JP5678721B2 - Seed crystal for growing silicon carbide single crystal and method for producing silicon carbide single crystal - Google Patents

Description

  The present invention relates to a seed crystal for growing a silicon carbide single crystal, a method for producing a silicon carbide single crystal, and a silicon carbide single crystal ingot.

  Silicon carbide (SiC) is attracting attention as an environmentally resistant semiconductor material because of its excellent heat resistance and mechanical strength, and physical and chemical properties such as resistance to radiation. SiC is a typical material having a polymorphic structure with many different crystal structures even though the chemical composition is the same. Polytype means that when a unit of Si and C bonded molecules in the crystal structure is considered as a unit, the unit structure molecule is different in the periodic structure when stacked in the c-axis direction ([0001] direction) of the crystal. Arise. Typical polytypes include 6H, 4H, 15R or 3C. Here, the first number represents the repetition period of the stack, and the alphabet represents a crystal system (H is a hexagonal system, R is a rhombohedral system, and C is a cubic system). Each polytype has different physical and electrical characteristics, and application to various uses is considered using the difference. For example, 6H is recently used as a substrate for short-wavelength optical devices from blue to ultraviolet, and 4H is considered to be used as a substrate wafer for high-frequency, high-voltage electronic devices.

  However, a crystal growth technique capable of stably supplying a high-quality, large-area SiC single crystal capable of controlling a large voltage / current with a high yield on an industrial scale has not yet been established. Therefore, practical application of SiC is extremely limited despite the semiconductor material having many advantages and possibilities as described above.

Conventionally, on a laboratory scale scale, for example, a SiC single crystal was grown by a sublimation recrystallization method (Rayleigh method) to obtain a SiC single crystal of a size capable of manufacturing a semiconductor element. However, with this method, the area of the obtained single crystal is small, and it is difficult to control its size and shape with high accuracy. Also, it is not easy to control the crystal polymorphism and impurity carrier concentration of SiC. In addition, a cubic SiC single crystal is grown by heteroepitaxial growth on a heterogeneous substrate such as silicon (Si) using a chemical vapor deposition method (CVD method). In this method, a large-area single crystal can be obtained, but only a SiC single crystal containing many defects (˜10 ⁷ cm ⁻² ) can be grown due to a lattice mismatch of about 20% with the substrate. It is not easy to obtain a high-quality SiC single crystal.

  In order to solve these problems, an improved Rayleigh method has been proposed in which sublimation recrystallization is performed using a SiC single crystal {0001} plane substrate as a seed crystal (Non-patent Document 1). In this method, since the seed crystal is used, the nucleation process of the crystal can be controlled, and by controlling the atmospheric pressure to about 100 Pa to 15 kPa with an inert gas, the growth rate of the crystal can be controlled with good reproducibility. . The principle of the improved Rayleigh method will be described with reference to FIG. The SiC single crystal as a seed crystal and the SiC crystal powder as a raw material are stored in a crucible (usually graphite) and heated to 2000 to 2400 ° C. in an inert gas atmosphere such as argon (100 to 15 kPa). At this time, the temperature gradient is set so that the seed crystal has a slightly lower temperature than the raw material powder. After sublimation, the raw material is diffused and transported in the direction of the seed crystal by a concentration gradient (formed by a temperature gradient). Single crystal growth is realized by recrystallization of the source gas that has arrived at the seed crystal on the seed crystal. At this time, the volume resistivity of the crystal is determined by adding an impurity gas in an atmosphere composed of an inert gas, or by mixing an impurity element or a compound thereof in the SiC raw material powder, It is possible to control (doping) by replacing the position of the carbon atom with an impurity element. Typical substitutional impurities in SiC single crystals include nitrogen (n-type), boron (p-type), and aluminum (p-type). A SiC single crystal can be grown while controlling the carrier type and concentration by these impurities. Currently, SiC single crystal substrates having a diameter of 2 inches (50.8 mm) to 4 inches (100.0 mm) are cut out from the SiC single crystals produced by the above-described improved Rayleigh method, and are used for epitaxial thin film growth and device fabrication.

