JP7433586B2 - SiC single crystal processing method, SiC ingot manufacturing method, and SiC single crystal - Google Patents

Description

The present invention relates to a method for processing a SiC single crystal, a method for manufacturing a SiC ingot, and a SiC single crystal.

Silicon carbide (SiC) has a dielectric breakdown field one order of magnitude larger and a band gap three times larger than silicon (Si). Furthermore, silicon carbide (SiC) has a thermal conductivity that is approximately 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.

BACKGROUND ART SiC epitaxial wafers, in which an epitaxial film is formed on a SiC wafer, are used for devices such as semiconductors. An epitaxial film formed on a SiC wafer by chemical vapor deposition (CVD) becomes an active region of a SiC semiconductor device.

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

For example, Patent Document 1 and Patent Document 2 disclose that by controlling the warpage and waviness of the external shape of a SiC single crystal used as a seed crystal, SiC ingots and SiC wafers obtained from this seed crystal can be produced with high quality. It is stated that it will be.

Japanese Patent Application Publication No. 2015-117143 Patent No. 4494856

One of the killer defects of SiC wafers is basal plane dislocation (BPD). A part of the BPD of the SiC wafer is carried over to the SiC epitaxial wafer, and becomes a factor in deterioration of forward characteristics when current is passed in the forward direction of the device. BPD is a defect that is thought to be caused by slippage occurring at the basal surface.

As described in Patent Documents 1 and 2, BPD cannot be sufficiently suppressed even if the warpage and waviness of the external shape of the SiC single crystal used as a seed crystal are controlled. Therefore, reduction of BPD is required.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for processing a SiC single crystal that can reduce the curvature of the atomic arrangement plane during crystal growth.

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

(1) The method for processing a SiC single crystal according to the first aspect includes changing the shape of the atomic arrangement plane of the SiC single crystal at least in a first direction passing through the center in plan view and in a second direction orthogonal to the first direction. a processing step of processing at least a first surface of the SiC single crystal along the atomic arrangement plane based on the measurement results; and a pasting step of pasting the single crystal onto the installation surface.

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

(3) In the processing step of the SiC single crystal processing method according to the above aspect, the SiC single crystal is vacuum-adsorbed to adsorption surfaces having different adsorption forces depending on the amount of curvature of the atomic arrangement surface, and the atomic arrangement surface is The method may include a vacuum suction step for flattening the SiC single crystal, and a surface leveling step for cutting or grinding the SiC single crystal along the flattened atomic arrangement plane.

(4) In the processing step of the SiC single crystal processing method according to the above aspect, the SiC single crystal is brought close to an electrode having a shape corresponding to the atomic arrangement plane, and the first surface of the SiC single crystal is processed by electric discharge. It may also include an electrical discharge machining step.

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

(6) In the pasting step of the SiC single crystal processing method according to the above aspect, if the first surface is curved convexly toward the installation surface, the load on the outer peripheral side of the SiC single crystal is stronger than the inside. However, when the first surface is curved concavely toward the installation surface, the load on the inside of the SiC single crystal may be stronger than on the outer peripheral side.

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

(8) In the method for manufacturing a SiC ingot according to the second aspect, in the method for processing a SiC single crystal according to the above aspect, 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 value of the amount of curvature of the atomic arrangement plane is 20 μm or more, and the amount of curvature of the SiC single crystal and the amount of curvature of the atomic arrangement plane are The absolute value of the difference is 10 μm or less.

