JP2017202969A - SiC SINGLE CRYSTAL, AND PRODUCTION METHOD THEREOF - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of an SiC single crystal that suppresses generation of a polytype other than 4H and grows a 4H-SiC single crystal.SOLUTION: In a production method of an SiC single crystal, a seed crystal substrate is brought into contact with an Si-C solution to grow an SiC single crystal, the solution having a temperature gradient that lowers the temperature from the inside toward the surface of the solution. The seed crystal substrate is 4H-SiC and the (000-1) plane of the seed crystal substrate is a growth surface. The surface of the SiC solution has a temperature of 1,900°C or higher at the center part of an area that the growth surface of the seed crystal substrate contacts. A ratio ΔTc/ΔTa is 1.7 or more, wherein ΔTc is a temperature gradient between the center part and a position 10 mm apart from the center part in the downward vertical direction; and ΔTa is a temperature gradient between the center part and a position 10 mm apart from the center part in the horizontal direction.SELECTED DRAWING: Figure 14

Description

  The present disclosure relates to a method for producing a SiC single crystal.

  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 drawbacks such as the formation of lattice defects such as hollow through defects called micropipe defects and stacking faults and heterogeneous polytypes (crystal polymorphism) in the grown single crystal. However, many of SiC bulk single crystals have been conventionally produced 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 a Si melt in which a metal other than Si is melted is formed in a graphite crucible, C is dissolved in the melt, and a SiC crystal is formed on a seed crystal substrate placed in a low temperature portion. In this method, the layer is deposited and grown. In the solution method, crystal growth is performed in a state close to thermal equilibrium as compared with the vapor phase method, so that the reduction in defects can be most expected and heterogeneous polytypes are hardly generated. For this reason, several methods for producing SiC single crystals by the solution method have recently been proposed.

  For example, in Patent Document 1, a (000-1) plane of a hexagonal SiC single crystal is used as a seed crystal substrate, and the temperature gradient in the depth direction of the melt is within a range of 1 to 5 ° C./mm. A method for producing a hexagonal SiC single crystal to be grown has been proposed. However, in the conventional method such as Patent Document 1, for example, even if crystal growth is performed on a 4H—SiC seed crystal, polytype control is sufficiently performed such that 6H, 15R, etc. grow and 4H cannot be maintained. It was difficult to do.

JP 2007-197274 A JP 2006-131433 A

  It is known that SiC crystals have polytypes (crystal polymorphs) such as 2H, 3C, 4H, 6H, and 15R. Since each polytype has different physical and electrical characteristics, it is necessary to control the polytype in order to apply the SiC crystal to the device. For device application, 4H-SiC is preferably used from the viewpoint of high on-hole mobility and low on-resistance when used as a power device. However, in the conventional method such as Patent Document 1, it is difficult to stably produce a 4H-SiC single crystal because a different polytype is generated.

  Therefore, a method for producing an SiC single crystal that can sufficiently control the polytype is desired.

  The inventor of the present application has conducted extensive research on polytype control, and in the prior art such as Patent Document 1, the temperature gradient in the horizontal direction (parallel to the growth surface) of the Si—C solution is not taken into consideration. When the temperature gradient in the direction becomes larger, the terrace width becomes wider, and nuclei of different polytypes are generated on the terrace, resulting in the knowledge that the polytype cannot be controlled sufficiently. And this inventor uses a 4H-SiC single crystal as a seed crystal substrate, and makes the (000-1) plane of a seed crystal substrate a growth surface, and is horizontal with respect to the temperature gradient of the vertical direction of a Si-C solution. It has been found that 4H-SiC single crystals can be grown while the generation of polytypes other than 4H can be suppressed by reducing the temperature gradient.

The present disclosure is a method for producing a SiC single crystal, wherein a SiC single crystal is grown by bringing a seed crystal substrate into contact with a Si-C solution having a temperature gradient that decreases from the inside toward the liquid surface,
The seed crystal substrate is 4H-SiC;
Making the (000-1) plane of the seed crystal substrate a growth plane;
The temperature of the central part of the region where the growth surface of the seed crystal substrate is in contact with the surface of the Si-C solution is set to 1900 ° C. or higher, and the central part and a position 10 mm vertically downward from the central part, The ratio ΔTc / ΔTa between the temperature gradient ΔTc between the central portion and the temperature gradient ΔTa between the central portion and a position 10 mm in the horizontal direction from the central portion is 1.7 or more. For manufacturing methods.

