JP2014231463A - MANUFACTURING METHOD OF SiC SINGLE CRYSTAL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a SiC single crystal by a solution method, which provides a large thickness while suppressing polycrystallization.SOLUTION: In a manufacturing method of SiC single crystal by a solution method, the manufacturing method includes steps of: (A) growing a SiC crystal 30 starting from a seed crystal 14; (B) removing at least a part of a polycrystalline part and/or a single crystal part 34 which has a low crystallinity from a side face of a growth direction of the SiC crystal 30 grown in the process (A) or a process (C); and (C) growing the SiC crystal starting from the SiC crystal 30 grown in the process (A) or from the SiC crystal 30 obtained in the process (B). The process (B) and the process (C) are performed one time or more.

Description

  The present invention relates to a method for producing a high-quality SiC single crystal suitable as a semiconductor element by a solution method.

  SiC single crystals are very thermally and chemically stable, excellent in mechanical strength, resistant to radiation, and have excellent physical properties such as higher breakdown voltage and higher thermal conductivity than Si single crystals. . Therefore, it is possible to realize high power, high frequency, withstand voltage, environmental resistance, etc. that cannot be realized with existing semiconductor materials such as Si single crystal and GaAs single crystal, and power devices that enable high power control and energy saving. Expectations are growing as next-generation semiconductor materials in a wide range of materials, high-speed and large-capacity information communication device materials, in-vehicle high-temperature device materials, radiation-resistant device materials, and the like.

  Conventionally, as a method for growing a SiC single crystal, a gas phase method, an Acheson method, and a solution method are typically known. Among the vapor phase methods, for example, the sublimation method has a defect that a grown single crystal is liable to cause a lattice defect such as a hollow through defect called a micropipe defect or a stacking fault and a crystal polymorphism, but the crystal growth. Because of its high speed, conventionally, most of SiC bulk single crystals have been manufactured by a sublimation method, and attempts have been made to reduce defects in grown crystals. In the Atchison method, since silica and coke are used as raw materials and heated in an electric furnace, it is impossible to obtain a single crystal with high crystallinity due to impurities in the raw materials.

  In the solution method, a Si melt or an alloy melt is formed in a graphite crucible, C is dissolved in the melt, and a SiC crystal layer is deposited on a seed crystal substrate placed in a low temperature portion. It is a method to let it grow. In the solution method, since crystal growth is performed in a state close to thermal equilibrium as compared with the gas phase method, the reduction of defects can be most expected. For this reason, several methods for producing SiC single crystals by the solution method have recently been proposed (Patent Document 1).

  Moreover, it is disclosed that the growth of a SiC single crystal is repeatedly performed in the production of an SiC single crystal by a solution method (Patent Document 2). It has been studied to grow a SiC single crystal having a large thickness (long) by using a method such as repeated growth.

JP 2008-105896 A International Publication No. 2013/005347 Pamphlet

  However, in order to obtain a high-quality SiC single crystal having a large thickness (long) by the solution method, various technical problems still remain. When long growth is performed by repeated growth as described above in the solution method, a single crystal having low crystallinity is generated at the outer peripheral portion of the crystal growth surface (side portion with respect to the growth direction), and further polycrystallization occurs. In particular, there is a problem that the entire surface of the grown crystal can be polycrystallized.

  This invention is made | formed in view of the said situation, and it aims at providing the manufacturing method by the solution method of a SiC single crystal which has big thickness, suppressing polycrystallization.

The present invention is a method for producing a SiC crystal by a solution method,
(A) a step of growing a SiC crystal starting from a seed crystal;
(B) removing at least a part of the polycrystalline portion and / or the single crystal portion having low crystallinity from the side surface with respect to the growth direction of the SiC crystal grown in step (A) or step (C); and (C) A step of growing a SiC crystal starting from the SiC crystal grown in the step (A) or the SiC crystal obtained in the step (B),
And the process (B) and the process (C) are performed once or more.

  According to the present invention, it is possible to obtain a SiC single crystal substantially free of polycrystals and having a large thickness.

FIG. 1 is an example of a schematic cross-sectional view of an SiC crystal grown using a seed crystal as a base point. FIG. 2 is an example of a schematic cross-sectional view of an SiC crystal grown using a seed crystal as a base point. FIG. 3 is a schematic diagram of a crystal growth surface when m-plane growth is performed and a part of the outer peripheral portion in contact with the (000-1) plane that is a side surface with respect to the growth direction is roughened. is there. FIG. 4 is a schematic cross-sectional view of an apparatus for producing a single crystal by a solution method that can be used in the present invention. FIG. 5 is a photograph observed from the crystal growth surface obtained in step (A) in Example 1. 6 is a photograph observed from the crystal growth surface obtained in the step (C) in Example 1. FIG. FIG. 7 is a photograph observed from the crystal growth surface obtained in the second step (C) in Example 2. FIG. 8 is a photograph observed from the crystal growth surface obtained in the fourth round of step (C) in Example 2. FIG. 9 is a photograph observed from the side of the crystal obtained in the fourth time of step (C) in Example 2. FIG. 10 is a photograph observed from the crystal growth surface obtained in the fifth step (C) in Example 2. FIG. 11 is a photograph observed from the side of the crystal obtained in the fifth step (C) in Example 2.

  In this specification, “−1” in the notation of the (000-1) plane or the like is a place where “−1” is originally written with a horizontal line on the number.

  When the SiC single crystal is repeatedly grown by the solution method, the SiC single crystal is further grown using the grown crystal as a seed crystal. However, a grown crystal used as a seed crystal may include a polycrystalline portion. If a crystal is further grown from a growth crystal containing a polycrystal as a starting point, a large amount of polycrystal will eventually be generated and single crystal SiC cannot be obtained. A measure is to remove the polycrystals. However, it has been found that it is not sufficient to polish the growth surface of the growth crystal to be a seed crystal in order to suppress the generation of polycrystals.

  Then, the inventor of the present application removes the polycrystalline portion on the side surface with respect to the growth direction of the grown crystal and / or the single crystal portion with low crystallinity when performing the repeated growth, so that the occurrence of polycrystal in the subsequent crystal growth occurs. Found to be effective in control.

