of the damaged layer, which is one parameter of the damaged layer, and the SORI. In developing 8-inch SiC single crystal substrates with high yields, the inventors focused on the in-plane variation in the depth of the remaining damaged layer. Even if the damaged layer can be almost completely removed by performing a planarization process over a sufficient period of time in the laboratory, it is expected that some amount of damaged layer will remain when the planarization process is performed within a practical time frame. Furthermore, the conceptual depth d of the remaining damaged layer in Figure 3 is drawn assuming an average depth. In reality, the remaining damaged layer may not remain at a strictly uniform depth. It is likely that a thin damaged layer remains across the entire surface, with some in-plane depth variation, or that the damaged layer remains locally within the surface. In such cases, it is expected that the in-plane variation in the depth of the damaged layer will have a greater impact on the SORI in 8-inch SiC single crystal substrates than in 6-inch SiC single crystal substrates. It is believed that the in-plane variation in the substrate thickness of the SiC single crystal substrate 1 reflects the in-plane variation in the depth of the process-affected layer.

[0047] The SiC single crystal substrate 1 has a micropipe defect density of 1 / cm 2 It is preferable that:

[0048] The total number of etch pits that appeared in the SiC single crystal substrate 1 after KOH etching was 5 × 10 9 Preferably, it is 5×10 or less. 8 It is more preferable that the number is 5×10 or less. 7 In this case, the KOH etching was carried out at 550° C. for 10 minutes. The total number of etch pits corresponds to the total number of dislocations.

[0049] The SiC single crystal substrate 1 has an etch pit density of 2×10 3 pieces / cm 2 and the density of etch pits identified as basal plane dislocations is 5×10 3 pieces / cm 2 It is preferable that: The density of etch pits identified as threading dislocations (TDs) is 1×10 3 pieces / cm 2 It is more preferable that it is 5×10 or less. 2 pieces / cm 2 It is even more preferable that: The density of etch pits identified as basal plane dislocations is 2×10 3 pieces / cm 2 More preferably, it is 1×10 or less. 3 pieces / cm 2 More preferably, it is 5×10 or less. 2 pieces / cm 2 More preferably, it is: Here, threading dislocations are a combination of threading screw dislocations (TSDs) and threading edge dislocations (TEDs). The type of dislocation can be identified using an optical microscope or other device from the shape of the etch pits revealed by KOH etching, and the number of etch pits per unit area can be counted. In general, medium-sized hexagonal etch pits correspond to threading screw dislocations (TSDs), small-sized hexagonal etch pits correspond to threading edge dislocations (TEDs), and elliptical (scallop) etch pits correspond to basal plane dislocations (BPDs). Large-sized hexagonal etch pits correspond to micropipes (MPs).

[0050] (Method of manufacturing SiC single crystal substrate) The manufacturing method of the SiC single crystal substrate according to this embodiment will be described by dividing it into the manufacturing process of an n-type SiC single crystal ingot and the manufacturing process of the SiC single crystal substrate from the ingot. In the following, the manufacturing process of an n-type SiC single crystal ingot into which nitrogen is introduced as a dopant will be described as an example.

[0051] <Manufacturing Process of n-Type SiC Single Crystal Ingot> In the process of continuous intensive research, the inventor has found that in the production of an 8-inch diameter SiC single crystal ingot, more precise control of the temperature gradients in the radial direction and the vertical direction (crystal growth direction) with respect to a 6-inch diameter SiC single crystal ingot is the key point. And by applying the method disclosed in Patent Document 4, it has been found that more precise control of the temperature gradients in the radial direction and the vertical direction (crystal growth direction) can be achieved. Specifically, a SiC single crystal manufacturing apparatus provided with a heat insulating material that can move along the extending direction of the guide member on the outside of the guide member that guides crystal growth can be used. Note that the method for more precisely controlling the temperature gradients in the radial direction and the vertical direction (crystal growth direction) is not limited to the method disclosed in Patent Document 4.

[0052] In the transition period of increasing the diameter of the SiC single crystal ingot, there is a problem that a SiC single crystal ingot with the same crystal quality cannot be obtained by applying the manufacturing method of the SiC single crystal ingot with the previous diameter. For example, in the transition period from a 4-inch diameter SiC single crystal ingot to a 6-inch diameter SiC single crystal ingot, there were the following problems (see Patent Document 1).

[0053] In the growth of SiC single crystals by the sublimation recrystallization method using a seed crystal, one of the growth conditions for achieving high crystal quality is that the surface shape of the single crystal ingot during growth must be approximately convex in the growth direction. For example, in the case of 4H-type SiC single crystals used in power devices, <0001> When growing SiC single crystals along the c-axis, i.e., the crystal's axis, single crystal growth occurs via the propagation of spiral steps generated by threading screw dislocations. Therefore, by forming a roughly convex growth surface, the step supply source on the growth surface is essentially single, which is believed to improve polytype stability. If the growth surface is concave or has multiple peaks, the growth step supply source becomes multiple, resulting in areas where different steps generated from each supply source collide. In such cases, not only do defects such as dislocations occur at the collision points, but the atomic stacking state along the c-axis, which is unique to the 4H polytype, tends to become disrupted, resulting in heterogeneous polytypes with different stacking structures, such as 6H and 15R, and the formation of micropipe defects.

