JP7601272B2 - n-type SiC single crystal substrate, SiC epitaxial wafer, and n-type SiC single crystal ingot - 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 one order of magnitude larger than silicon (Si) and a band gap three times larger. Silicon carbide (SiC) also has properties such as a thermal conductivity about three times higher than silicon (Si). For this reason, silicon carbide (SiC) is expected to be used in power devices, high-frequency devices, high-temperature operating devices, and the like. For this reason, SiC epitaxial wafers have come to be used in the above-mentioned semiconductor devices in recent years.

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 is referred to as the SiC single crystal substrate, and the substrate after the SiC epitaxial layer is stacked is referred to as the SiC epitaxial wafer. SiC single crystal substrates are cut from SiC single crystal ingots.

The current market trend for SiC single crystal substrates is for 6-inch (150 mm) diameter SiC single crystal substrates, but development is also underway for 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 widespread as a trump card in energy-saving technology.

When manufacturing the next generation of large-diameter SiC single crystal substrates, the same level of quality cannot be obtained even if the manufacturing conditions optimized for the current diameter SiC single crystal substrates are applied. This is because new problems arise according to the new size. For example, Patent Document 1 describes a problem that when manufacturing a 4-inch SiC single crystal substrate, thermal decomposition frequently occurs around the outer periphery of the seed crystal, which causes macro defects, making it difficult to obtain single crystals with high crystal quality with a good yield. Patent Document 1 describes an invention that solves this problem by using a seed crystal of a specified thickness. In this way, it is necessary to establish manufacturing conditions for SiC single crystal substrates of new sizes while solving new problems that arise according to 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. In addition, 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 JP 2020-17627 A JP 2019-189499 A

SiC single crystal substrates are obtained through a SiC single crystal ingot production process and a SiC single crystal substrate process in which a SiC single crystal substrate is produced from the SiC single crystal ingot. Establishing the manufacturing technology for 8-inch SiC single crystal substrates requires solving new issues 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 an 8-inch substrate with the same dislocation density as that of a 6-inch substrate in the SiC single crystal ingot manufacturing process. If an 8-inch substrate is manufactured by simply applying a manufacturing technology for SiC single crystal substrates optimized for manufacturing 6-inch substrates, an 8-inch substrate with a higher dislocation density than that of a 6-inch substrate will be produced. This is because the hurdle for obtaining the same quality increases significantly as the size increases. Therefore, in evaluating a manufacturing technology for an 8-inch SiC single crystal substrate, the starting point is the dislocation density of an 8-inch substrate obtained by simply applying a manufacturing technology for SiC single crystal substrates optimized for manufacturing 6-inch substrates, and the technical value should be evaluated based on the degree of improvement based on the dislocation density at the 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 those for 6-inch SiC single crystal substrates or stricter evaluation standards. Step-by-step improvements will lead to the establishment of manufacturing technology for 8-inch SiC single crystal substrates.

In addition, 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 variation in concentration distribution.

The present invention has been 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 suppressed 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 x 10 ¹⁸ /cm ³ or more and 6 x 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 circumference, 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 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.

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 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.

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 having 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 when a substrate having a diameter in the range of 195 to 205 mm is cut out from the n-type SiC single crystal ingot and a dopant concentration is measured, the dopant concentration of the cut out substrate is 2×10 ¹⁸ /cm ³ or more and 6×10 ¹⁹ /cm ³ or less, and the dopant concentration at at least five points in a radial direction, including points within 1 mm from the outermost circumference, is 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 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 cut substrate.

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

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

The n-type SiC single crystal substrate of the present invention can provide an 8-inch SiC single crystal substrate that has a high dopant concentration and suppresses 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. 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. 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. FIG. 1 is a schematic cross-sectional view of a SiC single crystal manufacturing apparatus. FIG. 2 is a schematic cross-sectional view of another example of a SiC single crystal production apparatus. 1 is a schematic cross-sectional view 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 relative positions of the bottom surface of the insulation material and the surface of the single crystal, as well as the relationship with the isothermal surface in the vicinity of the single crystal. FIG. 2 is a schematic diagram showing the shape of an isothermal surface in the vicinity of a single crystal during crystal growth. FIG. 2 is a schematic plan view showing an example of a 10 mm square mesh.