  The present invention is a method for producing an SiC crystal by a solution method, wherein (A) a step of growing an SiC crystal starting from a seed crystal, (B) an SiC crystal grown in step (A) or step (C) Obtained by the step of removing at least part of the polycrystalline portion and / or the single crystal portion having low crystallinity from the side surface with respect to the growth direction, and the SiC crystal grown in the step (A) or the step (B). And a step of growing the SiC crystal from the SiC crystal as a starting point, and a manufacturing method in which the step (B) and the step (C) are performed once or more.

  The solution method is a method for producing a SiC single crystal in which a SiC single crystal is grown by bringing a SiC seed crystal into contact with a Si—C solution having a temperature gradient that decreases from the inside toward the surface. The surface region of the Si-C solution is supersaturated by forming a temperature gradient that lowers the temperature from the inside of the Si-C solution toward the surface of the solution, and the seed crystal brought into contact with the Si-C solution is used as a base point. Single crystals can be grown.

  In the step (A), an SiC crystal is grown using a seed crystal that is an SiC single crystal as a base point. However, the SiC crystal to be grown may include not only a single crystal with good crystallinity but also a polycrystalline portion and / or a single crystal portion with low crystallinity. The polycrystalline portion and the single crystal portion having low crystallinity can be generated particularly on the side surface with respect to the growth direction of the grown crystal.

  When the SiC crystal grown in the step (A) includes a polycrystalline portion and / or a single crystal portion having low crystallinity, the side surface of the SiC crystal grown in the step (A) with respect to the growth direction in the step (B) The polycrystalline portion and / or the single crystal portion having low crystallinity can be removed.

  In the step (C), the SiC crystal can be further grown from the SiC crystal from which the polycrystal portion and / or the single crystal portion having low crystallinity is removed in the step (B).

  As described above, in the manufacturing method according to the present invention, in the step (A), the SiC crystal is grown from the seed crystal, and then the step (B) and the step (C) are sequentially performed at least once. it can.

  Moreover, in the manufacturing method which concerns on this invention, you may perform a process (B) and a process (C) in multiple times. The SiC crystal grown in the step (C) may include a polycrystalline portion and / or a single crystal portion having low crystallinity. In this case, again, in the step (B), from the side surface with respect to the growth direction of the SiC crystal. The polycrystalline portion and / or the single crystal portion having low crystallinity can be removed. Next, a SiC crystal can be further grown in the step (C). Thus, for example, after the step (A), the step (B) and the step (C) may be repeated a plurality of times in order.

  In the manufacturing method according to the present invention, the step (B) and the step (C) may be performed a plurality of times and different times. For example, in the step (A), an SiC crystal grown using a seed crystal as a base point does not include a polycrystalline portion and / or a single crystal portion having low crystallinity, or an included polycrystalline portion and / or a single crystal having low crystallinity. When it is judged that the crystal part is small and the influence on the subsequent crystal growth is small, the process proceeds to step (C) without passing through step (B) after step (A), and then the SiC crystal is formed. It may be grown. When the SiC crystal grown in the step (C) includes a polycrystal part and / or a single crystal part with low crystallinity, the polycrystal part and / or the single crystal part with low crystallinity is again formed in the step (B). Can be removed.

  Further, in the SiC crystal grown in the step (C), a polycrystalline portion and / or a single crystal portion having low crystallinity is not generated, or a polycrystalline portion and / or a single crystal portion having low crystallinity is small, and the subsequent crystal When it is judged that the influence on the growth is small, the step (C) can be repeated until a polycrystalline portion exceeding the allowable range and / or a single crystal portion having low crystallinity is generated.

  In the step (C), when a polycrystalline portion exceeding the allowable range and / or a single crystal portion having low crystallinity is generated in the SiC grown crystal, the polycrystalline portion is viewed from the side with respect to the growth direction of the SiC grown crystal in the step (B). And / or a single crystal part having low crystallinity can be removed. Thereafter, an SiC crystal can be grown again in the step (C).

  The allowable range is a criterion that can be arbitrarily determined as long as the polycrystalline portion and / or the single crystal portion having low crystallinity can be removed to a desired amount or less in the step (B). Moreover, the single crystal part with low crystallinity means a single crystal part including a large amount of stacking faults that can affect subsequent crystal growth.

  In the manufacturing method which concerns on this invention, you may complete | finish at any process of a process (B) and a process (C).

  In the step (B), the method of removing the polycrystalline portion and / or the single crystal portion having low crystallinity from the side surface with respect to the growth direction of the SiC crystal can be any method, for example, by cutting and / or polishing. The crystal part and / or the single crystal part with low crystallinity can be removed from the SiC crystal.

  FIG. 1 shows a schematic cross-sectional view of an SiC crystal grown using a seed crystal as a base point. As shown in FIG. 1, the SiC crystal 30 can be grown on the basis of the seed crystal substrate 14, but generally the SiC crystal 30 can be grown so that the diameter is larger than the lower surface 16 of the seed crystal substrate 14. Thus, when growing so that the diameter is enlarged, the crystallinity of the diameter-enlarged portion 32 is generally low, and a single crystal having a polycrystal and / or low crystallinity can be generated.

  When the polycrystalline and / or single crystal generation part 34 having low crystallinity is the same area as the enlarged diameter part 32 or smaller than the enlarged diameter part 32, the enlarged diameter part 32 is removed as shown in FIG. In this way, the removal position 36 can be determined and cut and / or polished. That is, as shown in FIG. 1, it is perpendicular to the lower surface 16 of the seed crystal substrate 14 or parallel to the side surface of the seed crystal substrate 14 and expands outward from the same position as the end of the lower surface 16 of the seed crystal substrate 14. Cutting and / or polishing may be performed so as to remove the removed portion.

  In addition, as shown in FIG. 2, when the polycrystalline and / or low crystallinity single crystal generating portion 34 is an area smaller than the enlarged-diameter portion 32, the polycrystalline and / or low crystalline single crystal generating portion 34 is used. The removal position 36 may be determined obliquely with respect to the lower surface 16 of the seed crystal substrate 14 so as to be removed and cut and / or polished.