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

FIG. 2 is a schematic diagram of a cross section of a SiC single crystal cut along a straight line extending in a first direction passing through the center in plan view. FIG. 2 is a diagram schematically showing an example of an atomic arrangement plane of a SiC single crystal. FIG. 3 is a diagram schematically showing another example of an atomic arrangement plane of a SiC single crystal. FIG. 3 is a diagram for specifically explaining a method of measuring the shape of an atomic arrangement surface. FIG. 3 is a diagram for specifically explaining a method of measuring the shape of an atomic arrangement surface. FIG. 3 is a diagram for specifically explaining a method of measuring the shape of an atomic arrangement surface. FIG. 3 is a diagram for specifically explaining a method of measuring the shape of an atomic arrangement surface. An example will be shown in which the radius of curvature of the atomic arrangement surface was determined from a plurality of XRD measurement points. FIG. 7 is a diagram for specifically explaining another example of a method for measuring the shape of an atomic arrangement surface. FIG. 7 is a diagram for specifically explaining another example of a method for measuring the shape of an atomic arrangement surface. FIG. 3 is a schematic diagram for explaining a first processing method. FIG. 3 is a schematic plan view of the suction surface. FIG. 7 is a schematic diagram for explaining a third processing method. FIG. 3 is a schematic diagram for explaining a pasting process. 1 is a schematic diagram of an example of a manufacturing apparatus used in a sublimation method. It 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.

Hereinafter, this embodiment will be described in detail with reference to the drawings as appropriate. The drawings used in the following description may show characteristic parts enlarged for convenience, and the dimensional ratio of each component may differ from the actual one. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and can be practiced with appropriate changes within the scope of the invention.

"SiC single crystal processing method"
The SiC single crystal processing method according to this embodiment includes a measurement step, a processing step, and a pasting step. In the measurement step, the shape of the atomic arrangement plane of the SiC single crystal is measured along at least a first direction passing through the center in plan view and a second direction orthogonal to the first direction. In the processing step, at least the first surface of the SiC single crystal is processed along the atomic arrangement plane based on the measurement results. Further, in the attaching step, the SiC single crystal is attached to the installation surface with the first surface of the SiC single crystal as the attaching surface. Each step will be specifically explained below.

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

Here, the crystal orientation and plane are expressed using the following parentheses as Miller indices. () and {} are used to represent faces. () is used to represent a specific surface, and {} is used to represent a generic term for equivalent surfaces (collective surface) due to the symmetry of the crystal. 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 the symmetry of the crystal.

As shown in FIG. 1, a SiC single crystal 1 is a single crystal in which a plurality of atoms A are aligned. Therefore, as shown in FIG. 1, when looking microscopically at a cut surface of a 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 cut surface is expressed as a line extending in a direction substantially 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 plane, regardless of the shape of the outermost surface of the SiC single crystal 1. 2 and 3 are diagrams schematically showing the shape of the atomic arrangement plane 2. FIG. The atomic arrangement surface 2 shown in FIG. 2 has a concave shape toward the center. Therefore, the atomic arrangement plane 2 shown in FIG. 2 has the same curved direction in the [1-100] direction and in the [11-20] direction orthogonal to the [1-100] direction. On the other hand, the atomic arrangement surface 2 shown in FIG. 3 has a potato chip-shaped (saddle-shaped) shape that is concave at a predetermined cut plane and convex at a different cut plane. Therefore, the atomic arrangement plane 2 shown in FIG. 3 has different curve directions in the [1-100] direction and in the [11-20] direction orthogonal to the [1-100] direction.

In other words, in order to accurately grasp the shape of the atomic arrangement plane 2, it is necessary to examine the atomic arrangement plane of the SiC single crystal along at least two directions (first direction and second direction) passing through the center in plan view and orthogonal to each other. It is necessary to measure the shape of 2. Further, the crystal structure of the SiC single crystal 1 is hexagonal, and it is preferable to measure the shape of the atomic arrangement plane 2 along six directions symmetrical about the center. By measuring the shape of the atomic arrangement surface 2 along six directions 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 surface to be measured is determined depending on the direction of measurement. When the measurement direction is [hkil], the measurement surface needs to 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, the (22-416) plane is selected with m=2 and n=16, etc. On the other hand, when measuring in the [11-20] direction, the (0004) plane is selected with m=0 and n=4, the (3-3016) plane is selected with m=3 and n=16, etc. That is, the measurement plane may be a different plane 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 lattice curvature in the a-plane or m-plane direction, which has little effect on crystal growth, from being mistaken as lattice curvature in the c-plane direction. Further, the measurement may be performed on either the C surface or the Si surface, 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 predetermined direction: the center, the ends, and the midpoint between the center and the ends. When the atomic arrangement surface 2 is curved, the direction of reflection of X-rays changes, so the ω-angle position of the peak of the output X-ray diffraction image varies between the center and other parts. The direction of curvature of the atomic arrangement plane 2 can be determined from the variation in the position of this diffraction peak. Furthermore, the radius of curvature of the atomic array surface 2 can also be determined from the positional variation of the diffraction peak, and the amount of curvature of the atomic array surface 2 can also be determined. Then, the shape of the atomic arrangement surface 2 can be determined from the direction of curvature and the amount of curvature of the atomic arrangement surface 2.