  As described above, the SiC single crystal is diffused and transported by the concentration gradient formed by the temperature gradient in the raw material sublimated at a high temperature in the graphite crucible and reaches the seed crystal where it is recrystallized. Grow in. At this time, due to the crystal damage remaining on the outermost surface of the seed crystal due to the process of planarizing the seed crystal, various dislocation defects due to the processing damage are likely to occur in the growth ingot grown on the seed crystal. It was a cause of quality degradation. In particular, dislocations that penetrate the crystal in the growth direction (threading screw dislocations, threading edge dislocations, etc., hereinafter collectively referred to as threading dislocations) once propagate through the crystal ingot along the crystal growth direction. Therefore, it becomes a dislocation defect common to all wafers cut out from the ingot. In order to suppress the occurrence of various dislocation defects at the interface between the seed crystal and the grown crystal ingot, it is necessary to remove the crystal damage layer on the outermost surface of the seed crystal. As a method aimed at removing the crystal damage layer, before starting the crystal growth, the temperature gradient of the raw material portion and the seed crystal is reversed (by setting the temperature distribution so that the seed crystal has a higher temperature). ) A technique for sublimating the seed crystal surface has been reported (Non-Patent Document 2). However, when this method was actually performed, it was found that the condition ranges required for the parameters such as temperature, pressure, and sublimation gas composition were very narrow and could not be controlled substantially. For example, in the case of a relatively high temperature of 1800 ° C. as described in Non-Patent Document 2, when a seed crystal having a size of 3 inches (76.2 mm) is actually used, the temperature distribution in the seed crystal plane The control becomes difficult because of a large variation and a variation in whether or not sublimation partially occurs. In addition, regarding the pressure and sublimation gas composition, the range of conditions in which etching occurs stably is very narrow, and depending on the location, carbon atoms remain on the surface as a result of excessive sublimation of silicon atoms and grow on it. The crystal quality is significantly reduced. For this reason, in practice, it was very difficult to grow a high-quality crystal on a large-area seed crystal by this method.

Further, another method, for example, a method of removing the crystal damage layer by etching the surface of the seed crystal by dipping in a molten potassium hydroxide bath is also conceivable. However, in this case as well, when actually tried, there is a considerable unevenness in the etching rate due to the temperature distribution of the etching bath, and it cannot be suppressed that the surface shape becomes wavy. Furthermore, while it is desirable that the removal of the etching layer on the surface and the subsequent crystal growth be performed continuously without interrupting the process, this is not possible with this method. It was still difficult to grow a high quality crystal ingot over the entire surface of a large area seed crystal by this method.
Patent Document 1 describes a method of preventing propagation of threading dislocation defects of a seed crystal to the growth crystal side by forming a rectangular groove on the crystal growth surface of the seed crystal. It does not teach how to suppress threading dislocations such as threading screw dislocations and threading edge dislocations that occur due to seed crystal processing damage at the start.

JP 2006-52097 A

Yu. M. Tairov and V.F.Tsvetkov, Journal of Crystal Growth, vol. 52 (1981) pp. 146-150. M. Anikin, O. Chaix, E. Pernot, B. Pelissier, M. Pons, A. Pisch, C. Bernard, P. Grosse, C. Faure, Y. Grange, G. Basset, C. Moulin and R. Madar, Material Science Forum, vol. 338-342 (2000) pp. 13-16.

As described above, in the conventional growth method, various dislocation defects are generated due to the influence of the processing damage layer remaining on the outermost surface of the seed crystal, and a high-quality SiC single crystal wafer cannot be manufactured.
Accordingly, an object of the present invention is to solve the above-described problems in the prior art and to provide an SiC single crystal manufacturing method and an SiC single crystal ingot for obtaining an SiC single crystal with good crystallinity.