  In general, since the crystal quality of the enlarged-diameter portion 32 is lower than that of the center portion of the grown crystal, it is preferable to perform cutting and / or polishing so as to remove the enlarged-diameter portion 32. Further, it is preferable to perform mirror polishing after cutting and / or polishing.

  In addition, when the polycrystalline portion and / or the single crystal portion having low crystallinity is generated inside the enlarged diameter portion 32, or when the crystal is grown without the enlarged diameter portion 32, the side surface of the grown crystal is formed. When a polycrystal and / or a single crystal having low crystallinity is generated, a polycrystalline portion and / or a single crystal having low crystallinity is grown from a more central region (region immediately below the lower surface 16 of the seed crystal substrate) of the grown crystal. The crystal part may be removed.

  In the step (B), all the polycrystalline portions and / or single crystal portions having low crystallinity on the side surfaces with respect to the growth direction of the grown crystal may be removed. In this case, in the subsequent crystal growth, it is possible to further suppress the generation of a polycrystalline portion and / or a single crystal portion having low crystallinity in the grown crystal.

  In the step (B), a part of the outer peripheral portion of the growth surface of the grown crystal may be roughened. By making a part of the outer peripheral portion of the growth surface of the growth crystal rough, when the growth crystal is pulled up from the Si-C solution after crystal growth, the Si-C solution (melt) adhering to the growth crystal is The Si—C solution (melt) can be attracted to the outer peripheral part of the growth surface and solidified by being drawn to the rough part of the outer peripheral part. This prevents the Si—C solution (melt) from solidifying at the center of the crystal growth surface, reduces the stress applied to the grown crystal during cooling after the SiC crystal growth, and prevents the SiC grown crystal from cracking. Can be prevented.

  For example, in the case of m-plane growth, the roughened portion on the growth surface is preferably at least a part of the outer peripheral portion in contact with the side surface parallel to the streak-like stacking fault that may occur in the SiC growth crystal. The side surface perpendicular to the streak-like stacking fault is likely to be the starting point for stacking faults and polycrystals, and if the outer peripheral portion in contact with the side surface perpendicular to the stacking fault is rough on the growth surface, It was found that crystals and / or single crystals with low crystallinity are likely to be generated.

  A state in which a part of the outer peripheral portion of the growth surface is rough means that when the grown crystal is pulled up from the Si-C solution after crystal growth, the Si-C solution can be drawn to the outer peripheral portion of the growth surface. The surface condition. Without being bound by theory, it is considered that the Si-C solution is attracted to the rough part of the outer peripheral part of the growth surface because the rough part has many irregularities and the surface area increases, and the adhesion force increases. It is done.

  The method for making a part of the outer peripheral portion of the growth surface rough can be performed by any method. For example, in the method for removing a polycrystalline portion and / or a single crystal portion having low crystallinity, the polycrystalline portion and / or the single crystal portion having low crystallinity are all removed from the side surface with respect to the growth direction of the grown SiC crystal. Instead, the polycrystalline portion and / or the single crystal portion with low crystallinity may be removed so as to leave a part. In addition, if there are no polycrystal parts and single crystal parts with low crystallinity on the crystal growth surface, a part of the outer peripheral part of the growth surface is intentionally scratched with coarse abrasive paper or a diamond pen. May be attached.

  As an example, FIG. 3 is a schematic diagram of a crystal growth surface 38 having a state portion 44 in which a part of the outer peripheral portion in contact with the (000-1) plane, which is a side surface with respect to the growth direction when m-plane growth is performed, is rough. Indicates.

  As shown in FIG. 3, the width 40 of the rough portion 44 on the growth surface 38 is preferably about 0.1 to 3 mm, more preferably about 0.2 to 2 mm, and still more preferably about 0.3 to 1 mm. is there.

  Further, as shown in FIG. 3, the length 42 in a rough state on the growth surface is preferably about 0.1 to 10 mm in length parallel to the stacking fault, more preferably about 0.5 to 6 mm. More preferably, it has a length of about 1 to 3 mm.

  The shape of the rough state portion 44 may be not only a strip shape as shown in FIG. 3 but also various shapes, and the rough state portion 44 may have various shapes, but the rough state portion 44 is averaged. When generally having the width and length as described above, the Si-C solution can be better collected at the outer periphery of the growth surface. The above numerical range is a preferable range when crystal growth is performed using a seed crystal substrate having a length of about 10 mm and a width of 10 mm, and can be appropriately adjusted according to the size of the seed crystal substrate.

  The method for removing the polycrystalline portion and / or the single crystal portion having low crystallinity is not particularly limited. For example, the polycrystalline portion and / or the single crystal portion having low crystallinity is diced with a diamond coating blade. Can be cut off.

  The mirror polishing of the growth crystal side surface can be performed by the same method as the mirror polishing generally performed. For example, mirror polishing can be performed by buffing using diamond slurry (slurry particle size 1 μm).

  In the step (B), when removing at least part of the polycrystalline portion and / or the single crystal portion having low crystallinity from the side surface with respect to the growth direction of the grown crystal, the growth surface of the grown crystal is polished and / or mirror-polished Also good. Usually, a solidified Si—C solution is attached to the crystal growth surface. However, when the height of the solidified Si—C solution attached to the growth surface is large, a growth base point is used when crystal growth is performed again. The position where the lower surface of the crystal comes into contact with the Si-C solution is changed. In this case, in order to remove the solidified Si—C solution, the growth surface may be polished and / or mirror-polished. In addition, if many streak of stacking faults are generated, inclusion may be involved during crystal growth. Therefore, the growth surface may be polished and / or mirror polished to eliminate stacking fault streaks. When the growth surface is polished and / or mirror-polished, in order to make a part of the outer peripheral portion of the growth surface rough, either the part of the outer peripheral portion of the growth surface is not mirror-polished or mirror-polished. Later, a part of the outer peripheral portion may be scratched using coarse abrasive paper or a diamond pen.

