JP2020026372A - METHOD FOR EVALUATING SiC SINGLE CRYSTAL AND METHOD FOR PRODUCING SiC WAFER - Google Patents

Abstract

To provide efficiently a high-quality SiC single crystal wafer.SOLUTION: This method for evaluating an SiC single crystal evaluates the curved state of an atomic arrangement surface at least in two directions, namely in a first direction that passes through the center of the plan view of an SiC single crystal and extends along the <1-100> direction and in a second direction that is perpendicular to the first direction, while passing through the center of the plan view of the SiC single crystal and extending along the <11-20> direction.SELECTED DRAWING: Figure 1

Description

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

  Silicon carbide (SiC) has a breakdown electric field one order of magnitude higher than silicon (Si) and a band gap three times larger. Further, silicon carbide (SiC) has characteristics such as a thermal conductivity that is about three times higher than 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.

  For devices such as semiconductors, an SiC epitaxial wafer having an epitaxial film formed on a SiC wafer is used. An epitaxial film provided on a SiC wafer by a chemical vapor deposition (CVD) becomes an active region of the 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 amount of warpage of the wafer and the amount of deviation of the crystal orientation within a predetermined range.

  Patent Document 2 describes that a good quality epitaxial film can be obtained by setting the deviation of the growth plane orientation in the wafer plane within a predetermined range.

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

JP 2011-219296 A JP 2011-16721 A JP-A-2005-188003

  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 of several weeks occurs between the processing of the SiC ingot and the processing of the SiC wafer.

  Further, as in the case of the SiC wafers described in Patent Literature 1 and Patent Literature 2, the occurrence of basal plane dislocation (BPD) cannot be sufficiently suppressed only by controlling the degree of lattice displacement in a predetermined direction. . The basal plane dislocation (BPD) is one of the killer defects of the SiC wafer, and is a defect that is considered to be one of the causes of the occurrence of the slip generated on the basal plane.

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

As a result of intensive studies, the present inventors have evaluated the bending state of the atomic arrangement plane (lattice plane) of the SiC single crystal in at least two directions, and have obtained a simple SiC single crystal in which basal plane dislocation (BPD) is not easily generated. It was found that it can be evaluated.
Also, 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 cutting conditions of the SiC ingot and the next growth condition of the single crystal can be quickly fed back.
That is, the present invention provides the following means in order to solve the above problems.

(1) In the method for evaluating a SiC single crystal according to the first aspect, the SiC single crystal is perpendicular to the first direction along a <1-100> direction passing through the center of the SiC single crystal in a plan view. And the second direction along the <11-20> direction passing through the center in plan view, and the curved state of the atom arrangement surface in at least two directions.

(2) In the method for evaluating a SiC single crystal according to the above aspect, 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 method for evaluating a SiC single crystal according to the above aspect, the bending state of the atomic arrangement plane may be evaluated based on whether or not the bending direction of the atomic arrangement plane in the measurement direction matches.

(4) In the method for evaluating a SiC single crystal according to the above aspect, the bending state of the atomic arrangement surface may be evaluated from a difference between a maximum value and a minimum value of the amount of curvature of the atomic arrangement surface in a measurement direction.

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

(6) In the method for producing a SiC single crystal according to the second aspect, the method for slicing the SiC ingot or the growth condition for the SiC single crystal is determined based on the evaluation result of the evaluation method for the SiC single crystal according to the above aspect.

  When the method for evaluating a SiC single crystal according to the above aspect is used, a high-quality SiC single crystal wafer can be efficiently provided.