The present invention
(1) A seed crystal composed of a silicon carbide single crystal used for growing a silicon carbide single crystal by a sublimation recrystallization method, wherein the seed crystal has a plurality of recesses having openings on the crystal growth surface side, The length between any two points on the periphery of the opening is a maximum of 2 mm or less, and has an initial growth space surrounded by a side wall on which a silicon carbide single crystal can be grown, and the opening A seed crystal for growing a silicon carbide single crystal, wherein the recesses are formed adjacent to each other so that there is an opening of another recess at a distance within 2 mm from an arbitrary point on the circumference of the part,
(2) The aspect ratio of the depression defined by the value obtained by dividing the depth of the depression by the maximum length of the length connecting any two points on the circumference of the opening is 0.1 or more and 10 or less ( A seed crystal for growing a silicon carbide single crystal according to 1),
(3) The silicon carbide single crystal growth seed crystal according to (1) or (2), wherein the total area of the openings, which is the sum of the areas of the openings of the recesses, occupies 20% or more of the crystal growth surface,
(4) The seed crystal for growing silicon carbide single crystal according to any one of (1) to (3), having a diameter of 50 mm or more and 300 mm or less,
(5) A seed crystal for growing a silicon carbide single crystal according to any one of (1) to (4), which is a seed crystal having a 4H polytype,
(6) A method for producing a silicon carbide single crystal comprising a step of growing a silicon carbide single crystal on a seed crystal by a sublimation recrystallization method, wherein the silicon carbide according to any one of claims 1 to 4 is used as the seed crystal. Using a seed crystal for single crystal growth, crystal growth is performed in an atmosphere of 2000 ° C. or higher and 2400 ° C. or lower and 100 Pa or higher and 15 kPa or lower. A method for producing a silicon carbide single crystal, characterized in that
(7) The method for producing a silicon carbide single crystal according to (6), wherein the surface of the remaining portion is sublimated before the silicon carbide single crystal grows on the remaining portion of the crystal growth surface formed between adjacent recesses,
It is.

  According to the present invention, in the manufacture of a SiC single crystal in which a SiC raw material is sublimated and a SiC crystal is grown on the seed crystal, recesses having a specific size and shape are provided on the seed crystal surface in a desired ratio and arrangement. As a result, the threading dislocation defects at the start of growth immediately above the seed crystal can be coalesced and the generation density thereof can be greatly reduced, so that a SiC single crystal with good crystallinity can be grown with a high yield. A semiconductor device manufactured on a wafer obtained by cutting from such a high-quality single crystal ingot can be stably operated at a high yield because the density of threading dislocation defects that cause the device operation to deteriorate is reduced. .

Illustration of the improved Rayleigh method Explanatory drawing of the hollow structure (conical shape) formed on the seed crystal surface Explanatory drawing of the hollow structure (square pyramid type) formed on the seed crystal surface Schematic diagram of SiC crystal growth equipment Schematic illustration of wafer cutting position from SiC single crystal ingot Explanatory drawing of the hollow structure (square pyramid type) formed on the seed crystal surface

The seed crystal according to the present invention includes a plurality of depressions having an initial growth space surrounded by a predetermined opening and a side wall on the crystal growth surface side. Therefore, when a SiC single crystal is grown by a sublimation recrystallization method, The remaining surface of the crystal growth surface formed between the recesses is sublimated to remove the damage layer generated by processing the seed crystal, and the SiC single crystal grown in the initial growth space is generated at the start of crystal growth. Since the formed threading dislocation defects can be coalesced, the generation density of threading dislocations can be greatly reduced, and a SiC single crystal with good crystallinity can be grown with a high yield.
Embodiments are described below.

  First, the sublimation recrystallization method will be described. The sublimation recrystallization method is a method for producing a SiC crystal by sublimating SiC powder at a high temperature exceeding 2000 ° C. and recrystallizing the sublimation gas in a low temperature part. In this method, a method for producing an SiC single crystal using a seed crystal composed of an SiC single crystal is called an improved Rayleigh method and is used for producing a bulk SiC single crystal. The modified Rayleigh method uses a seed crystal to control the nucleation process of the crystal, and the atmosphere pressure is controlled to about 100 Pa to 15 kPa with an inert gas to control the crystal growth rate with good reproducibility. it can.