[0054] Therefore, for example, in order to stabilize the 4H polytype suitable for power devices and grow a so-called single-polytype crystal consisting only of the 4H polytype, it is important to make the growth surface shape of the grown crystal approximately convex. Specifically, the convex shape of the grown crystal is achieved by optimizing the temperature at the center of the grown crystal in terms of growth rate, etc., and controlling the temperature distribution during growth, i.e., the shape of the isotherm, to make the crystal approximately convex. It was thought that a SiC single crystal ingot grown under such growth conditions, where an approximately convex isotherm is realized, would grow approximately parallel to the isotherm, thereby ensuring the above-mentioned polytype stability.

[0055] However, when the diameter of the grown crystal is increased to 150 mm (6 inches) or more, optimizing the temperature of the center of the grown crystal to be equivalent to that of conventional 100 mm (4 inch) diameter single crystal growth in terms of growth rate, etc., while controlling the temperature gradient during growth so that the growth surface shape of the grown crystal is roughly convex in the growth direction, inevitably results in a higher temperature at the periphery of the seed crystal compared to small diameter crystal growth. As a result, there was a problem in that the SiC single crystal of the seed crystal itself was prone to thermal decomposition at its outer periphery. Patent Document 1 solves this problem mainly by using a seed crystal made of a silicon carbide single crystal with a thickness of 2.0 mm or more.

[0056] In the present invention, in producing an 8-inch diameter n-type SiC single crystal ingot, a technique not used in the typical method for producing a 6-inch diameter n-type SiC single crystal ingot as shown in Patent Document 1 is used. This involves using a heat insulating material that can move around the outside of the guide member that guides the crystal growth in the direction of extension of the guide member, and by controlling the temperature gradient not only in the radial direction but also in the vertical direction (crystal growth direction), we have succeeded in producing an 8-inch diameter n-type SiC single crystal ingot with properties comparable to a 6-inch diameter n-type SiC single crystal ingot. Below, we will explain the SiC single crystal production apparatus and the SiC single crystal ingot production process.

[0057] FIG. 5 is a cross-sectional schematic diagram of an example of a SiC single crystal manufacturing apparatus for carrying out the process of manufacturing an n-type SiC single crystal ingot.

[0058] 5 includes a crucible 10 equipped with a seed crystal installation section 11, a guide member 20, and a heat insulating material 30, a chamber (not shown) for accommodating these components, and a gas inlet pipe (not shown) connected to the chamber for introducing nitrogen gas. For ease of understanding, FIG. 5 simultaneously illustrates a raw material G, a seed crystal S, and a single crystal C grown on the seed crystal S. In the drawings below, the direction in which the seed crystal setting part 11 and the raw material G face each other is referred to as the up-down direction, and the direction perpendicular to the up-down direction is referred to as the left-right direction.

[0059] The crucible 10 surrounds a film-forming space K in which the single crystal C is grown. Any known crucible for producing the single crystal C by sublimation can be used as the crucible 10. For example, graphite, tantalum carbide, etc. can be used. The crucible 10 becomes very hot during growth. Therefore, it must be made of a material that can withstand high temperatures. For example, graphite has an extremely high sublimation temperature of 3550°C and can withstand the high temperatures during growth.

[0060] The seed crystal mounting part 11 is provided at a position facing the raw material G in the crucible 10. By positioning the seed crystal mounting part 11 facing the raw material G, the raw material gas can be efficiently supplied to the seed crystal S and the single crystal C.

[0061] The guide member 20 extends from the periphery of the seed crystal setting part 11 toward the raw material G. That is, the guide member 20 is disposed along the crystal growth direction of the single crystal C. Therefore, the guide member 20 functions as a guide when the single crystal C grows from the seed crystal S.

[0062] The lower end of guide member 20 is supported by support 21. Support 21 blocks the gap between the lower end of guide member 20 and crucible 10, and prevents source gas from entering the region outside guide member 20. If source gas enters this region, polycrystals grow between guide member 20 and insulating material 30, hindering the free movement of insulating material 30.

[0063] The connection between the guide member 20 and the support 21 preferably has a crimped structure. A crimped structure is a structure designed so that the connection between the guide member 20 and the support 21 is tightened when a physical force is applied to the guide member 20. For example, a screw structure in which the connection is threaded is an example of a crimped structure. The guide member 20 may come into physical contact with the growing single crystal C, and in such cases, the guide member 20 can be prevented from falling off.

[0064] Guide member 20 in Fig. 5 extends vertically in the up-down direction. The shape of guide member 20 is not limited to this shape. Fig. 6 is a cross-sectional schematic diagram of another example of SiC single crystal manufacturing apparatus 101 according to this embodiment. Guide member 25 in Fig. 6 expands in diameter from seed crystal installation section 11 toward raw material G. By expanding the diameter of guide member 25, the diameter of single crystal C can be increased.

[0065] Furthermore, although the upper end of guide member 20 in FIG. 5 is open, the upper end of guide member 20 may be connected to the inner surface of crucible 10, making the space in which heat insulating material 30 exists a closed space.

[0066] The surface of the guide member 20 is preferably coated with tantalum carbide. The guide member 20 is constantly exposed to the source gas in order to control the flow of the source gas. If the guide member 20 is used with exposed graphite, the graphite may react with the source gas, causing deterioration and damage. Deterioration and damage may cause holes to form in the guide member 20. Furthermore, carbon powder that peels off due to deterioration may be incorporated into the single crystal C, leading to deterioration of the quality of the single crystal C. In contrast, tantalum carbide can withstand high temperatures and does not undergo unnecessary reactions with the source gas. Therefore, high-quality SiC single crystal growth can be achieved stably.