  Since the solidified Si-C solution dissolves when immersed in the Si-C solution (melt), if the amount of solidified Si-C solution is small or the amount of stacking faults is small, Mirror polishing of the growth surface may not be performed. The mirror polishing of the growth surface can be performed by the same method as the mirror polishing of the side surface.

  When mirror polishing is performed on the crystal growth surface, a predetermined thickness may be cut off by dicing before mirror polishing. Generally, however, the growth surface is less required to be cut off thicker than the side surface of the grown crystal, and it is normal. If necessary, only polishing and mirror polishing are sufficient.

  In the method according to the present invention, the crystal growth plane may be a (1-100) plane (m plane). Even when threading dislocations are included in the seed crystal, when m-plane growth is performed, a grown crystal that does not easily generate threading dislocations and does not include threading dislocations can be obtained.

  Therefore, when m-plane growth is performed by the method according to the present invention, in addition to suppressing the generation of polycrystalline and low-crystallinity single crystals, it is possible to suppress the occurrence of threading dislocations. A high-quality SiC single crystal free from crystals and threading dislocations can be obtained.

  Then, the SiC single crystal having a predetermined thickness obtained by performing the m-plane growth by the method according to the present invention is perpendicular to the plane grown by the m-plane so as to give the (000-1) plane (C plane). The face can be cut out and used as a seed crystal for C-plane bulk growth.

  When m-plane growth is performed, stacking faults and basal plane dislocations can occur in the grown crystal. Since stacking faults and basal plane dislocations are generally generated parallel to the C plane, if a C plane is cut out from a crystal grown on m-plane and mirror-polished as necessary, stacking faults and basal plane dislocations are not observed. An SiC single crystal having a C plane can be obtained. Therefore, when the C-plane is cut out from the crystal grown on the m-plane and used as a seed crystal for C-plane growth, generally, stacking faults and basal plane dislocations do not propagate to the grown crystal, and stacking faults and basal plane dislocations are substantially eliminated. C-plane grown crystals that are not included in the crystal can be obtained.

  Therefore, when an SiC single crystal grown by m-plane by the method according to the present invention is used as a seed crystal for C-plane growth, a high-quality SiC single crystal substantially free of threading dislocations, stacking faults, and basal plane dislocations. Crystals can be obtained.

  Since a conventional SiC single crystal includes threading dislocations, there is a problem that threading dislocations can propagate to the grown crystal when C-plane growth is performed, and an SiC single crystal that does not include threading dislocations that can be used as a seed crystal has been desired. In response to such a problem, when m-plane growth is performed by the method according to the present invention, a SiC single crystal that does not include threading dislocations can be obtained.

  On the other hand, in order to use it as a seed crystal for C-plane growth, an SiC single crystal having a C-plane with a predetermined area is required, and for that purpose, an m-plane growth crystal with a predetermined thickness is required. In order to obtain an m-plane grown crystal having a predetermined thickness (long), it is effective to perform m-plane growth for a long time or to repeat m-plane growth a plurality of times. However, when performing such long growth, streaky stacking faults may occur on the m-plane growth surface of the grown crystal. When the number of single crystal parts having low crystallinity with a large number of stacking faults increases, finally, polycrystals may be generated on the entire growth surface of the grown crystal.

  When m-plane growth is performed, the outer peripheral portion in contact with the (11-20) plane and the (-1-120) plane among the side surfaces with respect to the growth direction tends to be the starting point of stacking faults. I understood.

  Therefore, when m-plane growth is performed, it is preferable to remove the polycrystalline portion and / or the single crystal portion having low crystallinity from at least two of the (11-20) plane and the (-1-120) plane. Thereby, in the next crystal growth, the generation of a polycrystalline portion and / or a single crystal portion having low crystallinity can be suppressed. On the other hand, the other two surfaces (0001) and (000-1) are both in a rough state without removing the polycrystalline portion and / or the single crystal portion having low crystallinity. However, it has little influence on the next crystal growth.

  When m-plane growth is performed, two planes, (11-20) plane and (-1-120) plane, and (0001) plane and (000-1) plane, which are side faces with respect to the growth direction of the grown crystal, are formed. Polycrystalline portions and / or single crystal portions having low crystallinity may be removed from the four faces.

  When m-plane growth is performed, it is preferable to make the outer peripheral portion of the growth surface in contact with any one of the (0001) plane and the (000-1) plane rough.

  By making the outer peripheral portion of the growth surface in contact with any one of the (0001) plane and the (000-1) plane rough, the generation of polycrystals and / or single crystals with low crystallinity is suppressed. On the other hand, the Si—C solution is attracted to the rough outer periphery, and cracking of the grown crystal due to adhesion of the Si—C solution during cooling can be suppressed.

  By making the outer peripheral portion of the growth surface in contact with one of the (0001) plane and the (000-1) plane mirror-polished and making the outer peripheral portion of the growth surface in contact with the other surface roughened When the grown crystal is pulled up from the Si-C solution after crystal growth, the Si-C solution (melt) is attracted to the rough state portion and gathers at the outer peripheral portion of the growth surface. ) Is prevented from remaining in the center, stress applied to the grown crystal during cooling after crystal growth is reduced, and cracking of the grown crystal can be suppressed.

  Both the (0001) plane and the (000-1) plane may be roughened. Even in this case, when the grown crystal was pulled up from the Si-C solution after crystal growth, the Si-C solution (melt) was rough at the outer peripheral portion of the growth surface in contact with the (0001) plane and the (000-1) plane. The Si-C solution (melt) is prevented from remaining in the center because it is attracted to one or both of the state portions and gathers at the end of the growth surface, and the stress applied to the grown crystal during cooling after crystal growth Can be reduced, and cracking of the grown crystal can be suppressed.

  During m-plane growth, it is preferable to remove the polycrystalline portion and / or the single crystal portion having low crystallinity every 2 to 4 mm of crystal growth from the viewpoint of the balance between the manufacturing cost and the quality of the grown crystal.

