JP7117938B2 - SiC single crystal evaluation method and SiC wafer manufacturing method - Google Patents

Description

The present invention relates to a SiC single crystal evaluation method and a SiC wafer manufacturing method.

Silicon carbide (SiC) has a dielectric breakdown field one order of magnitude larger and a bandgap three times larger than silicon (Si). In addition, silicon carbide (SiC) has properties such as a thermal conductivity that is about three times as high as that of silicon (Si). Silicon carbide (SiC) is expected to be applied to power devices, high frequency devices, high temperature operation devices and the like.

Devices such as semiconductors use SiC epitaxial wafers obtained by forming an epitaxial film on a SiC wafer. An epitaxial film provided on a SiC wafer by chemical vapor deposition (CVD) serves as an active region of a SiC semiconductor device.

Therefore, there is a demand for a high-quality SiC wafer that is free from damage such as cracks and has few defects. In this specification, the SiC epitaxial wafer means a wafer after forming an epitaxial film, and the SiC wafer means a wafer before forming an epitaxial film.

For example, Patent Literature 1 describes that an epitaxial film formed on a SiC wafer is improved by setting the warp amount of the wafer and the crystal orientation deviation amount within a predetermined range.

Further, Patent Document 2 describes that a high-quality epitaxial film can be obtained by keeping the deviation of the growth plane orientation within the wafer plane within a predetermined range.

In order to obtain high-quality SiC wafers, quality evaluation is performed in each process. For example, the quality of SiC ingots is evaluated using X-ray topography analysis (XRT), KOH etching, etc. after cutting a wafer for evaluation (Patent Document 3). If the number of SiC wafers and the number of seed crystals to be obtained are determined after sufficiently evaluating the quality of the SiC ingot, the amount of SiC single crystal loss can be reduced.

JP 2011-219296 A JP 2011-16721 A JP 2015-188003 A

However, in the method described in Patent Document 3, it takes time to process the SiC ingot into an evaluation wafer and evaluate the quality by etching or the like. As a result, a time loss on the order of several weeks occurs between the SiC ingot and the SiC wafer being processed.

In addition, as in the SiC wafers described in Patent Documents 1 and 2, it may not be possible to sufficiently suppress the occurrence of basal plane dislocations (BPDs) simply by controlling the degree of lattice misalignment in a predetermined direction. . A basal plane dislocation (BPD) is one of the killer defects of SiC wafers, and is a defect considered to be one of the causes of slip occurring on the basal plane.

The present invention has been made in view of the above problems, and an object of the present invention is to efficiently provide a high-quality SiC single crystal wafer.

As a result of intensive studies, the present inventors have found that by evaluating the curved state of the atomic arrangement plane (lattice plane) of the SiC single crystal in at least two directions, it is possible to easily obtain a SiC single crystal that is unlikely to generate basal plane dislocations (BPD). It was found that it can be evaluated to
In addition, by simply evaluating the atomic arrangement plane of the SiC single crystal, it was found that the rough quality of the SiC ingot can be grasped, and the SiC ingot cutting conditions and the next single crystal growth conditions can be quickly fed back.
That is, the present invention provides the following means in order to solve the above problems.

(1) A method for evaluating a SiC single crystal according to a first aspect includes: and a second direction along the <11-20> direction passing through the center of the planar view, and the bending state of the atomic arrangement plane in at least two directions.

(2) In the SiC single crystal evaluation method according to the aspect described above, the curved state of the atomic arrangement plane may be evaluated in at least six directions rotated by 30° with respect to the first direction.

(3) In the SiC single crystal evaluation method according to the aspect described above, the curved state of the atomic arrangement plane may be evaluated based on whether or not the curved direction of the atomic arrangement plane matches the measurement direction.

(4) In the SiC single crystal evaluation method according to the aspect described above, the curved state of the atomic arrangement plane may be evaluated from the difference between the maximum value and the minimum value of the amount of curvature of the atomic arrangement plane in the measurement direction.