[0067] The heat insulating material 30 moves outside the guide member 20 along the extension direction of the guide member 20. By moving the heat insulating material 30, it is possible to control the positional relationship between the end face of the heat insulating material 30 on the raw material G side (hereinafter referred to as the lower face 30a) and the surface Ca of the single crystal C. Therefore, it is possible to freely control the temperature distribution in the vicinity of the surface Ca of the single crystal C, and to freely control the surface shape of the single crystal C that is grown. In the process of crystal growth, the positional relationship between the end face 30a of the heat insulating material 30 on the raw material side and the surface Ca of the single crystal C can be controlled. Furthermore, during the crystal growth process, the end face 30a of the heat insulating material 30 on the raw material side can be positioned within 20 mm from the surface Ca of the single crystal C. Furthermore, during the crystal growth process, the end face 30a of the heat insulating material 30 on the raw material side can be arranged closer to the seed crystal setting part 11 than the surface Ca of the single crystal C. Furthermore, when the thickness of the heat insulating material 30 is 0.2 mm or more, it can be made half or less of the growth amount of the SiC single crystal ingot to be manufactured.

[0068] FIG. 6 is a cross-sectional schematic diagram of a driving means for moving the insulating material 30 up and down. The driving means may be any means capable of moving the insulating material 30 up and down. For example, as shown in FIG. 6(a), a driving member 31 extending from above the insulating material 30 to the outside of the crucible 10 may be provided, and the insulating material 30 may be moved by pushing and pulling the driving member up and down. Alternatively, as shown in FIG. 6(b), a lifting driving member 32 may be provided to support the insulating material 30 from below. Furthermore, as shown in FIG. 6(c), a notch may be provided in a portion of the side of the crucible 10, and a driving member 33 extending through the notch to the outside of the crucible 10 may be provided, and the insulating material 30 may be moved by raising and lowering the driving member.

[0069] The heat insulating material 30 is preferably made of a material having a thermal conductivity of 40 W / mk or less at high temperatures of 2000°C or higher. Examples of materials having a thermal conductivity of 40 W / mk or less at high temperatures of 2000°C or higher include graphite members and the like having a thermal conductivity of 120 W / mk or less at room temperature. It is more preferable that the heat insulating material 30 be made of a material having a thermal conductivity of 5 W / mk or less at high temperatures of 2000°C or higher. Examples of materials having a thermal conductivity of 5 W / mk or less at high temperatures of 2000°C or higher include graphite and felt materials whose main component is carbon.

[0070] The shape of the heat insulating material 30 is designed appropriately to fit the shape of the area sandwiched between the guide member 20 and the inner surface of the crucible 10. As shown in FIG. 5, when the distance between the guide member 20 and the inner surface of the crucible 10 is constant, the heat insulating material 30 is arranged to fill the gap between them. Also, as shown in FIG. 5, when the distance between the guide member 25 and the inner surface of the crucible 10 varies, the shape of the heat insulating material 35 is designed to fit the position where the gap between them is narrowest. By designing it in this way, it is possible to prevent the heat insulating material 35 from getting stuck between the guide member 25 and the inner surface of the crucible 10 and becoming stuck.

[0071] The thickness of the insulating material 30 is preferably 0.2 mm or more, more preferably 5 mm or more, and even more preferably 20 mm or more. If the insulating material 30 is too thin, it may not provide sufficient insulating effect. Furthermore, the thickness of the insulating material 30 is preferably less than half the length of the final single crystal produced. Here, the single crystal length refers to the vertical length of the single crystal C after crystal growth (the growth amount of the single crystal C). If the growth amount of the single crystal is 100 mm, the thickness of the insulating material 30 is preferably 50 mm or less. If the growth amount of the single crystal is within 50 mm, the thickness of the insulating material 30 is preferably 25 mm or less. If the insulating material 30 is too thick, its movement will be hindered. Furthermore, if the thickness of the insulating material 30 is within this range, a temperature difference can be created in the vertical direction within the single crystal C via the insulating material 30. Therefore, recrystallization of the raw material gas in areas other than the surface Ca of the single crystal C can be prevented.

[0072] As described above, the SiC single crystal manufacturing apparatus allows the position of the heat insulating material to be controlled relative to the growing single crystal. By controlling the position of the heat insulating material, the temperature distribution near the surface of the single crystal C during crystal growth can be freely controlled. Since the single crystal C grows along an isothermal surface, controlling the temperature distribution near the surface of the single crystal C leads to controlling the shape of the single crystal C.

[0073] The n-type SiC single crystal ingot can be produced using the SiC single crystal production apparatus described above. The following describes an example in which the SiC single crystal production apparatus 100 shown in Figure 5 is used.

[0074] In the process of producing an n-type SiC single crystal ingot, a single crystal C is grown from a seed crystal S placed in a seed crystal placement section 11. The n-type single crystal C grows when nitrogen gas is introduced and the raw material gas sublimated from the raw material G recrystallizes on the surface of the seed crystal S. The nitrogen gas reacts with the crystal surface at high temperatures, and nitrogen atoms are doped into the SiC single crystal. This nitrogen doping concentration depends on the nitrogen gas concentration; the higher the nitrogen gas concentration, the higher the doping concentration. The resulting SiC single crystal exhibits a conductivity (resistivity) corresponding to this doping concentration. The raw material G is sublimated by heating the crucible 10 with an external heating means. The sublimated raw material gas is supplied toward the seed crystal S along a guide member 20.

