JP7800632B2 - n-type SiC single crystal substrate and SiC epitaxial wafer - Google Patents

Description

The present invention relates to n-type SiC single crystal substrates, SiC epitaxial wafers, and n-type SiC single crystal ingots.

Silicon carbide (SiC) has an electric breakdown field that is an order of magnitude larger than that of silicon (Si), and a band gap that is three times larger. Silicon carbide (SiC) also has other properties, such as a thermal conductivity that is approximately three times higher than that of silicon (Si). Therefore, silicon carbide (SiC) is expected to be used in power devices, high-frequency devices, high-temperature operating devices, and more. For this reason, SiC epitaxial wafers have recently begun to be used in these types of semiconductor devices.

SiC epitaxial wafers are obtained by depositing a SiC epitaxial layer on the surface of a SiC single crystal substrate. Hereinafter, the substrate before the SiC epitaxial layer is deposited will be referred to as the SiC single crystal substrate, and the substrate after the SiC epitaxial layer is deposited will be referred to as the SiC epitaxial wafer. SiC single crystal substrates are cut from SiC single crystal ingots.

Currently, the mainstream SiC single crystal substrate market is 6-inch (150 mm) diameter SiC single crystal substrates, but development is also underway toward mass production of 8-inch (200 mm) 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 popular as a trump card in energy-saving technology.

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 issue that when manufacturing 6-inch SiC single crystal substrates using manufacturing techniques for 4-inch SiC single crystal substrates, frequent thermal decomposition occurs around the outer periphery of the seed crystal, which causes macro-defects, making it difficult to obtain high-quality single crystals with a high yield. Patent Document 1 describes an invention that solves this issue by using a seed crystal of a specified thickness. As such, it will be necessary to establish manufacturing conditions for SiC single crystal substrates of new sizes while resolving new issues that arise depending on the new sizes.

In SiC devices used as power semiconductors, it is extremely important to increase the doping concentration and reduce resistance in order to reduce loss. Furthermore, to reduce the variation in characteristics between SiC devices, it is necessary to minimize the variation in dopant concentration.

Patent No. 6594146 Patent No. 6598150 Japanese Patent Application Laid-Open No. 2020-17627 JP 2019-189499 A

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

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 an 8-inch substrate were produced by simply applying a SiC single crystal substrate production technology optimized for producing 6-inch substrates, the resulting 8-inch substrate would have a higher dislocation density than that of a 6-inch substrate. This is because the hurdle for achieving the same quality increases significantly as the size increases. Therefore, when evaluating production technology for 8-inch SiC single crystal substrates, the starting point is the dislocation density of an 8-inch substrate obtained by simply applying a SiC single crystal substrate production technology optimized for producing 6-inch substrates, and the technical value should be evaluated based on the degree of improvement achieved relative to the dislocation density at that starting point.
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.

In addition, to meet the growing 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.

The present invention was made in consideration of the above circumstances, and aims to provide an 8-inch SiC single crystal substrate, an n-type SiC single crystal substrate, and a SiC epitaxial wafer, that have a high dopant concentration and reduced variation in concentration distribution.

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

Aspect 1 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, a dopant concentration of 2×10 ¹⁸ /cm ³ or more and 6×10 ¹⁹ /cm ³ or less, and a dopant concentration of at least five points in the radial direction, including points within 1 mm from the outermost periphery, that is within ±20% of the dopant concentration at the in-plane center at the same depth from the main surface.

Aspect 2 of the present invention is an n-type SiC single crystal substrate according to aspect 1, in which 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.

Aspect 3 of the present invention is an n-type SiC single crystal substrate according to aspect 1 or 2, in which 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.

Aspect 4 of the present invention is an n-type SiC single crystal substrate according to any one of aspects 1 to 3, in which the dopant is nitrogen.

Aspect 5 of the present invention is a SiC epitaxial wafer comprising an n-type SiC single crystal substrate according to any one of aspects 1 to 4 and a SiC epitaxial layer laminated on the surface of the n-type SiC single crystal substrate.