  The method for producing a SiC single crystal according to the present invention is a category of the sublimation recrystallization method, and specifically, the improved Rayleigh method described above. Usually, the SiC seed crystal with the {0001} plane as the crystal growth surface and the SiC crystal powder as the raw material (usually used are those prepared by cleaning and pretreating an abrasive prepared by the Acheson method) Stored in a crucible (usually the crucible is made of graphite, but materials other than graphite such as high melting point material, graphite coated high melting point material, high melting point material coated graphite may be partially used), It is heated to 2000 to 2400 ° C. in an inert gas atmosphere such as argon (100 Pa to 15 kPa). At this time, the temperature gradient is set so that the seed crystal is slightly lower in temperature than the raw material powder (for example, lower by 100 to 200 ° C.). After sublimation, the raw material is diffused and transported in the direction of the seed crystal by a concentration gradient (formed by a temperature gradient). The shape of the crucible may be any shape such as a cylinder, a cone, a polygonal column, or a polygonal pyramid, as long as it can hold a seed crystal and accommodate raw material powder. Among these, a cylindrical shape that is excellent in the uniformity of the heat radiation amount in the circumferential direction is more suitable for heat radiation from the crucible to the outside. Single crystal growth is realized by recrystallization of the source gas that has arrived at the seed crystal on the seed crystal.

  Here, as shown in FIG. 2, a plurality of depressions are formed over the entire crystal growth surface on which the crystal ingot of the seed crystal used for growth is grown. In the case of using a seed crystal in which a plurality of depressions are formed on the crystal growth surface side in this way, the “mountain” portion formed between adjacent depressions (that is, the remainder of the crystal growth surface) is shown in the cross-sectional view of FIG. As indicated by the dotted line, before the sublimation gas from the raw material reaches and crystal growth starts, the top portion of the “mountain” (the surface of the remaining portion) sublimates (etchback phenomenon). This is because the vapor pressure of the “mountain” portion (projection portion) is higher than that of the other portions and destabilizes under high temperature and low vapor pressure. As a result, the processing damage layer originally present near the surface of the top of the “mountain” is removed, and when the sublimation gas from the raw material reaches and crystal growth starts, Crystal growth can be performed on a seed crystal that does not exist.

  This continuous process of removing the processing damage layer → crystal growth is realized in the crystal growth atmosphere of the SiC single crystal by the sublimation recrystallization method such as 2000 ° C. or more and 2400 ° C. or less and 100 Pa or more and 15 kPa or less. It occurs almost uniformly in the “mountain” area. Here, the interval between adjacent depressions is 2 mm or less. If the interval exceeds 2 mm, the area of the “mountain” portion becomes too large, and a region where no etchback occurs occurs on the seed crystal. That is, in the seed crystal of the present invention, it is necessary to form a plurality of recesses adjacent to each other so that an opening of another recess exists at a distance within 2 mm from an arbitrary point on the periphery of the opening ( As shown in FIG. 2A, the distance d from any point on the periphery of the opening to another adjacent opening is always 2 mm or less.

  On the other hand, since the etch-back phenomenon does not occur in the “valley” portion, as shown in the cross-sectional view of FIG. New threading dislocation defects are generated, but as the crystals grow, they are propagated perpendicularly to the growth surface because of dislocation mirror image effects (dislocations, which are line defects, try to take a stable arrangement in terms of energy). Nature), threading dislocation defects are collected in the center of the depression. When a dislocation is originally generated, a dislocation having a Burgers vector with an opposite sign (equal in magnitude and opposite in direction) is always generated in a pair. For this reason, when the dislocations generated inside the depression are collected at the center of the depression, those having the Burgers vector of opposite signs cancel each other and disappear. Due to this mechanism, dislocations generated inside the recess are recombined inside the recess and disappear. As a result, the generated dislocation does not propagate to the grown crystal.

  Regarding the processing on the crystal growth surface side of the seed crystal, for example, in Patent Document 1, by providing a groove having a specific shape on the surface of the seed crystal, threading dislocation defects existing in the seed crystal are grown on the side of the growth crystal. It is disclosed that the quality of the grown crystal is improved by preventing the propagation of the crystal. However, the method disclosed in this document suppresses the occurrence of threading dislocations such as threading screw dislocations and threading edge dislocations that occur at the start of crystal growth due to processing damage to the seed crystal as in the present invention. This is not intended for the purpose, but intended to suppress the propagation of defects in the seed crystal, and is different from the present invention in both purpose and effect. When the groove-like structure is imparted to the surface of the seed crystal as in the invention described in Patent Document 1, when the longitudinal direction of the groove (the direction in which the groove extends) is seen, there is no side wall that collects dislocations in the center, The dislocations generated in pairs propagate in the opposite direction along the direction in which the grooves extend, and are thought to be taken over by the grown crystal as they are.As in the present invention, the threading dislocations generated at the start of crystal growth are inside the depression. It is impossible to obtain SiC single crystals that are eliminated from each other and the generation density of threading dislocations is greatly reduced.

