JP7571902B2 - Method for manufacturing SiC single crystal, SiC seed crystal, and SiC ingot - Google Patents

Description

The present invention relates to a method for producing SiC single crystals, SiC seed crystals, and SiC ingots.

Silicon carbide (SiC) has an electric breakdown field one order of magnitude larger than that of silicon (Si) and a band gap three times larger. Silicon carbide (SiC) also has a thermal conductivity about three times higher than that of silicon (Si). Silicon carbide (SiC) is expected to be used in power devices, high-frequency devices, high-temperature operating devices, and other applications.

For semiconductor devices, SiC epitaxial wafers are used, which are made by forming an epitaxial film on a SiC wafer. The epitaxial film formed on the SiC wafer by chemical vapor deposition (CVD) becomes the active region of the SiC semiconductor device.

Therefore, there is a demand for high-quality SiC wafers that are free from cracks and other damage and have few defects. In this specification, SiC epitaxial wafers refer to wafers after the epitaxial film has been formed, and SiC wafers refer to wafers before the epitaxial film has been formed.

For example, Patent Documents 1 and 2 describe how controlling the warpage and waviness of the outer shape of a SiC single crystal used as a seed crystal can result in high-quality SiC ingots and SiC wafers obtained from the seed crystal.

JP 2015-117143 A Patent No. 4494856

One of the killer defects in SiC wafers is the basal plane dislocation (BPD). Some of the BPDs in SiC wafers are carried over to SiC epitaxial wafers, and are a cause of degradation of forward characteristics when a forward current is passed through the device. BPDs are defects that are thought to be caused in part by slippage that occurs on the basal plane.

As described in Patent Documents 1 and 2, BPD cannot be sufficiently suppressed by controlling the warpage and waviness of the outer shape of the SiC single crystal used as the seed crystal. Therefore, there is a demand for reducing BPD.

The present invention was made in consideration of the above problems, and aims to provide a method for processing SiC single crystals that can reduce the curvature of the atomic arrangement plane during crystal growth.

As a result of intensive research, the inventors have found that there is a correlation between the curvature of the atomic arrangement plane (lattice plane) of a SiC single crystal and the density of basal plane dislocations (BPDs). Therefore, they have found that the atomic arrangement plane can be flattened during crystal growth by processing the back surface of a seed crystal into a shape that follows the curvature of the atomic arrangement plane and attaching it to a flat attachment surface of a crucible.
That is, in order to solve the above problems, the present invention provides the following means.

(1) The method for processing a SiC single crystal according to the first aspect includes a measurement step of measuring the shape of an atomic arrangement surface of the SiC single crystal at least along a first direction passing through the center in a plan view and a second direction perpendicular to the first direction, a processing step of processing at least a first surface of the SiC single crystal along the atomic arrangement surface based on the measurement results, and an attachment step of attaching the SiC single crystal to a mounting surface using the first surface as an attachment surface.

(2) The processing step in the method for processing a SiC single crystal according to the above aspect may include a planarization step of attaching the SiC single crystal to a spacer having a curved surface that curves in a direction opposite to the curvature direction of the atomic arrangement surface and planarizing the atomic arrangement surface, and a surface preparation step of cutting or grinding the SiC single crystal along the planarized atomic arrangement surface.

(3) The processing step in the method for processing a SiC single crystal according to the above aspect may include a vacuum adsorption step of vacuum adsorbing the SiC single crystal onto an adsorption surface having an adsorption force that varies depending on the amount of curvature of the atomic arrangement surface, and flattening the atomic arrangement surface, and a surface preparation step of cutting or grinding the SiC single crystal along the flattened atomic arrangement surface.

(4) The machining step in the method for machining a SiC single crystal according to the above aspect may include an electric discharge machining step in which the SiC single crystal is brought close to an electrode having a shape corresponding to the atomic arrangement surface, and the first surface of the SiC single crystal is machined by electric discharge.

(5) In the method for processing a SiC single crystal according to the above aspect, the thickness of the SiC single crystal when the bonding step is performed may be 5 mm or less.

(6) In the attachment step of the method for processing a SiC single crystal according to the above aspect, if the first surface is curved convexly toward the installation surface, the load on the outer periphery of the SiC single crystal may be stronger than that on the inner side, and if the first surface is curved concavely toward the installation surface, the load on the inner side of the SiC single crystal may be stronger than that on the outer periphery.