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 parts in an enlarged scale for the sake of convenience in order to make the features of the present invention easier to understand, and the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited to them. Appropriate changes can be made within the scope of the effects of the present invention. In addition, components well known to those skilled in the art other than those illustrated in each figure may be omitted.

(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 processing-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 limitations 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 in the range of 300 to 650 μm, for example.

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

One surface of the SiC single crystal substrate 1 is a surface (main surface) on which a SiC epitaxial layer is formed, and it is preferable that the main surface is a c-plane (the (0001) plane of a 4H-SiC crystal) or a surface obtained by inclining 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 in the <11-20> direction.
Since the number of wafers obtained from a SiC single crystal ingot decreases as the off-angle increases, a small off-angle is preferable from the viewpoint of cost reduction. A SiC single crystal substrate having 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 can be performed.

The n-type dopant may be, but is 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 is 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 illustrates nine points, including the in-plane center O, as measurement points for the dopant concentration in the surface 1A.

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 circumference 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.

The in-plane distribution of the dopant concentration can be adjusted by known methods. 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 number 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. Also, for example, the amount of dopant supplied to the outer periphery can be adjusted by providing an opening in the guide member (see reference number 20 in FIG. 5 and reference number 25 in FIG. 6) or by 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 meshes M of 10 mm square, and the dopant concentration at any point within each mesh is taken 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 is 80% or more.

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

The SiC single crystal substrate 1 has a process-induced layer thickness of 0.1 nm or less on both the front and back sides.

The main surface (hereinafter sometimes referred to as the "front surface") of the SiC single crystal substrate 1 is a mirror surface. This is because the front surface of the SiC single crystal substrate needs 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 (a portion that will become the substrate) from a SiC single crystal ingot manufactured by sublimation or the like, and 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 a SiC single crystal substrate having a mirror surface on the front side and a non-mirror surface on the rear side has a problem in that a difference in residual stress occurs between the front side and the rear side, causing the substrate to warp to compensate for the residual stress (the Twyman effect). By making the rear side a mirror surface as well, the warping of the substrate caused by the Twyman effect can be suppressed. A method for producing a SiC single crystal substrate with small warping has been developed even when the front side is a mirror surface and the rear side is a non-mirror surface (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 OF (orientation flat) instead of the notch 2.

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

SORI is one of the parameters that indicates the degree of warping of a substrate, and is expressed as the sum of the normal distances from a least-squares plane calculated by the least-squares method using all data on the substrate surface when the substrate is supported on its back side and measured without changing its 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.

<Relationship between processing-affected layer and SORI>
A SiC single crystal substrate is produced by slicing a SiC single crystal ingot and flattening the surface. When such mechanical processing is performed, processing strain is introduced 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, processing strain differs between the front and back surfaces, and residual stress also differs, causing warping of the substrate due to the Twyman effect. The shape (warping) of the substrate is determined by the balance of the stress states generated by the processing-affected layers on both sides 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 each process of lapping, (b) is a cross section after polishing, (c) is a cross section after finish grinding, and (d) is a cross section after CMP.

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. In addition, 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 has an even larger SORI. Therefore, it is more important to remove the process-affected layer in order to reduce warpage for an 8-inch SiC single crystal substrate than for a 6-inch SiC single crystal substrate.

The SiC single crystal substrate 1 has an in-plane variation in substrate thickness of 2.0 μm or less. The in-plane variation in thickness is preferably 1.5 μm or less, and more preferably 1.0 μm or less.
In the SiC single crystal substrate according to this embodiment, a novel lapping slurry is used for lapping, thereby realizing a reduction in in-plane variation in thickness.