(5) In the SiC single crystal evaluation method according to the aspect described above, the curved state of the atomic arrangement plane may be evaluated by X-ray diffraction.

(6) The SiC single crystal manufacturing method according to the second aspect determines the SiC ingot slicing method or the SiC single crystal growth conditions based on the evaluation result of the SiC single crystal evaluation method according to the above aspect.

Using the SiC single crystal evaluation method according to the aspect described above can efficiently provide a high-quality SiC single crystal wafer.

It is the figure which showed typically the manufacturing method of the SiC wafer concerning this embodiment. 1 is a schematic diagram of an example of a manufacturing apparatus used when manufacturing a SiC ingot; FIG. It is a cross-sectional schematic diagram of the SiC ingot crystal-grown on the seed crystal. It is a figure which showed typically the quality evaluation method of the SiC ingot concerning this embodiment. FIG. 2 is a schematic diagram of a cross section of a SiC single crystal forming a tail or head along a straight line extending in the [1-100] direction passing through the center in plan view. FIG. 4 is a schematic diagram of a cross section of a SiC single crystal forming a tail or a head cut along a straight line extending in the [11-20] direction passing through the center in plan view. 1 is a diagram schematically showing an example of an atomic arrangement plane of a SiC single crystal; FIG. FIG. 4 is a diagram schematically showing another example of an atomic arrangement plane of a SiC single crystal; It is a figure for demonstrating concretely the measuring method of the curvature amount of an atomic arrangement plane. It is a figure for demonstrating concretely the measuring method of the curvature amount of an atomic arrangement plane. It is a figure for demonstrating concretely the measuring method of the curvature amount of an atomic arrangement plane. It is a figure for demonstrating concretely the measuring method of the curvature amount of an atomic arrangement plane. An example in which the radius of curvature of an atomic arrangement surface is obtained from a plurality of XRD measurement points is shown. FIG. 5 is a diagram for specifically explaining another example of a method for measuring the amount of curvature of an atomic arrangement plane; FIG. 5 is a diagram for specifically explaining another example of a method for measuring the amount of curvature of an atomic arrangement plane; FIG. 4 is a diagram showing the relationship between BPD densities contained in a crystal growth portion when a single crystal is crystal-grown on a predetermined SiC single crystal. It is the result of measuring the amount of lattice plane curvature of the head and tail of the SiC ingot. FIG. 2 is a diagram schematically showing a conventional SiC ingot quality evaluation method;

Hereinafter, this embodiment will be described in detail with appropriate reference to the drawings. In the drawings used in the following description, characteristic portions may be enlarged for the sake of convenience, and the dimensional ratio of each component may differ from the actual one. The materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be modified as appropriate without changing the gist of the invention.

FIG. 1 is a diagram schematically showing a method for manufacturing a SiC wafer according to this embodiment. As shown in FIG. 1, a seed crystal is first prepared. Then, SiC is crystal-grown on the seed crystal to produce a SiC ingot. The obtained SiC ingot undergoes quality evaluation, is processed into SiC wafers, and is shipped. Also, part of the SiC ingot is processed into seed crystals for producing the next SiC ingot. The manufactured SiC wafer is processed into a SiC epitaxial wafer having an epitaxial film formed on its surface and a SiC device having a part of the epitaxial film processed.

FIG. 2 is a schematic diagram of an example of a manufacturing apparatus used when manufacturing a SiC ingot. A manufacturing apparatus 100 shown in FIG. 2 is one of SiC single crystal manufacturing apparatuses using a sublimation method. The sublimation method is a method of recrystallizing a raw material gas generated by heating a raw material on a single crystal (seed crystal) to obtain a large single crystal (ingot).

A manufacturing apparatus 100 shown in FIG. 2 has a crucible 10 and a coil 20 . Between the crucible 10 and the coil 20 , there may be provided a heating element (not shown) that generates heat by induction heating of the coil 20 .

The crucible 10 has a crystal installation portion 11 provided at a position facing the raw material G. As shown in FIG. The crucible 10 may have a taper guide 12 that expands in diameter from the crystal installation portion 11 toward the raw material G inside. In FIG. 2, the raw material G, the seed crystal 5, and the SiC ingot 6 grown from the seed crystal are shown at the same time for easy understanding.