  When m-plane growth is repeated, the polycrystalline portion and / or the single crystal portion having low crystallinity can be removed each time or once every several degrees. For example, when the growth is repeated by 1 mm with one m-plane growth, the removal of the polycrystalline portion and / or the single crystal portion having low crystallinity is preferably performed every 2 to 4 times, and the growth is repeated by growing 2 mm. When growing, it is preferable to remove the polycrystalline portion and / or the single crystal portion having low crystallinity once or twice.

  In the method according to the present invention, the growth plane may be a (000-1) plane (C plane). When C-plane growth is performed, C-plane bulk growth in which generation of polycrystals and / or single crystal parts having low crystallinity is suppressed can be performed.

  In the method according to the present invention, when performing C-plane growth, polycrystals and / or single crystal parts with low crystallinity are likely to be generated on all side surfaces with respect to the growth surface. It is preferable to remove all of the polycrystalline portion and / or the single crystal portion having low crystallinity. Thereby, in the next crystal growth, the generation of a polycrystalline portion and / or a single crystal portion having low crystallinity can be suppressed.

  When performing C-plane growth, the polycrystalline portion and / or the single crystal portion having low crystallinity are all removed so that the growth surface of the growth crystal becomes a columnar shape (so that the growth surface is circular). May be.

  At the time of C-plane growth, it is preferable to remove the polycrystalline portion and / or the single crystal portion having low crystallinity every 3 to 6 mm from the viewpoint of the balance between the manufacturing cost and the quality of the grown crystal.

  Further, when the C-plane growth is repeated, the polycrystalline portion can be removed every time or once every several degrees. For example, when the growth is repeated by 3 mm growth by one C-plane growth, the removal of the polycrystalline portion is preferably performed once or twice, and more preferably every time.

  In the method according to the present invention, as the seed crystal used in the step (A), a SiC single crystal having a quality generally used for producing a SiC single crystal can be used. For example, a SiC single crystal generally prepared by a sublimation method can be used as a seed crystal. The SiC single crystal generally produced by such a sublimation method generally contains many threading dislocations. In addition, the seed crystal that can be used in the present method can have any shape such as a plate shape, a disk shape, a columnar shape, a prism shape, a truncated cone shape, or a truncated pyramid shape.

  The seed crystal can be installed in the single crystal manufacturing apparatus by holding the upper surface of the seed crystal on the seed crystal holding shaft.

  The contact of the seed crystal with the Si-C solution is performed by lowering the seed crystal holding axis holding the seed crystal toward the Si-C solution surface, and with the lower surface of the seed crystal parallel to the Si-C solution surface. It can be performed by contacting with a -C solution. Then, the SiC single crystal can be grown by holding the seed crystal at a predetermined position with respect to the Si—C solution surface.

  The holding position of the seed crystal is such that the position of the lower surface of the seed crystal coincides with the Si-C solution surface, is below the Si-C solution surface, or is above the Si-C solution surface. There may be. When the lower surface of the seed crystal is held at a position above the Si-C solution surface, the seed crystal is once brought into contact with the Si-C solution and the Si-C solution is brought into contact with the lower surface of the seed crystal. Pull up into place. The position of the lower surface of the seed crystal may coincide with the Si-C solution surface or be lower than the Si-C solution surface. It is preferable to prevent the -C solution from contacting. In these methods, the position of the seed crystal may be adjusted during crystal growth.

  The seed crystal holding axis may be a graphite axis that holds the seed crystal substrate on its end face. The seed crystal holding shaft may have an arbitrary shape such as a columnar shape or a prismatic shape, and a graphite shaft having the same end surface shape as the shape of the upper surface of the seed crystal may be used.

  In the present invention, the Si—C solution refers to a solution in which C is dissolved using a melt of Si or Si / X (X is one or more metals other than Si) as a solvent. X is one or more kinds of metals, and is not particularly limited as long as it can form a liquid phase (solution) in thermodynamic equilibrium with SiC (solid phase). Examples of suitable metals X include Ti, Mn, Cr, Ni, Ce, Co, V, Fe and the like.

  The Si—C solution is preferably a Si—C solution using a melt of Si / Cr / X (X is one or more metals other than Si and Cr) as a solvent. Furthermore, a Si—C solution using a melt of Si / Cr / X = 30 to 80/20 to 60/0 to 10 in terms of atomic composition percentage as a solvent is preferable since there is little variation in the dissolved amount of C. For example, in addition to Si, Cr, Ni, or the like can be charged into the crucible to form a Si—Cr solution, a Si—Cr—Ni solution, or the like.

  The surface temperature of the Si—C solution is preferably 1800 to 2200 ° C. with little variation in the amount of C dissolved in the Si—C solution.

  The temperature of the Si—C solution can be measured using a thermocouple, a radiation thermometer, or the like. Regarding the thermocouple, from the viewpoint of high temperature measurement and prevention of impurity contamination, a thermocouple in which a tungsten-rhenium strand coated with zirconia or magnesia glass is placed in a graphite protective tube is preferable.

  FIG. 4 shows an example of a SiC single crystal manufacturing apparatus suitable for carrying out the method of the present invention. The illustrated SiC single crystal manufacturing apparatus 100 includes a crucible 10 containing a Si-C solution 24 in which C is dissolved in a Si or Si / X melt, and is provided on the surface of the solution from the inside of the Si-C solution. A SiC single crystal can be grown by forming a temperature gradient that decreases toward the surface and bringing the seed crystal substrate 14 held at the tip of the graphite shaft 12 that can be moved up and down into contact with the Si-C solution 24. The crucible 10 and / or the graphite shaft 12 may be rotated.

  The Si-C solution 24 is prepared by charging a raw material into a crucible and dissolving C in a Si or Si / X melt prepared by heating and melting. By making the crucible 10 a carbonaceous crucible such as a graphite crucible or an SiC crucible, C is dissolved in the melt by melting the crucible 10 to form an Si-C solution. In this way, undissolved C does not exist in the Si—C solution 24, and waste of SiC due to precipitation of the SiC single crystal in the undissolved C can be prevented. The supply of C may be performed by, for example, a method of injecting hydrocarbon gas or charging a solid C supply source together with the melt raw material, or combining these methods with melting of a crucible. Also good.