A sixth aspect of the present invention is an n-type SiC single crystal ingot, wherein substrates having diameters in the range of 195 to 205 mm are cut out from the n-type SiC single crystal ingot, and when the dopant concentrations of the cut out substrates are measured, the dopant concentrations of the cut out substrates are 2×10 ¹⁸ /cm or more and ^{6 ×} 10 ¹⁹ /cm or less, and the dopant concentrations at at least five points in the radial direction, including points within 1 mm from the outermost periphery, are within ±20% of the dopant concentration at the in-plane center at the same depth from the main surface of the cut out substrate.

Aspect 7 of the present invention is an n-type SiC single crystal ingot according to aspect 6, in which 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 of the sliced substrate.

Aspect 8 of the present invention is an n-type SiC single crystal ingot according to aspect 6 or 7, 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 of the sliced substrate.

Aspect 9 of the present invention is an n-type SiC single crystal ingot according to any one of aspects 6 to 8, wherein the dopant is nitrogen.

The n-type SiC single crystal substrate of the present invention is an 8-inch SiC single crystal substrate that has a high dopant concentration and reduced variation in concentration distribution.

1A is a schematic cross-sectional view of a SiC single crystal substrate according to this embodiment, and FIG. 1B is a schematic plan view thereof. 1A is a schematic cross-sectional view of a SiC single crystal substrate according to this embodiment, and FIG. 1B is a schematic plan view thereof. FIG. 1 is a conceptual diagram showing the definition of SORI. 1 is a conceptual diagram showing a process in which the depth of a work-affected layer is reduced by mechanical processing. FIG. 1 is a cross-sectional schematic view of a SiC single crystal manufacturing apparatus. FIG. 1 is a cross-sectional schematic view of another example of a SiC single crystal production apparatus. 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. FIG. 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. 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. FIG. 2 is a plan view showing an example of a 10 mm square mesh.

The present invention will now be described in detail, with appropriate reference to the drawings. 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 to them. Appropriate modifications can be made within the scope of the effects of the present invention. Furthermore, components well known to those skilled in the art other than those illustrated in the drawings may be omitted in each drawing.

(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 on both the front and back surfaces having a thickness of 0.1 nm or less, and a dopant concentration of 2×10 ¹⁸ /cm ³ or more and 6×10 ¹⁹ /cm ³ or less.

There are no particular restrictions on the external shape of the SiC single crystal substrate 1, and various flat plate shapes and thicknesses can be used, but it is typically disk-shaped. The thickness of the SiC single crystal substrate can be, for example, in the range of 300 to 650 μm.

The SiC single crystal substrate 1 is preferably 4H-SiC. Although there are various polytypes of SiC, 4H-SiC is the one primarily used to fabricate practical SiC devices.

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 obtained by tilting 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.

N-type dopants can generally be nitrogen, but are not limited to nitrogen.

The dopant concentration of the SiC single crystal substrate 1 is not less than 2×10 ¹⁸ /cm ³ and not more than 6×10 ¹⁹ /cm ³ .
This is because if the dopant concentration of the SiC single crystal substrate is less than 2×10 ¹⁸ /cm ³ , the resistivity of the SiC single crystal substrate becomes too high, and if the dopant concentration exceeds 6×10 ¹⁹ /cm ³ , it becomes difficult to suppress stacking faults in the SiC single crystal substrate. By setting the dopant concentration of the SiC single crystal substrate within the range of 2×10 ¹⁸ /cm ³ or more and 6×10 ¹⁹ /cm ³ or less, 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.

It is preferable that the dopant concentration be 2×10 ¹⁸ /cm ³ or more and 6×10 19 /cm 3 or less at at least five arbitrarily selected points within a surface 1A within 5% of the plate thickness in the depth direction from the main surface 1a of the SiC ^single crystal substrate ¹ .
FIG. 1 shows nine points, including the center O of the surface, as measurement points for the dopant concentration in the surface 1A.

In the SiC single crystal substrate 1, the dopant concentrations at at least five points in the radial direction, including point p1 within 1 mm from the outermost periphery 1b, are 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.