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

FIG. 14 of Patent Document 3 shows the relationship between the depth of the process-affected layer, which is one parameter of the process-affected layer, and the SORI. In developing an 8-inch SiC single crystal substrate with a high yield, the present inventor focused on the in-plane variation in the depth of the remaining process-affected layer. Even if the process-affected layer can be almost completely removed when the planarization process is performed over a sufficient time period at the laboratory level, it is assumed that some of the process-affected layer will remain when the planarization process is performed over a practical time period. In addition, the depth d of the process-affected layer conceptually shown in FIG. 3 is drawn assuming an average depth, but in reality, it does not remain at a strictly uniform depth, and it is believed that the process-affected layer remains thinly over the entire surface with some in-plane depth variation, or that the process-affected layer remains locally within the surface. In such a case, it is presumed that the effect of the in-plane variation in the depth of the process-affected layer on the SORI is greater in the case of an 8-inch SiC single crystal substrate than in the case of a 6-inch SiC single crystal substrate.
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 density of micropipe defects of 1 defect/cm ² or less.

In the SiC single crystal substrate 1, the total number of etch pits appearing due to 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 further 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, the threading dislocation refers to a combination of threading screw dislocations (TSDs) and threading edge dislocations (TEDs).
The type of dislocation can be determined from the shape of the etch pits that appear by KOH etching using an optical microscope or the like, and the number of etch pits per unit area can be counted. In general, etch pits with a medium-sized hexagonal shape correspond to threading screw dislocations (TSDs), etch pits with a small-sized hexagonal shape correspond to threading edge dislocations (TEDs), and etch pits with an elliptical (shell) shape correspond to basal plane dislocations (BPDs). Also, etch pits with a large-sized hexagonal shape 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 separately for the process of producing an n-type SiC single crystal ingot and the process of producing a SiC single crystal substrate from the ingot. In the following, the process of producing an n-type SiC single crystal ingot into which nitrogen is introduced as a dopant will be described as an example.

<Process for producing n-type SiC single crystal ingot>
In the course of intensive research, the present inventors have found that in producing an 8-inch SiC single crystal ingot, the key is to more precisely control the temperature gradients in the radial and vertical directions (crystal growth direction) of a 6-inch SiC single crystal ingot. They have also found that by applying the method disclosed in Patent Document 4, it is possible to achieve more precise control of the temperature gradients in the radial and vertical directions (crystal growth direction). Specifically, a SiC single crystal manufacturing apparatus can be used that is provided with a heat insulating material that can move along the extension direction of a guide member that guides the crystal growth on the outside. Note that the method of 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 arises in that large diameter SiC single crystal ingots with similar crystal quality cannot be obtained by applying the manufacturing methods used to produce SiC single crystal ingots of previous diameters. For example, during the transition from 4-inch diameter SiC single crystal ingots to 6-inch diameter SiC single crystal ingots, the following problems arose (see Patent Document 1).

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, when the crystal grows approximately parallel to the <0001> axis, i.e., the c-axis direction of the crystal, the SiC single crystal grows as a single crystal by the progression of spiral steps generated from threading screw dislocations. Therefore, it is said that by making the surface approximately convex, the step supply source on the growth surface becomes substantially one point, making it possible to improve polytype stability. If the growth surface is concave or has multiple apexes, there will be multiple supply sources of growth steps, which will result in areas where different steps generated from each supply source collide with each other. In such cases, not only will defects such as dislocations occur from the colliding areas, but the atomic stacking state in the c-axis direction specific to the 4H-type polytype will be easily disturbed, resulting in heterogeneous polytypes with different stacking structures such as 6H-type and 15R-type, and 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 grown crystal roughly convex. Specifically, the convex shape of the grown crystal is realized by optimizing the temperature at the center of the grown crystal in terms of growth rate, etc., while controlling the temperature distribution during growth, i.e., the isothermal shape, to make it roughly convex. It was thought that a SiC single crystal ingot grown under such growth conditions where a roughly convex isotherm is realized would grow roughly parallel to the isothermal line, thereby ensuring the polytype stability described above.