  In order to keep warm, the outer periphery of the crucible 10 is covered with a heat insulating material 18. These are collectively accommodated in the quartz tube 26. A high frequency coil 22 for heating is disposed on the outer periphery of the quartz tube 26. The high frequency coil 22 may be composed of an upper coil 22A and a lower coil 22B, and the upper coil 22A and the lower coil 22B can be independently controlled.

Since the crucible 10, the heat insulating material 18, the quartz tube 26, and the high frequency coil 22 become high temperature, they are disposed inside the water cooling chamber. The water-cooled chamber includes a gas introduction port and a gas exhaust port so that the atmosphere in the apparatus can be adjusted using Ar, He, N ₂ or the like.

  The temperature of the Si—C solution usually has a temperature distribution in which the surface temperature is lower than the inside of the Si—C solution due to radiation or the like. Further, the number and interval of the high frequency coil 22, the high frequency coil 22 and the crucible 10 By adjusting the positional relationship in the height direction and the output of the high-frequency coil, the Si—C solution 24 is so heated that the upper part of the solution in which the seed crystal substrate 14 is immersed is at a low temperature and the lower part of the solution is at a high temperature. A predetermined temperature gradient in the vertical direction can be formed on the surface of the solution 24. For example, the output of the upper coil 22A can be made smaller than the output of the lower coil 22B, and a predetermined temperature gradient can be formed in the Si—C solution 24 such that the upper part of the solution is low and the lower part of the solution is high. The temperature gradient can be, for example, 1 to 30 ° C./cm when the depth from the solution surface is approximately 10 mm.

  C dissolved in the Si-C solution 24 is dispersed by diffusion and convection. The vicinity of the lower surface of the seed crystal substrate 14 has a lower temperature than the lower part of the Si—C solution 24 due to the output control of the upper / lower stages of the coil 22, the heat radiation from the surface of the Si—C solution, and the heat removal through the graphite shaft 12. A temperature gradient is formed. When C dissolved in the lower part of the solution having high solubility at high temperature reaches the vicinity of the lower surface of the seed crystal substrate having low solubility at low temperature, a supersaturated state is reached. Can do.

  In some embodiments, before the growth of the SiC single crystal, meltback may be performed to dissolve and remove the surface layer of the SiC seed crystal substrate in the Si—C solution. The surface layer of the seed crystal substrate on which the SiC single crystal is grown may have a work-affected layer such as dislocations or a natural oxide film, which must be dissolved and removed before the SiC single crystal is grown. However, it is effective for growing a high-quality SiC single crystal. Although the thickness to melt | dissolves also depends on the processing state of the surface of a SiC seed crystal substrate, about 5-50 micrometers is preferable in order to fully remove a work-affected layer and a natural oxide film.

  The meltback can be performed by forming a temperature gradient in the Si-C solution in which the temperature increases from the inside of the Si-C solution toward the surface of the solution, that is, a temperature gradient opposite to the SiC single crystal growth. it can. The temperature gradient in the reverse direction can be formed by controlling the output of the high frequency coil.

  Melt back can also be performed by immersing the seed crystal substrate in a Si—C solution heated to a temperature higher than the liquidus temperature without forming a temperature gradient in the Si—C solution. In this case, the higher the Si-C solution temperature, the higher the dissolution rate, but it becomes difficult to control the dissolution amount.

  In some embodiments, the seed crystal substrate may be preheated before contacting the seed crystal substrate with the Si-C solution. When a low-temperature seed crystal substrate is brought into contact with a high-temperature Si—C solution, heat shock dislocation may occur in the seed crystal. Heating the seed crystal substrate before bringing the seed crystal substrate into contact with the Si—C solution is effective for preventing thermal shock dislocation and growing a high-quality SiC single crystal. The seed crystal substrate can be heated by heating the entire graphite axis. In this case, after the seed crystal substrate is brought into contact with the Si—C solution, the heating of the seed crystal holding shaft is stopped before the SiC single crystal is grown. Alternatively, instead of this method, the Si—C solution may be heated to a temperature at which the crystal grows after contacting the seed crystal with a relatively low temperature Si—C solution. This case is also effective for preventing heat shock dislocation and growing a high-quality SiC single crystal.

(Example 1)
It is a rectangular parallelepiped 4H—SiC single crystal having a length of 10 mm, a width of 10 mm, and a thickness of 1 mm, and its side surfaces are (11-20) plane, (−1−120) plane, (0001) plane, and (000−1). ) Surface, and a SiC single crystal produced by a sublimation method having a (1-100) plane (m-plane) on the lower surface was prepared and used as a seed crystal substrate. The upper surface of the seed crystal substrate was bonded to the substantially central portion of the end surface of the columnar graphite shaft using a graphite adhesive.

  Using the single crystal manufacturing apparatus shown in FIG. 4, Si / Cr / Ni was charged as a melt raw material at a ratio of atomic composition percentage of 50:40:10 into a graphite crucible containing the Si—C solution 24. The air inside the single crystal manufacturing apparatus was replaced with helium. The high-frequency coil 22 disposed around the graphite crucible 10 was energized and heated to melt the raw material in the graphite crucible 10 to form a Si / Cr / Ni alloy melt. Then, a sufficient amount of C was dissolved from the graphite crucible 10 in the Si / Cr / Ni alloy melt to form a Si—C solution 24.

  The graphite crucible 10 was heated by adjusting the outputs of the upper coil 22A and the lower coil 22B to form a temperature gradient in which the temperature decreased from the inside of the Si—C solution 24 toward the surface of the solution. To confirm that the predetermined temperature gradient is formed, the temperature of the Si-C solution 24 is measured by using a thermocouple in which a zirconia-coated tungsten-rhenium strand can be moved up and down and placed in a graphite protective tube. Was done by. The temperature on the surface of the Si—C solution 24 was set to 2000 ° C. by controlling the outputs of the high frequency coils 22A and 22B. The temperature difference between the temperature at the surface of the Si—C solution and the temperature at a depth of 10 mm in the vertical direction from the surface of the Si—C solution 24 toward the inside of the solution is 10 C.