  Here, as the size of the recess provided in the seed crystal of the present invention, the maximum length connecting any two points on the periphery of the opening, that is, the maximum width (L) of the opening is 2 mm or less. . If the maximum width exceeds 2 mm, the effect of collecting threading dislocations inside the groove is weakened, and the dislocations may not be eliminated reliably. In addition, regarding the shape of the depression, an initial growth space surrounded by a side wall that allows a SiC single crystal to grow at the start of crystal growth is provided. That is, the threading dislocations generated by crystal growth inside the depression can be canceled with each other inside the depression. More specifically, for example, the shape of the depression is substantially cylindrical as shown in FIG. 2 and the bottom is narrowed, or may be conical, but a square pyramid or triangle as shown in FIG. The bottom may be narrowed by a pyramid, hexagonal pyramid, triangular prism, or hexagonal prism, and there are always sidewalls on which the SiC single crystal can be grown around the inside of the recess, so that threading dislocations can be canceled each other. In the case of these quadrangular pyramids, triangular pyramids, hexagonal pyramids, etc., the maximum width of the opening is 2 mm or less for the same reason as in the case of cones.

  The size of the opening may be as small as the above-described dislocation mirror image effect appears, but when the size of the opening is approximately the same as the size of the dislocation core. Since it is considered that the mirror image effect does not appear, the lower limit value of the maximum opening width (L) is considered to be about 10 nm.

  In addition, when the value obtained by dividing the depth of the dent by the maximum length (L) connecting any two points on the circumference of the opening is defined as “the aspect ratio of the dent”, this aspect ratio is 0.1 or more. 10 or less, more preferably 0.2 or more and 5 or less. If it is less than 0.1, the dent is too shallow and there is no significant difference from a normal planar seed crystal. On the other hand, if it exceeds 10, it has a needle-like shape and is extremely difficult to produce in terms of processing.

  In addition, the area ratio of the recessed openings in the total area of the seed crystal is 20% or more, and more preferably 50% or more and 100% or less. If it is less than 20%, the area ratio at which the effect of the present invention is obtained is too small, and the role of reducing the generated dislocation density is too small.

  There are several methods for making a depression on the crystal growth surface side of the seed crystal, and it is not specified. The simplest method is a method by machining (for example, cutting with a diamond drill). By selecting the tip diameter of the drill, circular grooves of various diameters and arrangements can be formed. Further, it is possible to form a recess by laser processing. Using high-power laser light in the ultraviolet region or visible region, it is possible to form a recess from a minimum diameter of about several μm in any shape and arrangement. Further, the depression can be formed by a lithography process used in a semiconductor process or the like. Pattern the mask material made of polymer, inorganic material, metal, etc. on the seed crystal surface, and then form a depression in the opening of the mask material by etching (for example, dry etching with reactive plasma or wet etching with chemicals) To do. Since the mask material can be patterned in almost any shape two-dimensionally, the shape and arrangement of the opening of any recess can be made. Further, the shape of the sidewall of the recess can be controlled by selecting the etching conditions. In addition, the recess can be formed by electrochemical etching, selective epitaxial growth of a SiC single crystal film on the seed crystal, or the like.

  After producing a SiC single crystal ingot by the sublimation recrystallization method using the seed crystal thus produced, the number of etch pits generated by etching the threading dislocation density in the wafer cut out from the ingot in a potassium hydroxide molten salt bath is counted. As a result of the examination, wafers were obtained that were 5000 or less per square centimeter, and 1000 or less for particularly good quality. About these data, although there is little change in the height direction of an ingot, it can confirm in arbitrary cross sections, More certainly, in ingot real length excluding the part which grew to 2 mm in height from the seed crystal side It was confirmed that the ingot was a high-quality ingot having a low threading dislocation density over the entire ingot. Moreover, there was almost no difference depending on the diameter of the manufactured ingot, and similar results were obtained at any diameter.