However, when the diameter of the grown crystal is increased to 150 mm (6 inches) or more, optimizing the temperature at the center of the grown crystal in terms of growth rate and other factors to be equivalent to that of conventional 100 mm (4 inch) diameter single crystal growth, 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 the case of 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, in producing an 8-inch diameter n-type SiC single crystal ingot, a method that is 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. A heat insulating material that can move around the outside of the guide member that guides the crystal growth in the extension direction of the guide member is used, and by controlling not only the radial temperature gradient but also the vertical temperature gradient (crystal growth direction), it has been possible to successfully produce 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 device and the process for producing a SiC single crystal ingot are described below.

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

The SiC single crystal manufacturing apparatus 100 shown in Fig. 5 includes a crucible 10 including a seed crystal installation part 11, a guide member 20, and a heat insulating material 30, a chamber (not shown) for accommodating these, and a gas introduction pipe (not shown) connected to the chamber and 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 following drawings, the direction in which the seed crystal mounting portion 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.

The crucible 10 surrounds the deposition space K in which the single crystal C is grown. Any known crucible for producing the single crystal C by sublimation can be used for the crucible 10. For example, graphite, tantalum carbide, etc. can be used. The crucible 10 becomes hot during growth. Therefore, it needs to 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.

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, the 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 disposed along the crystal growth direction of the single crystal C. Therefore, the guide member 20 functions as a guide for the single crystal C growing 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 raw material gas from entering the area outside the guide member 20. If the raw material gas enters this area, polycrystals 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 is preferably 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 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 a case, it is possible to prevent the guide member 20 from falling off.

The guide member 20 in FIG. 5 extends vertically in the up-down direction. The shape of the guide member 20 is not limited to this shape. FIG. 6 is a schematic cross-sectional view of another example of the SiC single crystal manufacturing apparatus 101 according to this embodiment. The guide member 25 in FIG. 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, the guide member 20 in FIG. 5 has an open upper end, but the upper end of the guide member 20 may be connected to the inner surface of the crucible 10 to make 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 raw material gas in order to control the flow of the raw material gas. If the guide member 20 is used with exposed graphite, the graphite may react with the raw material gas and deteriorate and become damaged. Deterioration and damage may cause holes to form in the guide member 20. In addition, carbon powder that peels off due to deterioration may be incorporated into the single crystal C, which may lead to deterioration of the quality of the single crystal C. In contrast, tantalum carbide can withstand high temperatures and does not react unnecessarily with the raw material gas. Therefore, stable, high-quality SiC single crystal growth can be achieved.

The heat insulating material 30 moves outside the guide member 20 along the extending 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 (hereinafter referred to as the lower face 30a) of the heat insulating material 30 on the raw material G side 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.
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.
In addition, during the crystal growth process, the end face 30a of the heat insulating material 30 on the raw material side can be located within 20 mm from the surface Ca of the single crystal C.
In addition, 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, the thickness of the heat insulating material 30 can be set to 0.2 mm or more, which is less than half the growth amount of the SiC single crystal ingot to be manufactured.

Figure 6 is a schematic cross-sectional view of a driving means for moving the insulating material 30 up and down. The driving means can be any means capable of moving the insulating material 30 up and down. For example, as shown in Figure 6(a), a driving 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 driving member up and down. Also, as shown in Figure 6(b), for example, a lifting driving member 32 may be provided to support the insulating material 30 from its bottom. Furthermore, as shown in Figure 6(c), for example, a cut may be provided in a part of the side of the crucible 10, and a driving member 33 extending through the cut 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.

It is preferable that the insulating material 30 is made of a material that has a thermal conductivity of 40 W/mk or less at high temperatures of 2000°C or more. Examples of materials that have a thermal conductivity of 40 W/mk or less at high temperatures of 2000°C or more include graphite members that have a thermal conductivity of 120 W/mk or less at room temperature. It is more preferable that the insulating material 30 is made of a material that has a thermal conductivity of 5 W/mk or less at high temperatures of 2000°C or more. Examples of materials that have a thermal conductivity of 5 W/mk or less at high temperatures of 2000°C or more include graphite and felt materials whose main components are carbon.