The in-plane distribution of dopant concentration can be adjusted using known methods. For example, to increase the amount of dopant supplied to the outer periphery compared to the inner periphery, a dopant gas flow path can be provided in the crucible (see reference numeral 10 in Figure 5) and the gas permeability of the crucible can be adjusted to increase the amount of dopant supplied to the outer periphery compared to the inner periphery. Furthermore, the amount of dopant supplied to the outer periphery can be adjusted by providing an opening in the guide member (see reference numeral 20 in Figure 5 and reference numeral 25 in Figure 6) or adjusting the thickness of the guide member.

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.

Dopant concentrations can be measured using secondary ion mass spectrometry (SIMS).

The SiC single crystal substrate 1 has a process-affected layer on both the front and back surfaces that is 0.1 nm or less in thickness.

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 by sublimation 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 side and a non-mirror surface on the back side have a problem in that a difference in residual stress occurs between the front side and the back side, causing the substrate to warp to compensate for the residual stress (the Twyman effect). By making the back side a mirror surface as well, it is possible to suppress 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 side is a mirror surface and the back side is not (see, for example, Patent Document 2).

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.

The SiC single crystal substrate 1 preferably has an SORI of 50 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less, and most preferably 20 μm or less.

SORI is one of the parameters that indicates the degree of warpage of a substrate. When the substrate is supported on its backside and measured without changing its original shape, it is expressed as the sum of the normal distances from a least-squares plane calculated using the least-squares method using all data on the substrate surface 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.

<Relationship between processing-affected layer and SORI>
SiC single crystal substrates are produced 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 result in differences in residual stress, resulting in warpage of the substrate 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.

Figure 4 is a conceptual diagram showing the process by which the depth d (d1, d2, d3, d4) of the work-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.

Figure 14 of Patent Document 3 shows the relationship between the depth of the process-affected layer and SORI in single crystal SiC wafers. According to this graph, the deeper the process-affected layer, the larger the SORI value. Furthermore, when comparing 6-inch SiC single crystal substrates with 4-inch SiC single crystal substrates, the 6-inch SiC single crystal substrate is more susceptible to the effects of the process-affected layer, resulting in a larger SORI. From this, it can be inferred that when comparing 8-inch SiC single crystal substrates with 6-inch SiC single crystal substrates, the 8-inch SiC single crystal substrate is even more susceptible to the effects of the process-affected layer, resulting in an even larger SORI. Therefore, removing the process-affected layer to reduce warpage is more important for 8-inch SiC single crystal substrates than for 6-inch SiC single crystal substrates.

The SiC single crystal substrate 1 has an in-plane variation in substrate thickness of 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.

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 half radius (at the positions of the inclined angles of 0°, 90°, 180°, and 270°)).

FIG. 14 of Patent Document 3 shows the relationship between the depth of the damaged layer, which is one parameter for the damaged layer, and SORI. The present inventors, in developing 8-inch SiC single crystal substrates with high yields, 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 a laboratory setting, it is expected that some amount of damaged layer will remain when the planarization process is performed within a practical time frame. Furthermore, the depth d of the remaining damaged layer, conceptually shown in FIG. 3 , is an average depth. However, in reality, the remaining layer may not be strictly uniform in depth. It is likely that a thin damaged layer remains across the entire surface, with some in-plane variation in depth, 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 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.

The SiC single crystal substrate 1 preferably has a micropipe defect density of 1 defect/cm ² or less.

In the SiC single crystal substrate 1, the total number of etch pits that appear as a result of KOH etching is preferably 5× ¹⁰ or less, more preferably 5× ¹⁰ or less, and even more preferably 5× ¹⁰ or less. In this case, the KOH etching is performed at 550° C. for 10 minutes.
The total number of etch pits corresponds to the total number of dislocations.

In the SiC single crystal substrate 1, it is preferable that the density of etch pits identified as threading dislocations (TD) is 2×10 ³ /cm ² or less, and the density of etch pits identified as basal plane dislocations is 5×10 ³ /cm ² or less.
The density of etch pits identified as threading dislocations (TD) is more preferably 1×10 ³ /cm ² or less, and even more preferably 5×10 ² /cm ² or less.
The density of etch pits identified as basal plane dislocations is more preferably 2×10 ³ /cm ² or less, even more preferably 1×10 ³ /cm ² or less, and even more preferably 5×10 ² /cm ² or less.
Here, threading dislocations are a combination of threading screw dislocations (TSDs) and threading edge dislocations (TEDs).
The type of dislocation can be identified from the shape of the etch pits revealed by KOH etching using an optical microscope or the like, 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-shaped) etch pits correspond to basal plane dislocations (BPDs). Large-sized hexagonal etch pits correspond to micropipes (MPs).