  The present disclosure is also directed to a SiC single crystal having a terrace width on a growth surface of 11 μm or less and a 4H ratio of 46% or more.

  According to the method of the present disclosure, it is possible to grow a 4H—SiC single crystal while suppressing the generation of polytypes other than 4H.

FIG. 1 is a schematic cross-sectional view of an SiC single crystal manufacturing apparatus that can be used in the manufacturing method of the present disclosure. FIG. 2 is an enlarged schematic view of the vicinity of the center of the region of the surface of the Si—C solution 24 where the growth surface of the seed crystal substrate contacts. FIG. 3 is a schematic cross-sectional view showing a mode in which two-dimensional nuclei other than 4H are generated on a terrace having a large width. FIG. 4 is a schematic cross-sectional view showing an aspect in which the terrace width is small and no two-dimensional nucleus other than 4H is generated. FIG. 5 is a schematic cross-sectional view of a meniscus 34 formed between the seed crystal substrate 14 and the Si—C solution 24. FIG. 6 is a Raman spectrum of the grown crystal determined to be 4H. FIG. 7 is an appearance photograph of the obtained grown crystal observed from the growth surface. FIG. 8 is an optical micrograph showing an enlarged growth surface of the obtained grown crystal. FIG. 9 is an appearance photograph of the obtained grown crystal observed from the growth surface. FIG. 10 is an optical micrograph in which the growth surface of the obtained grown crystal is enlarged. FIG. 11 is a Raman spectrum of a grown crystal in which a polytype other than 4H is generated. FIG. 12 is an appearance photograph of the obtained grown crystal observed from the growth surface. FIG. 13 is an optical micrograph in which the growth surface of the obtained grown crystal is enlarged. FIG. 14 is a graph showing the 4H rate by ΔTc / ΔTa. FIG. 15 is a graph showing the relationship between the temperature at the center of the region where the growth surface of the seed crystal substrate contacts the surface of the Si—C solution and the 4H ratio.

  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.

  Since there are various polytypes of SiC crystals and there is almost no difference in free energy, even when crystal growth is conventionally performed on a 4H-SiC seed crystal substrate using the solution method, 6H, 15R, etc. are crystallized. It was difficult to grow and stably obtain a 4H—SiC single crystal.

  In contrast, the inventor of the present application uses a 4H—SiC single crystal as a seed crystal substrate, and uses the (000-1) plane of the seed crystal substrate as a growth surface, while against the temperature gradient in the vertical direction of the Si—C solution. Thus, it has been found that by reducing the temperature gradient in the horizontal direction, it is possible to stably grow a 4H—SiC single crystal while suppressing the generation of polytypes other than 4H.

  The present disclosure is a method for producing a SiC single crystal, in which a SiC single crystal is grown by bringing a seed crystal substrate into contact with a Si-C solution having a temperature gradient that decreases from the inside toward the liquid surface. The crystal substrate is 4H-SiC, and the (000-1) plane of the seed crystal substrate is used as a growth surface, and the central portion of the region of the surface of the Si-C solution where the growth surface of the seed crystal substrate contacts And a temperature gradient ΔTc between the central part and a position 10 mm vertically downward from the central part, and a position 10 mm horizontally from the central part and the central part. A method for producing a SiC single crystal, which includes setting a ratio ΔTc / ΔTa to a temperature gradient ΔTa between 1.7 and 1.7 or more, is targeted.

  According to the method of the present disclosure, it is possible to stably grow a 4H—SiC single crystal while suppressing generation of polytypes other than 4H.

  In the method of the present disclosure, a solution method is used. The solution method is a method of growing a SiC single crystal by bringing a SiC seed crystal substrate into contact with a Si—C solution having a temperature gradient that decreases in temperature from the inside (deep part) toward the liquid level (surface). It is a manufacturing method. By forming a temperature gradient in which the temperature decreases from the inside of the Si-C solution toward the surface of the Si-C solution, the surface region of the Si-C solution is supersaturated, and the seed crystal is brought into contact with the Si-C solution. A SiC single crystal can be grown from the substrate.

  In FIG. 1, an example of the cross-sectional schematic diagram of the SiC single crystal manufacturing apparatus which can be used for the manufacturing method of this indication is shown. 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 melt of Si or Si / X (X is one or more metals other than Si). The seed crystal substrate 14 held at the tip of the seed crystal holding shaft 12 that forms a temperature gradient that decreases in temperature from the inside of the Si—C solution toward the liquid surface of the solution and that can be moved up and down in the vertical direction is used as the Si—C solution. 24, the SiC single crystal can be grown from the seed crystal substrate 14.