The shape of the insulating material 30 is designed appropriately to match the shape of the area 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 insulating material 30 is positioned 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 changes, the shape of the insulating material 35 is designed to match the position where the gap between them is narrowest. Designing in this way makes it possible to prevent the insulating material 35 from becoming clogged 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 more preferably 20 mm or more. If the thickness of the insulating material 30 is too thin, it may not be possible to exert a sufficient insulating effect. In addition, the thickness of the insulating material 30 is preferably half or less of the length of the single crystal finally produced. Here, the single crystal length means the length in the vertical direction of the single crystal C after crystal growth (the growth amount of the single crystal C). When the growth amount of the single crystal is 100 mm, the thickness of the insulating material 30 is preferably 50 mm or less, and when 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, the movement of the insulating material 30 is hindered. Also, if the thickness of the insulating material 30 is within this range, a temperature difference can be formed in the vertical direction within the single crystal C via the insulating material 30. Therefore, it is possible to prevent the raw material gas from recrystallizing in parts other than the surface Ca of the single crystal C.

As described above, the SiC single crystal manufacturing apparatus allows the position of the insulating material to be controlled relative to the growing single crystal. By controlling the position of the 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.

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 by introducing nitrogen gas and recrystallizing the raw material gas sublimated from the raw material G on the surface of the seed crystal S. The nitrogen gas reacts on the crystal surface at high temperature, and nitrogen atoms are doped into the SiC single crystal. This nitrogen doping concentration depends on the nitrogen gas concentration, and the higher the nitrogen gas concentration, the higher the doping concentration. The resulting SiC single crystal exhibits a conductivity (resistivity) according 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 insulating material 30 and the surface Ca of the single crystal C is controlled during the process of crystal growth of the single crystal C from the seed crystal S. By controlling these positional relationships, 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 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) is an example where the surface Ca (crystal growth surface) of the single crystal C is flat, Figure 8(b) is an example where the surface Ca (crystal growth surface) of the single crystal C is concave, and Figure 8(c) is an example where the surface Ca (crystal growth surface) of the single crystal C is convex.

As shown in Figures 8(a) to (c), 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. 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 schematic diagram showing the shape of the isothermal surface T near the single crystal C during crystal growth. Figure 9(a) is a diagram showing the case where the insulating material 30 is not provided, and Figure 9(b) is a diagram showing the case where the insulating material 30 is provided.

The SiC single crystal C has a heat insulating effect by itself 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.

In contrast, when the 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 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 in advance by simulation or the like. In this way, by controlling the position of the insulating material 30 relative to the single crystal C, the shape of the surface Ca of the single crystal C can be freely designed.

In addition, controlling the position of the 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 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, it disrupts the crystallinity of single crystal C and causes defects. In contrast, as shown in FIG. 9(b), if there is a heat insulating material 30 near surface Ca of single crystal C, the temperature difference between single crystal C and guide member 20 can be reduced, and the growth of polycrystals can be suppressed.

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

So far, it has been explained that 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 insulating material 30 are made approximately the same, or the surface Ca of the single crystal C is provided on the raw material G side of the lower surface 30a of the 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 a 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 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 insulating material 30 are in approximately the same 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 is close to completely the same, and it is preferable that the lower surface 30a of the insulating material 30 is 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 raw material G than the lower surface 30a of the insulating material 30. In other words, it is preferable that the lower surface 30a of the 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 fluctuation occurs in the film formation space K, it is possible to prevent the surface Ca of the single crystal C from becoming concave.

The position of the insulating material 30 is preferably controlled 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 the start of crystal growth, the seed crystal installation section 11 is present around the seed crystal S, and the seed crystal S is close to the crucible 10. Therefore, the isothermal surface T in the film formation space K is also affected by the temperature (thermal conductivity) of these members. 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 effect of the insulating material 30 is not exerted immediately after the start of crystal growth.

For example, if the shape of the crystal growth surface of the single crystal C immediately after crystal growth becomes concave without providing the insulating material 30, it becomes 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 accumulates in the single crystal C, making it more likely to develop defects. 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.

