JP2006124244A - Method for producing silicon carbide single crystal and silicon carbide wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an SiC single crystal which can produce a large-diameter and high quality SiC single crystal and to provide an SiC wafer comprising the SiC single crystal obtained from the method. <P>SOLUTION: The method for producing an SiC single crystal comprises a step for cutting away or grooving a part of the peripheral region 15 of an SiC substrate 1, and a step for growing the SiC single crystal on the surface of the substrate which has been cut away or grooved as the seed substrate. The SiC wafer is composed of the SiC single crystal obtained from the method for producing an SiC single crystal and has the number of small tilt angle grain boundaries of 10 or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a silicon carbide (SiC) single crystal and a SiC wafer, and more particularly to a method for manufacturing a large-diameter, high-quality SiC single crystal and a SiC wafer made of the SiC single crystal.

  SiC has about 3 times the band gap, about 10 times the dielectric breakdown voltage, about 2 times the electron saturation rate, and about 3 times the thermal conductivity compared to silicon (Si). ing. In addition, SiC is a thermally and chemically stable semiconductor material. Taking advantage of these features, SiC has recently been applied to power devices that break the physical limitations of Si devices and environmentally resistant devices that operate at high temperatures. Is expected.

  On the other hand, gallium nitride (GaN) -based materials have been developed to reduce the wavelength in optical device research, but SiC has a much smaller lattice mismatch with GaN than other compound semiconductors. Has attracted attention as a substrate for epitaxial growth of GaN layers.

  Conventionally, SiC single crystals have been artificially synthesized by the Atchison method or the Rayleigh method. The Atchison method is a method of industrially producing an artificial abrasive by heating silicic anhydride and carbon to a high temperature of 2000 ° C. or higher, and a SiC single crystal is produced as a byproduct. The Rayleigh method is a sublimation recrystallization method that has been attempted for the first time as a crystal growth method with good purity. In a graphite crucible, SiC powder as a raw material is sublimated at a high temperature part of 2000 ° C. or higher, and a SiC single crystal is produced at a low temperature part. Is recrystallized.

  However, in these methods, only a SiC single crystal of about 10 to 15 mm at the maximum can be obtained, which is not suitable for the production of SiC wafers for semiconductor device applications.

  Therefore, in recent years, SiC single crystals are mainly manufactured using an improved Rayleigh method. In the modified Rayleigh method, a SiC seed substrate is used, and the inside of a graphite crucible containing powdered SiC crystals is made an inert gas atmosphere, and then the inside of the crucible is heated to sublimate the SiC crystals. The vapor of Si and C that has been sublimated is diffused in an inert gas to be transported to the vicinity of the seed substrate, and this vapor is condensed in the vicinity of the surface of the seed substrate set at a low temperature, thereby condensing the seed. A SiC single crystal is grown on the surface of the substrate.

  The seed substrate made of SiC used in the improved Rayleigh method is obtained by cutting a SiC single crystal grown by the improved Rayleigh method. However, in this seed substrate, as shown in the schematic top view of FIG. 10A, a small-angle grain boundary 2 tends to be generated from the end of the seed substrate 1a toward the center, and the small-angle grain boundary is formed in the seed substrate 1a. When 2 is present, there is a problem in that the low-inclination grain boundary 2 is inherited also in the SiC single crystal grown on the surface of the seed substrate 1a. When a low-angle grain boundary exists in the SiC single crystal, a small-angle grain boundary also exists in the SiC wafer obtained by cutting the SiC single crystal, and a semiconductor layer is formed on the surface of the SiC wafer. There is a problem in that the characteristics of the obtained semiconductor device are also adversely affected. In addition, the SiC wafer is also a cause of warping and cracking.

  Therefore, as shown in the schematic top view of FIG. 10B, the SiC single crystal is formed on the surface of the seed substrate 1b after the small-angle grain boundaries 2 are removed by cutting away the peripheral region 15 of the seed substrate 1a. A bulk growth method can be considered. However, this method has a problem that the surface area of the seed substrate 1b becomes too small, and the diameter of the SiC single crystal grown on the surface of the seed substrate 1b becomes small.