[0075] In the process of producing a SiC single crystal ingot, the positional relationship between the lower surface 30a of the heat insulating material 30 and the surface Ca of the single crystal C is controlled during the crystal growth of the single crystal C from the seed crystal S. By controlling this positional relationship, the shape of the surface Ca of the single crystal C can be freely controlled.

[0076] Figure 8 shows the positional relationship between the lower surface 30a of the heat insulating material 30 and the surface Ca of the single crystal C, and the relationship with the isothermal surface near the single crystal C. Figure 8(a) shows an example where the surface Ca (crystal growth surface) of the single crystal C is flat, Figure 8(b) shows an example where the surface Ca (crystal growth surface) of the single crystal C is concave, and Figure 8(c) shows an example where the surface Ca (crystal growth surface) of the single crystal C is convex.

[0077] As shown in Figures 8(a) to 8(c), the shape of the surface Ca of the single crystal C varies depending on the position of the heat insulating material 30 relative to the surface Ca of the single crystal C. As shown in Figure 8(a), when the surface Ca of the single crystal C and the lower surface 30a of the heat insulating material 30 are located at approximately the same position, the surface Ca of the single crystal C is flat. In contrast, as shown in Figure 8(b), when the lower surface 30a of the heat insulating material 30 is located closer to the raw material G than the surface Ca of the single crystal C, the surface Ca of the single crystal C is concave, and as shown in Figure 8(c), when the surface Ca of the single crystal C is located closer to the raw material G than the lower surface 30a of the heat insulating material 30, the surface Ca of the single crystal C is convex.

[0078] The shape of the surface Ca of the single crystal C changes depending on the position of the heat insulating material 30 relative to the surface Ca of the single crystal C because the shape of the isothermal surface T in the film formation space K changes. Figure 9 is a diagram schematically showing the shape of the isothermal surface T near the single crystal C during crystal growth. Figure 9(a) is a diagram when the heat insulating material 30 is not provided, and Figure 9(b) is a diagram when the heat insulating material 30 is provided.

[0079] The SiC single crystal C itself has a heat insulating effect due to its low thermal conductivity. On the other hand, the thermal conductivity of the guide member 20 is higher than that of the single crystal C. Therefore, as shown in FIG. 9(a), when there is no heat insulating material 30, the isothermal surface T is formed to extend from the single crystal C. The crystal growth surface of the single crystal C grows along the isothermal surface T. Therefore, when there is no heat insulating material 30, the shape of the surface Ca (crystal growth surface) of the single crystal C is fixed to a concave shape.

[0080] In contrast, when a heat insulating material 30 is provided as shown in FIG. 9(b), the shape of the isothermal surface T changes. The shape of the isothermal surface T can be freely designed by controlling the position of the heat insulating material 30 relative to the single crystal C. The design of the shape of the isothermal surface T can be performed with high accuracy by checking it in advance using simulations, etc. In this way, by controlling the position of the heat insulating material 30 relative to the single crystal C, the shape of the surface Ca of the single crystal C can be freely designed.

[0081] Furthermore, controlling the position of the heat insulating material 30 relative to the single crystal C has the effect of suppressing adhesion of polycrystals to the guide member 20 and the effect of reducing the temperature difference in the in-plane direction within the single crystal C.

[0082] Polycrystals are formed in low-temperature areas near the crystal growth surface of single crystal C. For example, as shown in FIG. 9(a), when there is a large temperature difference between single crystal C and guide member 20, polycrystals grow on guide member 20. When the polycrystals grown on guide member 20 come into contact with single crystal C, the crystallinity of single crystal C is disrupted, causing defects. In contrast, as shown in FIG. 9(b), if a heat insulating material 30 is present near the surface Ca of single crystal C, the temperature difference between single crystal C and guide member 20 can be reduced, and polycrystal growth can be suppressed.

[0083] Furthermore, if the temperature difference in the in-plane direction within the single crystal C is large, stress occurs during the growth of the single crystal C. Stress generated within single crystal C causes distortion and misalignment of the crystal plane. Distortion and misalignment of the lattice plane within single crystal C can cause killer defects such as basal plane dislocations (BPDs).

[0084] So far, we have explained how the shape of the surface Ca of the single crystal C can be controlled. The shape of the surface Ca of the single crystal C is preferably flat or convex toward the raw material G. This is because if the shape of the surface Ca of the single crystal C is concave toward the raw material G, the quality will be inferior. In order to make the shape of the surface Ca of the single crystal C flat or convex, the position of the surface Ca of the single crystal C and the lower surface 30a of the heat insulating material 30 are made to be approximately the same, or the surface Ca of the single crystal C is located closer to the raw material G than the lower surface 30a of the heat insulating material 30.

[0085] Here, "substantially the same" does not mean that the surface Ca of the single crystal C and the lower surface 30a of the thermal insulator 30 are positioned at exactly the same height, but means that a positional deviation is allowed within a range that does not significantly affect the isothermal surface T. Specifically, if the lower surface 30a of the thermal insulator 30 is positioned within 30 mm from the surface Ca of the single crystal C, it can be said that the surface Ca of the single crystal C and the lower surface 30a of the thermal insulator 30 are in a substantially identical positional relationship. On the other hand, in order to make the shape of the surface Ca of the single crystal C flat, it is preferable that the positional relationship between the surface Ca of the single crystal C and the lower surface 30a of the thermal insulator 30 be nearly identical, and the lower surface 30a of the thermal insulator 30 is preferably positioned within 20 mm, and more preferably within 10 mm, of the surface Ca of the single crystal C.