(7) The method for processing a SiC single crystal according to the above aspect may further include a decompression step of reducing the pressure around the SiC single crystal during the attachment step.

(8) The second aspect of the method for producing a SiC ingot is the method for processing a SiC single crystal according to the above aspect, in which crystal growth is performed using the SiC single crystal attached to the installation surface as a seed crystal.

(9) The SiC single crystal according to the third aspect is a SiC single crystal in which the maximum curvature of the atomic arrangement plane is 20 μm or more, and the absolute value of the difference between the warpage of the SiC single crystal and the curvature of the atomic arrangement plane is 10 μm or less.

By using the SiC single crystal evaluation method according to the above aspect, the atomic arrangement surface during crystal growth can be flattened, and the occurrence of basal plane dislocations (BPDs) can be suppressed.

2 is a schematic diagram of a cross section of a SiC single crystal cut along a straight line passing through the center in a plan view and extending in a first direction. FIG. FIG. 2 is a diagram showing a schematic diagram of an example of an atomic arrangement plane of a SiC single crystal. FIG. 2 is a diagram showing another example of an atomic arrangement plane of a SiC single crystal. 1A to 1C are diagrams for specifically explaining a method for measuring the shape of an atomic arrangement plane. 1A to 1C are diagrams for specifically explaining a method for measuring the shape of an atomic arrangement plane. 1A to 1C are diagrams for specifically explaining a method for measuring the shape of an atomic arrangement plane. 1A to 1C are diagrams for specifically explaining a method for measuring the shape of an atomic arrangement plane. An example is shown in which the radius of curvature of an atomic arrangement plane is determined from a plurality of XRD measurement points. 11A to 11C are diagrams for specifically explaining another example of a method for measuring the shape of an atomic arrangement plane. 11A to 11C are diagrams for specifically explaining another example of a method for measuring the shape of an atomic arrangement plane. FIG. 11 is a schematic diagram for explaining a first processing method. FIG. 2 is a schematic diagram showing an adsorption surface in plan view. FIG. 11 is a schematic diagram for explaining a third processing method. FIG. 11 is a schematic diagram for explaining a bonding step. FIG. 1 is a schematic diagram of an example of a production apparatus used in a sublimation method. 1 is a graph showing the relationship between the radius of curvature of an atomic arrangement plane of a SiC single crystal and the BPD density.

The present embodiment 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 convenience, 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, and may be modified as appropriate within the scope of the present invention.

"Method of processing SiC single crystals"
The method for processing a SiC single crystal according to this embodiment includes a measurement step, a processing step, and an attachment step. In the measurement step, the shape of the atomic arrangement surface of the SiC single crystal is measured at least along a first direction passing through the center in a plan view and a second direction perpendicular to the first direction. In the processing step, at least the first surface of the SiC single crystal is processed along the atomic arrangement surface based on the measurement results. In addition, in the attachment step, the SiC single crystal is attached to a mounting surface with the first surface of the SiC single crystal as an attachment surface. Each step will be specifically described below.

<Measurement process>
FIG. 1 is a schematic diagram of a cut surface of a SiC single crystal 1 cut along a straight line extending in a first direction passing through the center in a plan view. The first direction can be set to any direction. In FIG. 1, the first direction is set to [1-100]. The upper side in FIG. 1 is the [000-1] direction, that is, the direction in which a carbon surface (C surface, (000-1) surface) appears when cut perpendicularly to the <0001> direction. Below, an example will be described in which the first direction is set to [1-100].

Here, crystal orientations and faces are expressed using the following brackets as Miller indices. () and {} are used to represent faces. () is used to represent a specific face, and {} is used to represent a collective term (collective face) for equivalent faces due to the symmetry of the crystal. On the other hand, <> and [] are specifically used to represent directions. [] is used to represent a specific direction, and <> is used to represent equivalent directions due to the symmetry of the crystal.

As shown in Figure 1, SiC single crystal 1 is a single crystal formed by arranging multiple atoms A. Therefore, as shown in Figure 1, when a cut surface of SiC single crystal is viewed microscopically, an atomic arrangement plane 2 is formed in which multiple atoms A are arranged. The atomic arrangement plane 2 on the cut surface is represented as a line extending in a direction approximately parallel to the cutting direction obtained by connecting the atoms A arranged along the cut surface.