  Examples of the present invention will be described below.

Example 1
An example of manufacturing an SiC single crystal using the single crystal growth apparatus shown in FIG. 4 will be described. The seed crystal 1 used for crystal growth is attached to the inner surface of the lid 4 of the graphite crucible 3. Crystal growth is performed by sublimating the SiC crystal powder 2 and recrystallizing it on the SiC single crystal seed crystal 1 in which a hollow structure is formed. The raw material SiC crystal powder 2 is filled in a graphite crucible container 3. Such a graphite crucible (the crucible container 3 and the crucible lid 4) is installed inside a double quartz tube 5 by a support rod 6 of graphite. Around the graphite crucible, a graphite heat insulating material 7 for heat shielding is installed. The double quartz tube 5 can be highly evacuated (10 ⁻³ Pa or less) by the evacuation device 11, and the internal atmosphere is pressure-controlled by Ar gas introduced through the gas flow rate controller 10. Can do. Various doping gases (nitrogen, trimethylaluminum, trimethylboron) can also be introduced through the gas flow controller 10. In addition, a work coil 8 is provided on the outer periphery of the double quartz tube 5, and a graphite crucible can be heated by flowing a high-frequency current to heat the raw material and the seed crystal. The temperature of the crucible is measured using a two-color thermometer by providing an optical path having a diameter of 2 to 4 mm at the center of the heat insulating material covering the upper and lower parts of the crucible, taking out light from the upper and lower parts of the crucible.

As a seed crystal, a 4H polytype SiC single crystal wafer having a (000-1) C face with a diameter of 76 mm was prepared. The offset angle of the same crystal was 4 ° in the <11-20> direction from the {0001} plane. When the threading dislocation density of the seed crystal was previously measured by etching etch pit measurement, it was 802 / cm ² (measured at the center of the seed crystal). On the surface on which the seed crystal ingot was grown, a hollow structure having a substantially cylindrical shape with a bottom narrowed as shown in FIG. 2 was formed in advance by laser processing. That is, a plurality of depressions are formed on the crystal growth surface side while maintaining the relationship that the center of a circular opening having a diameter of 1 mm is positioned at the apex of a regular triangle having a side length of 1.5 mm (of openings arranged on one side). The aspect ratio of the depressions defined by the value obtained by dividing the depth of each depression by the aperture diameter was set to 1. In this case, the ratio of the total area of the opening of the depression to the total area of the crystal growth surface is about 62%.

Next, this seed crystal was attached to the inner surface of the crucible lid 4 of the graphite crucible. The inside of the graphite crucible container 3 was filled with SiC crystal raw material powder 2 produced by the Atchison method. Next, the crucible lid 4 was set in the graphite crucible container 3 filled with the SiC raw material, covered with the graphite felt 7, placed on the graphite support rod 6, and installed inside the double quartz tube 5. Then, after evacuating the inside of the quartz tube, high-purity Ar gas (purity 99.9995%) was introduced as an atmospheric gas, and the pressure in the quartz tube was maintained at 1.3 kPa throughout the growth. Under this pressure, a current was passed through the work coil to raise the temperature, the seed crystal temperature was raised to the target temperature of 2300 ° C., and then the growth was continued for 45 hours while maintaining the same temperature. During this growth time, the nitrogen flow rate was set to 0.5 × 10 ⁻⁶ m ³ / sec (at the same flow rate, the nitrogen concentration in the grown crystal was 1 × 10 ¹⁹ cm ⁻³ ) and maintained until the end of growth. .
The diameter of the obtained crystal was 77 mm, and the height was about 35 mm.

  When the SiC single crystal thus obtained was analyzed by Raman scattering, it was confirmed that the SiC single crystal having the same 4H polytype as the seed crystal was grown over the entire surface.