(Method for manufacturing SiC single crystal substrate)
The method for manufacturing a SiC single crystal substrate according to this embodiment will be described below, with a step of manufacturing an n-type SiC single crystal ingot and a step of manufacturing a SiC single crystal substrate from the ingot. The following describes the step of manufacturing an n-type SiC single crystal ingot doped with nitrogen as a dopant as an example.

<Process for producing n-type SiC single crystal ingot>
Through continued research, the present inventors have discovered that, when producing an 8-inch diameter SiC single crystal ingot, more precise control of the temperature gradients in the radial and vertical directions (crystal growth direction) is key compared to a 6-inch diameter SiC single crystal ingot. They have also discovered that more precise control of the temperature gradients in the radial and vertical directions (crystal growth direction) can be achieved by applying the method disclosed in Patent Document 4. Specifically, a SiC single crystal production apparatus can be used that includes a heat insulating material that can move around the outside of a guide member that guides crystal growth along the extension direction of the guide member. Note that the method for more precise control of the temperature gradients in the radial and vertical directions (crystal growth direction) is not limited to the method disclosed in Patent Document 4.

During the transition to larger diameter SiC single crystal ingots, a problem has arisen: large diameter SiC single crystal ingots with the same crystal quality cannot be obtained by applying the methods used to produce SiC single crystal ingots of previous diameters. For example, the following problems arose during the transition from 4-inch diameter SiC single crystal ingots to 6-inch diameter SiC single crystal ingots (see Patent Document 1).

In the growth of SiC single crystals using the sublimation recrystallization method with a seed crystal, one of the growth conditions for achieving high crystal quality is to ensure that the surface shape of the single crystal ingot during growth is approximately convex in the growth direction. For example, in the case of 4H-type SiC single crystals used in power devices, when growth is performed approximately parallel to the <0001> axis, i.e., the c-axis direction of the crystal, the SiC single crystal grows by the progression of spiral steps generated by threading screw dislocations. Therefore, by achieving a substantially convex shape, it is believed that the step supply source on the growth surface is essentially a single point, improving polytype stability. If the growth surface were concave or had multiple peaks, there would be multiple supply sources for growth steps, resulting in areas where different steps generated from each supply source collide. In such cases, not only would defects such as dislocations be generated at the collision points, but the atomic stacking state in the c-axis direction, which is unique to the 4H-type polytype, would be easily disrupted, resulting in the formation of heterogeneous polytypes with different stacking structures, such as 6H-type and 15R-type, and the generation of micropipe defects.

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 growing crystal roughly convex. Specifically, a convex shape of the growing crystal is achieved by optimizing the temperature at the center of the growing crystal in terms of growth rate, etc., and controlling the temperature distribution during growth, i.e., the shape of the isotherm, to make it roughly convex. It was thought that a SiC single crystal ingot grown under growth conditions that achieve such roughly convex isotherms would grow roughly parallel to the isotherm, thereby ensuring the polytype stability described above.

However, when the diameter of the growing crystal is increased to 150 mm (6 inches) or more, optimizing the temperature at the center of the growing 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 growing 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 is a problem in that the SiC single crystal of the seed crystal itself is prone to thermal decomposition at its outer periphery. Patent Document 1 solves this problem primarily by using a seed crystal made of a silicon carbide single crystal with a thickness of 2.0 mm or more.

In the present invention, an 8-inch diameter n-type SiC single crystal ingot is produced using a technique not used in the typical 6-inch diameter n-type SiC single crystal ingot production method shown in Patent Document 1. 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 its extension, and by controlling not only the radial temperature gradient but also the vertical temperature gradient (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. The SiC single crystal production apparatus and the SiC single crystal ingot production process are described below.

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

5 includes a crucible 10 including a seed crystal installation portion 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 also illustrates a raw material G, a seed crystal S, and a single crystal C grown on the seed crystal S.
In the following drawings, 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.