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

FIG. 4 schematically shows a cut plane cut along the measurement direction of the atomic arrangement plane, for example, the [1-100] direction, passing through the center in plan view. If the radius of the wafer 20 is r, then the lateral length of the cross section is 2r. FIG. 4 also shows the shape of the atomic arrangement surface 22 in the wafer 20. As shown in FIG. 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 FIG. 4 is bilaterally symmetrical and curved in a concave shape. This symmetry is due to the fact that the SiC single crystal (ingot) manufacturing conditions are usually symmetrical about the center. Note that this symmetry does not necessarily have to be complete symmetry, but means symmetry as an approximation that allows for fluctuations due to fluctuations in manufacturing conditions, etc.

Next, as shown in FIG. 5, XRD is performed on both outer circumferential ends of the wafer 20, and the difference Δθ in the X-ray diffraction peak angle between the two measured points is determined. This Δθ is the difference in inclination of the two measured atomic arrangement planes 22. As the diffraction surface used for X-ray diffraction measurement, an appropriate surface is selected according to the cutting surface as described above.

Next, as shown in FIG. 6, the radius of curvature of the curved atomic arrangement surface 22 is determined from the obtained Δθ. FIG. 6 shows a circle C that is in contact with the 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. Geometrically, it can be seen from FIG. 6 that the central angle φ of the sector-shaped arc including the arc having both ends at the contact 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 circular arc. The radius R of the circular arc is determined by the following relational expression.

Then, the amount of curvature d of the atomic arrangement surface 22 is determined from the radius R of this circular 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 a 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 from the Pythagorean theorem, and the following formula holds true. In this specification, the amount of curvature d when the radius of curvature is positive (concave surface) is defined as a positive value, and the amount of curvature d when the radius of curvature is negative (convex surface) is defined as a negative value.

As mentioned above, R can also be measured only from the XRD measurements of both outer edges of the wafer 20. On the other hand, when this method is used, there is a possibility that the shape may be misjudged if there is local distortion or the like at the measurement location. Therefore, the X-ray diffraction peak angles are measured at multiple locations, and the curvature per unit length is calculated using the following formula.

FIG. 8 shows an example in which the radius of curvature of the atomic arrangement surface was determined from a plurality of XRD measurement points. The horizontal axis in FIG. 8 represents the relative position from the wafer center, and the vertical axis represents the relative diffraction peak angle of each measurement point with respect to the wafer center diffraction peak angle. FIG. 8 is an example in which the measurement is performed in the [1-100] direction of the wafer, and the measurement surface is set to (3-3016). Measurements were taken at five locations. The five points are almost lined up in a straight line, and from this slope, dθ/dr=8.69×10 ⁻⁴ deg/mm can be determined. By applying this result to the above equation, it can be calculated that the concave surface has 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 found to be 42.6 μm.

Up to this point, the example in which the shape of the atomic arrangement surface is a concave surface has been described, but the calculation can be made in the same way when the shape is a convex surface. In the case of a convex surface, R is calculated as a negative value.

(Explanation of another method for measuring the shape of the atomic arrangement surface (method 2))
The shape of the atomic arrangement surface may be determined by another method. FIG. 9 schematically shows a cut plane cut along the measurement direction of the atomic arrangement plane, for example, the [1-100] direction, passing through the center in plan view. In FIG. 9, an example will be explained in which the shape of the atomic arrangement surface 22 is concavely curved.