Next, after processing the outer periphery of the SiC single crystal, the wafer was cut out with a wire saw so as to be horizontal to the growth direction. Among a plurality of wafers obtained, the wafer corresponding to the position of the seed crystal, the wafer corresponding to the position immediately above the seed crystal, the wafer corresponding to the center position as the ingot height, and the wafer corresponding to the position closest to the top of the ingot A total of four wafers were selected, and the (0001) Si surface was polished with diamond powder and finished to a mirror surface (see FIG. 5 for the wafer cutting position from the ingot). These wafers were immersed in a potassium hydroxide molten salt maintained at 520 ° C. for 5 minutes for etching treatment, and the etch pit density corresponding to the threading dislocations appearing in the center of the wafer was observed. 810 wafers / cm ² for wafers corresponding to 805, 805 wafers / cm ² for wafers corresponding to the position immediately above the seed crystal, 776 wafers / cm ² for wafers corresponding to the center position with the ingot height, the position closest to the top of the ingot 721 / cm ² for the wafers corresponding to 1 and it was found that all had threading dislocation density almost the same as threading dislocation density in the seed crystal. From this result, it was confirmed that a high-quality SiC single crystal in which the threading dislocation density did not increase as compared with the seed crystal was obtained throughout the ingot.

(Example 2)
An experiment similar to that of Example 1 was performed except that a seed crystal having a diameter of 100 mm was used as the seed crystal and the concave structure had a square pyramid shape as shown in FIG. That is, a plurality of depressions are formed on the crystal growth surface side while maintaining the relationship that the center of a square-shaped opening having a side length of 1 mm is located at the corner of a regular square having a side length of 1.5 mm (one side The distance between the openings on the top is 0.5mm, the depth of the recess is 1mm), and the depth defined by dividing the depth of each recess by the maximum length connecting any two points on the circumference of the opening Was set to 1 / √2 = 0.71. In this case, the ratio of the total area of the opening of the depression to the total area of the crystal growth surface is about 44%.
The threading dislocation density of the seed crystal was 2010 / cm ² by the same measurement method as in Example 1 (measured at the center of the seed crystal). The diameter of the obtained crystal was 101 mm, and the height was about 30 mm.

  When the SiC single crystal thus obtained was analyzed by Raman scattering, it was confirmed that the SiC single crystal having the same 4H polytype as the seed crystal was grown over the entire surface.

Next, four wafers taken out in the same manner as in Example 1 were etched by immersing them in potassium hydroxide molten salt for 5 minutes, and the etch pit density corresponding to threading dislocations appearing at the center of the wafer was observed. As a result, the wafer corresponding to the seed crystal was 2002 / cm ² , the wafer corresponding to the position immediately above the seed crystal was 1998 / cm ² , the wafer corresponding to the center position with the ingot height being 1902 / cm ² , The wafer corresponding to the position close to the top of the ingot was 1811 pieces / cm ² , and all had threading dislocation density almost the same as threading dislocation density in the seed crystal.

(Comparative Example 1)
Crystal growth was carried out in the same manner as in Example 1 except that no depression structure was formed on the seed crystal surface. The threading dislocation density of the seed crystal was 1832 / cm ² by the same measurement method as in Example 1 (measured at the center of the seed crystal).

  When the SiC single crystal thus obtained was analyzed by Raman scattering, it was confirmed that the SiC single crystal having the same 4H polytype as the seed crystal was grown over the entire surface.

Next, four wafers taken out in the same manner as in Example 1 were etched by immersing them in potassium hydroxide molten salt for 5 minutes, and the etch pit density corresponding to the threading dislocations appearing at the center of the wafer was observed. As a result, 1829 wafers / cm ² for the wafer corresponding to the seed crystal, 6552 wafers / cm ² for the wafer corresponding to the position immediately above the seed crystal, 5325 wafers / cm ² for the wafer corresponding to the center position at the height of the ingot, The wafer corresponding to the position near the top of the ingot was 4805 / cm ² . Although some decrease in the density is observed because some threading dislocations coalesce and disappear from the position just above the seed crystal to the top of the ingot, the value is significantly higher than the threading dislocation density in the seed crystal in any wafer. showed that.