FIG. 4 is a view schematically showing a method for manufacturing a SiC wafer according to the embodiment. It is a schematic diagram of an example of the manufacturing apparatus used when manufacturing a SiC ingot. It is a cross section of an SiC ingot which grew on a seed crystal. It is the figure which showed typically the quality evaluation method of the SiC ingot concerning this embodiment. It is a schematic diagram of the cut surface which cut | disconnected the SiC single crystal which comprises a tail or a head along the straight line extended in the [1-100] direction which passes through the center in planar view. It is the schematic diagram of the cut surface which cut | disconnected the SiC single crystal which comprises a tail or a head along the straight line extended in the [11-20] direction which passes the center in planar view. It is the figure which showed typically an example of the atomic arrangement surface of a SiC single crystal. FIG. 4 is a diagram schematically showing another example of the atomic arrangement plane of the SiC single crystal. FIG. 4 is a diagram for specifically explaining a method of measuring the amount of curvature of an atomic arrangement surface. FIG. 4 is a diagram for specifically explaining a method of measuring the amount of curvature of an atomic arrangement surface. FIG. 4 is a diagram for specifically explaining a method of measuring the amount of curvature of an atomic arrangement surface. FIG. 4 is a diagram for specifically explaining a method of measuring the amount of curvature of an atomic arrangement surface. An example in which a radius of curvature of an atomic arrangement surface is obtained from a plurality of XRD measurement points will be described. FIG. 9 is a diagram for specifically explaining another example of a method for measuring the amount of curvature of an atomic arrangement surface. FIG. 9 is a diagram for specifically explaining another example of a method for measuring the amount of curvature of an atomic arrangement surface. FIG. 4 is a diagram showing a relationship between BPD densities contained in a crystal growth portion when a single crystal is grown on a predetermined SiC single crystal. It is the result of having measured the lattice curvature of the head and tail of the SiC ingot. It is the figure which showed typically the quality evaluation method of the conventional SiC ingot.

  Hereinafter, the present embodiment will be described in detail with reference to the drawings as appropriate. In the drawings used in the following description, a characteristic portion may be enlarged for convenience, and a dimensional ratio of each component may be different from an actual one. The materials, dimensions, and the like illustrated in the following description are merely examples, and the present invention is not limited thereto, and can be implemented with appropriate changes without departing from the scope of the invention.

  FIG. 1 is a diagram schematically illustrating a method for manufacturing a SiC wafer according to the present embodiment. As shown in FIG. 1, first, a seed crystal is prepared. Then, SiC is grown on the seed crystal to produce a SiC ingot. The obtained SiC ingot undergoes quality evaluation, is processed into a SiC wafer, and is shipped. Further, a part of the SiC ingot is processed into a seed crystal for producing the next SiC ingot. The manufactured SiC wafer is processed into a SiC epitaxial wafer having an epitaxial film formed on the surface and an 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 an SiC ingot. The manufacturing apparatus 100 shown in FIG. 2 is one of the SiC single crystal manufacturing apparatuses using the sublimation method. The sublimation method is a method in which a raw material gas generated by heating a raw material is recrystallized on a single crystal (seed crystal) to obtain a large single crystal (ingot).

  2 includes a crucible 10 and a coil 20. Between the crucible 10 and the coil 20, a heating element (not shown) that generates heat by induction heating of the coil 20 may be provided.

  The crucible 10 has a crystal setting part 11 provided at a position facing the raw material G. The crucible 10 may have a taper guide 12 that expands in diameter from the crystal setting part 11 toward the raw material G inside. FIG. 2 simultaneously shows the raw material G, the seed crystal 5, and the SiC ingot 6 grown from the seed crystal for easy understanding.

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

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

  FIG. 4 is a diagram schematically illustrating a method for evaluating the quality of a SiC ingot according to the present embodiment. As shown in FIG. 4, first, the tail or head of the SiC ingot is cut and obtained (step S1). As described above, the step of obtaining the head 6A or the tail 6B or the like is necessary for cutting with a multi-wire saw or the like. Therefore, by using the evaluation method, it is not necessary to newly generate an additional cutting step or to obtain an evaluation sample at the expense of a product obtaining unit.

  Next, the bending state of the atomic arrangement surface in the head 6A or the tail 6B is evaluated (FIG. 4, step S2). First, the atomic arrangement plane will be described. FIG. 5 is a schematic view of a cut surface obtained by cutting the SiC single crystal constituting 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 view of a cut surface obtained by cutting the SiC single crystal constituting 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 direction in which the carbon plane (C plane, (000-1) plane) appears when cut perpendicularly to the [000-1] direction, that is, the <0001> direction. Hereinafter, the case where the first direction and the second direction are the [1-100] direction and the [11-20] direction, respectively, will be described as an example.