As shown in FIG. 9, the diffraction peaks of X-ray diffraction 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 approximated to be bilaterally symmetrical, and it can be assumed that the atomic arrangement plane 22 is flat at the center of the wafer 20. Therefore, if the difference in the inclination of the atomic arrangement plane 22 at two points measured as shown in FIG. 10 is Δθ, the relative position y of the atomic arrangement plane 22 can be expressed by the following formula.

By performing measurements at a plurality of locations while varying the distance x from the center, the relative atomic positions of the atomic array surface 22 between the wafer center and the measurement point can be determined at each point.
In this method, the relative positions of atoms on the atomic arrangement plane are determined at each measurement location. Therefore, the amount of curvature of the local atomic arrangement plane can be determined. Furthermore, 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 understanding the arrangement of the atomic arrangement surface 22.

Here, the case where the measurement target is the wafer 20 has been explained as an example. Even when the measurement target is a SiC ingot or a cut body cut from a SiC ingot, the amount of curvature of the atomic arrangement plane can be similarly determined.

According to the above-described procedure, the amount of curvature of the atomic arrangement plane 2 of the SiC single crystal is measured at least along two directions (first direction and second direction) that pass through the center in plan view and are perpendicular to each other. By determining the amount of curvature and the direction of curvature in each direction, the approximate shape of the atomic arrangement surface 2 as shown in FIGS. 2 and 3 can be determined.

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

(First processing method)
The first processing method includes a flattening process in which a SiC single crystal is attached to a spacer having a curved surface that curves in the opposite direction to the curved direction of the atomic arrangement surface, and the atomic arrangement surface 2 is flattened; and a surface-leveling step of cutting or grinding the SiC single crystal along the surface 2. When using the first processing method, it is preferable that the thickness of the SiC single crystal is 5 mm or less so that it can be elastically deformed.

FIG. 11 is a schematic diagram for explaining the first processing method. As shown in FIG. 11(a), a spacer 30 and a support base 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 curve direction of the atomic arrangement surface 2.

The second surface 30B of the spacer 30 may be processed after measuring the shape of the atomic arrangement surface 2 of the SiC single crystal 1, or by preparing a plurality of spacers with different curved directions and amounts in advance. , the one that can most flatten the atomic arrangement surface 2 after pasting may be selected from among them.

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

Next, as shown in FIG. 11(b), the spacer 30 is placed on the support stand 31, and the SiC single crystal 1 is bonded to the second surface 30B of the spacer 30. The SiC single crystals 1 are bonded together so that the direction of curvature of the atomic arrangement plane 2 is opposite to the direction of curvature of the second surface 30B. The bonding is performed using an adhesive, for example. As the adhesive, a thermoplastic resin-based solid wax commonly used in precision processing can be used, and it is preferable to select one with strong adhesive strength. Even if the SiC single crystal is elastically deformed with an adhesive and fixed to the support base 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 flattened compared to 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 base 31.

Next, as shown in FIG. 11(c), the SiC single crystal 1 is cut. The cut surface is parallel to the surface of the support base 31. Since the atomic arrangement plane 2 is flattened with respect to the surface of the support stand 31, when cut parallel to the surface of the support stand 31, the SiC single crystal 1 will inevitably be cut along the flattened atomic arrangement plane 2. disconnected. For example, a wire saw or the like can be used for cutting. Further, in the surface leveling process, the surface level of the atomic arrangement surface 2 may be leveled 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 to the support base 31.

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

(Second processing method)
The second processing method consists of a vacuum adsorption step in which the SiC single crystal 1 is vacuum-adsorbed to an adsorption surface with different adsorption forces depending on the amount of curvature of the atomic arrangement surface 2, and the atomic arrangement surface 2 is flattened; It includes a surface-leveling step of cutting or grinding the SiC single crystal along the array plane 2. The second processing method differs from the first processing method in that the atomic arrangement surface 2 is flattened by the difference in strength of adsorption force without using the spacer 30. The other processing steps are the same and will not be explained here. Even when using the second processing method, it is preferable that the thickness of the SiC single crystal is 5 mm or less so that it can be elastically deformed.