[0086] Furthermore, the surface Ca of the single crystal C is preferably located closer to the source material G than the lower surface 30a of the heat insulating material 30. In other words, the lower surface 30a of the heat insulating material 30 is preferably located closer to the seed crystal setting part 11 than the surface Ca of the single crystal C. Even if an external factor such as temperature fluctuation occurs in the film formation space K, the surface Ca of the single crystal C can be prevented from becoming concave.

[0087] Also, it is preferable to control the position of the heat insulating material 30 from the start of crystal growth. That is, it is preferable to control the positional relationship between the lower surface 30a of the heat insulating material 30 and the surface of the seed crystal S at the start of crystal growth.

[0088] Immediately after the start of crystal growth, the seed crystal installation part 11 exists around the seed crystal S, and the distance between the seed crystal S and the crucible 10 is also short. Therefore, the isothermal surface T in the film formation space K is also affected by the temperatures (thermal conductivities) of these members. That is, the effect of using the heat insulating material 30 is most exhibited in the region where the single crystal C has grown 30 mm or more from the seed crystal S. On the other hand, it does not mean that the effect of the heat insulating material 30 is not exhibited immediately after the start of crystal growth.

[0089] For example, when the shape of the crystal growth surface of the single crystal C immediately after crystal growth becomes concave without providing the heat insulating material 30, it is necessary to return the shape of the crystal growth surface of the single crystal C to convex in the subsequent growth process. When the shape of the crystal growth surface changes from concave to convex during the growth process, stress accumulates in the single crystal C, and defects are likely to occur. Therefore, it is preferable to control the position of the heat insulating material 30 from the start of crystal growth. The positional relationship of the heat insulating material 30 with respect to the seed crystal S can be designed in the same manner as the positional relationship between the heat insulating material 30 and the single crystal C during the crystal growth process.

[0090] <Manufacturing process of SiC single crystal substrate> In the process of manufacturing a SiC single crystal substrate from the obtained n-type SiC single crystal ingot, a planarization process including lapping using a predetermined polishing slurry and a process for removing a processed damaged layer are included. In the manufacturing of a SiC single crystal substrate, lapping can be performed using a slurry characteristic in lapping. Other than that, known methods can be used for the processing from the SiC single crystal ingot until a SiC single crystal substrate is obtained. Hereinafter, the lapping process will be described.

[0091] Next, the lapping slurry that can be used will be described in detail. In the loose abrasive processing process, a slurry containing, for example, water, boron carbide abrasive grains, and an additive for dispersing the boron carbide abrasive grains is poured between the upper and lower platens, and pressure is applied to the SiC substrate 1 by the upper and lower platens to planarize the surface of the SiC substrate 1. The slurry used in the processing process is, for example, a slurry containing water as its main component. Using a slurry containing water as its main component improves the dispersibility of the boron carbide abrasive grains and reduces the occurrence of secondary aggregation during the processing process. Furthermore, when using a slurry containing water as its main component, the surface of the SiC substrate facing the upper platen, which has a slurry supply hole, is cleaned by directly supplying water, while the surface facing the lower platen, which does not have a slurry supply hole, is cleaned by water supplied through the gap between the SiC substrate and the carrier plate. The slurry used in the lapping process is collected in a tank and then resupplied from the tank.

[0092] The modified Mohs hardness (14) of boron carbide abrasive grains is slightly greater than the modified Mohs hardness (13) of a SiC substrate (a non-polished object), but less than the modified Mohs hardness (15) of diamond. Therefore, by using such a slurry, it is possible to relatively increase the processing speed while suppressing the occurrence of cracks in the SiC substrate, which has a modified Mohs hardness (13), and also to suppress a decrease in the particle size of the boron carbide abrasive grains.

[0093] The proportion of boron carbide abrasive grains in the slurry is, for example, 15% by mass or more and 45% by mass or less, preferably 20% by mass or more and 40% by mass or less, and more preferably 25% by mass or more and 35% by mass or less. By making the proportion of boron carbide abrasive grains in the slurry 15% by mass or more, the content of boron carbide abrasive grains in the slurry can be increased, thereby increasing the processing speed of the lapping process. Furthermore, by making the proportion of boron carbide abrasive grains in the slurry 45% by mass or less, the frequency and area of ​​contact between boron carbide abrasive grains can be reduced, making it easier to suppress the reduction in the particle size of the boron carbide abrasive grains and the wear of the boron carbide abrasive grains.

[0094] The boron carbide abrasive grains in the slurry used in the processing step have, for example, an average particle size of 15 μm to 40 μm, preferably 25 μm to 35 μm. Using boron carbide abrasive grains with an average particle size of 15 μm or more facilitates increased lapping speed of the surface of the SiC substrate 1 and allows sufficient adhesion of the additives described below to the surface, leading to improved dispersibility and reduced particle size reduction. Furthermore, setting the average particle size to 40 μm or less facilitates the suppression of cracking and breakage of the SiC substrate. Furthermore, excessive adhesion of the additives described below to the surface is suppressed, thereby preventing a decrease in processing speed due to a reduced contact area with the SiC substrate (the workpiece). Furthermore, using such boron carbide abrasive grains facilitates the suppression of changes in particle size before and after lapping. Here, the average particle size of the boron carbide abrasive grains is the average particle size of the boron carbide abrasive grains before processing, and the average particle size of the boron carbide abrasive grains after processing is, for example, 14 μm or more and 48 μm or less, and preferably 23 μm or more and 42 μm or less, since the ratio of the average particle sizes of the boron carbide abrasive grains before and after processing is 0.91 or more and 1.2 or less.