When an alternating current is applied to the coil 20, the crucible 10 is heated and the raw material G is produced as raw material gas. The generated raw material gas is supplied along the taper guide 12 to the seed crystal 5 placed in the crystal placement section 11 . By supplying the raw material gas to the seed crystal 5 , the SiC ingot 6 is crystal-grown on the main surface of the seed crystal 5 . The crystal growth surface of the seed crystal 5 is preferably a carbon surface or a surface with an off angle of 10° or less from the carbon surface.

FIG. 3 is a schematic cross-sectional view of SiC ingot 6 crystal-grown on seed crystal 5 . In general, before a cutting process such as a multi-wire saw is performed, a step of cutting the SiC ingot 6 in the vicinity of the crystal growth surface (hereinafter referred to as head 6A) and in the vicinity of the seed crystal 5 (hereinafter referred to as tail 6B) is required. be.

FIG. 4 is a diagram schematically showing the SiC ingot quality evaluation method according to the present embodiment. First, as shown in FIG. 4, the tail or head of the SiC ingot is cut and obtained (step S1). As described above, cutting with a multi-wire saw or the like requires a step of obtaining the head 6A or the tail 6B or the like in advance. Therefore, by using the evaluation method, there is no need to newly generate an additional cutting process or to obtain an evaluation sample at the expense of the product obtaining section.

Next, the curved state of the atomic arrangement plane in the head 6A or the tail 6B is evaluated (FIG. 4, step S2). First, the atomic arrangement plane will be explained. FIG. 5 is a schematic diagram of a cross section obtained by cutting the SiC single crystal forming the head 6A or the tail 6B along a straight line extending in the [1-100] direction passing through the center in plan view. FIG. 6 is a schematic diagram of a cross section obtained by cutting the SiC single crystal forming the head 6A or the tail 6B along a straight line extending in the [11-20] direction passing through the center in plan view. 5 and 6, the upper side is the [000-1] direction, that is, the direction in which the carbon plane (C plane, (000-1) plane) appears when cut perpendicular to the <0001> direction. An example in which the first direction and the second direction are the [1-100] direction and the [11-20] direction will be described below.

Here, crystal orientations and planes are expressed using the following parentheses as Miller indices. ( ) and { } are used when representing faces. ( ) is used to express a specific plane, and { } is used to express a generic term (aggregate plane) of equivalent planes based on crystal symmetry. On the other hand, < > and [ ] are especially used to indicate direction. [ ] is used to express a specific direction, and < > is used to express an equivalent direction due to crystal symmetry.

As shown in FIGS. 5 and 6, the SiC single crystal 1 forming the head 6A or the tail 6B is a single crystal in which a plurality of atoms A are aligned. Therefore, as shown in FIGS. 5 and 6, when microscopically looking at the cut surface of the SiC single crystal, an atomic arrangement plane 2 in which a plurality of atoms A are arranged is formed. The atomic arrangement plane 2 on the cutting plane is expressed as a line extending in a direction substantially parallel to the cutting direction obtained by connecting the atoms A arranged along the cutting plane.

The shape of the atomic arrangement plane 2 on the cut surface may be convex or concave regardless of the shape of the outermost surface of the SiC single crystal 1 . Also, the shape of the atomic arrangement plane 2 may differ depending on the cutting direction. The shape of the atomic arrangement plane 2 is, for example, a concave shape that is concave toward the center as shown in FIG. saddle type).

The shape of the atomic arrangement plane 2 can be measured by X-ray diffraction (XRD). The surface to be measured is determined according to the direction of measurement. Assuming that the measurement direction is [hkil], the measurement surface must satisfy the relationship (mh mk min). Here, m is an integer greater than or equal to 0, and n is a natural number. For example, when measuring in the [11-20] direction, the (0004) plane is selected with m=0 and n=4, and the (22-416) plane with m=2 and n=16. On the other hand, when measuring in the [11-20] direction, the (0004) plane is selected with m=0 and n=4, and the (3-3016) plane with m=3 and n=16. That is, the measurement plane may be a different plane depending on the measurement direction, and the atomic arrangement plane 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. For measurement, either the C plane or the Si plane may be selected, but the measurement direction is not changed for one sample.