  Here, the crystal orientation and the plane are indicated using the following parentheses as Miller indices. () And ｛｝ are used to represent a surface. () Is used to represent a specific plane, and ｛｝ is used to represent a generic term (collective plane) of equivalent planes due to crystal symmetry. On the other hand, <> and [] are particularly used to indicate directions. [] Is used to represent a specific direction, and <> is used to represent an equivalent direction due to crystal symmetry.

  As shown in FIGS. 5 and 6, the SiC single crystal 1 constituting 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 the cut surface of the SiC single crystal is viewed microscopically, an atomic arrangement surface 2 in which a plurality of atoms A are arranged is formed. The atom arrangement surface 2 in the cutting plane is represented 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 in the cut plane may be a convex shape or a concave shape regardless of the shape of the outermost surface of the SiC single crystal 1. The shape of the atomic arrangement plane 2 may be different depending on the cutting direction. As the shape of the atom arrangement surface 2, for example, a concave shape concave toward the center as shown in FIG. 7, a concave shape on a predetermined cut surface as shown in FIG. Saddle type).

  The shape of the atomic arrangement surface 2 can be measured by X-ray diffraction (XRD). The surface to be measured is determined according to the measurement direction. Assuming that the measurement direction is [hkill], the measurement surface needs to satisfy the relationship of (mh mk min). Here, m is an integer of 0 or more, 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 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. That is, the measurement surface may be different depending on the measurement direction, and the atom arrangement surface does not necessarily have to be the same surface. By satisfying the above relationship, it is possible to prevent the lattice curvature in the a-plane or m-plane direction, which has little influence during crystal growth, from being mistaken for the lattice curvature in the c-plane direction. For the measurement, either the C plane or the Si plane may be selected, but the measurement direction is not changed in one sample.

  The X-ray diffraction data is acquired at five points along the predetermined direction: the center, the end, and the midpoint between the center and the end. When the atomic arrangement surface 2 is curved, the reflection direction of the X-ray changes, so that the position of the ω angle of the peak of the X-ray diffraction image output at the center and other portions changes. The bending direction of the atomic arrangement surface 2 can be obtained from the position fluctuation of the diffraction peak. Further, the radius of curvature of the atomic arrangement surface 2 can be obtained from the position fluctuation of the diffraction peak, and the amount of curvature of the atomic arrangement surface 2 can also be obtained.

(Specific description of the method of measuring the bending direction and amount of bending of the atomic arrangement surface)
A method for measuring a bending direction and a bending amount of an atomic arrangement surface from a measured value of XRD of an outer peripheral end portion of a sample (hereinafter, referred to as a wafer 20) obtained by slicing a part of a SiC single crystal (ingot) will be specifically described. .

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

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

  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 circles C that are in contact with two measured atomic arrangement surfaces, assuming that the curved surface of the atomic arrangement surface 22 of the wafer 20 is a part of a circle. From FIG. 11, geometrically, the center angle φ of the sector including the arc having the contact at both ends becomes 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 is obtained by the following relational expression.

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

  As described above, R can be measured only from the measured values at both outer ends of the XRD wafer 20. On the other hand, when this method is used, there is a possibility that the shape may be mistaken when local distortion or the like exists at the measurement location. Therefore, the X-ray diffraction peak angles are measured at a plurality of locations, and the curvature per unit length is converted from the following equation.

FIG. 13 shows an example in which the radius of curvature of the atomic arrangement surface is determined from a plurality of XRD measurement points. The horizontal axis in FIG. 13 is the relative position from the wafer center, and the vertical axis is the relative diffraction peak angle of each measurement point with respect 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 surface is set to (3-3016). The measurement was performed at five places. The five points are substantially arranged in a straight line, and dθ / dr = 8.69 × 10 ⁻⁴ deg / mm is obtained from the inclination. By applying this result to the above equation, it can be calculated that the concave surface is R = 66 m. Then, from this R and the radius r (75 mm) of the wafer, the amount of curvature d of the atomic arrangement surface is determined to be 42.6 μm.

  So far, an example has been described in which the shape of the atomic arrangement surface is a concave surface. In the case of a convex surface, R is calculated as minus.