The shape of the atomic arrangement plane 2 may vary depending on the direction of the cut surface, regardless of the shape of the outermost surface of the SiC single crystal 1. Figures 2 and 3 are diagrams showing the shape of the atomic arrangement plane 2. The atomic arrangement plane 2 shown in Figure 2 is concave toward the center. Therefore, the atomic arrangement plane 2 shown in Figure 2 has the same curvature direction in the [1-100] direction and the [11-20] direction perpendicular to the [1-100] direction. In contrast, the atomic arrangement plane 2 shown in Figure 3 has a potato chip (saddle) shape that is concave on a certain cut surface and convex on a different cut surface. Therefore, the atomic arrangement plane 2 shown in Figure 3 has different curvature directions in the [1-100] direction and the [11-20] direction perpendicular to the [1-100] direction.

In other words, to accurately grasp the shape of the atomic arrangement surface 2, it is necessary to measure the shape of the atomic arrangement surface 2 of the SiC single crystal at least along two directions (a first direction and a second direction) that pass through the center in a plan view and are perpendicular to each other. In addition, the crystal structure of the SiC single crystal 1 is hexagonal, and it is preferable to measure the shape of the atomic arrangement surface 2 along six directions that are symmetrical about the center. If the shape of the atomic arrangement surface 2 is measured along six directions that are symmetrical about the center, the shape of the atomic arrangement surface 2 can be determined more precisely.

The shape of the atomic arrangement plane 2 can be measured by X-ray diffraction (XRD). The plane to be measured is determined according to the direction to be measured. If the measurement direction is [hkil], the measurement plane must satisfy the relationship (mh mk min n). Here, m is an integer equal to or greater than 0, and n is a natural number. For example, when measuring in the [11-20] direction, the (0004) plane is selected as m = 0 and n = 4, and the (22-416) plane is selected as m = 2 and n = 16. On the other hand, when measuring in the [11-20] direction, the (0004) plane is selected as m = 0 and n = 4, and the (3-3016) plane is selected as m = 3 and n = 16. In other words, the measurement plane may be different depending on the measurement direction, and the atomic arrangement plane 2 to be measured does not necessarily have to be the same plane. By satisfying the above relationship, it is possible to prevent the lattice curvature in the a-plane or m-plane direction, which has little effect on crystal growth, from being mistaken for the lattice curvature in the c-plane direction. The measurement may be performed on either the C-face or the Si-face, but it is performed on the attachment surface (first surface) that is attached to the installation surface of the crucible.

X-ray diffraction data is acquired at five points along a specified direction: the center, the edge, and the midpoint between the center and the edge. If the atomic arrangement surface 2 is curved, the reflection direction of the X-rays changes, and the position of the ω angle of the peak of the X-ray diffraction image output at the center and other parts varies. The direction of curvature of the atomic arrangement surface 2 can be obtained from this positional variation of the diffraction peak. The radius of curvature of the atomic arrangement surface 2 can also be obtained from the positional variation of the diffraction peak, and the amount of curvature of the atomic arrangement surface 2 can also be obtained. The shape of the atomic arrangement surface 2 can then be obtained from the direction and amount of curvature of the atomic arrangement surface 2.

(Specific explanation of the method for measuring the shape of the atomic arrangement plane (Method 1))
A method for measuring the curvature direction and curvature amount of the atomic arrangement plane from the XRD measurement value of the outer peripheral edge portion of a sample (hereinafter referred to as a wafer 20) sliced from a SiC single crystal will be specifically described. The measurement method will be described using the wafer 20 as an example, but a similar method can also be used for measurement of an ingot-shaped SiC single crystal before slicing.

Figure 4 shows a schematic cross section cut through the center of the plan view along the direction of measurement of the atomic arrangement surface, for example, the [1-100] direction. If the radius of the wafer 20 is r, the horizontal length of the cross section is 2r. Figure 4 also shows the shape of the atomic arrangement surface 22 in the wafer 20. As shown in Figure 4, the shape of the wafer 20 itself is flat, but the atomic arrangement surface 22 may be curved. The atomic arrangement surface 22 shown in Figure 4 is symmetrical and concavely curved. This symmetry is due to the fact that the manufacturing conditions for SiC single crystals (ingots) are usually symmetrical with respect to the center. Note that this symmetry does not need to be perfect symmetry, but means an approximate symmetry that allows for deviations due to fluctuations in the manufacturing conditions, etc.