X-ray diffraction data are acquired at five points along a given direction: the center, the edge, and the midpoint between the center and the edge. If the atomic arrangement plane 2 is curved, the X-ray reflection direction changes, so the ω angle position of the peak of the output X-ray diffraction image varies between the center and other portions. The bending direction of the atomic arrangement plane 2 can be determined from the positional variation of the diffraction peak. Also, the radius of curvature of the atomic array surface 2 can be obtained from the positional variation of the diffraction peak, and the amount of curvature of the atomic array surface 2 can also be obtained.

(Specific explanation of the method of measuring the bending direction and bending amount of the atomic arrangement plane)
A specific description will be given of a method for measuring the bending direction and bending amount of the atomic arrangement plane from the XRD measurement values of the outer peripheral end portion of a sample obtained by slicing a portion of a SiC single crystal (ingot) (hereinafter referred to as a wafer 20). .

FIG. 9 schematically shows a cross section cut along the direction of measurement of the atomic arrangement plane, for example, the [1-100] direction, passing through the center in plan view. Assuming that the radius of the wafer 20 is r, the lateral length of the cross section is 2r. 9 also shows the shape of the atomic arrangement surface 22 in the wafer 20. As shown in FIG. As shown in FIG. 9, although the shape of the wafer 20 itself is flat, the atomic arrangement surface 22 may be curved. The atomic arrangement plane 22 shown in FIG. 9 is symmetrical and curved concavely. This symmetry is due to the fact that ingot manufacturing conditions are usually symmetrical about the center. Note that this symmetry does not have to be perfect symmetry, but means symmetry as an approximation that allows fluctuations due to fluctuations in manufacturing conditions and the like.

Next, as shown in FIG. 10, XRD is performed on both outer peripheral end portions of the wafer 20 to obtain the difference Δθ between the X-ray diffraction peak angles between the two measured points. This .DELTA..theta. is the difference between the tilts of the atomic arrangement plane 22 at the two points measured. As for the diffraction surface used for the X-ray diffraction measurement, an appropriate surface is selected according to the cut surface as described above.

Next, as shown in FIG. 11, the radius of curvature of the curved atomic arrangement surface 22 is obtained from the obtained Δθ. FIG. 11 shows a circle C in contact with two measured atomic arrangement planes, assuming that the curved surface of the atomic arrangement plane 22 of the wafer 20 is a part of a circle. Geometrically from FIG. 11, the central angle φ of the sector containing the circular arc with both ends at the points of contact is equal to the measured X-ray diffraction peak angle difference Δθ. The radius of curvature of the atomic arrangement plane 22 corresponds to the radius R of the arc. The arc radius R is obtained by the following relational expression.

Then, from the radius R of this arc and the radius r of the wafer 20, the amount of curvature d of the atomic array surface 22 is obtained. As shown in FIG. 12, the amount of curvature d of the atomic arrangement plane 22 corresponds to the radius of the arc minus the distance of the perpendicular line from the center of the arc to the wafer 20 . The distance of the perpendicular from the center of the arc to the wafer 20 is calculated from the Pythagorean theorem, and the following equation holds. In this specification, the curvature amount d is defined as a positive value when the curvature radius is positive (concave surface), and the curvature amount d is defined as a negative value when the curvature radius is negative (convex surface).

As mentioned above, R can also be measured from only the outer edge measurements of the wafer 20 in XRD. On the other hand, if this method is used, there is a possibility that the shape may be misunderstood when there is local distortion or the like at the measurement location. Therefore, the X-ray diffraction peak angle is measured at multiple points, and the curvature per unit length is converted from the following formula.