FIG. 12 is a schematic plan view of the suction surface 40. The suction surface 40 includes a plurality of suction holes 41 . In the second processing method, the atomic arrangement surface 2 is flattened by the difference in the adsorption force of these adsorption holes 41.

For example, as shown in FIG. 2, when the atomic arrangement plane 2 of the SiC single crystal 1 is concave toward the center, the suction force of the suction hole 41I is made smaller than the suction force of the other suction holes 41A to 41H. Then, the outer circumferential side of the atomic array surface 2 is attracted relatively more strongly than the inner side, and the atomic array surface 2 is flattened. For example, as shown in FIG. 3, when the atomic arrangement plane 2 of the SiC single crystal 1 has a saddle shape in which the curvature directions are different in the [1-100] direction and the [11-20] direction, the [11-20] ] The suction force is increased as the position of the suction hole 41 is further away from the central axis in the direction. 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, by using the difference in the adsorption force of the adsorption holes 41, the atomic arrangement surface 2 can be flattened. Then, the SiC single crystal 1 whose atomic arrangement plane 2 has been flattened is cut parallel to the installation plane as in FIGS. 11(c) and 11(d). By going through the above-described process, a SiC single crystal 10 whose first surface 10A is along the atomic arrangement plane 2 is obtained.

(Third processing method)
The third machining method includes an electrical discharge machining step in which the SiC single crystal 1 is brought close to an electrode having a shape corresponding to the atomic arrangement plane 2, and the first surface 1A of the SiC single crystal 1 is machined by electric discharge. When using the third processing method, unlike the first processing method and the second processing method, the thickness of the SiC single crystal 1 does not matter.

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

The first surface 50A of the electrode 50 may be processed after measuring the shape of the atomic arrangement surface 2 of the SiC single crystal 1, or by preparing a plurality of electrodes with different bending directions and amounts in advance. , the one closest to the shape of the atomic arrangement surface 2 may be selected from among them.

Next, the electrode 50 is brought close to the SiC single crystal 1 with the first surface 50A of the electrode 50 facing the SiC single crystal 1. The shorter 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 whose first surface 10A is along the atomic arrangement plane 2 is obtained.

<Application process>
FIG. 14 is a schematic diagram for explaining the pasting process. As shown in FIG. 14(a), in the attaching step, the SiC single crystal 10 is attached to the installation surface 60A of the installation stand 60, using the first surface 10A of the SiC single crystal 10 obtained by processing as the attachment surface. The installation stand 60 corresponds to, for example, a single crystal installation part of a crucible.

The thickness of the SiC single crystal 10 during the pasting process is preferably 5 mm or less. If the SiC single crystal 10 is thick, it is difficult to bend when pasting it, making it difficult to stick it flat to the pedestal, and it may be difficult to arrange the atomic arrangement plane (lattice plane) of the SiC single crystal flatly.

Moreover, in the pasting process, it is preferable that the load for pressing the SiC single crystal 10 against the installation surface 60A is changed depending on the amount of curvature of the first surface 10A with respect to the installation surface 60A. For example, when the first surface 10A of the SiC single crystal 10 is curved convexly toward the installation surface 60A, it is preferable to make the load on the outer peripheral side of the SiC single crystal 1 stronger than on the inside. Further, when the first surface 10A of the SiC single crystal 10 is curved concavely toward the installation surface 60A, it is preferable to make the load on the inside of the SiC single crystal 10 stronger than on the outer peripheral side.

Further, the pasting step is performed using an adhesive, for example. A thermosetting resin or the like can be used as the adhesive.

In addition, during the pasting process, before the adhesive is cured, a depressurization process of reducing the pressure around the SiC single crystal 10 may be further performed. Even if air bubbles are trapped on the adhesive surface, they can be removed by creating a reduced pressure environment. As a result, it is possible to further suppress uneven thickness of the adhesive during application.