Crucible 10 surrounds deposition space K, where single crystal C is grown. Any known crucible for producing single crystal C by sublimation can be used for crucible 10. For example, graphite, tantalum carbide, etc. can be used. 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 that occur during growth.

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

The guide member 20 extends from the periphery of the seed crystal installation section 11 toward the raw material G. In other words, the guide member 20 is arranged along the crystal growth direction of the single crystal C. Therefore, the guide member 20 functions as a guide for the single crystal C as it grows from the seed crystal S.

The lower end of the guide member 20 is supported by a support 21. The support 21 blocks the gap between the lower end of the guide member 20 and the crucible 10, preventing the source gas from entering the area outside the guide member 20. If the source gas enters this area, polycrystals will grow between the guide member 20 and the insulating material 30, preventing the insulating material 30 from moving freely.

The connection between the guide member 20 and the support 21 preferably has a crimped structure. A crimped structure is a structure designed to tighten the connection between the guide member 20 and the support 21 when a physical force is applied to the guide member 20. For example, a threaded 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, this can prevent the guide member 20 from falling off.

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

In addition, although the guide member 20 in Figure 5 has an open upper end, the upper end of the guide member 20 may be connected to the inner surface of the crucible 10, making the space in which the insulating material 30 is present a closed space.

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 can lead to holes appearing in the guide member 20. Furthermore, carbon powder that peels off due to deterioration can be incorporated into the single crystal C, leading to a deterioration in 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. This allows for stable growth of high-quality SiC single crystals.

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 growing.
During the crystal growth process, 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 surface 30a of the heat insulating material 30 on the raw material side can be arranged closer to the seed crystal setting section 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 reduced to half or less of the growth amount of the SiC single crystal ingot to be manufactured.

Figure 6 is a cross-sectional schematic diagram of a drive means for moving the insulating material 30 up and down. There is no particular restriction on the drive means, as long as it can move the insulating material 30 up and down. For example, as shown in Figure 6(a), a drive member 31 extending from the top of 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 drive member up and down. Alternatively, as shown in Figure 6(b), a lifting drive member 32 may be provided to support the insulating material 30 from below. Furthermore, as shown in Figure 6(c), a notch may be provided in part of the side of the crucible 10, and a drive member 33 extending through this notch to the outside of the crucible 10 may be provided, and the insulating material 30 may be moved by raising and lowering the drive member.

The insulating material 30 is preferably made of a material with a thermal conductivity of 40 W/mK or less at high temperatures of 2000°C or higher. Examples of materials with a thermal conductivity of 40 W/mK or less at high temperatures of 2000°C or higher include graphite members with a thermal conductivity of 120 W/mK or less at room temperature. It is more preferable that the insulating material 30 be made of a material with a thermal conductivity of 5 W/mK or less at high temperatures of 2000°C or higher. Examples of materials with a thermal conductivity of 5 W/mK or less at high temperatures of 2000°C or higher include graphite and carbon-based felt materials.

The shape of the insulating material 30 is designed appropriately to match the shape of the area sandwiched between the guide member 20 and the inner surface of the crucible 10. As shown in Figure 5, if the distance between the guide member 20 and the inner surface of the crucible 10 is constant, the insulating material 30 is positioned to fill the gap. Also, as shown in Figure 5, if the distance between the guide member 20 and the inner surface of the crucible 10 varies, the shape of the insulating material 35 is designed to match the position where the gap is narrowest. Designing it in this way prevents the insulating material 35 from getting stuck between the guide member 25 and the inner surface of the crucible 10 and becoming stuck.

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 thickness of 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. This prevents the raw material gas from recrystallizing in areas other than the surface Ca of the single crystal C.

As described above, the SiC single crystal manufacturing apparatus allows for 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. Because the single crystal C grows along an isothermal surface, controlling the temperature distribution near the surface of the single crystal C leads to control of the shape of the single crystal C.

The above-mentioned SiC single crystal manufacturing apparatus can be used to produce n-type SiC single crystal ingots. Below, we will explain the case where the SiC single crystal manufacturing apparatus 100 shown in Figure 5 is used as an example.

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 the 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 at high temperatures on the crystal surface, doping nitrogen atoms 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 the guide member 20.

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 process 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.