FIG. 13 shows an example in which the radius of curvature of the atomic arrangement surface is obtained from a plurality of XRD measurement points. The horizontal axis of FIG. 13 indicates the relative position from the wafer center, and the vertical axis indicates the diffraction peak angle of each measurement point relative to the wafer center diffraction peak angle. FIG. 13 shows an example in which the [1-100] direction of the wafer is measured and the measurement plane is (3-3016). Measurement was performed at five locations. The five points are arranged substantially on a straight line, and dθ/dr=8.69×10 ⁻⁴ deg/mm can be obtained from this slope. By applying this result to the above formula, it is possible to calculate a concave surface with R=66 m. Then, from this R and the radius r (75 mm) of the wafer, the amount of curvature d of the atomic array plane is found to be 42.6 μm.

Although the example in which the shape of the atomic arrangement surface is concave has been described so far, the same is required for the convex surface. For convex surfaces, R is calculated as negative.

(Description of another method for measuring the bending direction and bending amount of the atomic arrangement plane)
The bending direction and bending amount of the atomic arrangement plane may be obtained by another method. FIG. 14 schematically shows a cross section cut along the direction of measurement of the atomic arrangement plane, eg, the [1-100] direction, passing through the center in plan view. In FIG. 9, an example in which the lattice arrangement surface 22 is curved in a concave shape will be described.

As shown in FIG. 14, diffraction peaks of X-ray diffraction are measured at two locations, the center of the wafer 20 and the location a distance x away from the center of the wafer 20 . From the symmetry of the ingot manufacturing conditions, the shape of the wafer 20 can be approximately left-right symmetrical, and the atomic arrangement plane 22 can be assumed to be flat at the center of the wafer 20 . Therefore, assuming that the difference in inclination of the atomic arrangement plane 22 at two points measured as shown in FIG.

By performing measurements at a plurality of points while changing the positions of the distance x from the center, it is possible to obtain the relative atomic positions of the atomic array surface 22 between the wafer center and the measurement points at each point.
This method obtains the relative positions of atoms on the plane of atomic arrangement at each measurement point. Therefore, the relative atomic positions of the atomic arrangement plane 22 can be shown as a graph over the entire wafer 20, which is useful for intuitively grasping the arrangement of the atomic arrangement plane 22. FIG.

On the other hand, since the measurement at each point is based on the measurement value at one location, depending on the diffraction conditions, some locations (especially near one edge of the wafer) may be difficult to measure partially. In addition, if there is a part with poor crystallinity, it may easily contain errors. Therefore, in the current measurement technology, this method is used to obtain a reference value for intuitively grasping the arrangement of the atomic arrangement plane, rather than to measure the degree of warpage of the atomic arrangement plane 22. is preferred.

The thickness of the sample for measuring the amount of curvature of the atomic arrangement plane 2 is preferably 500 μm or more. If the thickness of the sample is 500 μm or more, warping of the sample can be suppressed. If the sample itself warps, it becomes difficult to accurately estimate the amount of curvature of the atomic array plane 2 . The amount of warpage of the sample is preferably 5 μm or less in any direction. Here, the amount of warpage of a sample refers to the maximum distance of a vertical line drawn from the mounting surface on the flat side of the sample toward the flat surface when the sample is placed on the flat surface.

The curved state of the atomic arrangement plane 2 functions as one index of quality. A first direction along the <1-100> direction passing through the plane view center and a second direction perpendicular to the first direction passing through the plane view center of the SiC single crystal along the <11-20> direction are curved. 2 direction and at least two directions are evaluated.

The bending state of the atomic arrangement plane 2 is evaluated from the bending direction of the atomic arrangement plane 2 measured along each direction, or the maximum value, the minimum value, and the difference between the bending amounts (FIG. 4, step S3).