Further, it is preferable that the thermal expansion coefficient of the mounting base 60 to be attached is close to that of the SiC single crystal 10. Specifically, it is preferable that the difference in thermal expansion coefficient is 0.3×10 ⁻⁶ /° C. or less. Note that the thermal expansion coefficient shown here means a thermal expansion coefficient in a temperature range in which crystal growth is performed 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 manufacturing conditions, contained materials, etc. Since the difference in thermal expansion coefficient between the installation table 60 and the SiC single crystal 10 is close, it is possible to prevent the SiC single crystal 10 from warping and the atomic arrangement plane 2 from curving due to the difference in thermal expansion coefficient during single crystal growth.

Then, by performing the pasting process as described above, a SiC single crystal 10 with little curvature in which the atomic arrangement plane 2 is parallel to the installation surface 60A, as shown in FIG. 14(b), is obtained.

"SiC single crystal"
The SiC single crystal that has been processed up to the stage before the above-mentioned pasting process is processed into a shape in which the first surface follows the curve of the atomic arrangement plane. 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 curved shape of the atomic arrangement plane 2 become approximately parallel. In other words, the absolute value of the difference between the amount of warpage of SiC single crystal 10 and the amount of curvature of atomic arrangement plane 2 is 10 μm or less. Here, the "amount of warpage" 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 mounted 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, the warped shape of the first surface 10A of the SiC single crystal 10 and the curvature of the atomic arrangement surface 2 are obtained without performing the above-mentioned processing. It is difficult to imagine that the shapes will be approximately parallel. In other words, the SiC single crystal 10 in which the maximum value of the amount of curvature of the atomic arrangement plane is 20 μm or more and the absolute value of the difference between the amount of warpage of the SiC single crystal 10 and the amount of curvature of the atomic arrangement plane 2 is 10 μm or less is as described above. This can be achieved through the following steps.

“SiC ingot manufacturing method”
In the SiC ingot manufacturing method according to the present embodiment, crystal growth is performed using the SiC single crystal 10 attached to the installation surface 60A as a seed crystal in the above-described SiC single crystal processing method. A SiC ingot can be manufactured using, for example, a sublimation method. The sublimation method is a method of recrystallizing raw material gas generated by heating the raw material on a single crystal (seed crystal) to obtain a large single crystal (ingot).

FIG. 15 is a schematic diagram of an example of a manufacturing apparatus used in the sublimation method. Manufacturing apparatus 200 includes a crucible 100 and a coil 101. A heating element (not shown) that generates heat by induction heating of the coil 101 may be provided between the crucible 100 and the coil 101.

The crucible 100 has an installation stand 60 provided at a position facing the raw material G. A SiC single crystal 10 processed by the above-described SiC single crystal processing method is attached to the installation stand 60 as a seed crystal. Further, inside the crucible 100, a taper guide 102 whose diameter increases toward the raw material G from the installation table 60 is provided.

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 installed on the installation table 60 along the taper guide 102. By supplying the raw material gas to the SiC single crystal 10, a SiC ingot I is crystal-grown on the main surface of the SiC single crystal 10. The crystal growth plane of the SiC single crystal 10 is preferably a carbon plane or a plane having an off angle of 10° or less from the carbon plane.

SiC ingot I inherits much of the crystal information of SiC single crystal 10. Since the atomic arrangement plane 2 of the SiC single crystal 10 is flattened, the occurrence of BPD within the SiC ingot I can be suppressed.

FIG. 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 FIG. 16, the radius of curvature of the atomic arrangement plane 2 and the BPD density within the SiC ingot I have a corresponding relationship. The larger the radius of curvature of the atomic arrangement surface 2 (the smaller the amount of curvature of the atomic arrangement surface 2), the lower the BPD density tends to be. It is thought that a crystal in which stress remains inside induces crystal plane slippage, causing BPD to occur and curving the atomic arrangement plane 2. Alternatively, conversely, the atomic arrangement surface 2 having a large amount of curvature may have distortion, which may cause BPD. In either case, the larger the radius of curvature of the atomic arrangement surface (that is, the smaller the amount of curvature of the atomic arrangement surface), the smaller the BPD density becomes.