Next, as shown in FIG. 5, XRD is performed on both outer peripheral edges of the wafer 20, and the difference Δθ in the X-ray diffraction peak angles between the two measured points is determined. This Δθ is the difference in the inclination of the atomic arrangement plane 22 at the two measured points. The diffraction plane used for the X-ray diffraction measurement is selected as an appropriate plane according to the cut surface, as described above.

Next, as shown in Figure 6, the radius of curvature of the curved atomic arrangement surface 22 is calculated from the obtained Δθ. Figure 6 shows a circle C that is tangent to the atomic arrangement surface at two measured locations, assuming that the curved surface of the atomic arrangement surface 22 of the wafer 20 is a part of a circle. Geometrically, from Figure 6, the central angle φ of a sector containing arcs with both ends at the tangent points is equal to the difference Δθ between the measured X-ray diffraction peak angles. The radius of curvature of the atomic arrangement surface 22 corresponds to the radius R of the arc. The radius R of the arc can be calculated by the following relational expression.

The amount of curvature d of the atomic arrangement surface 22 is then calculated from the radius R of the arc and the radius r of the wafer 20. As shown in FIG. 7, the amount of curvature d of the atomic arrangement surface 22 corresponds to the radius of the arc minus the distance of the perpendicular line drawn from the center of the arc to the wafer 20. The distance of the perpendicular line drawn from the center of the arc to the wafer 20 is calculated using Pythagoras' theorem, and the following formula holds. Note that in this specification, the amount of curvature d is defined as a positive value when the radius of curvature is positive (concave surface), and as a negative value when the radius of curvature is negative (convex surface).

As mentioned above, it is also possible to measure R from only the XRD measurements of both outer ends of the wafer 20. However, when using this method, there is a possibility that the shape may be misjudged if there is local distortion at the measurement point. For this reason, the X-ray diffraction peak angle is measured at multiple points, and the curvature per unit length is calculated using the following formula.

FIG. 8 shows an example of the radius of curvature of the atomic arrangement plane obtained from a plurality of XRD measurement points. The horizontal axis of FIG. 8 indicates the relative position from the center of the wafer, and the vertical axis indicates the relative diffraction peak angle of each measurement point with respect to the wafer center diffraction peak angle. FIG. 8 shows an example in which the [1-100] direction of the wafer was measured, and the measurement plane was (3-3016). Measurements were performed at five locations. The five points are arranged almost in a straight line, and from this inclination, dθ/dr = 8.69 × 10 ^-4 deg/mm can be obtained. By applying this result to the above formula, it can be calculated that the concave surface has a radius of R = 66 m. Then, from this radius and the radius r (75 mm) of the wafer, the curvature amount d of the atomic arrangement plane is obtained as 42.6 μm.

So far, we have used an example in which the shape of the atomic arrangement surface is concave, but the calculation can be done in the same way for a convex surface. In the case of a convex surface, R is calculated as a negative value.

(Description of another method for measuring the shape of an atomic arrangement surface (Method 2))
The shape of the atomic arrangement surface may be obtained by another method. Fig. 9 shows a schematic cross section cut through the center of the plan view along the measurement direction of the atomic arrangement surface, for example, the [1-100] direction. In Fig. 9, an example will be described in which the shape of the atomic arrangement surface 22 is curved in a concave shape.

As shown in Figure 9, X-ray diffraction peaks are measured at two locations: the center of the wafer 20 and a location a distance x away from the center of the wafer 20. Due to the symmetry of the ingot manufacturing conditions, the shape of the wafer 20 can be approximately bilaterally symmetrical, and it can be assumed that the atomic arrangement surface 22 is flat at the center of the wafer 20. Therefore, if the difference in the inclination of the atomic arrangement surface 22 at the two measured points as shown in Figure 10 is Δθ, the relative position y of the atomic arrangement surface 22 can be expressed by the following equation.