When evaluating from the bending direction of the atomic arrangement plane 2, does the bending direction of the atomic arrangement plane 2 measured along the first direction match the bending direction of the atomic arrangement plane 2 measured along the second direction? determine whether or not The bending direction in each direction can be determined by the method described above. For example, the atomic arrangement surface 2 in the embodiment shown in FIG. 7 has a concave shape that is depressed in the opposite direction to the stacking direction in both the first direction and the second direction, and the curved directions are the same. On the other hand, the atomic arrangement plane 2 in the embodiment shown in FIG. 8 has a convex shape that protrudes toward the stacking direction in the first direction, and a concave shape that is depressed toward the side opposite to the stacking direction in the second direction. . That is, the bending directions are different in the two directions.

When the bending directions of the atomic arrangement plane 2 in the first direction and the second direction are the same, the BPD density in the crystal growth portion where crystal growth is performed using the SiC single crystal as a seed crystal is low. Although the reason for this is not clear, when the atomic arrangement plane 2 is curved in two different directions, the atomic arrangement plane 2 is distorted (see FIG. 8). If the atomic arrangement surface 2 is distorted, stresses are generated in a plurality of directions when the temperature changes, and the atomic arrangement surface 2 is likely to be distorted. It is considered that the strain of the atomic arrangement plane 2 induces the slip of the crystal plane and causes BPD.

That is, when the bending direction of the atomic arrangement plane 2 measured along the first direction and the bending direction of the atomic arrangement plane 2 measured along the second direction are the same, the BPD is unlikely to occur under appropriate conditions. It can be judged that a SiC ingot is produced. That is, based on this result, the conditions for cutting the SiC wafer or the conditions for growing the next SiC ingot can be set. If the SiC ingot can be produced under suitable conditions, the next production conditions are made similar to the current production conditions. Further, the SiC wafer cutting conditions may be adjusted so as to increase the number of high-quality SiC wafers to be obtained, or may be adjusted to increase the number of high-quality seed crystals to be obtained.

Further, when a SiC wafer of higher quality is required, it is preferable to evaluate the curved state of the atomic arrangement plane in at least six directions rotated by 30° with respect to the first direction. The crystal structure of SiC single crystal 1 is hexagonal. Therefore, it can be determined that a high-quality SiC wafer in which distortion is less likely to occur and BPD is less likely to occur can be obtained if the curved directions of the cut surfaces cut along six directions symmetrical with respect to the center are the same.

On the other hand, when evaluating from the amount of curvature of the atomic arrangement plane 2, the amount of curvature d1 (see FIG. 5) of the atomic arrangement plane 2 measured along the first direction and the amount of curvature d1 (see FIG. 5) of the atomic arrangement plane 2 measured along the second direction 2 (see FIG. 6). The amount of curvature in each direction can be determined by the method described above. Here, the amount of curvature of the atomic arrangement plane 2 means the difference between the atomic positions at the center of the SiC single crystal 1 in plan view and the atomic positions at the ends of the SiC single crystal 1 . The amount of curvature is positive when the atomic arrangement plane 2 is concave toward the center, and the amount of curvature is negative when it is convex toward the center.

FIG. 16 is a diagram showing the relationship between BPD densities contained in a crystal growth portion when a single crystal is crystal-grown on a predetermined SiC single crystal. FIG. 16(a) is a diagram showing the relationship between the absolute value of the bending amount d1 of the atomic arrangement plane 2 measured along the first direction and the BPD density contained in the crystal growth portion. FIG. 16(b) is a diagram showing the relationship between the absolute value of the bending amount d2 of the atomic arrangement plane 2 measured along the second direction and the density of BPDs contained in the crystal growth portion. FIG. 16(c) is a diagram showing the relative values of the amount of curvature d1 and the amount of curvature d2 and the density of BPDs contained in the crystal growth portion.

The SiC single crystal shown in FIG. 16 was produced by a sublimation method. The diameter of the seed crystal was 16 cm. A SiC single crystal was grown to a thickness of about 20 mm on the seed crystal. BPD density was determined using a KOH etch.

As shown in FIGS. 16(a) and 16(b), no correlation is confirmed between the bending amounts d1 and d2 and the BPD. Therefore, when a SiC single crystal with small absolute values of the bending amounts d1 and d2 is used, the frequency of occurrence of BPD does not necessarily decrease. That is, the absolute values of the curvature amounts d1 and d2 do not sufficiently function as indicators of the BPD density.