Step (1-A)
The lower surface (m-plane) of the seed crystal bonded to the graphite shaft is immersed in the Si-C solution in parallel with the Si-C solution surface, and the graphite shaft is wetted with the Si-C solution. The graphite shaft was pulled up so as to be located 1 mm above the liquid level of the -C solution. The SiC crystal was grown by holding for 10 hours at the position where it was pulled up by 1 mm.

  After the completion of crystal growth, the graphite axis was raised, and the seed crystal and the SiC crystal grown from the seed crystal as a base point were separated from the Si-C solution and the graphite axis and collected. The obtained grown crystal grows so that the diameter is increased with respect to the lower surface of the seed crystal, and has a diameter of 16 mm and a thickness of 1.1 mm (excluding the thickness of the seed crystal produced by the sublimation method; the same applies hereinafter). Had. The diameter of the growth crystal is the diameter of the smallest circle surrounding the growth surface, and the thickness of the growth crystal is the thickness at the center of the growth surface of the growth crystal.

  A photomicrograph observed from the growth surface of the crystal obtained in the step (1-A) is shown in FIG. It was found that the center part of the growth surface of the obtained crystal was flat and a SiC single crystal was obtained, and a polycrystalline part was generated at the outer peripheral part (diameter enlarged part) of the growth surface. Moreover, the solidified Si—C solution was attracted to the polycrystalline portion at the outer peripheral portion of the grown crystal, and no crack was observed in the grown SiC single crystal.

Step (1-B)
The grown crystal obtained in the step (1-A) is parallel to each of the (11-20) plane, the (-1-120) plane, and the (000-1) plane, which are the side surfaces with respect to the growth direction of the grown crystal. Then, the polycrystalline portion was removed by dicing and cutting with a diamond blade so as to remove the enlarged diameter portion. For the (0001) plane, the polycrystalline part was left without being cut out. Next, the three side surfaces, which are cut surfaces, were mirror-polished.

Step (1-C)
The crystal obtained in the step (1-B) was used as a seed crystal. In order to prevent the graphite axis from getting wet with the Si-C solution, the position of the lower surface (m-plane) of the seed crystal is arranged at a position coinciding with the liquid surface of the Si-C solution. A seed touch was made to contact the lower surface, and then the graphite shaft was pulled up so that the position of the lower surface of the seed crystal was positioned 1 mm above the liquid surface of the Si—C solution. Thus, except that the crystal obtained in the step (1-B) was used as a seed crystal to prevent the Si—C solution from getting wet on the graphite axis and the growth time was 24 hours, the step (1 M-plane crystal growth was performed under the same conditions as in -A).

  After the completion of crystal growth, the graphite axis was raised, and the seed crystal and the SiC crystal grown from the seed crystal as a base point were separated from the Si-C solution and the graphite axis and collected. The grown crystal obtained had a diameter of 14 mm and a total thickness of 2.7 mm.

  A photomicrograph observed from the growth surface of the obtained crystal is shown in FIG. The center part of the growth surface of the obtained crystal was flat, a SiC single crystal was obtained, and no threading dislocation was observed. In the step (1-B), a polycrystalline portion is generated in the outer peripheral portion of the growth surface corresponding to the position where the polycrystalline portion is left, and the solidified Si—C solution is attracted to the polycrystalline portion, No cracks were found in the grown SiC single crystal.

(Example 2)
Step (2-A)
A SiC single crystal produced by the same sublimation method as in step (1-A) of Example 1 was prepared and used as a seed crystal substrate. Then, the lower surface of the seed crystal is brought into contact with the Si-C solution by arranging the position of the lower surface of the seed crystal at a position corresponding to the liquid surface of the Si-C solution so that the graphite axis does not get wet with the Si-C solution. The seed touch was performed, and then the graphite shaft was pulled up so that the position of the lower surface of the seed crystal was 1 mm above the liquid surface of the Si—C solution. Thus, m-plane crystal growth was performed under the same conditions as in Step (1-A) of Example 1 except that the Si—C solution did not wet onto the graphite axis and the growth time was 15 hours.

  After the completion of crystal growth, the graphite axis was raised, and the seed crystal and the SiC crystal grown from the seed crystal as a base point were separated from the Si-C solution and the graphite axis and collected. The obtained grown crystal had a diameter of 12 mm and a thickness of 2.0 mm (excluding the thickness of the seed crystal produced by the sublimation method; the same applies hereinafter).

Step (2-C) First Time Using the grown crystal obtained in Step (2-A) as a seed crystal, m-plane crystal growth was performed under the same conditions as in Step (2-A).

  After the completion of crystal growth, the graphite axis was raised, and the seed crystal and the SiC crystal grown from the seed crystal as a base point were separated from the Si-C solution and the graphite axis and collected. The obtained grown crystal had a diameter of 14 mm and a thickness of 3.0 mm.

Step (2-C) 2nd Step (2-C) The same conditions as in Step (2-C) 1st time except that the growth crystal obtained in the 1st time was used as a seed crystal and the growth time was 24 hours. Then, m-plane crystal growth was performed.

  After the completion of crystal growth, the graphite axis was raised, and the seed crystal and the SiC crystal grown from the seed crystal as a base point were separated from the Si-C solution and the graphite axis and collected. The obtained grown crystal had a diameter of 15 mm and a thickness of 5.0 mm.

  A micrograph observed from the growth surface of the obtained crystal is shown in FIG. Although the center part of the growth surface of the obtained crystal was almost flat and a SiC single crystal was obtained, some streaks of stacking faults were observed.

Step (2-C) Third Time Using the grown crystal obtained in the second step (2-C) as a seed crystal, m-plane crystal growth was performed under the same conditions as in the first step (2-C).

  After the completion of crystal growth, the graphite axis was raised, and the seed crystal and the SiC crystal grown from the seed crystal as a base point were separated from the Si-C solution and the graphite axis and collected. The obtained grown crystal had a diameter of 1.6 mm and a thickness of 6.1 mm.