(Explanation of another measurement method of the bending direction and bending amount of the atomic arrangement surface)
The bending direction and the bending amount of the atomic arrangement surface may be obtained by another method. FIG. 14 schematically shows a cut surface cut along a direction of measurement of the atomic arrangement plane, for example, along the [1-100] direction, passing through the center in plan view. FIG. 9 illustrates an example in which the shape of the lattice array surface 22 is concavely curved.

  As shown in FIG. 14, the diffraction peaks of the X-ray diffraction are measured at two positions, that is, the center of the wafer 20 and a position that is separated from the center of the wafer 20 by a distance x. From the symmetry of the manufacturing conditions of the ingot, it is possible to assume that the shape of the wafer 20 is bilaterally symmetric as an approximation, and that the atomic arrangement surface 22 is flat at the center of the wafer 20. Therefore, assuming that the difference between the inclinations of the atomic arrangement surface 22 at two points measured as shown in FIG. 15 is Δθ, the relative position y of the atomic arrangement surface 22 can be expressed by the following equation.

By changing the position of the distance x from the center and measuring a plurality of points, it is possible to obtain the relative atomic position of the atom arrangement surface 22 at the wafer center and the measurement point at each point.
In this method, the relative positions of the atoms on the atomic arrangement plane are obtained at each measurement point. Therefore, the relative atomic positions of the atomic arrangement surface 22 in the entire wafer 20 can be shown as a graph, which is useful for intuitively grasping the arrangement of the atomic arrangement surface 22.

  On the other hand, since the measurement at each point is based on the measurement value at one point, a position (particularly near one end of the wafer) that is difficult to measure partially may occur depending on diffraction conditions. In some cases, if there is a portion having poor crystallinity, an error may easily be included. Therefore, in the current measurement technology, this method is used to obtain a reference value for intuitively grasping the arrangement of the atomic arrangement planes, rather than using the method for measuring the magnitude of the warpage of the atomic arrangement planes 22. Is preferred.

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

  The curved state of the atomic arrangement surface 2 functions as one index of quality. The curved state of the atomic arrangement plane includes a first direction passing through the center in plan view along the <1-100> direction, and a first direction perpendicular to the first direction passing through the center of the SiC single crystal in plan view along the <11-20> direction. Evaluation is made in at least two directions, namely, two directions.

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

  When evaluating from the bending direction of the atomic arrangement surface 2, whether the bending direction of the atomic arrangement surface 2 measured along the first direction matches the bending direction of the atomic arrangement surface 2 measured along the second direction. Determine whether or not. The bending direction in each direction can be obtained by the method described above. For example, the atomic arrangement surface 2 in the embodiment shown in FIG. 7 has a concave shape depressed in the first direction and the second direction in a direction opposite to the stacking direction, and has the same curved direction. On the other hand, the atomic arrangement surface 2 in the embodiment shown in FIG. 8 has a convex shape protruding in the first direction in the laminating direction and a concave shape concave in the opposite direction to the laminating 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 part where the crystal growth is performed using the SiC single crystal as a seed crystal becomes low. Although the reason is not clear, if the atomic arrangement surface 2 bends in two different directions, the atomic arrangement surface 2 is distorted (see FIG. 8). When the atomic arrangement surface 2 is distorted, stress is generated in a plurality of directions when a temperature change occurs, and the atomic arrangement surface 2 is likely to be distorted. It is considered that the strain on the atomic arrangement plane 2 induces the slip of the crystal plane, and may cause BPD.

  That is, when the bending direction of the atomic arrangement surface 2 measured along the first direction coincides with the curving direction of the atomic arrangement surface 2 measured along the second direction, under appropriate conditions where BPD does not easily occur. It can be determined that the SiC ingot has been manufactured. That is, based on the result, the cutting condition of the SiC wafer or the growth condition of the next SiC ingot can be set. If the SiC ingot can be manufactured under appropriate conditions, the next manufacturing conditions are made similar to the current manufacturing conditions. The conditions for cutting the SiC wafer may be adjusted so as to increase the number of acquired high-quality SiC wafers, or may be adjusted so as to increase the number of acquired high-quality seed crystals.

  When a higher quality SiC wafer 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 if the bending directions of the cut surfaces cut along the six directions symmetric with respect to the center are the same, a high-quality SiC wafer that hardly generates distortion and hardly generates BPD can be obtained.