<Process for Producing SiC Single Crystal Substrate>
The process of producing a SiC single crystal substrate from the obtained n-type SiC single crystal ingot includes a planarization process including lapping using a predetermined polishing slurry, and a process of removing a layer affected by processing. In the production of a SiC single crystal substrate, lapping can be performed using a slurry that is characteristic of lapping. Other than that, a known method can be used for processing from the SiC single crystal ingot to obtain a SiC single crystal substrate. The lapping process will be described below.

Next, usable lapping slurries will be described in detail.
In the processing step of the free abrasive type, for example, a slurry containing water, boron carbide abrasive grains, and an additive for dispersing the boron carbide abrasive grains is poured between the upper and lower plates, and pressure is applied to the SiC substrate 1 by the upper and lower plates to flatten the surface of the SiC substrate 1. The slurry used in the processing step is, for example, a slurry containing water as a main component. When a slurry containing water as a main component is used, the dispersibility of the boron carbide abrasive grains is increased, and secondary aggregation is less likely to occur in the processing step. In addition, when a slurry containing water as a main component is used, the surface of the SiC substrate on the upper platen side where the slurry supply hole is provided is cleaned by directly supplying water, and the surface on the lower platen side where the slurry supply hole is not provided 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 supplied again 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, which is not the object to be polished, and is 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 to suppress the reduction in the grain 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 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, and the processing speed of the lapping process can be increased. In addition, by making the proportion of boron carbide abrasive grains in the slurry 45% by mass or less, the frequency and area of contact between the 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.

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, and preferably 25 μm or more and 35 μm or less. By using boron carbide abrasive grains with an average particle size of 15 μm or more, it is easy to increase the processing speed for lapping the surface of the SiC substrate 1, and further, the additives described later can be sufficiently attached to the surface, which leads to improved dispersibility and suppression of particle size reduction. In addition, by making the average particle size 40 μm or less, it is easy to obtain the effect of suppressing the generation of cracks in the SiC substrate and the cracking of the SiC substrate, and further, it is possible to suppress the excessive attachment of the additives described later to the surface, and to suppress the decrease in processing speed due to the decrease in the contact area with the SiC substrate as the workpiece. In addition, by using such boron carbide abrasive grains, it is easy to suppress the change in particle size before and after the lapping process. 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 size of the boron carbide abrasive grains before and after processing is 0.91 or more and 1.2 or less.

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

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, sodium coconut oil fatty acid methyl taurate, sodium lauric acid amide ether sulfate, sodium myristic acid amide ether sulfate, polyacrylic acid, and acrylic acid-maleic acid copolymer.

It is believed that these additives can improve the dispersion of boron carbide abrasive grains in the slurry.

The additive adheres to the surface of the boron carbide abrasive grains and prevents the boron carbide abrasive grains from coming into direct contact with each other. In this way, the additive increases the dispersibility of the boron carbide abrasive grains in the slurry and prevents the grain size from decreasing during the processing process.

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, a preferable degree of dispersion of the boron carbide abrasive grains in the slurry is obtained, and it is easy to suppress the reduction in the particle size of the boron carbide abrasive grains 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 or more and 45 μm/h or less, preferably 16 μm/h or more and 40 μm/h or less, and more preferably 18 μm/h or more and 25 μm/h or less. The processing speed depends on the processing pressure and the average particle size of the boron carbide abrasive grains described above. By setting the processing speed to 45 μm/h or less, it is easy to obtain the effect of suppressing the reduction in the particle size of the boron carbide abrasive grains and the wear of the boron carbide abrasive grains. By setting the processing speed to 14 μm/h or more, the throughput can be increased. When the lapping process is performed in multiple steps, it is sufficient that the processing speed calculated by dividing the total change in the thickness of the SiC substrate by the total processing time is within the above range, and it is preferable that the processing speed at each timing is within the above range. In other words, when the lapping process is performed in multiple steps, it is preferable that the processing speed calculated for each step is within the above range.