By measuring a plurality of points by changing the position of the distance x from the center, the relative atomic positions of the atomic arrangement surface 22 at each measurement point and the wafer center can be obtained.
This method determines the relative positions of atoms on the atomic arrangement surface at each measurement point. Therefore, the amount of curvature of the local atomic arrangement surface can be determined. In addition, the relative atomic positions of the atomic arrangement surface 22 on the entire wafer 20 can be displayed as a graph, which is useful for intuitively grasping the arrangement of the atomic arrangement surface 22.

Here, the example has been described in which the measurement object is a wafer 20. If the measurement object is a SiC ingot or a cut piece cut from a SiC ingot, the amount of curvature of the atomic arrangement plane can be determined in a similar manner.

Using the above procedure, the amount of curvature of the atomic arrangement surface 2 of the SiC single crystal is measured at least along two directions (first direction and second direction) that pass through the center in a plan view and are perpendicular to each other. By determining the amount of curvature and the direction of curvature in each direction, it is possible to determine the outline shape of the atomic arrangement surface 2 as shown in Figures 2 and 3.

<Processing steps>
In the processing step, based on the measurement results of the measurement step, the attachment surface (first surface) of the SiC single crystal 1 is processed along the atomic arrangement surface 2. The processing method is not particularly limited, but for example, the following three methods can be used.

(First Processing Method)
The first processing method includes a planarizing step of attaching the SiC single crystal to a spacer having a curved surface that curves in the opposite direction to the curvature of the atomic arrangement surface 2 and planarizing the atomic arrangement surface 2, and a face-finishing step of cutting or grinding the SiC single crystal along the planarized atomic arrangement surface 2. When using the first processing method, the thickness of the SiC single crystal is preferably 5 mm or less to allow elastic deformation.

Figure 11 is a schematic diagram for explaining the first processing method. As shown in Figure 11 (a), a spacer 30 and a support table 31 are prepared. The first surface 30A of the spacer 30 is a flat surface, and the second surface 30B is a curved surface that curves in the opposite direction to the curvature of the atomic arrangement surface 2.

The second surface 30B of the spacer 30 may be machined after measuring the shape of the atomic arrangement surface 2 of the SiC single crystal 1, or multiple spacers with different curvature directions and amounts of curvature may be prepared in advance, and the one that can best flatten the atomic arrangement surface 2 after application may be selected from among them.

The spacer 30 and the support base 31 can be made of glass, ceramics, etc. From the viewpoint of workability, it is preferable to make the spacer 30 using ceramics. It is preferable to use a support base 31 that has excellent surface flatness and rigidity.

Next, as shown in FIG. 11(b), a spacer 30 is placed on a support table 31, and the SiC single crystal 1 is bonded to the second surface 30B of the spacer 30. The SiC single crystal 1 is bonded so that the curvature direction of the atomic arrangement surface 2 is opposite to the curvature direction of the second surface 30B. The bonding is performed, for example, using an adhesive. The adhesive may be a thermoplastic resin-based solid wax that is typically used in precision machining, and it is preferable to select an adhesive with strong adhesive strength. Even if the SiC single crystal is elastically deformed by the adhesive and fixed to the support table 31, it can be fixed in the deformed state.

The atomic arrangement surface 2 of the SiC single crystal 1 after bonding to the spacer 30 is flatter than the atomic arrangement surface 2 before bonding. It is most preferable that the atomic arrangement surface 2 after bonding to the spacer 30 is parallel to the surface of the support table 31.

Then, as shown in FIG. 11(c), the SiC single crystal 1 is cut. The cut surface is parallel to the surface of the support table 31. Since the atomic arrangement surface 2 is flattened relative to the surface of the support table 31, cutting parallel to the surface of the support table 31 necessarily cuts the SiC single crystal 1 along the flattened atomic arrangement surface 2. For example, a wire saw or the like can be used for cutting. In the surface finishing step, the atomic arrangement surface 2 may be finished by a method other than cutting. As a method other than cutting, for example, the SiC single crystal 1 may be ground from the surface opposite the support table 31.

By going through the above process, a SiC single crystal 10 is obtained after cutting, in which the first surface 10A is aligned with the atomic arrangement plane 2, as shown in FIG. 11(d).