Further, Patent Document 1 discloses a method for growing a SiC single crystal using a seed crystal having a groove on the growth surface of the SiC single crystal as a method for producing a high-quality large-diameter SiC single crystal with few defects. . However, in this method, as shown in the schematic cross-sectional view of FIG. 11, the groove 22 is formed on the entire surface of the SiC single crystal growth surface of the seed crystal 21, and therefore the growth surface on which the groove 22 is not formed. The vertical growth from the bottom of the groove 22 does not catch up with the vertical growth of the SiC single crystal in the c-axis direction from 23, and the lower direction of the groove 22 by lateral growth from the growth surface 23 perpendicular to the c-axis direction. In some cases, the grown SiC single crystal has many defects such as cavities. Therefore, in this method, a high-quality SiC single crystal with few defects may not be manufactured.
JP 2002-121099 A

  An object of the present invention is to provide a method for producing a SiC single crystal capable of producing a SiC single crystal having a large diameter and a high quality, and a SiC wafer comprising the SiC single crystal.

  The present invention includes a step of cutting or grooving a part of the peripheral region of the SiC substrate, and a step of growing a SiC single crystal on the surface of the seed substrate using the SiC substrate after the cutting or grooving as a seed substrate. This is a method for producing a single crystal. Here, the “peripheral region of the SiC substrate” is the shortest line segment among the line segments connecting the end point of the low-angle grain boundary that is generated from the end of the SiC substrate toward the center and the center point of the SiC substrate. This is a region outside the imaginary circle centered on the center point of the SiC substrate with the length of the minute as the radius.

  Here, in the method for producing a SiC single crystal of the present invention, the step of cutting or grooving a part of the peripheral region of the SiC substrate is preferably performed in a region where a low-angle grain boundary exists.

  In the method for producing a SiC single crystal of the present invention, the step of cutting or grooving a part of the peripheral region of the SiC substrate is performed in a region ± 10 ° with respect to the <1-100> direction from the center of the SiC substrate. Preferably, it is done.

  In the method for producing a SiC single crystal according to the present invention, the SiC substrate is disk-shaped, and the length of the cut or grooved portion formed from the end of the SiC substrate toward the center is the SiC substrate. It is preferable that it is 1/3 or less of the diameter.

  In the method for producing a SiC single crystal of the present invention, the width of the cut portion or the groove portion formed from the end of the SiC substrate toward the center may be not more than twice the thickness of the SiC substrate. preferable.

  In the method for producing a SiC single crystal of the present invention, it is preferable that the thickness of the grooved portion formed from the end of the SiC substrate toward the center is 0.1 mm or more.

  Furthermore, the present invention is an SiC wafer made of an SiC single crystal obtained by the above-described method for producing an SiC single crystal, wherein the SiC wafer has 10 or less low-angle grain boundaries.

  According to the method for producing a SiC single crystal of the present invention, a large-diameter and high-quality SiC single crystal can be produced, and a SiC wafer made of this SiC single crystal can also have a large-diameter and high-quality. .

  Hereinafter, embodiments of the present invention will be described. In the drawings of the present application, the same reference numerals denote the same or corresponding parts.

  FIG. 1 shows a schematic top view of an example of a SiC substrate used in the present invention. In the disc-shaped SiC substrate 1 obtained by the improved Rayleigh method, a plurality of small-angle boundaries 2 are generated from the end of the SiC substrate 1 toward the center.

  Here, the peripheral region 15 of the SiC substrate 1 has the radius of the length of the shortest line segment 16 among the line segments connecting the end point Ep of the low-angle grain boundary 2 and the center point Cp of the SiC substrate 1. This is a region of the SiC substrate 1 outside the virtual circle 17 centered on one central point Cp.