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.

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 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 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 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 insulating material 30, the surface Ca of the single crystal C is convex.

The shape of the surface Ca of the single crystal C changes depending on the position of the 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 showing the shape of the isothermal surface T near the single crystal C during crystal growth. Figure 9(a) shows the case when the insulating material 30 is not provided, and Figure 9(b) shows the case when the insulating material 30 is provided.

SiC single crystal C has a low thermal conductivity and therefore has a thermal insulating effect. On the other hand, the thermal conductivity of guide member 20 is higher than that of single crystal C. Therefore, as shown in Figure 9(a), when there is no thermal insulator 30, the isothermal surface T extends from single crystal C. The crystal growth surface of single crystal C grows along isothermal surface T. Therefore, when there is no thermal insulator 30, the shape of surface Ca (crystal growth surface) of single crystal C is fixed to a concave shape.

In contrast, when a heat insulating material 30 is provided as shown in Figure 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 shape of the isothermal surface T can be designed 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.

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 reducing the temperature difference in the in-plane direction within the single crystal C.

Polycrystals are formed in low-temperature areas near the crystal growth surface of the single crystal C. For example, as shown in Figure 9(a), if there is a large temperature difference between the single crystal C and the guide member 20, polycrystals will grow on the guide member 20. If the polycrystals grown on the guide member 20 come into contact with the single crystal C, this will disrupt the crystallinity of the single crystal C and cause defects. In contrast, as shown in Figure 9(b), if there is a heat insulating material 30 near the surface Ca of the single crystal C, the temperature difference between the single crystal C and the guide member 20 can be reduced, suppressing the growth of polycrystals.

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

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. 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 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.

Here, "substantially the same" does not mean that the surface Ca of the single crystal C and the lower surface 30a of the insulating material 30 are at exactly the same height, but rather that some positional deviation is permitted within a range that does not significantly affect the isothermal surface T. Specifically, if the lower surface 30a of the insulating material 30 is located within 30 mm of 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 insulating material 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 insulating material 30 be as close to completely identical as possible, and it is preferable that the lower surface 30a of the insulating material 30 be located within 20 mm, and more preferably within 10 mm, of the surface Ca of the single crystal C.

Furthermore, it is preferable that the surface Ca of the single crystal C is located closer to the source material G than the lower surface 30a of the heat insulating material 30. In other words, it is preferable that the lower surface 30a of the heat insulating material 30 is located closer to the seed crystal installation section 11 than the surface Ca of the single crystal C. Even if an external factor such as temperature fluctuations occurs within the film formation space K, it is possible to prevent the surface Ca of the single crystal C from becoming concave.

It is also preferable to control the position of the insulating material 30 from the start of crystal growth. In other words, it is preferable to control the positional relationship between the lower surface 30a of the insulating material 30 and the surface of the seed crystal S at the start of crystal growth.

Immediately after crystal growth begins, the seed crystal mounting section 11 is located around the seed crystal S, and the seed crystal S is close to the crucible 10. Therefore, the isothermal surface T within the film formation space K is also affected by the temperature (thermal conductivity) of these components. In other words, the effect of using the insulating material 30 is most pronounced in the region where the single crystal C has grown 30 mm or more from the seed crystal S. However, this does not mean that the insulating material 30 is not effective immediately after crystal growth begins.

For example, if the shape of the crystal growth surface of the single crystal C becomes concave immediately after crystal growth without the provision of the insulating material 30, it will be necessary to return the shape of the crystal growth surface of the single crystal C to a convex shape during the subsequent growth process. If the shape of the crystal growth surface changes from concave to convex during the growth process, stress will accumulate within the single crystal C, making defects more likely to occur. Therefore, it is preferable to control the position of the insulating material 30 from the start of crystal growth. The positional relationship of the insulating material 30 to the seed crystal S can be designed in the same way as the positional relationship between the insulating material 30 and the single crystal C during the crystal growth process.

<SiC single crystal substrate manufacturing process>
The process of producing a SiC single crystal substrate from the obtained n-type SiC single crystal ingot includes a planarization step including lapping using a predetermined polishing slurry, and a process-affected layer removal step. In producing a SiC single crystal substrate, lapping can be performed using a slurry characteristic of lapping. Other than that, known methods can be used for processing the SiC single crystal ingot to obtain a SiC single crystal substrate. The lapping step will be described below.