  C dissolved in the Si-C solution 24 is dispersed by diffusion and convection. In the vicinity of the lower surface of the seed crystal substrate 14, a temperature gradient ΔTc that is lower than the inside of the Si—C solution 24 is formed. Therefore, C dissolved in the solution having a high solubility at a high temperature is a seed having a low solubility at a low temperature. When reaching the vicinity of the crystal substrate, a supersaturated state is reached, and an SiC crystal can be grown on the seed crystal substrate 14 by using the degree of supersaturation as a driving force.

  The seed crystal substrate used in the method of the present disclosure may be a 4H—SiC single crystal having a (000-1) plane, and a single crystal having a quality generally used for manufacturing a SiC single crystal may be used as the seed crystal substrate. it can. For example, a SiC single crystal generally prepared by a sublimation method can be used as a seed crystal substrate.

  The seed crystal substrate is a 4H—SiC single crystal and has an arbitrary shape such as a plate shape, a disc shape, a columnar shape, a prism shape, a truncated cone shape, or a truncated pyramid shape as long as it has a (000-1) plane. Can do.

  In the method of the present disclosure, the (000-1) plane of the seed crystal substrate is used as the growth plane. By using the (000-1) plane of the seed crystal substrate as the growth plane, single crystal growth can be performed without mixing metal ink into the growth interface.

  In the method of the present disclosure, as shown in FIG. 2, the center portion (center position) of the surface (liquid surface) of the Si—C solution 24 where the growth surface of the seed crystal substrate contacts and the center portion vertically A temperature gradient between a position 10 mm downward in the direction is ΔTc, a temperature gradient between the center portion and a position 10 mm horizontally from the center portion is ΔTa, and ΔTc / ΔTa is a ratio of ΔTc and ΔTa. ΔTa is set to 1.7 or more. FIG. 2 is an enlarged schematic view of the vicinity of the center of the region of the surface of the Si—C solution 24 where the growth surface of the seed crystal substrate contacts.

  ΔTc is a temperature gradient in a surface region in a direction perpendicular to the liquid level of the Si—C solution 24 and is a temperature gradient in which the temperature decreases from the inside of the Si—C solution toward the liquid level (surface) of the solution. . ΔTc is a temperature A on the low temperature side in the center of the region where the growth surface of the seed crystal substrate is in contact with the surface of the Si—C solution, and a temperature on the high temperature side at a depth of 10 mm vertically from the center. B is measured in advance using a thermocouple before contacting the seed crystal substrate with the Si-C solution, and the temperature difference is divided by the distance 10 mm between the positions where the temperature A and the temperature B are measured. It can be calculated as a value.

  ΔTa is a temperature gradient in the horizontal direction of the liquid surface (surface) of the Si—C solution. ΔTa is a temperature gradient in which the temperature rises in the horizontal direction from the center to the outer periphery of the region where the growth surface of the seed crystal substrate contacts the surface of the Si—C solution. ΔTa is a temperature C that is the low temperature side in the central portion of the region of the surface of the Si—C solution that contacts the growth surface of the seed crystal substrate, and a temperature D that is the high temperature side at a position 10 mm horizontally from the central portion. Is measured in advance using a thermocouple before bringing the seed crystal substrate into contact with the Si-C solution, and the temperature difference is divided by the distance 10 mm between the positions where the temperature C and the temperature D are measured. Can be calculated as

  ΔTc / ΔTa is 1.7 or more, preferably 2.0 or more, more preferably 3.0 or more, still more preferably 4.0 or more, still more preferably 5.0 or more, and even more preferably 5.3 or more. is there. By setting ΔTc / ΔTa within the above range, the terrace width is reduced and step flow growth proceeds. As a result, the 4H—SiC single crystal can be stably grown. By reducing the terrace width and growing the SiC single crystal, it is possible to suppress the generation of different types of polytypes other than 4H on the terrace, and the proportion of 4H in the SiC single crystal to be grown (hereinafter referred to as 4H rate). Say).

  ΔTc and ΔTa are not particularly limited as long as ΔTc / ΔTa can be within the above range, but ΔTc is preferably 5 ° C./cm to 50 ° C./cm, more preferably 7 ° C./cm to 30 ° C / cm, more preferably 8 ° C / cm to 25 ° C / cm, and ΔTa is preferably 0 ° C / cm to 15 ° C / cm, more preferably 0 ° C / cm to 8 ° C / cm, still more preferably It is 0 ° C./cm to 4 ° C./cm, more preferably 0 ° C./cm to 1.5 ° C./cm, and most preferably 0 ° C./cm.