  On the other hand, when evaluating from the amount of curvature of the atomic arrangement surface 2, the amount of curvature d1 of the atomic arrangement surface 2 measured along the first direction (see FIG. 5) and the amount of atomic arrangement surface measured along the second direction The determination is made based on the magnitude of the difference from the second bending amount d2 (see FIG. 6). The amount of bending in each direction can be obtained by the above-described method. Here, the amount of curvature of the atomic arrangement plane 2 means the difference between the atomic position at the center of the SiC single crystal 1 in plan view and the atomic position at the end of the SiC single crystal 1. The amount of curvature when the atomic arrangement surface 2 is concave toward the center is positive, and the amount of curvature when the atomic arrangement surface 2 is convex toward the center is negative.

  FIG. 16 is a diagram showing a relationship between BPD densities contained in a crystal growth portion when a single crystal is grown on a predetermined SiC single crystal. FIG. 16A is a diagram illustrating a relationship between the absolute value of the amount of curvature d1 of the atomic arrangement surface 2 measured along the first direction and the BPD density included in the crystal growth part. FIG. 16B is a diagram showing the relationship between the absolute value of the amount of curvature d2 of the atomic arrangement plane 2 measured in the second direction and the density of the BPD contained in the crystal growth part. FIG. 16C is a diagram illustrating the relative values of the amount of curvature d1 and the amount of curvature d2 and the density of the BPD included in the crystal growth part.

  The SiC single crystal shown in FIG. 16 was produced by a sublimation method. The diameter of the seed crystal was 16 cm. On the seed crystal, a SiC single crystal was grown by about 20 mm. BPD density was determined using KOH etching.

  As shown in FIGS. 16A and 16B, no correlation is confirmed between the bending amounts d1 and d2 and the BPD. Therefore, the frequency of occurrence of BPD does not necessarily decrease when using an SiC single crystal having small absolute values of the bending amounts d1 and d2. That is, the absolute values of the bending amounts d1 and d2 do not sufficiently function as an index of the BPD density.

  On the other hand, as shown in FIG. 16C, there is a correlation between the relative value of the amount of bending d1 and the amount of bending d2 and the BPD. When the relative value between 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 density of BPD 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 where BPD is unlikely to occur.

  The above-mentioned relationship is found between the relative value of the amount of curvature d1 and the amount of curvature d2 and the density of the BPD for the following reasons. A small value of the relative value between the bending amount d1 and the bending amount 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 surface 2 has a shape that is greatly bent in a predetermined direction. When the shape of the atomic arrangement surface 2 has a large anisotropy in a predetermined direction, when a temperature change occurs, stress concentration tends to occur in that direction. The stress concentration induces the slip of the crystal plane and may cause BPD.

  Note that, as shown in FIG. 8, in the case of a potato chips type in which the bending direction of the atomic arrangement surface 2 is different between the first direction and the second direction, the bending amount d1 shows a negative value, and the bending amount d2 shows a positive value. Therefore, for example, if the bending amount d1 is -α and the bending amount d2 is β, the absolute value of these differences is α + β, and the difference between the bending amounts d1 and d2 is necessarily large.

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

  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 value of the bending amount in the six directions is measured. It is preferable to evaluate the difference between the minimum values. The crystal structure of SiC single crystal 1 is hexagonal. Therefore, if the amount of curvature of the atomic arrangement plane measured along the six directions symmetric with respect to the center is small, the atomic arrangement plane 2 is less likely to have anisotropy, and a high-quality SiC wafer in which BPD is less likely to be generated. can get.

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

  FIG. 17 shows the results of measuring the shapes of the atomic arrangement planes of the head 6A and the tail 6B of the SiC ingot. The total growth amount of this ingot was 28 mm, and the tail 6B and the 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] when the counterclockwise direction is defined as positive and the measurement direction, and the vertical axis represents the amount of lattice bending. That is, 90 ° and −90 ° in this drawing represent the same [1-100] direction.