(Second Processing Method)
The second processing method includes a vacuum suction step of vacuum suctioning the SiC single crystal 1 onto an adsorption surface having a different adsorption force according to the amount of curvature of the atomic arrangement surface 2, and flattening the atomic arrangement surface 2, and a surface preparation step of cutting or grinding the SiC single crystal along the flattened atomic arrangement surface 2. The second processing method differs from the first processing method in that the atomic arrangement surface 2 is flattened by the difference in the strength of the adsorption force without using a spacer 30. The other processing procedures are the same, and will not be described. Even when the second processing method is used, the thickness of the SiC single crystal is preferably 5 mm or less, which allows elastic deformation.

Figure 12 is a schematic diagram of the suction surface 40 viewed from above. The suction surface 40 has a number of suction holes 41. The second processing method flattens the atomic arrangement surface 2 by utilizing the difference in suction force of these suction holes 41.

For example, as shown in FIG. 2, when the atomic arrangement surface 2 of the SiC single crystal 1 is concave toward the center, the suction force of the suction hole 41I is made smaller than that of the other suction holes 41A to 41H. Then, the outer periphery of the atomic arrangement surface 2 is suctioned relatively stronger than the inside, and the atomic arrangement surface 2 is flattened. Also, as shown in FIG. 3, when the atomic arrangement surface 2 of the SiC single crystal 1 is saddle-shaped with different curvature directions in the [1-100] direction and the [11-20] direction, the suction force of the suction holes 41 located farther from the central axis in the [11-20] direction is made larger. That is, the suction force of the suction holes 41G, 41I, 41C is made smaller than that of the suction holes 41H, 41B, 41F, 41D, and the suction force of the suction holes 41H, 41B, 41F, 41D is made smaller than that of the suction holes 41A, 41E.

As described above, the atomic arrangement surface 2 can be flattened by utilizing the difference in suction force of the suction holes 41. Then, the SiC single crystal 1 with the flattened atomic arrangement surface 2 is cut parallel to the mounting surface, as in Figures 11(c) and 11(d). Through the above process, a SiC single crystal 10 is obtained in which the first surface 10A is aligned with the atomic arrangement surface 2.

(Third Processing Method)
The third machining method includes an electric discharge machining step of bringing SiC single crystal 1 close to an electrode having a shape corresponding to atomic arrangement surface 2 and machining first surface 1A of SiC single crystal 1 by electric discharge. When using the third machining method, unlike the first and second machining methods, the thickness of SiC single crystal 1 does not matter.

Figure 13 is a schematic diagram for explaining the third processing method. As shown in Figure 13 (a), an electrode 50 is prepared. The first surface 50A of the electrode 50 shown in Figure 13 (a) that faces the SiC single crystal 1 is a curved surface processed along the atomic arrangement surface 2.

The first surface 50A of the electrode 50 may be machined after measuring the shape of the atomic arrangement surface 2 of the SiC single crystal 1, or multiple electrodes with different curvature directions and amounts of curvature may be prepared in advance, and the one that is closest to the shape of the atomic arrangement surface 2 may be selected from among them.

Next, with the first surface 50A of the electrode 50 facing the SiC single crystal 1, the electrode 50 is brought closer to the SiC single crystal 1. The closer the distance between the electrode 50 and the SiC single crystal 1, the stronger the discharge, so the first surface 1A of the SiC single crystal 1 evaporates along the shape of the first surface 50A of the electrode 50. As a result, as shown in FIG. 13(b), a SiC single crystal 10 is obtained in which the first surface 10A is aligned with the atomic arrangement plane 2.

<Attachment process>
Fig. 14 is a schematic diagram for explaining the bonding step. As shown in Fig. 14(a), in the bonding step, the first surface 10A of the SiC single crystal 10 obtained by processing is used as a bonding surface, and the SiC single crystal 10 is bonded to a mounting surface 60A of a mounting table 60. The mounting table 60 corresponds to, for example, a single crystal mounting portion of a crucible.

The thickness of the SiC single crystal 10 during the attachment process is preferably 5 mm or less. If the SiC single crystal 10 is too thick, it is less likely to bend during attachment, making it difficult to attach it flat to the base, and it may be difficult to arrange the atomic arrangement plane (lattice plane) of the SiC single crystal flat.