  ΔTc, which is the temperature gradient in the vertical direction of the Si—C solution, can be controlled by the same method as before, adjusting the output of the heating device arranged around the crucible, the size of the opening of the lid on the top of the crucible, etc. Can be controlled. 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 ΔTc can be formed in the Si—C solution 24 so that the upper part of the solution is low and the lower part of the solution is high. ΔTa, which is the temperature gradient in the horizontal direction of the Si—C solution, can be controlled by the crucible inner diameter, the thickness of the heat insulating material disposed around the crucible, and the like. For example, if the crucible inner diameter is reduced, the temperature gradient ΔTa in the horizontal direction can be reduced. Even if the thickness of the heat insulating material disposed around the crucible is increased, the temperature gradient ΔTa in the horizontal direction can be reduced. By controlling ΔTc and ΔTa in this way, ΔTc / ΔTa can be controlled.

  In the method of the present disclosure, the temperature of the central portion of the region where the growth surface of the seed crystal substrate is in contact with the surface of the Si—C solution is 1900 ° C. or higher, more preferably 1950 ° C. or higher, more preferably 2000 ° C. or higher. Preferably it is 2050 degreeC or more. By setting the temperature of the central portion within the above range, the 4H ratio of the SiC single crystal to be grown can be further increased. The upper limit of the temperature of the central portion can be 2200 ° C. or less, for example.

  According to the method of the present disclosure, the 4H rate of the SiC single crystal to be grown can be increased as compared with the conventional case. According to the method of the present disclosure, SiC having a 4H ratio of 46% or more, preferably 50% or more, more preferably 68% or more, still more preferably 80% or more, even more preferably 90% or more, and particularly preferably 100%. A single crystal can be obtained.

  The 4H ratio in the grown crystal can be measured by performing Raman spectroscopic analysis on the growth surface of the grown crystal. A specific example of the procedure for measuring the 4H rate will be described in the examples described later.

  Although not bound by theory, the mechanism of 4H rate improvement by the method of the present disclosure will be described below.

  SiC crystal growth proceeds by step flow growth. Step flow growth refers to an aspect in which crystals grow in such a manner that steps having the same direction and substantially equal intervals are sequentially formed on the crystal growth surface. The portion of the step that is not covered by the next grown step is called a terrace.

  As shown in FIG. 3, when the terrace width is increased during crystal growth, the probability that two-dimensional nuclei other than 4H are generated on the terrace increases, and different polytypes such as 6H and 15R are generated starting from the nuclei. Will lead to. When the temperature gradient in the horizontal direction of the Si—C solution is larger than the temperature gradient in the vertical direction, the step advance speed is increased, and thus the terrace width is increased. FIG. 3 is a schematic cross-sectional view showing a mode in which two-dimensional nuclei other than 4H are generated on a terrace having a large width.

  If the horizontal temperature gradient on the liquid surface of the Si—C solution is reduced, the growth rate of step flow growth using the horizontal temperature gradient on the liquid surface of the Si—C solution as a driving force is reduced. When the step flow growth rate using a horizontal temperature gradient on the liquid surface of the Si—C solution as a driving force becomes slow, the terrace width becomes small as shown in FIG. As the terrace width is reduced, it is considered that two-dimensional nuclei other than 4H are less likely to adhere to the terrace, and 4H-SiC is easily generated stably. FIG. 4 is a schematic cross-sectional view showing an aspect in which the terrace width is small and no two-dimensional nucleus other than 4H is generated.

  According to the method of the present disclosure, it is considered that the 4H ratio of the SiC grown crystal can be improved by the above mechanism.

  The terrace is formed concentrically on the outer periphery of the growth surface. According to the method of the present disclosure, a 4H—SiC single crystal having a terrace width on the growth surface of 11 μm or less, preferably 4 μm or less can be obtained. In the present application, the terrace width means a viewing area of 600 μm square (when observed at 10 ×) at three locations of 1 mm, 5 mm, and 10 mm from the outer peripheral portion of the growth surface toward the center of the growth surface to 1.times. It is the average value of terrace widths measured by observing at 5 mm square (when observed at 20 times), and is measured by observing the growth surface with an optical microscope (magnification 10 to 20 times).