On the other hand, as shown in FIG. 16(c), there is a correlation between the relative values of the amount of curvature d1 and the amount of curvature d2 and the BPD. As the relative value of the amount of bending d1 and the amount of bending d2 increases, the frequency of occurrence of BPD tends to increase. In other words, the BPD density can be reduced by using a SiC single crystal in which the difference between the amount of curvature d1 and the amount of curvature d2 is within a predetermined range. That is, when the difference between the amount of curvature d1 and the amount of curvature d2 is small, it can be determined that the SiC ingot is manufactured under appropriate conditions in which BPD is unlikely to occur.

The reason why the above relationship is observed between the relative values of the amount of curvature d1 and the amount of curvature d2 and the BPD density is as follows. A small relative value between the amount of curvature d1 and the amount of curvature d2 means that the shape of the atomic arrangement surface 2 does not have anisotropy in a predetermined direction. For example, when the difference between the amount of curvature d1 in the first direction and the amount of curvature d2 in the second direction is large, the atomic arrangement plane 2 has a shape greatly curved in a predetermined direction. If the shape of the atomic arrangement plane 2 has a large anisotropy in a predetermined direction, stress concentration tends to occur in that direction when temperature changes occur. Stress concentration induces slippage of crystal planes and can cause BPD.

As shown in FIG. 8, in the case of a potato chip type in which the atomic array surface 2 is curved in different directions in the first direction and the second direction, the amount of curvature d1 indicates a negative value, and the amount of curvature d2 indicates a positive value. Therefore, for example, if the amount of curvature d1 is −α and the amount of curvature d2 is β, the absolute value of the difference between them is α+β, and the difference between the amount of curvature d1 and the amount of curvature d2 inevitably increases.

As described above, based on the result of the difference between the amount of curvature d1 of the atomic arrangement plane 2 measured along the first direction and the amount of curvature d2 of the atomic arrangement plane 2 measured along the second direction, the SiC wafer Cutting conditions or next SiC ingot growth conditions can be set.

In addition, when a higher quality SiC wafer is required, the bending state of the atomic arrangement plane is measured in at least six directions rotated by 30° with respect to the first direction, and the maximum amount of bending in the six directions is measured. It is preferable to evaluate by the difference of the minimum value. The crystal structure of SiC single crystal 1 is hexagonal. Therefore, if the amount of curvature of the atomic arrangement surface measured along the six directions symmetrical with respect to the center is small, the atomic arrangement surface 2 is less likely to have anisotropy, and a high-quality SiC wafer that is unlikely to generate BPD can be obtained. can get.

Here, the shape of the atomic arrangement plane 2 is evaluated with the head 6A or the tail 6B of the SiC ingot 6. FIG. The evaluation result of the head 6A or the tail 6B is not significantly different from the evaluation result of the inside of the SiC ingot. Therefore, based on the evaluation result of the head 6A or the tail 6B, the quality of the obtained SiC ingot can be fully evaluated.

FIG. 17 shows the results of measuring the shape of the atomic array surface of the head 6A and tail 6B of the SiC ingot. The total growth amount of this ingot was 28 mm, and the tail 6B and head 6A were located at positions where the growth amounts were 4 mm and 24 mm, respectively. The horizontal axis represents the angle between [11-20] and the measurement direction when the counterclockwise rotation is positive, and the vertical axis represents the amount of lattice curvature. That is, 90° and -90° in this figure represent the same [1-100] direction.

The most concave direction in the head 6A is the direction forming 30° with respect to [11-20], the amount of curvature is 25.0 μm, and the most convex direction is in the [11-20] direction. The amount of curvature is -2.5 μm in the direction forming −60° to the direction. The most concave direction in tail 6B is the direction at 30° to [11-20], the amount of curvature is 21.4 μm, and the most convex direction is to [11-20]. The amount of curvature is -2.5 μm in the direction forming −60°. That is, it can be said that there is no great difference in the shape and curvature of the atomic array surface 2 in the SiC ingot from the tail portion in the early stage of growth to the head portion in the late stage of growth. Therefore, it is possible to grasp the lattice curvature of the SiC ingot as a whole by measuring the amount of lattice curvature at an arbitrary point in the stacking direction of the manufactured SiC ingot.