In addition, in the attachment process, the load with which the SiC single crystal 10 is pressed against the mounting surface 60A is preferably changed according to the amount of curvature of the first surface 10A relative to the mounting surface 60A. For example, if the first surface 10A of the SiC single crystal 10 is curved convexly toward the mounting surface 60A, it is preferable to make the load on the outer periphery of the SiC single crystal 10 stronger than that on the inside. Also, if the first surface 10A of the SiC single crystal 10 is curved concavely toward the mounting surface 60A, it is preferable to make the load on the inside of the SiC single crystal 10 stronger than that on the outer periphery.

The attachment step is performed, for example, using an adhesive. The adhesive may be a thermosetting resin or the like.

During the attachment process, a decompression process may be performed to reduce the pressure around the SiC single crystal 10 before the adhesive is cured. Even if air bubbles or the like are trapped on the adhesive surface, they can be degassed by creating a reduced pressure environment. As a result, unevenness in the thickness of the adhesive when applied can be further suppressed.

The thermal expansion coefficient of the mounting base 60 to be attached is preferably close to that of the SiC single crystal 10. Specifically, the difference in thermal expansion coefficient is preferably 0.3×10 ⁻⁶ /° C. or less. The thermal expansion coefficient referred to here means the thermal expansion coefficient in the temperature range in which crystal growth occurs using the SiC single crystal 10 as a seed crystal, and means a temperature in the vicinity of 2000° C. For example, the thermal expansion coefficient of graphite can be selected in the range of 4.3×10 ⁻⁶ /° C. to 7.1× ^{10 −6} /° C. depending on the manufacturing conditions, the materials contained, and the like. Since the difference in thermal expansion coefficient between the mounting base 60 and the SiC single crystal 10 is close to each other, it is possible to prevent the SiC single crystal 10 from warping due to the difference in thermal expansion coefficient during single crystal growth, and the atomic arrangement plane 2 from curving.

When the attachment process is carried out as described above, a SiC single crystal 10 with little curvature and with the atomic arrangement surface 2 parallel to the mounting surface 60A is obtained, as shown in FIG. 14(b).

"SiC single crystal"
The SiC single crystal processed up to the stage before the above-mentioned bonding process is processed so that the first surface is shaped to follow the curvature of the atomic arrangement surface. As a result, as shown in FIG. 14(a), the warped shape of the first surface 10A of the SiC single crystal 10 and the curvature of the atomic arrangement surface 2 are substantially parallel. In other words, the absolute value of the difference between the amount of warping of the SiC single crystal 10 and the amount of curvature of the atomic arrangement surface 2 is 10 μm or less. Here, the "amount of warping" means the maximum value of the distance between the mounting surface and the first surface of the SiC single crystal on the mounting surface side when the SiC single crystal is placed on a flat surface. When the maximum amount of curvature of the atomic arrangement surface 2 of the SiC single crystal 10 is 20 μm or more, it is difficult to imagine that the warped shape of the first surface 10A of the SiC single crystal 10 and the curvature of the atomic arrangement surface 2 become substantially parallel without carrying out the above-mentioned processing. In other words, SiC single crystal 10 in which the maximum curvature of the atomic arrangement plane is 20 μm or more and the absolute value of the difference between the warpage of SiC single crystal 10 and the curvature of atomic arrangement plane 2 is 10 μm or less can be realized through the above-mentioned process.

"Method for manufacturing SiC ingot"
In the method for producing a SiC ingot according to the present embodiment, in the above-described method for processing a SiC single crystal, crystal growth is performed using a SiC single crystal 10 attached to the mounting surface 60A as a seed crystal. The SiC ingot can be produced, for example, by sublimation. The sublimation method is a method in which a source gas generated by heating a source material is recrystallized on a single crystal (seed crystal) to obtain a large single crystal (ingot).

Figure 15 is a schematic diagram of an example of a manufacturing apparatus used in the sublimation method. The manufacturing apparatus 200 has a crucible 100 and a coil 101. Between the crucible 100 and the coil 101, there may be a heating element (not shown) that generates heat by induction heating of the coil 101.

The crucible 100 has a mounting table 60 provided at a position facing the raw material G. A SiC single crystal 10 processed by the above-mentioned SiC single crystal processing method is attached to the mounting table 60 as a seed crystal. In addition, a taper guide 102 is provided inside the crucible 100, the diameter of which expands from the mounting table 60 toward the raw material G.