  The crucible is preferably a carbonaceous crucible such as a graphite crucible or a SiC crucible. The crucible is preferably cylindrical. The inner diameter of the crucible can be appropriately set according to the size of the single crystal manufacturing apparatus to be used, and can be set to 30 to 200 mm, 40 to 120 mm, or the like, for example.

  In order to keep warm, the outer periphery of the crucible 10 is covered with a heat insulating material 18. The heat insulating material 18 can be a graphite-based heat insulating material, a carbon fiber molded heat insulating material, or the like, and the thickness of the heat insulating material can be, for example, 4 to 15 mm.

  In the method of the present disclosure, 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. Si- with a melt of 30 to 80, Cr of 20 to 60, and X of 0 to 10 (Si: Cr: X = 30 to 80:20 to 60: 0 to 10) in atomic composition percentage as a solvent The C solution is more preferable because the variation in the dissolved amount of C is small. 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 Si-C solution 24 is prepared by charging a raw material into a crucible and dissolving C in a melt of Si or Si / X prepared by heating and melting. By making the crucible 10 into a carbonaceous crucible such as a graphite crucible or a SiC crucible, C is dissolved in the melt by melting the crucible 10 to form a 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.

  The seed crystal substrate can be installed in the single crystal manufacturing apparatus by holding the upper surface of the seed crystal substrate on the seed crystal holding shaft. A carbon adhesive can be used for holding the seed crystal substrate on the seed crystal holding shaft.

  The seed crystal holding shaft 12 is an axis that holds the seed crystal substrate 14 on its end face, can be a graphite shaft, and can have any shape such as a columnar shape or a prismatic shape.

  The contact of the seed crystal substrate 14 with the Si—C solution 24 is the lower surface of the seed crystal substrate 14 by lowering the seed crystal holding shaft 12 holding the seed crystal substrate 14 toward the liquid surface of the Si—C solution 24. It can be performed by bringing the (000-1) plane into contact with the Si—C solution 24 in parallel with the liquid surface of the Si—C solution 24. The SiC single crystal can be grown by holding the seed crystal substrate 14 at a predetermined position with respect to the liquid surface of the Si—C solution 24.

  The horizontal holding position of the seed crystal substrate 14 is such that the ratio of ΔTc / ΔTa is within the above range, and the surface temperature of the Si—C solution 24 is within the above temperature range, and crystal growth is performed from the growth surface of the seed crystal substrate 14. Although it is not particularly limited as long as it is possible, it is preferably held substantially at the center of the surface of the Si-C solution 24 accommodated in the crucible 10.

  The vertical holding position of the seed crystal substrate 14 is such that the position of the lower surface of the seed crystal substrate 14 coincides with the Si—C solution surface, is below the Si—C solution surface, or is Si—C. It may be above the solution surface. As shown in FIG. 5, the position of the lower surface of the seed crystal substrate is above the Si-C solution surface so that the Si-C solution 24 is wetted only on the lower surface of the seed crystal substrate 14 to form the meniscus 34. May be located. FIG. 5 is a schematic cross-sectional view of a meniscus 34 formed between the seed crystal substrate 14 and the Si—C solution 24.

  When forming a meniscus, it is preferable to hold the position of the lower surface of the seed crystal substrate at a position 0.5 to 3 mm above the Si-C solution surface. When the lower surface of the seed crystal substrate is held at a position above the Si-C solution surface, the seed crystal substrate 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 substrate. Then, pull it up to a predetermined position. By forming a meniscus and growing the crystal, it is possible to easily prevent the Si—C solution from coming into contact with the seed crystal holding shaft and to prevent the generation of polycrystals.

  The position of the lower surface of the seed crystal substrate may coincide with the Si-C solution surface or be lower than the Si-C solution surface, but in order to prevent the occurrence of polycrystals, It is preferable to prevent the Si—C solution from coming into contact. In these methods, the position of the seed crystal substrate may be adjusted during the growth of the SiC single crystal.

  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.

  The crucibles 10 covered with the heat insulating material 18 are collectively accommodated in the quartz tube 26. On the outer periphery of the quartz tube 26, a high frequency coil 22 is disposed as a heating device. 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 cooling chamber includes a gas introduction port and a gas exhaust port in order to enable adjustment of the atmosphere in the apparatus.