  By cutting or grooving a part of the peripheral region 15 of the SiC substrate 1, the low-inclination grain boundaries 2 generated in the SiC substrate 1 are removed. In the present invention, the excision means that the SiC substrate 1 is cut out over the entire thickness direction of the SiC substrate 1 as shown in the schematic top view of FIG. 2A and the schematic enlarged side view of FIG. It means to end. Groove cutting refers to the SiC substrate 1 leaving a part in the thickness direction of the SiC substrate 1 as shown in the schematic top view of FIG. 3A and the schematic enlarged side view of FIG. It means to cut off. In addition, the low-inclination grain boundary is obtained by an X-ray topography method for taking an X-ray topographic image, or an orthogonal Nicol method in which an SiC substrate is sandwiched between two polarizing plates in an orthogonal relationship to view the image by applying light. The position can be grasped.

  Then, the SiC single crystal 14 is grown on the surface of the seed substrate 1a as shown in the schematic side view of FIG. 4 by using the SiC substrate after the cutting or grooving as a seed substrate and using a modified Rayleigh method or the like. Here, in the present invention, a cut portion or a grooved portion exists only in the peripheral region 15 of the seed substrate 1a, and a cut portion or a grooved portion exists in the central region 18 other than the peripheral region 15 of the seed substrate 1a. Not. Therefore, the cut portion or the groove portion of the peripheral region 15 corresponds to the arrow of the SiC single crystal 14 grown in the cut portion direction or the groove portion direction of the SiC single crystal 14 grown in the peripheral region 15 and the central region 18. It is covered from above by the growth in the 19 direction and buried in the SiC single crystal 14. Therefore, after the cut portion or the grooving portion is filled, the influence of the cut portion or the grooving portion is not carried over to the subsequent grown crystal. Therefore, in the present invention, a high-quality SiC single crystal is manufactured. can do. Further, in the present invention, not all the region of the SiC substrate having the small tilt grain boundary is cut out, but only a part of the region having the small tilt grain boundary is cut out. Since the region where the SiC single crystal 14 grows on the surface is widened, the SiC single crystal 14 having a large diameter can be manufactured.

  The SiC single crystal thus obtained is cut to a desired thickness and crystal orientation with a wire saw or the like, and then polished until the desired surface and thickness are obtained. This SiC wafer is obtained.

  Here, the length L1 of the cut or grooved portion of SiC substrate 1 shown in FIGS. 2 (A) and 3 (A) is preferably 1/3 or less of the diameter of SiC substrate 1. More preferably, it is 5 or less. Since the length of the low-inclination grain boundary generated in the SiC substrate 1 is generally 1/3 or less, particularly 2/5 or less of the diameter of the SiC substrate 1, it is longer than 1/3 of the diameter of the SiC substrate 1. In particular, when cutting or grooving longer than 2/5, the cut or grooved portion of the SiC substrate 1 tends to be too long to produce a large-diameter SiC single crystal, and SiC In the growth process of the single crystal, the cut portion or the groove portion cannot escape to the outside of the SiC substrate 1, and the cut portion or the groove portion tends not to be sufficiently filled.

  2B and FIG. 3B, the width W1 of the cut or grooved portion of SiC substrate 1 is preferably not more than twice the thickness of SiC substrate 1. When the width W1 of the cut or grooved portion of the SiC substrate 1 is larger than twice the thickness of the SiC substrate 1, the width of the cut or grooved portion is too wide, and the SiC substrate is grown by the grown SiC single crystal. There is a tendency that it is difficult to fill a cut portion or groove portion of one. Here, the width W1 of the cut or grooved portion of the SiC substrate 1 is obtained by measuring the length of a line segment connecting both ends of the cut or grooved portion.

  Moreover, it is preferable that the thickness T1 of the grooved portion of SiC substrate 1 shown in FIG. 3B is 0.1 mm or more. When the thickness T1 of the grooved portion of the SiC substrate 1 is less than 0.1 mm, there is a tendency that the small-angle grain boundary generated in the SiC substrate 1 cannot be sufficiently removed. Here, the thickness T1 of the grooved portion of the SiC substrate 1 is obtained by measuring the shortest distance between the surface of the SiC substrate 1 and the surface of the grooved portion.