[0095] Here, the average particle size of the boron carbide abrasive grains is measured based on the particle size distribution measured by laser scattered light measurement using a particle size distribution measuring device, Mastersizer Hydro 2000MU (Spectris Co., Ltd.) or MT3000II (Microtrac Bell Co., Ltd.).

[0096] The additive may be a polyhydric alcohol, an ester and its salt, a homopolymer and its salt, a copolymer, etc. Specific examples include one or more selected from the group consisting of glycerin, 1-vinylimidazole, coconut oil fatty acid methyl taurate sodium, lauric acid amide ether sulfate sodium salt, myristate amide ether sulfate sodium salt, polyacrylic acid, and acrylic acid-maleic acid copolymer.

[0097] It is believed that these additives can improve the dispersibility of the boron carbide abrasive grains in the slurry.

[0098] The additive adheres to the surface of the boron carbide abrasive grains and prevents direct contact between the boron carbide abrasive grains, thereby improving the dispersibility of the boron carbide abrasive grains in the slurry and preventing particle size reduction of the abrasive grains during the processing step.

[0099] The proportion of additives in the slurry is, for example, 3% by volume or more and 20% by volume or less, preferably 5% by volume or more and 15% by volume or less, and more preferably 10% by volume or more and 15% by volume or less. Here, the proportion of additives in the slurry refers to the ratio obtained by dividing the volume of additives (additive components) such as glycerin by the volume of the slurry. When the additives in the slurry are within the above range, they adhere sufficiently to the surface of the boron carbide in the slurry, achieving a desirable degree of dispersion of the boron carbide abrasive grains in the slurry and making it easier to prevent the particle size of the boron carbide abrasive grains from decreasing during the processing step.

[0100] In this lapping process, the processing speed for processing the surface of the SiC substrate in the processing step is, for example, 14 μm / h to 45 μm / h, preferably 16 μm / h to 40 μm / h, and more preferably 18 μm / h to 25 μm / h. The processing speed depends on the processing pressure and the average particle size of the boron carbide abrasive grains described above. Setting the processing speed to 45 μm / h or less is likely to achieve the effect of suppressing the reduction in particle size of the boron carbide abrasive grains and the wear of the boron carbide abrasive grains. Setting the processing speed to 14 μm / h or more increases throughput. When lapping is performed in multiple steps, the processing speed calculated by dividing the total change in thickness of the SiC substrate by the total processing time should be within the above range, and it is preferable that the processing speed at each timing be within the above range. In other words, when lapping is performed in multiple steps, it is preferable that the processing speed calculated for each step be within the above range.

[0101] Here, the processing speed is calculated from the difference in thickness of the SiC substrate 1 before and after lapping and the processing time. Specifically, the processing speed is calculated as follows. The thickness of the SiC substrate 1 is measured at the following positions: position 1c, which corresponds to the center of the SiC substrate 1 before the orientation flat OF is formed on the SiC substrate 1; position 1a, which is 5 to 10 mm away from the midpoint of the orientation flat OF toward position 1c; position 1b, which is on the same line c as positions 1a and 1c and is 5 to 10 mm away from the outer periphery of the SiC substrate 1 toward position 1a; and positions 1d and 1e, which are on a line perpendicular to line c and are 5 to 10 mm away from the outer periphery of the SiC substrate 1 toward position 1a. The thicknesses of the SiC substrate 1 at these five positions 1a to 1e are measured using an indicator (ID-C150XB, manufactured by Mitutoyo), and the obtained thicknesses are treated as the thickness of the SiC substrate 1. The processing speed is calculated by dividing the difference in thickness (μm) of the SiC substrate 1 before and after processing thus obtained by the processing time (h).

[0102] By attaching an additive to the surface of the boron carbide abrasive grains in the slurry used in the processing process, the dispersibility of the boron carbide abrasive grains can be improved and contact of the boron carbide abrasive grains can be suppressed, thereby suppressing a reduction in the particle size of the boron carbide abrasive grains. Specifically, the change in particle size of the boron carbide abrasive grains can be suppressed to the extent that the ratio of the average particle size of the processed boron carbide abrasive grains to the average particle size of the boron carbide abrasive grains before processing is 0.91 or more and 1.2 or less. The reason why this ratio includes a value greater than 1 is that the boron carbide abrasive grains may undergo secondary aggregation during the processing, causing some of the boron carbide abrasive grains to have a larger particle size than before processing.

[0103] In conventional lapping processes, the particle size of the boron carbide abrasive grains in the slurry is significantly reduced during the lapping process. Therefore, when lapping is performed again, it is necessary to add abrasive grains to the slurry each time. Furthermore, each time, it is necessary to carry out complicated management to determine the particle size distribution of the abrasive grains in the slurry, which depends on the number of times the slurry has been used for lapping. In this way, this lapping process makes it easier to control the particle size of the boron carbide abrasive grains, reduces costs, reduces the environmental impact, and suppresses the occurrence of cracks.

[0104] Furthermore, since the particle size of the boron carbide abrasive grains does not change significantly during this lapping process, changes in the lapping speed are suppressed, and the lapping process can be continued under the same conditions. This lapping process is particularly effective when using boron carbide as the abrasive grains, which has a slightly higher modified Mohs hardness than silicon carbide, the object being polished. Because this lapping process uses such abrasive grains and substrate, it is also possible to suppress cracks that frequently occur when diamond is used as the abrasive grains and a SiC substrate is used as the object being polished.