  The crucible 10 is provided with an opening 28 through which the seed crystal holding shaft 12 passes. By adjusting a gap (interval) between the crucible 10 and the seed crystal holding shaft 12 in the opening 28, the Si—C The degree of radiation extraction heat from the liquid surface of the solution 24 can be changed. Generally, it is necessary to keep the inside of the crucible 10 at a high temperature. However, if the gap between the crucible 10 and the seed crystal holding shaft 12 in the opening 28 is set large, radiation heat from the liquid surface of the Si—C solution 24 is reduced. When the gap between the crucible 10 and the seed crystal holding shaft 12 in the opening 28 is narrowed, the heat of radiation extraction from the liquid surface of the Si—C solution 24 can be reduced. The gap (interval) between the crucible 10 and the seed crystal holding shaft 12 in the opening 28 is preferably about 2 to 10 mm on one side. When the meniscus is formed, radiation heat can also be removed from the meniscus portion.

  In one embodiment, before the growth of the SiC single crystal, meltback may be performed to dissolve and remove the surface layer of the 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 changes with the processing state of the surface of a seed crystal substrate, about 5-50 micrometers is preferable in order to fully remove a work-affected layer and a natural oxide film.

  Melt back forms 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 Si-C solution, that is, in the opposite direction to the growth of the SiC single crystal. Can be performed. The temperature gradient in the reverse direction can be formed by controlling the output of the high frequency coil.

  In one embodiment, the seed crystal substrate may be previously heated and then contacted 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 seed crystal holding shaft. 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 crystals grow after contacting the seed crystal substrate 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.

  The present disclosure is also directed to a SiC single crystal having a terrace width on the growth surface of 11 μm or less and a higher 4H ratio than the conventional one, particularly a 4H ratio of 46% or more.

  The terrace is formed concentrically on the outer periphery of the growth surface. Since the 4H-SiC single crystal having a terrace width on the growth surface within the above range can suppress the generation of heterogeneous polytype nuclei on the terrace, an SiC single crystal having a higher 4H ratio than the conventional one can be obtained.

  The terrace width is preferably 4 μm or less. The 4H ratio is preferably 50% or more, more preferably 68% or more, still more preferably 80% or more, still more preferably 90% or more, and particularly preferably 100%.

  The contents of the terrace width observation, measurement method and the like described in the above manufacturing method are also applied to the present SiC single crystal.

  Calculation of the 4H ratio in the following examples and comparative examples was performed by the following method.

  The growth surface of the grown crystal was equally divided at intervals of 1 mm, and Raman spectroscopic analysis was performed on the approximate center of each section. The analysis conditions are as follows: excitation wavelength of 532 nm, 20 mW, laser irradiation diameter of 2.7 μm, backscattering arrangement, exposure time of 2 seconds, number of integrations, diffraction grating of 1600 gr / mm, confocal hole diameter of 10 μm, room temperature, in the air.

  When all the sections of the growth surface analyzed by Raman spectroscopy were 4H, the grown crystal was determined to be 4H—SiC. The determination of whether each block is 4H was determined to be 4H if a Raman peak of only 4H was obtained, and was determined not to be 4H if a Raman peak other than 4H was observed. In each example and comparative example, a plurality of grown crystals were obtained under the same conditions to obtain a plurality of grown crystals, and the growth surfaces of the plurality of grown crystals were analyzed by Raman spectroscopy, and determined to be 4H-SiC. The ratio of the number of grown crystals to the number of the plurality of grown crystals was 4H rate. That is, the 4H rate is 100%, for example, among 30 grown crystals, where all the sections of the growth surface of each of the 30 grown crystals are determined to be 4H-SiC, and the 4H rate is 50%. For example, among 30 grown crystals, all the sections of the growth surface of each of the 15 grown crystals are determined to be 4H—SiC, and the remaining 15 grown crystals are not determined to be 4H—SiC. When at least one of all the sections of the growth surface was not determined to be 4H—SiC, it was determined that the grown crystal was not 4H—SiC.

Example 1
The single crystal manufacturing apparatus shown in FIG. 1 was used. A SiC single crystal having a diameter of 12.7 mm and a thickness of 700 μm, which is a disc-shaped 4H—SiC single crystal and having a (000-1) plane on the bottom surface, is prepared and used as a seed crystal substrate 14 It was. A cylindrical graphite seed crystal holding shaft 12 having a diameter of 12.7 mm and a length of 200 mm and having an end surface having the same shape as the upper surface of the seed crystal substrate was prepared. The upper surface of the seed crystal substrate 14 was bonded to the substantially central portion of the end surface of the seed crystal holding shaft 12 using a graphite adhesive so that the lower surface of the seed crystal substrate 14 became the (000-1) plane.