  Further, the step of cutting or grooving a part of the peripheral region of the SiC substrate is preferably performed in a region where a low-angle grain boundary exists. In this case, since the small-angle grain boundary can be removed while leaving a part of the peripheral region of the SiC substrate, when the SiC single crystal is grown using the SiC substrate after removal of the small-angle grain boundary as a seed substrate, There is a tendency that a high-quality SiC single crystal having a large diameter can be produced. Here, the region where the low-angle boundary is present means a region of the SiC substrate including the small-angle grain boundary, and even if only one small-angle grain boundary is included in this region. Well, a plurality may be included. Therefore, when a plurality of low-angle grain boundaries are generated in the SiC substrate, there may be a plurality of regions where the low-angle grain boundaries exist in the SiC substrate.

  Further, the step of cutting or grooving a part of the peripheral region of the SiC substrate is preferably performed in a region of ± 10 ° with respect to the <1-100> direction from the center of the SiC substrate. The low-angle grain boundary is particularly likely to occur in a region of ± 10 ° with respect to the <1-100> direction from the center of the SiC substrate. Tend to be removed.

  Moreover, it is preferable that there are 10 or less small-angle grain boundaries generated in the SiC wafer of the present invention. This is because when there are 10 or less low-angle grain boundaries generated in the SiC wafer of the present invention, a high-quality semiconductor device tends to be manufactured.

(Embodiment 1)
First, as shown in the schematic top view of FIG. 5A, in the peripheral region 15 of the SiC substrate 1, a wire saw is used to extend along the small-angle grain boundary 2 from the end of the SiC substrate 1 toward the center. The first notch 3 is made by L1. Next, as shown in the schematic top view of FIG. 5B, the width W1 further extends along the low-angle grain boundary 2 in the direction substantially perpendicular to the direction of the first notch 3 from the end point of the first notch 3. Make a second notch 4. Then, as shown in the schematic top view of FIG. 5C, from the end of the SiC substrate 1 toward the end point of the second notch 4, only the length L1 is perpendicular to the direction of the second notch 4. Make a third notch 5. Thereby, a part of the peripheral region 15 of the SiC substrate 1 is cut away from the end of the SiC substrate 1 toward the center, and the low-angle grain boundary 2 is removed from the SiC substrate 1.

  Here, since the third notch 5 only needs to be between the end of the SiC substrate 1 and the end point of the second notch 4, the third notch 5 is changed from the end point of the second notch 4 to the SiC substrate 1. You can also put it towards the end of the.

  By performing this operation for all the low-angle grain boundaries existing in the SiC substrate 1, all the low-angle grain boundaries are removed from the SiC substrate 1 as shown in the schematic top view of FIG. A plurality of cut portions 6 are formed at the ends.

  Then, using the growth apparatus 7 shown in the schematic cross-sectional view of FIG. 7, a SiC single crystal is grown on the surface of the seed substrate 1a by the modified Rayleigh method using the SiC substrate after removal of the low-angle grain boundaries as the seed substrate 1a.

  Here, the seed substrate 1 a having a plurality of cut portions 6 is attached to the lower surface of the lid 10 of the graphite crucible 9 installed inside the quartz tube 8 of the growth apparatus 7. Further, a graphite felt 11 for heat shielding is installed around the crucible 9 and the lid 10, and a work coil 12 is installed on the outer periphery of the quartz tube 8.