Next, usable lapping slurries will be described in detail.
In the loose abrasive processing step, 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 step 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, making secondary aggregation less likely to occur during the processing step. 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.

The modified Mohs hardness (14) of boron carbide abrasive grains is slightly greater than the modified Mohs hardness (13) of the SiC substrate (the object not being polished), 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 suppress a reduction in the particle size of the boron carbide abrasive grains.

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 having the proportion of boron carbide abrasive grains in the slurry be 15% by mass or more, the boron carbide abrasive grain content in the slurry can be increased, thereby increasing the processing speed of the lapping process. Furthermore, by having the proportion of boron carbide abrasive grains in the slurry be 45% by mass or less, the frequency and area of contact between boron carbide abrasive grains can be reduced, making it easier to suppress a decrease in the particle size of the boron carbide abrasive grains and wear of the boron carbide abrasive grains.

The boron carbide abrasive grains in the slurry used in the processing step have, for example, an average particle size of 15 μm or more and 40 μm or less, preferably 25 μm or more and 35 μm or less. Using boron carbide abrasive grains with an average particle size of 15 μm or more facilitates increasing the 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 prevention of cracks and breakage in the SiC substrate, and further prevents excessive adhesion of the additives described below to the surface, thereby preventing a decrease in processing speed due to a reduced contact area with the SiC substrate as the workpiece. Furthermore, using such boron carbide abrasive grains facilitates the reduction of particle size change 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 such that 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, and is therefore, for example, 14 μm or more and 48 μm or less, and preferably 23 μm or more and 42 μm or less.

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.).

Additives that can be used include polyhydric alcohols, esters and their salts, homopolymers and their salts, and copolymers. 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.

These additives are thought to improve the dispersibility of boron carbide abrasive grains in the slurry.

The additive adheres to the surface of the boron carbide abrasive grains and prevents direct contact between the boron carbide abrasive grains. In this way, the additive improves the dispersibility of the boron carbide abrasive grains in the slurry and prevents the abrasive grain size from decreasing during the processing process.

The proportion of additives in the slurry is, for example, 3% to 20% by volume, preferably 5% to 15% by volume, and more preferably 10% to 15% by volume. 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 favorable 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 process.

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, as described above. Setting the processing speed to 45 μm/h or less tends to suppress 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 needs to 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.

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 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 5 to 10 mm away from the outer periphery of the SiC substrate 1 toward position 1a. The thickness of the SiC substrate 1 at these five positions 1a to 1e is 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 by the processing time (h).

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 the particle size of some of the boron carbide abrasive grains to become larger than before processing.

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.

In addition, because the particle size of the boron carbide abrasive grains does not change significantly during this lapping process, changes in the processing 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.

In addition, this lapping process suppresses 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 suppresses variation in particle size of the abrasive grains. Therefore, 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.

The following describes examples of the present invention, but the present invention is not limited to the following examples.

Example 1
First, an n-type SiC single crystal ingot was produced using the SiC single crystal production apparatus shown in FIG.
First, a 4H—SiC single crystal having a diameter of 200 mm and a thickness of 5.0 mm, with a (0001) plane as the main surface and an off-angle of 4°, was used as the seed crystal S. At the initial stage of crystal growth, the temperature (Tr) of the crucible body side wall 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. Crystal growth was performed while gradually moving the insulating material 30 so that the raw material side end face (lower surface) of the insulating material 30 was closer to the lid than the surface of the single crystal and so that the distance in the growth direction between the raw material side end face of the insulating material 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.

The n-type SiC single crystal ingot was then processed using a known processing method to obtain an 8-inch SiC substrate with a thickness of 0.9 mm and a (0001) plane with an off-angle of 4°.

The thickness of this SiC substrate was measured.
The SiC substrate with the measured thickness was then placed on the carrier plate of a polishing machine and subjected to lapping. The lapping slurry was prepared by adding a predetermined amount of boron carbide abrasive grains and AD8 (10% by volume) as an additive to water and dispersing the mixture. The boron carbide abrasive grains used had a particle 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 by a loose abrasive method while supplying a lapping slurry at a rate of 16 L/min. The lapping slurry was circulated and used.