Here, the processing speed is calculated from the difference in thickness of the SiC substrate 1 before and after the lapping process and the processing time. Specifically, the processing speed is calculated by the following method. The measurement positions of the thickness of the SiC substrate 1 are position 1c corresponding to the center of the SiC substrate before the orientation flat OF is formed on the SiC substrate 1, position 1a 5 to 10 mm away from the midpoint of the orientation flat OF toward position 1c, position 1b 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 in the direction of position 1a, and positions 1d and 1e on a line perpendicular to line c and 5 to 10 mm away from the outer periphery of the SiC substrate 1 in the direction of position 1a. The thicknesses of the SiC substrate 1 at these five positions 1a to 1e are measured with 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 step, the dispersibility of the boron carbide abrasive grains can be increased and contact of the boron carbide abrasive grains can be suppressed, thereby suppressing reduction in the grain size of the boron carbide abrasive grains.
Specifically, the change in the particle size of the boron carbide abrasive grains can be suppressed to a degree that the ratio of the average particle size of the boron carbide abrasive grains after processing to the average particle size of the boron carbide abrasive grains before processing in the processing step is 0.91 or more and 1.2 or less. Here, the reason why the ratio includes a value greater than 1 is that the boron carbide abrasive grains undergo secondary aggregation in the processing step, and the particle size of some of the boron carbide abrasive grains may become larger than that before processing.

In conventional lapping processes, the particle size of the boron carbide abrasive grains in the slurry is significantly reduced by the lapping process. This means that when lapping is performed again, it is necessary to add abrasive grains to the slurry each time. In addition, each time a complicated management is required 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 easy to control the grain size of the boron carbide abrasive grains, reduces costs, reduces the environmental impact, and suppresses the occurrence of cracks.

In addition, in this lapping process, the grain size of the boron carbide abrasive grains does not change much, so changes in the processing speed during the lapping process 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, which is the non-polished object. Because this lapping process uses such abrasive grains and substrates, 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 polished object.

In addition, this lapping process can suppress the reduction in grain size and wear of the boron carbide abrasive grains, which reduces the variation in grain size of the boron carbide abrasive grains in the slurry during the lapping process. The processing speed of the lapping process depends on the grain size of the abrasive grains used, but this lapping process can suppress the variation in grain size of the abrasive grains, so the entire surface of the SiC substrate is processed with abrasive grains of roughly uniform grain size, which reduces 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 was used as the seed crystal S, with the (0001) plane as the main surface and an off angle of 4°. In the initial crystal growth, the temperature (Tr) of the side wall of the crucible body at 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. The heat insulating material 30 was moved stepwise in accordance with the crystal growth so that the end surface (lower surface) of the heat insulating material 30 on the raw material side was closer to the lid than the surface of the single crystal, and the distance in the growth direction between the end surface of the heat insulating material 30 on the raw material side and the surface of the single crystal was within 10 mm, while the crystal was grown. 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.

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

The thickness of this SiC substrate was measured.
Next, the SiC substrate whose thickness was measured was placed on the carrier plate of a polishing machine, and lapping was performed. 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). Here, the proportion of glycerin (manufactured by Aichi Chemitechno Co., Ltd.) as an additive in the slurry was 6% by volume.
The lapping was performed by a free abrasive method while supplying a lapping slurry at a supply 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 measured in the same manner as before the lapping process, and the processing speed was calculated. In this lapping process, the average processing speed of 15 SiC substrates was 18 μm/h.
After the measurement, the slurry used in the previous lapping process was supplied and the second lapping process and measurement were performed while circulating the slurry. In Example 1, this was repeated to perform the lapping process and measurement eight times in total.

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

Example 2
In producing the SiC single crystal ingot, the temperature at the highest temperature point of the raw material was increased by 20°C, the operating conditions of the polishing device in the lapping process were adjusted so that the in-plane variation in the substrate thickness after lapping was smaller than in Example 1, and further, the amount of nitrogen gas introduced was changed, but other than these, SiC single crystal substrates were obtained under the same conditions as in the Example.

(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 thermal insulator 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 an 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 thermal insulation material 30, and a SiC single crystal substrate was obtained under the same conditions as in Example 1, except that in the lapping process, a lapping slurry not containing the additive (AD8) was used and the amount of nitrogen gas introduced was changed.