  And after filling the inside of the crucible 9 with the powdery SiC crystal 13 and making the inside of the crucible 9 an inert gas atmosphere such as argon gas, the SiC crystal 13 is heated by flowing a high-frequency current through the work coil 12. And sublimate. Here, the inside of the crucible 9 is heated to, for example, 2200 ° C. to 2800 ° C., and the temperature gradient gradually decreases from the lower side of the crucible 9 filled with the SiC crystal 13 to the upper side of the crucible 9 with the lid 10. Is attached. Therefore, the sublimation gas of SiC crystal 13 that has reached the vicinity of seed substrate 1a becomes supersaturated on the surface of seed substrate 1a and condenses in the vicinity of the surface of seed substrate 1a, and SiC single crystal 14 is formed on the surface of seed substrate 1a. Will grow. In this way, SiC single crystal 14 is manufactured. Here, when the SiC single crystal 14 is grown, the temperature of the seed substrate 1a is a high temperature of 2000 ° C. or more, so that the seed substrate 1a expands. Generation | occurrence | production of an inclination grain boundary can be suppressed and distortion which seed substrate 1a itself has can also be eased.

  According to the present embodiment, all of the small-angle grain boundaries of the SiC substrate where 50 low-angle grain boundaries are generated are excised, and an SiC single crystal is grown on the surface of the seed substrate using the SiC substrate after the excision as a seed substrate. When the number of low-angle grain boundaries of the SiC wafer obtained by cutting to a predetermined thickness after the etching was examined, it was reduced to 8.

(Embodiment 2)
The present embodiment is characterized in that the low-inclination grain boundary is cut by making a smaller number of cuts than in the first embodiment.

  As shown in a schematic top view of FIG. 8A, a plurality of small-angle grain boundaries 2 are generated in the peripheral region 15 of the SiC substrate 1 used in the present embodiment.

  Then, as shown in the schematic top view of FIG. 8B, the first notch 3 is made from the end of the SiC substrate 1 toward the end point EB of the low-angle grain boundary 2 using a wire saw. Next, as shown in the schematic top view of FIG. 8C, a second notch 4 is made from the end of the SiC substrate 1 toward the end point EB of the low-inclination grain boundary 2. Thereby, a part of the peripheral region 15 of the SiC substrate 1 is cut away from the end of the SiC substrate 1 toward the center, and the low-angle grain boundary 2 is removed from the SiC substrate 1.

  By performing this operation on all the low-angle grain boundaries 2 existing in the peripheral region of the SiC substrate 1, all the low-angle grain boundaries 2 are removed from the SiC substrate 1 as shown in the schematic top view of FIG. A plurality of cut portions 6 are formed at the end of the SiC substrate 1.

  Then, as in the first embodiment, the SiC substrate 1 after removal of the low-inclination grain boundaries 2 is used as a seed substrate 1a, and is attached to the lower surface of the lid 10 of the crucible 9 of the growth apparatus 7 shown in the schematic sectional view of FIG. The SiC single crystal 14 is grown on the surface of the seed substrate 1a by the modified Rayleigh method. In this way, SiC single crystal 14 is manufactured.

  In the present embodiment, unlike the first embodiment, the low-inclination grain boundary can be removed simply by making two slits in the SiC substrate. The field can be removed.

  Here, in the present embodiment, the second notch 4 only needs to be between the end of the SiC substrate 1 and the end point EB of the low-inclination grain boundary 2, so the second incision 4 is reduced to the small-inclination grain. It is also possible to enter from the end point EB of the boundary 2 toward the end of the substrate 1.

  In the first and second embodiments, the peripheral region is excised for each single low-angle grain boundary. However, the peripheral regions in which a plurality of small-angle grain boundaries exist can also be excised together.

  In the first and second embodiments, a part of the peripheral region of the SiC substrate is removed by making cuts in all the thickness directions of the SiC substrate, but a part of the thickness direction of the SiC substrate is left. The SiC substrate can also be grooved by cutting.

  In Embodiments 1 and 2, only the peripheral region of the SiC substrate is excised, but the peripheral region of the SiC substrate may be excised and grooved together.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  According to the SiC single crystal manufacturing method of the present invention, a large-diameter and high-quality SiC single crystal can be manufactured. Therefore, a semiconductor is formed on the surface of the SiC wafer made of the SiC single crystal obtained by using the present invention. By forming the layer, a high-performance semiconductor device can be obtained. Therefore, the present invention is suitably used in the semiconductor device field.