The driving conditions of the polishing device in the lapping process were processing pressure 160 g/cm ² , lower platen rotation speed 16 rpm, upper platen rotation speed 5.5 rpm, central gear rotation speed 2.8 rpm, internal gear rotation speed 6.0 rpm, and processing time 40 minutes.
After the lapping process, the particle size distribution of the boron carbide abrasive grains in the slurry was measured in the same manner as before the lapping process, and the plate thickness was also measured in the same manner as before the lapping process, and the processing speed was also 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 a total of eight times.

Next, an etching process was performed to remove the process-affected layer, and a CMP process was performed to polish the surface to a mirror finish, yielding the SiC single crystal substrate of Example 1.

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.

(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 not having a heat insulating material 30 was used, a seed crystal S having a diameter of 150 mm was used, Tr, Tg, and ΔT were not controlled during crystal growth, a lapping slurry not containing the additive (AD8) was used in the lapping step, and the amount of nitrogen gas introduced was changed.

(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 temperature point of the raw material was increased by 10° C. and the amount of nitrogen gas introduced was changed.

(Comparative Example 3)
A SiC single crystal ingot was produced using a SiC single crystal manufacturing apparatus not having 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 not containing the additive (AD8) was used in the lapping step and the amount of nitrogen gas introduced was changed.

(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 outer periphery, and three points (p2, p3, and p4) dividing the area between them into four equal parts (see FIG. 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 mesh number in Table 1 represent the percentage of meshes in which the substrate is divided into 10 mm square meshes and the dopant concentration at the center of each mesh is within ±20% of the dopant concentration at mesh _M0 , which includes the in-plane center. 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.

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 were able to obtain high-quality SiC single crystals by performing more precise temperature control compared to Comparative Examples 1 to 3.

The n-type SiC single crystal substrates of Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 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.

The micropipe density was 1/cm ² or less in all of Examples 1 and 2 and Comparative Examples 1 to 3.
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 or greater than that of Comparative Examples 1 and 2 (6-inch substrates), and both the TD etch pit density and the BPD etch pit density were also 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 in the production of 8-inch SiC single crystal substrates than in the production of 6-inch SiC single crystal substrates.

1. SiC single crystal substrate

Claims (13)

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. The n-type SiC single crystal substrate according to claim 1, wherein the SORI is 14 μm or less. Dopant concentration is 2×10 ¹⁸ /cm ³ That's it, 6 x 10 ¹⁹ /cm ³ 2. The n-type SiC single crystal substrate according to claim 1, wherein: 2. The n-type SiC single crystal substrate according to claim 1, wherein an 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 a circumference of a circle having a radius of (½) of the substrate, is 2.0 μm or less. 2. The n-type SiC single crystal substrate according to claim 1, wherein the total number of etch pits appearing after KOH etching at 550°C for 10 minutes is 2.1 x 10 ⁶ or less. 2. The n-type SiC single crystal substrate according to claim ¹ , wherein, among etch pits appearing after KOH etching at 550°C for 10 minutes, the density of etch pits identified as threading dislocations is 1 x ¹⁰³ /cm2 or less. 7. The n-type SiC single crystal substrate according to claim 6 , wherein, among etch pits appearing after KOH etching at 550°C for ¹⁰ minutes, the density of etch pits identified as threading dislocations is 5 x ¹⁰² /cm2 or less. 2. The n-type SiC single crystal substrate according to claim 1, wherein, among etch pits appearing after KOH etching at 550°C for ¹⁰ minutes, the density of etch pits identified as basal plane dislocations is 2 x ¹⁰³ /cm2 or less. 9. The n-type SiC single crystal substrate according to claim 8 , wherein, among etch pits appearing after KOH etching at 550°C for 10 minutes, the density of etch pits identified as threading dislocations is 1 x ¹⁰³ /cm2 or ^less . 10. The n-type SiC single crystal substrate according to claim 9 , wherein, among etch pits appearing after KOH etching at 550°C for 10 minutes, the density of etch pits identified as threading dislocations is 5 x 10 ² /cm ² or less. 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. 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. 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.