[0105] Furthermore, this lapping process can suppress the reduction in particle size and wear of the boron carbide abrasive grains, thereby reducing the variation in particle size of the boron carbide abrasive grains in the slurry during the lapping process. While the lapping speed depends on the particle size of the abrasive grains used, this lapping process can suppress the variation in particle size of the abrasive grains, so the entire surface of the SiC substrate is processed with abrasive grains of roughly uniform particle size, reducing the in-plane variation in the substrate thickness of the processed SiC substrate. [Example]

[0106] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0107] Example 1 First, an n-type SiC single crystal ingot was produced using the SiC single crystal production apparatus shown in Figure 5. First, a 4H-SiC single crystal with a diameter of 200 mm and a thickness of 5.0 mm was used as the seed crystal S. The (0001) plane was the main surface, the off-angle was 4°, and the crucible temperature was controlled so that the temperature (Tr) of the side wall of the crucible body near the same height as the seed crystal surface was 30 to 150°C, the temperature (Tg) of the center of the seed crystal in a plan view of the outer wall of the crucible lid was 50 to 250°C, and the temperature difference (ΔT) between Tr and Tg was 20 to 100°C. During crystal growth, the thermal insulator 30 was moved stepwise so that its end face (bottom) on the source side was closer to the lid than the surface of the single crystal, and the distance in the growth direction between the end face on the source side of the thermal insulator 30 and the surface of the single crystal was within 10 mm. Nitrogen gas was introduced at a partial pressure of 554 Pa for 45 minutes one hour after the start of growth. The n-type SiC single crystal ingot thus obtained had a diameter of 208 mm and a height of 20.2 mm.

[0108] Next, the n-type SiC single crystal ingot was processed by a known method to obtain an 8-inch SiC substrate having a (0001) plane with an off-angle of 4° and a thickness of 0.9 mm.

[0109] The thickness of this SiC substrate was measured. Next, the SiC substrate whose thickness had been measured was placed on the carrier plate of a polishing machine and subjected to lapping. The lapping slurry was obtained by adding a predetermined amount of boron carbide abrasive grains and AD8 (10% by volume) as an additive to water and dispersing them. The boron carbide abrasive grains used had a grain size of F320 (JIS R6001). The proportion of glycerin (manufactured by Aichi Techno Co., Ltd.) as an additive in the slurry was 6% by volume. The lapping was carried out using a loose abrasive method, supplying a lapping slurry at a rate of 16 L / min. The lapping slurry was circulated and used.

[0110] The driving conditions of the polishing device in the lapping process are a processing pressure of 160 g / cm 2The rotation speed of the lower surface plate was 16 rpm, the rotation speed of the upper surface plate was 5.5 rpm, the rotation speed of the central gear was 2.8 rpm, the rotation speed of the internal gear was 6.0 rpm, and the processing time was 40 minutes. After lapping, the particle size distribution of the boron carbide abrasive grains in the slurry was measured in the same way as before lapping, and the thickness of the substrates was measured in the same way as before lapping, and the processing speed was calculated. In this lapping process, the average processing speed for 15 SiC substrates was 18 μm / h. After the measurement, the slurry used in the previous lapping process was supplied and a second lapping process and measurement were performed while circulating the slurry. In Example 1, this process was repeated for a total of eight lapping processes and measurements.

[0111] Next, an etching step for removing the process-affected layer and a CMP step for mirror polishing were carried out to obtain the SiC single crystal substrate of Example 1.

[0112] Example 2 In the production of the SiC single crystal ingot, the temperature at the highest temperature point of the raw material was increased by 20°C, and the operating conditions of the polishing device in the lapping process were adjusted so that the in-plane variation in substrate thickness after lapping was smaller than in Example 1. Furthermore, except for changing the amount of nitrogen gas introduced, SiC single crystal substrates were obtained under the same conditions as in Example 1.

[0113] (Comparative Example 1) A SiC single crystal substrate was obtained under the same conditions as in the example, except that a SiC single crystal manufacturing apparatus without a heat insulating material 30 was used, a seed crystal S with a diameter of 150 mm was used, Tr, Tg, and ΔT were not controlled during crystal growth, a lapping slurry not containing an additive (AD8) was used in the lapping process, and the amount of nitrogen gas introduced was changed.

[0114] (Comparative Example 2) A SiC single crystal substrate was obtained under the same conditions as in Comparative Example 1, except that the temperature at the highest raw material temperature point was increased by 10° C. and the amount of nitrogen gas introduced was changed.

[0115] (Comparative Example 3) A SiC single crystal ingot was produced using a SiC single crystal manufacturing apparatus that did not have a heat insulating material 30, and a SiC single crystal substrate was obtained under the same conditions as in Example 1, except that a lapping slurry that did not contain the additive (AD8) was used in the lapping process and the amount of nitrogen gas introduced was changed.

[0116] (evaluation) The concentrations of nitrogen, a dopant, at predetermined points on the SiC single crystal substrates of Examples 1, 2, and Comparative Examples 1 to 3 were measured using SIMS from the stacking surface toward the thickness direction. The results are shown in Table 1. The nitrogen concentrations at each point in Table 1 are the center point O on the surface at a depth of 3 μm, point p1 1.0 mm from the periphery, and three points (p2, p3, and p4) dividing the area between them into four equal parts (see Figure 1). The in-plane average nitrogen concentration in Table 1 is the average nitrogen concentration at these five points, and the five-point nitrogen concentration distribution indicates the ratio of the difference in nitrogen concentration between the center and the point with the largest difference from the center among the other four points. The percentages (%) of a predetermined number of meshes in Table 1 represent the percentage of meshes in which the dopant concentration at the center of each mesh is within ±20% of the dopant concentration of mesh M0, which includes the center of the surface, when the substrate is divided into 10 mm square meshes. Figure 10 shows a schematic diagram of the division into 10 mm square meshes. FIG. 10 shows an example of how to divide the 10 mm square mesh, but the invention is not limited to this.