It is a typical top view of an example of the SiC substrate used for the present invention. (A) is a schematic top view when part of the peripheral region of the SiC substrate shown in FIG. 1 is excised, and (B) is when part of the peripheral region of the SiC substrate shown in FIG. 1 is excised. It is a typical expanded side view. (A) is a schematic top view when a part of the peripheral region of the SiC substrate shown in FIG. 1 is grooved, and (B) is a part of the peripheral region of the SiC substrate shown in FIG. It is a typical enlarged side view at the time. It is a typical side view when a SiC single crystal is grown on the surface of the seed substrate used for the present invention. (A) is a schematic top view of the SiC substrate after the first cut is made in Embodiment 1 of the present invention, and (B) is the second cut made in Embodiment 1 of the present invention. FIG. 2C is a schematic top view of the SiC substrate after being cut, and FIG. 3C is a schematic top view of the SiC substrate after the third cut is made in the first embodiment of the present invention. FIG. 3 is a schematic top view of the SiC substrate after all the small-angle grain boundaries have been removed in the first embodiment. It is typical sectional drawing of a preferable example of the growth apparatus used for this invention. (A) is a schematic top view of the SiC substrate before making a cut in Embodiment 2, and (B) is a schematic view of the SiC substrate after making the first cut in Embodiment 2 of the present invention. It is a typical top view, (C) is a schematic top view of the SiC substrate after making the 2nd notch in Embodiment 2 of this invention. FIG. 10 is a schematic top view of an SiC substrate after all small-angle boundaries are removed in the second embodiment. (A) is a typical top view of an example of the seed substrate which consists of SiC used in the manufacturing method of the conventional SiC single crystal, (B) is the peripheral region of a seed substrate in the manufacturing method of the conventional SiC single crystal. It is a typical top view of an example of a seed substrate after all excision and removing a small inclination grain boundary. It is typical sectional drawing of an example of the seed crystal used in the manufacturing method of the conventional SiC single crystal.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 SiC substrate, 1a, 1b seed substrate, 2 small-angle grain boundary, 3 1st notch, 4 2nd notch, 5 3rd notch, 6 cutting part, 7 growth apparatus, 8 quartz tube, 9 crucible, 10 Lid, 11 felt, 12 work coil, 13 SiC crystal, 14 SiC single crystal, 15 peripheral region, 16 line segment, 17 virtual circle, 18 central region, 19 arrow, 21 seed crystal, 22 groove, 23 growth surface.

Claims (7)

  Cutting or grooving a part of the peripheral region of the silicon carbide substrate, and growing a silicon carbide single crystal on the surface of the seed substrate using the silicon carbide substrate after the cutting or grooving as a seed substrate; The manufacturing method of the silicon carbide single crystal containing these.   The process for cutting or grooving a part of the peripheral region of the silicon carbide substrate is performed in a region where a low-inclination grain boundary is present. Method.   The step of cutting or grooving a part of the peripheral region of the silicon carbide substrate is performed in a region of ± 10 ° with respect to the <1-100> direction from the center of the silicon carbide substrate. Item 3. A method for producing a silicon carbide single crystal according to Item 1 or 2.   The silicon carbide substrate is disk-shaped, and the length of the cut or grooved portion formed from the end of the silicon carbide substrate toward the center is not more than 1/3 of the diameter of the silicon carbide substrate. The method for producing a silicon carbide single crystal according to any one of claims 1 to 3, wherein:   The width of the cut portion or the groove portion formed from the end of the silicon carbide substrate toward the center is not more than twice the thickness of the silicon carbide substrate. The manufacturing method of the silicon carbide single crystal in any one.   6. The silicon carbide single crystal according to claim 1, wherein a thickness of a grooved portion formed from an end to the center of the silicon carbide substrate is 0.1 mm or more. Manufacturing method.   A silicon carbide wafer comprising a silicon carbide single crystal obtained by the method for producing a silicon carbide single crystal according to any one of claims 1 to 6, wherein the number of low-angle grain boundaries is 10 or less. , Silicon carbide wafer.

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