(Comparative Example 2)
Crystal growth was performed in the same manner as in Example 1 except that a groove structure was formed on the surface of the seed crystal instead of a recess structure. The threading dislocation density of the seed crystal was 4832 / cm ² by the same measurement method as in Example 1 (measured at the center of the seed crystal). Grooves having a substantially rectangular cross-sectional shape with a width of 1 mm and a depth of 1 mm were formed at intervals of 0.5 mm on the surface of the seed crystal by laser processing. In this case, the ratio of the total area of the opening of the depression to the total area of the crystal growth surface is about 67%.

  When the SiC single crystal thus obtained was analyzed by Raman scattering, it was confirmed that the SiC single crystal having the same 4H polytype as the seed crystal was grown over the entire surface.

Next, four wafers taken out in the same manner as in Example 1 were etched by immersing them in potassium hydroxide molten salt for 5 minutes, and the etch pit density corresponding to the threading dislocations appearing at the center of the wafer was observed. As a result, 4840 wafers / cm ² for the wafer corresponding to the seed crystal, 6017 wafers / cm ² for the wafer corresponding to the position immediately above the seed crystal, 4571 wafers / cm ² for the wafer corresponding to the center position at the height of the ingot, The wafer corresponding to the position near the top of the ingot was 3627 pieces / cm ² . As described in Patent Document 1, by forming a groove structure on the surface of the seed crystal, threading dislocations propagated from the seed crystal to the grown crystal, such as deflection of threading dislocations existing in the seed crystal. Although the effect of suppressing this was observed, the threading dislocations newly generated at the bottom of the groove did not completely disappear. As a result, the threading dislocation density could not be maintained equal to or less than that of the seed crystal over almost the entire length from the position immediately above the seed crystal to the top of the ingot.

1 Seed crystal (SiC single crystal)
2 Raw material for SiC crystal powder 3 Crucible container (refractory metal such as graphite or tantalum)
4 Graphite crucible lid 5 Double quartz tube 6 Support rod 7 Graphite felt (heat insulation)
8 Work coil 9 High purity Ar gas and impurity gas piping 10 Mass flow controller for high purity Ar gas and impurity gas 11 Vacuum exhaust system

Claims (7)

  A seed crystal composed of a silicon carbide single crystal used for growing a silicon carbide single crystal by a sublimation recrystallization method, the seed crystal having a plurality of recesses having openings on the crystal growth surface side, The length between any two points on the circumference is a maximum of 2 mm or less, and has an initial growth space surrounded by sidewalls on which a silicon carbide single crystal can be grown, and the circumference of the opening A seed crystal for growing a silicon carbide single crystal, wherein the recesses are formed adjacent to each other so that an opening of another recess exists within a distance of 2 mm from any point above.   The aspect ratio of the depression defined by a value obtained by dividing the depth of the depression by the maximum length of the length connecting any two points on the circumference of the opening is 0.1 or more and 10 or less. A seed crystal for growing a silicon carbide single crystal as described.   3. The seed crystal for growing a silicon carbide single crystal according to claim 1, wherein the total area of the openings, which is the sum of the areas of the openings of the recesses, occupies 20% or more of the crystal growth surface.   The seed crystal for growing a silicon carbide single crystal according to any one of claims 1 to 3, wherein the diameter is 50 mm or more and 300 mm or less.   The seed crystal for growing a silicon carbide single crystal according to any one of claims 1 to 4, which is a seed crystal having a 4H polytype.   A method for producing a silicon carbide single crystal comprising a step of growing a silicon carbide single crystal on a seed crystal by a sublimation recrystallization method, wherein the silicon carbide single crystal growth according to claim 1 is used as the seed crystal. Crystal growth is performed in an atmosphere of 2000 ° C. or higher and 2400 ° C. or lower and 100 Pa or higher and 15 kPa or lower by using a seed crystal, and a silicon carbide single crystal is grown in the initial growth space to close the recess, and then crystal growth is continued. A method for producing a silicon carbide single crystal.   The method for producing a silicon carbide single crystal according to claim 6, wherein the surface of the remaining portion is sublimated prior to the growth of the silicon carbide single crystal on the remaining portion of the crystal growth surface formed between adjacent recesses.

Images