[0117] [Table 1]

[0118] Based on the results shown in Table 1, it can be seen that Examples 1 and 2 have a reduced nitrogen concentration distribution at five points compared to Comparative Examples 1 to 3. It can also be seen that Examples 1 and 2 have a larger proportion of meshes that are within ±20% of the dopant concentration of mesh M0, which includes the in-plane center, compared to Comparative Examples 1 to 3. Thus, Examples 1 and 2 have a better nitrogen concentration distribution across the entire plane compared to Comparative Examples 1 to 3. It is believed that these results are due to the effect that Examples 1 and 2 have achieved higher quality SiC single crystals by performing more precise temperature control compared to Comparative Examples 1 to 3.

[0119] Furthermore, the n-type SiC single crystal substrates of Examples 1 and 2, Comparative Examples 1, 2, and 3 were evaluated for SORI, in-plane variation in substrate thickness, number of micropipes, total number of dislocations, threading dislocation density, and basal plane dislocation density. The number of micropipes, total number of dislocations, threading dislocation density, and basal plane dislocation density were evaluated by etch pits that appeared after KOH etching at 550°C for 10 minutes. The results are shown in Table 2. The TD etch pit density in Table 2 is the sum of the TSD etch pit density and TED etch pit density.

[0120] [Table 2]

[0121] The micropipe density was 1 / cm in all of Examples 1 and 2 and Comparative Examples 1 to 3. 2 It was as follows. In Examples 1 and 2, both the SORI and the substrate thickness were significantly reduced compared to Comparative Examples 1 to 3. Furthermore, in Examples 1 and 2 (8-inch substrates), the total number of etch pits was sufficiently reduced to a degree comparable to that of Comparative Examples 1 and 2 (6-inch substrates), and both the TD etch pit density and the BPD etch pit density were significantly reduced. This result is thought to be the effect of more precise temperature control in Examples 1 and 2. Furthermore, in Examples 1 and 2 (8-inch substrates), the total number of etch pits, the TD etch pit density, and the BPD etch pit density were all significantly reduced compared to Comparative Example 3 (8-inch substrate). This result demonstrates that more precise temperature control has a greater effect on the fabrication of 8-inch SiC single crystal substrates than on the fabrication of 6-inch SiC single crystal substrates. [Explanation of symbols]

[0122] 1. SiC single crystal substrate

Claims

1. An 8-inch n-type SiC single crystal substrate, The diameter is in the range of 195 to 205 mm, An n-type SiC single crystal substrate having a SORI of 21 μm or less.

2. An n-type SiC single crystal substrate as described in claim 1, wherein the SORI is 14 μm or less.

3. The n-type SiC single crystal substrate according to claim 1, wherein the dopant concentration is 2×10 18 / cm 3 or more and 6×10 19 / cm 3 or less.

4. An n-type SiC single crystal substrate as described in claim 1, in which the in-plane variation, which is the difference between the maximum and minimum values ​​of the substrate thickness at the center of the substrate and four points on the circumference of a circle with a radius of (1 / 2) of the substrate, is 2.0 μm or less.

5. The total number of etch pits that appeared after KOH etching at 550°C for 10 minutes was 2.1 × 10 ６ The n-type SiC single crystal substrate according to claim 1 , wherein the number of nanoparticles per nanoparticle is equal to or less than 100.

6. Among the etch pits that appeared after KOH etching at 550°C for 10 minutes, the density of etch pits identified as threading dislocations was 1 x 10 ３ pieces / cm ２ 2. The n-type SiC single crystal substrate according to claim 1, wherein:

7. Among the etch pits that appeared after KOH etching at 550°C for 10 minutes, the density of etch pits identified as threading dislocations was 5 × 10 ２ pieces / cm ２ 7. The n-type SiC single crystal substrate according to claim 6, wherein:

8. Among the etch pits that appeared after KOH etching at 550°C for 10 minutes, the density of etch pits identified as basal plane dislocations was 2 × 10 ３ pieces / cm ２ 2. The n-type SiC single crystal substrate according to claim 1, wherein:

9. Among the etch pits that appeared after KOH etching at 550°C for 10 minutes, the density of etch pits identified as threading dislocations was 1 x 10 ３ pieces / cm ２ 9. The n-type SiC single crystal substrate according to claim 8, wherein:

10. Among the etch pits that appeared after KOH etching at 550°C for 10 minutes, the density of etch pits identified as threading dislocations was 5 × 10 ２ pieces / cm ２ 10. The n-type SiC single crystal substrate according to claim 9, wherein:

11. The n-type SiC single crystal substrate according to any one of claims 1 to 10, having a thickness in the range of 300 to 650 µm.

12. An n-type SiC single crystal substrate according to any one of claims 1 to 10; a SiC epitaxial layer laminated on the surface of the n-type SiC single crystal substrate.

13. The n-type SiC single crystal substrate according to claim 11; a SiC epitaxial layer laminated on the surface of the n-type SiC single crystal substrate.

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