When an alternating current is applied to the coil 101, the crucible 100 is heated and raw material gas is generated from the raw material G. The generated raw material gas is supplied to the SiC single crystal 10 placed on the mounting table 60 along the tapered guide 102. As the raw material gas is supplied to the SiC single crystal 10, a SiC ingot I grows on the main surface of the SiC single crystal 10. The crystal growth surface of the SiC single crystal 10 is preferably a carbon surface or a surface with an off angle of 10° or less from the carbon surface.

SiC ingot I inherits much of the crystal information of SiC single crystal 10. Because atomic arrangement surface 2 of SiC single crystal 10 is flattened, the occurrence of BPDs in SiC ingot I can be suppressed.

Figure 16 is a graph showing the relationship between the radius of curvature of the atomic arrangement plane of a SiC single crystal and the BPD density. As shown in Figure 16, there is a corresponding relationship between the radius of curvature of the atomic arrangement plane 2 and the BPD density in the SiC ingot I. The larger the radius of curvature of the atomic arrangement plane 2 (the smaller the amount of curvature of the atomic arrangement plane 2), the lower the BPD density tends to be. It is thought that a crystal with residual stress inside induces slippage of the crystal plane, which causes the atomic arrangement plane 2 to curve along with the generation of BPD. Alternatively, conversely, it is thought that an atomic arrangement plane 2 with a large amount of curvature has distortion and becomes the cause of BPD. In either case, the larger the radius of curvature of the atomic arrangement plane (i.e., the smaller the amount of curvature of the atomic arrangement plane), the lower the BPD density.

As described above, in the method for producing a SiC ingot according to this embodiment, the atomic arrangement surface 2 of the SiC single crystal 10 used as the seed crystal is flattened, so that the occurrence of BPDs in the SiC ingot I is suppressed. Therefore, a high-quality SiC ingot I with a low BPD density can be obtained.

Finally, the obtained SiC ingot I is sliced to produce SiC wafers. The cutting direction is perpendicular to <0001> or at an off angle of 0 to 10 degrees, and wafers are produced with a surface parallel to the C-plane or at an off angle of 0 to 10 degrees from the C-plane. The surface of the wafer may be mirror-finished on the (0001) plane, i.e., the Si-plane. The Si-plane is the plane on which epitaxial growth is usually performed. Since SiC ingot I has few BPDs, SiC wafers with few BPDs can be obtained. By using SiC wafers with few BPDs, which are killer defects, high-quality SiC epitaxial wafers can be obtained, and the yield of SiC devices can be increased.

When the crucible 100 is heated to sublimate the raw material G, it is preferable to rotate the crucible 100 so that circumferential anisotropy does not occur. The rotation speed is preferably 0.1 rpm or more. It is also preferable to minimize temperature changes on the growth surface during growth.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to a specific embodiment, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims.

Reference Signs List 1, 10 SiC single crystal 10A first surface 2, 22 atomic arrangement surface 20 wafer 30 spacer 30A first surface 30B second surface 31 support base 40 suction surface 41 suction hole 50 electrode 50A first surface 60 mounting base 60A mounting surface 100 crucible 101 coil 102 taper guide A atom I SiC ingot G raw material

Claims (7)

a SiC single crystal having a main surface, the main surface being a carbon surface or having an off angle of 10° or less from the carbon surface, and the maximum curvature of the atomic arrangement plane being 20 μm or more;
an absolute value of a difference between the amount of warpage of the SiC single crystal and the amount of curvature of the atomic arrangement plane is 10 μm or less;
A SiC single crystal that is not attached to any other components. The SiC single crystal according to claim 1, having a thickness of 5 mm or less. The SiC single crystal according to claim 1 or 2, which is in the form of an ingot. a SiC seed crystal having a maximum curvature amount of an atomic arrangement plane of 20 μm or more;
an absolute value of a difference between the amount of warpage of the SiC seed crystal and the amount of curvature of the atomic arrangement plane is 10 μm or less;
A SiC seed crystal that is not attached to any other member. The SiC seed crystal according to claim 4, having a thickness of 5 mm or less. The SiC seed crystal according to claim 4 or 5, which has a main surface, the main surface being a carbon surface or having an off angle of 10° or less from the carbon surface. A method for producing a SiC ingot, in which crystal growth is carried out using the SiC seed crystal described in any one of claims 4 to 6.

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