(evaluation)
The concentration of nitrogen, which is a dopant, at a predetermined point was measured from the stacking surface toward the thickness direction for the SiC single crystal substrates of Example 1, Example 2, and Comparative Examples 1 to 3 using SIMS. The results are shown in Table 1. The nitrogen concentration at each point in Table 1 is the center point O on the surface at a depth of 3 μm, the point p1 at 1.0 mm from the outer periphery, and the three points (p2, p3, p4) that divide 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 nitrogen concentration distribution at the five points indicates the ratio of the difference in nitrogen concentration at the point with the largest difference from the nitrogen concentration at the center among the other four points to the nitrogen concentration at the center. The percentage [%] of the predetermined number of meshes in Table 1 is the percentage of meshes in which the substrate is divided into 10 mm square meshes and the dopant concentration at the center point in each mesh is within ±20% of the dopant concentration of the mesh M ₀ including the in-plane center. FIG. 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 the nitrogen concentration distribution at five points is reduced in Examples 1 and 2 compared to Comparative Examples 1 to 3. It can also be seen that the proportion of meshes within ±20% of the dopant concentration of mesh _M0 including the in-plane center is larger in Examples 1 and 2 compared to Comparative Examples 1 to 3. Thus, in Examples 1 and 2, a good nitrogen concentration distribution is obtained over the entire plane compared to Comparative Examples 1 to 3. It is believed that these results are the effect of Examples 1 and 2 being able to obtain high-quality SiC single crystals by performing more precise temperature control compared to Comparative Examples 1 to 3.

In addition, 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 based on 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 the TED etch pit density.

The micropipe density was 1/ ^cm2 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 as compared with Comparative Examples 1 to 3.
Moreover, in Examples 1 and 2 (8-inch substrate), the total number of etch pits was sufficiently reduced to a degree comparable to that of Comparative Examples 1 and 2 (6-inch substrate), and both the TD etch pit density and the BPD etch pit density were significantly reduced. This result is believed to be the effect of more precise temperature control in Examples 1 and 2.
Furthermore, in Examples 1 and 2 (8-inch substrate), 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). From these results, it was found that the effect of more precise temperature control is greater 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 (9)

An 8-inch n-type SiC single crystal substrate,
The diameter is in the range of 195 to 205 mm,
The dopant concentration is 2×10 ¹⁸ /cm ³ or more and 6×10 ¹⁹ /cm ³ or less,
An n-type SiC single crystal substrate, 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 ±20% of the dopant concentration at the in-plane center at the same depth from the main surface. The n-type SiC single crystal substrate according to claim 1, in which the dopant concentration at at least five points in the radial direction, including points within 1 mm from the outermost circumference, is within ±15% of the dopant concentration at the in-plane center at the same depth from the main surface. The n-type SiC single crystal substrate according to claim 1, in which the dopant concentration at at least five points in the radial direction, including points within 1 mm from the outermost circumference, is within ±10% of the dopant concentration at the in-plane center at the same depth from the main surface. The n-type SiC single crystal substrate according to claim 1, wherein the dopant is nitrogen. An n-type SiC single crystal substrate according to any one of claims 1 to 4;
and a SiC epitaxial layer laminated on a surface of the n-type SiC single crystal substrate. An n-type SiC single crystal ingot,
An n-type SiC single crystal ingot, wherein when a substrate having a diameter in the range of 195 to 205 mm is cut out from the n-type SiC single crystal ingot and the dopant concentration is measured, the dopant concentration of the cut out substrate is 2 x 10 ¹⁸ /cm ³ or more and 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 circumference, is within ±20% of the dopant concentration at the in-plane center at the same depth from the main surface of the cut out substrate. The n-type SiC single crystal ingot according to claim 6, 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 cut out substrate. The n-type SiC single crystal ingot according to claim 6, 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 cut substrate. The n-type SiC single crystal ingot according to any one of claims 6 to 8, wherein the dopant is nitrogen.

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