  The seed crystal holding shaft 12 and the seed crystal substrate 14 were arranged so that the seed crystal holding shaft 12 was passed through a circular opening 28 having a diameter of 18.7 mm opened at the center of the upper lid of the crucible 10. The gap between the crucible 10 and the seed crystal holding shaft 12 in the opening 28 was 3 mm on each side.

  In a graphite crucible having an inner diameter of 40 mm around which a carbon fiber felt molded heat insulating material having a thickness of 15 mm is arranged, Si, Cr, and Ni are in an atomic composition ratio of Si: Cr: Ni = 55: 40: 5 (at%), It was charged as a melt raw material for forming a Si-C solution.

The inside of the single crystal manufacturing apparatus was evacuated to 1 × 10 ⁻³ Pa, and then argon gas was introduced until the pressure became 1 atm. The air inside the single crystal manufacturing apparatus was replaced with argon. The raw material in the graphite crucible was melted by energizing and heating the high frequency coil to form a Si / Cr / Ni alloy melt. Then, a sufficient amount of C was dissolved in the melt of the Si / Cr / Ni alloy from the graphite crucible to form a Si—C solution.

  The graphite crucible is heated by adjusting the output of the upper coil and the lower coil, and the temperature in the center of the region where the growth surface of the seed crystal substrate is in contact with the surface of the Si-C solution is in the temperature range of 1900 ° C. or higher and lower than 1950 ° C. The temperature gradient ΔTc is controlled so as to be 8 ° C./cm in the vertical direction from the inside of the solution toward the surface of the Si—C solution within a range of 10 mm from the center of the surface of the Si—C solution. did. In this example, the central part of the region where the growth surface of the seed crystal substrate contacts the surface of the Si-C solution is the central part of the surface of the Si-C solution. At this time, the temperature gradient ΔTa between the center of the surface of the Si—C solution and a position 10 mm horizontally from the center of the surface was 1.5 ° C./cm. ΔTc / ΔTa was 5.3. The temperature in the horizontal direction of the liquid surface of the Si—C solution was measured with a radiation thermometer, and the temperature in the vertical direction of the Si—C solution was measured using a thermocouple movable in the vertical direction.

  The (000-1) plane, which is the lower surface of the seed crystal substrate bonded to the seed crystal holding shaft 12, is parallel to the Si-C solution surface, and the position of the lower surface of the seed crystal substrate coincides with the liquid surface of the Si-C solution. The crystal was grown by placing the Si-C solution in a position where the seed crystal substrate was brought into contact with the Si-C solution and bringing the Si-C solution into contact with the Si-C solution, and holding the Si-C solution for 10 hours.

  After the completion of the crystal growth, the seed crystal holding shaft 12 was raised, and the SiC single crystal grown from the seed crystal substrate 14 and the seed crystal substrate was separated from the Si—C solution 24 and the seed crystal holding shaft 12 and recovered. Next, crystal growth was performed 26 times under the same conditions to obtain a total of 27 grown crystals.

When the polytype of the grown crystal was examined by Raman spectroscopic analysis, the 4H ratio of the 27 grown crystals obtained was 100%. The 4H rate was calculated using the method described above. FIG. 6 shows a Raman spectrum of the grown crystal determined to be 4H. A peak of 4H was observed at 204 cm ^−1, but no polytype peak other than 4H was observed. FIG. 7 shows an appearance photograph observed from the growth surface of the obtained grown crystal. The growth thickness of the grown crystal was 2.8 mm. When an area of 600 μm square was observed at a magnification of 20 times using an optical microscope at three locations of 1 mm, 5 mm, and 10 mm from the outer periphery of the growth surface of the growth crystal toward the center of the growth surface, The terrace width of the growth surface was 4 μm. FIG. 8 shows an optical micrograph in which the growth surface of the obtained grown crystal is enlarged. The terrace width is indicated by an arrow.

(Example 2-1)
Using a SiC single crystal having a diameter of 50.4 mm and a graphite crucible having an inner diameter of 70 mm as a seed crystal substrate, ΔTc is set to 25 ° C./cm, ΔTa is set to 15 ° C./cm, ΔTc / ΔTa is set to 1.7, and 13 A SiC single crystal was grown and recovered under the same conditions as in Example 1 except that double crystal growth was performed.

  The obtained 13 grown crystals had a 4H ratio of 46%. FIG. 9 shows an appearance photograph observed from the growth surface of the obtained grown crystal. The growth thickness of the grown crystal was 2.4 mm. When an area of 600 μm square was observed at a magnification of 20 times using an optical microscope at three locations of 1 mm, 5 mm, and 10 mm from the outer periphery of the growth surface of the growth crystal toward the center of the growth surface, The terrace width of the growth surface was 11 μm. In FIG. 10, the optical microscope photograph which expanded the growth surface of the obtained growth crystal is shown. The terrace width is indicated by an arrow.