  Although the center part of the growth surface of the obtained crystal was almost flat and a SiC single crystal was obtained, the number of streak of stacking faults was larger than the crystal grown in the second step (2-C). .

Step (2-C) 4th Step (2-C) The growth surface of the growth crystal obtained in the 3rd step is mirror-polished, this growth crystal is used as a seed crystal, and the growth time is 24 hours. Step (2-C) m-plane crystal growth was performed under the same conditions as in the first time.

  After the completion of crystal growth, the graphite axis was raised, and the seed crystal and the SiC crystal grown from the seed crystal as a base point were separated from the Si-C solution and the graphite axis and collected. The obtained grown crystal had a diameter of 19 mm and a thickness of 8.0 mm.

  A photomicrograph of the obtained crystal observed from the growth surface is shown in FIG. 8, and a photomicrograph observed from the side is shown in FIG. The entire crystal growth surface was polycrystallized.

Step (2-B) 1st Step (2-C) About the grown crystal obtained in the 4th time, (11-20) plane, (-1-120) plane, (0001) plane, and (000-1) Parallel to each of the surfaces, the polycrystalline portion was removed by dicing using a diamond blade so as to remove the enlarged-diameter portion to obtain a block-like crystal. Subsequently, mirror polishing was performed on the four side surfaces and the growth surface, which were cut surfaces, to obtain SiC single crystals having a length of 8.6 mm, a width of 8.6 mm, and a thickness of 7.0 mm.

Step (2-C) 5th time Step (2-B) The same conditions as in Step (2-C) 1st time except that the growth crystal obtained in the 1st time was used as a seed crystal and the growth time was 14 hours. Then, m-plane crystal growth was performed.

  After the completion of crystal growth, the graphite axis was raised, and the seed crystal and the SiC crystal grown from the seed crystal as a base point were separated from the Si-C solution and the graphite axis and collected. The obtained grown crystal had a diameter of 9.5 mm and a thickness of 8.0 mm.

  A micrograph of the obtained crystal observed from the growth surface is shown in FIG. The obtained crystal growth surface was found to have good flatness although some stacking faults were observed. Moreover, the photograph observed from the side surface about the grown crystal is shown in FIG. It can be seen that the crystal has grown from a block-shaped seed crystal whose side surface is cut as a base point.

Step (2-B) 2nd time Step (2-C) About the grown crystal obtained in the 5th time, parallel to the (11-20) plane and the (-1-120) plane, which are the side surfaces of the grown crystal. The polycrystalline portion was removed by dicing using a diamond blade so as to remove the enlarged-diameter portion. Next, mirror polishing was performed on two of the side surfaces that were cut surfaces.

Step (2-C) Sixth Step Using the growth crystal obtained in the second step (2-B) as a seed crystal, m-plane crystal growth was performed under the same conditions as in the first step (2-C).

  After the completion of crystal growth, the graphite axis was raised, and the seed crystal and the SiC crystal grown from the seed crystal as a base point were separated from the Si-C solution and the graphite axis and collected. The obtained grown crystal had a diameter of 11 mm and a thickness of 8.5 mm.

  The obtained crystal growth surface was found to have good flatness although some stacking faults were observed.

Step (2-C) 7th time, Step (2-B) 3rd time, Step (2-C) 8th time Step (2-C) Using the grown crystal obtained in the 6th time as a seed crystal, C) m-plane crystal growth was performed under the same conditions as the first time. The obtained crystal growth surface had good flatness although some stacking faults were observed. Step (2-B) Side treatment was performed in the same manner as the second time, and this was used as a seed crystal, and the growth time was 24 hours. Crystal growth was performed.

  After the completion of crystal growth, the graphite axis was raised, and the seed crystal and the SiC crystal grown from the seed crystal as a base point were separated from the Si-C solution and the graphite axis and collected. The obtained grown crystal had a diameter of 10 mm and a thickness of 9.0 mm.

  The growth surface of the obtained crystal had good flatness although some stacking faults were observed, and no threading dislocation was observed.

DESCRIPTION OF SYMBOLS 100 Single crystal manufacturing apparatus 10 Graphite crucible 12 Graphite shaft 14 Seed crystal substrate 16 Lower surface of seed crystal substrate 18 Heat insulating material 22 High frequency coil 22A Upper high frequency coil 22B Lower high frequency coil 24 Si-C solution 26 Quartz tube 30 Grown SiC crystal 32 Diameter Enlarged portion 34 Polycrystalline and / or low crystallinity single crystal generating portion 36 Removal position 38 Growth surface of grown crystal 40 Width of rough state portion 42 Length of rough state portion 44 Rough state portion 46 Side cut Block seed crystals

Claims (7)

A method for producing a SiC crystal by a solution method,
(A) a step of growing a SiC crystal starting from a seed crystal;
(B) removing at least a part of the polycrystalline portion and / or the single crystal portion having low crystallinity from the side surface with respect to the growth direction of the SiC crystal grown in the step (A) or the step (C); ) Growing a SiC crystal starting from the SiC crystal grown in the step (A) or the SiC crystal obtained in the step (B),
And the step (B) and the step (C) are performed once or more.   The manufacturing method according to claim 1, wherein in the step (B), a part of the outer peripheral portion of the growth surface of the grown SiC crystal is roughened.   The part of the outer peripheral part is in a rough state, leaving part of the polycrystalline part and / or single crystal part having low crystallinity of the grown SiC crystal. Manufacturing method.   The manufacturing method as described in any one of Claims 1-3 whose growth surface of the said SiC crystal is m plane.   The growth surface of the SiC crystal is an m-plane, and at least a part of the outer peripheral portion of the growth surface that is in contact with the (0001) plane and the (000-1) plane is made rough. The manufacturing method of Claim 2 or 3.   The manufacturing method of Claim 1 whose growth surface of the said SiC crystal is a C surface.   The manufacturing method according to claim 6, wherein in the step (B), all of the polycrystalline portion and / or the single crystal portion having low crystallinity are removed from the side surface with respect to the growth direction of the grown SiC crystal.