As described above, in the method for manufacturing a SiC ingot according to the present embodiment, since the atomic arrangement plane 2 of the SiC single crystal 10 used as a seed crystal is flattened, the occurrence of BPD in the SiC ingot I is suppressed. has been done. Therefore, a high quality SiC ingot I with low BPD density can be obtained.

Finally, the obtained SiC ingot I is sliced to produce a SiC wafer. The cutting direction is perpendicular to <0001> or at an off angle of 0 to 10 degrees to create a wafer with a surface parallel to the C plane or at an angle of 0 to 10 degrees from the C plane. do. The surface of the wafer may be mirror-finished on the (0001) side, that is, on the Si side. The Si plane is the plane on which epitaxial growth is normally performed. Since SiC ingot I has less BPD, it is possible to obtain a SiC wafer with less BPD. By using a SiC wafer with less BPD, which is a killer defect, a high quality SiC epitaxial wafer can be obtained and the yield of SiC devices can be increased.

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

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications may be made within the scope of the gist of the present invention described within the scope of the claims. It is possible to transform and change.

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 stand 40 Adsorption surface 41 Adsorption hole 50 Electrode 50A First surface 60 Installation stand 60A Installation surface 100 Crucible 101 Coil 102 Taper guide A Atom I SiC ingot G Raw material

Claims (7)

a measuring step of measuring the shape of the atomic arrangement plane of the SiC single crystal along at least a first direction passing through the center in plan view and a second direction orthogonal to the first direction;
a processing step of processing at least a first surface of the SiC single crystal along the atomic arrangement plane based on the measurement results;
an attaching step of attaching the SiC single crystal to an installation surface using the first surface as an attaching surface;
The processing step is
a vacuum adsorption step of flattening the atomic arrangement surface by vacuum adsorbing the SiC single crystal to an adsorption surface having different adsorption forces depending on the amount of curvature of the atomic arrangement surface;
a surface-leveling step of cutting or grinding the SiC single crystal along the flattened atomic arrangement plane;
A method for processing a SiC single crystal, comprising: a measuring step of measuring the shape of the atomic arrangement plane of the SiC single crystal along at least a first direction passing through the center in plan view and a second direction orthogonal to the first direction;
a processing step of processing at least a first surface of the SiC single crystal along the atomic arrangement plane based on the measurement results;
an attaching step of attaching the SiC single crystal to an installation surface using the first surface as an attaching surface;
The processing step is
A method for processing a SiC single crystal, comprising an electric discharge machining step of bringing the SiC single crystal close to an electrode having a shape corresponding to the atomic arrangement plane, and machining the first surface of the SiC single crystal by electric discharge. The method for processing a SiC single crystal according to claim 1 or 2 , wherein the thickness of the SiC single crystal when performing the pasting step is 5 mm or less. In the pasting step, if the first surface curves convexly toward the installation surface, the load on the outer peripheral side of the SiC single crystal is made stronger than the inside, and the first surface curves convexly toward the installation surface. 4. The method for processing a SiC single crystal according to claim 1 , wherein when the SiC single crystal is curved, the load on the inner side of the SiC single crystal is made stronger than on the outer peripheral side. a measuring step of measuring the shape of the atomic arrangement plane of the SiC single crystal along at least a first direction passing through the center in plan view and a second direction orthogonal to the first direction;
a processing step of processing at least a first surface of the SiC single crystal along the atomic arrangement plane based on the measurement results;
an attaching step of attaching the SiC single crystal to an installation surface using the first surface as an attaching surface;
A method for processing a SiC single crystal, comprising a step of reducing pressure around the SiC single crystal during the pasting step. The method for manufacturing a SiC ingot according to any one of claims 1 to 5 , wherein crystal growth is performed using the SiC single crystal attached to the installation surface as a seed crystal. A SiC single crystal in which the maximum amount of curvature of the atomic arrangement plane is 20 μm or more,
The absolute value of the 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,
SiC single crystal that is not attached to other parts.

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