In this evaluation, a cut surface cut out by a wire saw or the like can be evaluated as it is, and polishing of the measurement surface is unnecessary. In addition, since the evaluation can be performed at an arbitrary portion that is cut out in a normal cutting process, there is no need to add a new processing process in carrying out the present invention. In addition, since the atomic arrangement plane can be easily measured by X-ray diffraction (XRD), it can be confirmed within several hours. That is, by using the SiC single crystal evaluation method according to the present embodiment, it is possible to easily determine whether the SiC ingot is good or bad. In addition, this evaluation result can be quickly fed back to the next SiC ingot manufacturing conditions and SiC wafer slicing method, and the time required to manufacture the SiC wafer can be greatly reduced.

Here, FIG. 18 is a diagram schematically showing a conventional SiC ingot quality evaluation method. As shown in FIG. 18, for a conventional SiC ingot, first, an evaluation wafer is obtained (step S11), and the evaluation wafer is processed so that evaluation can be performed (step S12). Thereafter, the presence or absence of stacking faults and dislocation concentration areas is confirmed by X-ray topography (step S13), and the number of defects is counted by KOH etching (step S14). Then, based on the obtained results, the next SiC ingot manufacturing conditions and the SiC wafer slicing method are determined.

It takes time to process evaluation wafers, perform KOH etching, and count the number of defects, and it takes several weeks to several months to confirm quality. That is, it takes time to feed back the next SiC ingot manufacturing conditions and the SiC wafer slicing method, and the overall time required for manufacturing the SiC wafer is lengthened. It is possible to produce the next ingot without waiting for the quality evaluation feedback, but if there is an abnormality in the quality due to a deviation in the production conditions, etc., if there is no abnormality in the appearance of the ingot, we will wait until the quality evaluation result is clarified. Since an abnormality cannot be detected, adjustment of manufacturing conditions cannot be performed. As a result, there is a risk that defective ingots will continue to be produced in the meantime, which is not preferable.

As described above, the SiC single crystal quality can be easily measured by using the SiC single crystal evaluation method according to the present embodiment. In addition, the curved state of the atomic arrangement plane functions as an indicator of the occurrence of BPDs, and SiC single crystals in which BPDs are unlikely to occur can be easily identified.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to specific embodiments, and various can be transformed or changed.

DESCRIPTION OF SYMBOLS 1... SiC single crystal, 2... Atomic arrangement surface, 5... Seed crystal, 6... SiC ingot, 6A... Head, 6B... Tail, 10... Crucible, 11... Crystal installation part, 12... Taper guide, 20... Coil, 100 ... production equipment, A ... atoms, G ... raw materials

Claims (4)

A first direction along the <1-100> direction passing through the plane view center of the SiC single crystal and a second direction perpendicular to the first direction and passing through the plane view center of the SiC single crystal and along the <11-20> direction and measure the amount of curvature of the atomic arrangement plane in two directions,
A method for evaluating a SiC single crystal, wherein a difference between the amount of bending in the first direction and the amount of bending in the second direction is obtained . A first direction along the <1-100> direction passing through the plane view center of the SiC single crystal and at least six directions rotated by 30° with respect to the first direction are measured to measure the amount of curvature of the atomic arrangement plane, and the curvature is measured. A SiC single crystal evaluation method for determining the difference between the maximum and minimum amounts . 3. The SiC single crystal evaluation method according to claim 1, wherein the amount of curvature of said atomic arrangement plane is measured by X-ray diffraction. A SiC wafer manufacturing method, wherein a SiC ingot slicing method or a next SiC single crystal growth condition is determined based on the evaluation result of the SiC single crystal evaluation method according to any one of claims 1 to 3 .

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