  The most concave direction of the head 6A is a direction forming 30 ° with respect to [11-20], the amount of bending is 25.0 μm, and the most convex direction is [11-20]. On the other hand, in the direction forming -60 °, the amount of bending is -2.5 μm. The most concave direction in the tail 6B is a direction of 30 ° with respect to [11-20], the amount of bending is 21.4 μm, and the most convex direction is with respect to [11-20]. In the direction forming −60 °, the amount of bending is −2.5 μm. That is, it can be said that there is no significant difference in the shape and the amount of curvature of the atomic arrangement surface 2 in the SiC ingot from the tail portion at the early growth stage to the head portion at the late growth stage. Therefore, it is possible to grasp the lattice curvature of the entire SiC ingot by measuring the lattice curvature amount at any one position in the stacking direction of the manufactured SiC ingot.

  In this evaluation, it is possible to directly evaluate the cut surface cut out by a wire saw or the like, and it is not necessary to polish the measurement surface. In addition, since the evaluation can be performed at an arbitrary position cut out in a normal cutting step, it is not necessary to add a new processing step in implementing the present invention. In addition, since the atomic arrangement plane can be easily measured by X-ray diffraction (XRD), it can be confirmed in about several hours. That is, if the method for evaluating a SiC single crystal according to the present embodiment is used, it is possible to easily determine whether the SiC ingot is good or bad. Further, the evaluation result can be promptly fed back to the next SiC ingot manufacturing condition and the SiC wafer slicing method, and the time required for manufacturing the SiC wafer can be greatly reduced.

  FIG. 18 is a diagram schematically showing a conventional method for evaluating the quality of a SiC ingot. As shown in FIG. 18, the conventional SiC ingot first obtains an evaluation wafer (step S11), and processes it so that the evaluation wafer can be used for evaluation (step S12). Thereafter, the presence or absence of stacking faults and dislocation concentrated portions is confirmed by an X-ray topograph (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 condition and the SiC wafer slicing method are determined.

  Processing of the wafer for evaluation, KOH etching and counting of the number of defects take time, and it takes several weeks to several months to check the 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 to manufacture the SiC wafer increases. The next ingot can be manufactured without waiting for the feedback of the quality evaluation.However, if there is an abnormality in the quality due to deviation of the manufacturing conditions, etc. Since no abnormality can be detected, adjustment of manufacturing conditions and the like cannot be performed. As a result, there is a risk that a defective ingot may be continuously produced during that time, which is not preferable.

  As described above, by using the method for evaluating a SiC single crystal according to the present embodiment, the quality of the SiC single crystal can be easily measured. In addition, the curved state of the atomic arrangement surface functions as an index of BPD generation, and a SiC single crystal in which BPD is unlikely to be generated can be easily determined.

  As described above, the preferred embodiments of the present invention have been described in detail, but the present invention is not limited to the specific embodiments, and various modifications may be made within the scope of the present invention described in the appended claims. Can be modified and changed.

DESCRIPTION OF SYMBOLS 1 ... SiC single crystal, 2 ... Atomic arrangement plane, 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 (6)

  A first direction passing through the center of the SiC single crystal in plan view and along the <1-100> direction, and a second direction perpendicular to the first direction and passing through the center of the SiC single crystal in plan view and along the <11-20> direction A method for evaluating a SiC single crystal, which evaluates a curved state of an atomic arrangement plane in at least two directions.   2. The method for evaluating a SiC single crystal according to claim 1, wherein the state of curvature of the atomic arrangement plane is evaluated in at least six directions rotated by 30 ° with respect to the first direction. 3.   3. The method for evaluating a SiC single crystal according to claim 1, wherein the bending state of the atomic arrangement surface is evaluated based on whether or not a bending direction of the atomic arrangement surface in a measurement direction matches.   The method for evaluating a SiC single crystal according to any one of claims 1 to 3, wherein a bending state of the atomic arrangement surface is evaluated from a difference between a maximum value and a minimum value of the amount of curvature of the atomic arrangement surface in a measurement direction. .   The method for evaluating a SiC single crystal according to any one of claims 1 to 4, wherein the bending state of the atomic arrangement surface is evaluated by X-ray diffraction.   A method for manufacturing a SiC wafer, comprising: determining a method for slicing an SiC ingot or a growth condition for a next SiC single crystal based on an evaluation result obtained by the method for evaluating a SiC single crystal according to claim 1.

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