(Example 2-2)
A SiC single crystal is grown under the same conditions as in Example 2-1, except that the temperature at the center of the surface of the Si—C solution is set to a temperature of 1950 ° C. or more and less than 2000 ° C., and crystal growth is performed 25 times in this temperature range. And recovered.

  The obtained 25 grown crystals had a 4H ratio of 68%.

(Example 2-3)
A SiC single crystal was grown under the same conditions as in Example 2-1, except that the temperature at the center of the surface of the Si-C solution was set to a temperature of 2000 ° C. or higher and lower than 2050 ° C., and crystal growth was performed 10 times in this temperature range. And recovered.

  The 10 grown crystals obtained had a 4H ratio of 70%.

(Example 2-4)
A SiC single crystal is grown under the same conditions as in Example 2-1, except that the temperature at the center of the surface of the Si—C solution is set to a temperature of 2050 ° C. or higher and lower than 2100 ° C., and crystal growth is performed 18 times in this temperature range. And recovered.

  The obtained 18 grown crystals had a 4H ratio of 100%.

(Example 3)
Except that an 8 mm thick heat insulating material was placed around the crucible, ΔTc was 8 ° C./cm, ΔTa was 4 ° C./cm, ΔTc / ΔTa was 2.0, and crystal growth was performed 11 times. A SiC single crystal was grown and recovered under the same conditions as in Example 1.

  The obtained 11 grown crystals had a 4H ratio of 100%.

(Comparative Example 1-1)
Using a SiC single crystal having a diameter of 50.4 mm and a graphite crucible having an inner diameter of 120 mm as a seed crystal substrate, ΔTc is set to 1.5 ° C./cm, ΔTa is set to 3 ° C./cm, and ΔTc / ΔTa is set to 0.5. A SiC single crystal was grown and recovered under the same conditions as in Example 1 except that the crystal growth was performed 10 times.

The obtained 10 grown crystals had a 4H ratio of 0%. FIG. 11 shows a Raman spectrum of a grown crystal in which a polytype other than 4H is generated. A peak of 6H was observed at 155 cm ⁻¹ , but a peak of 4H was not observed. FIG. 12 shows an appearance photograph observed from the growth surface of the obtained grown crystal. The growth thickness of the grown crystal was 2.3 mm. When a 1.5 mm square area was observed at 10 times magnification using an optical microscope at three locations of 1 mm, 5 mm, and 10 mm from the outer peripheral portion of the growth surface of the growth crystal toward the center of the growth surface, this growth was observed. The terrace width of the crystal growth surface was 56.8 μm. FIG. 13 shows an optical microscope photograph in which the growth surface of the obtained grown crystal is enlarged. The terrace width is indicated by an arrow.

(Comparative Example 1-2)
A SiC single crystal is grown under the same conditions as in Comparative Example 1-1 except that the temperature at the center of the surface of the Si—C solution is set to a temperature of 1950 ° C. or higher and lower than 2000 ° C., and crystal growth is performed 18 times in this temperature range. And recovered.

  The obtained 18 grown crystals had a 4H ratio of 0%.

(Comparative Example 1-3)
A SiC single crystal is grown under the same conditions as in Comparative Example 1-1 except that the temperature at the center of the surface of the Si—C solution is set to a temperature of 2000 ° C. or higher and lower than 2050 ° C., and the crystal is grown 56 times in this temperature range. And recovered.

  The 4H ratio of the obtained 56 grown crystals was 0%.

(Comparative Example 1-4)
A SiC single crystal is grown under the same conditions as in Comparative Example 1-1 except that the temperature at the center of the surface of the Si—C solution is set to a temperature of 2050 ° C. or higher and lower than 2100 ° C. and the crystal growth is performed 26 times in this temperature range. And recovered.

  The obtained 26 grown crystals had a 4H ratio of 0%.

(Comparative Example 2)
Except that a 4 mm thick heat insulating material was arranged around the crucible, ΔTc was 8 ° C./cm, ΔTa was 8 ° C./cm, ΔTc / ΔTa was 1.0, and crystal growth was performed 28 times. A SiC single crystal was grown and recovered under the same conditions as in Example 1.

  The obtained 28 grown crystals had a 4H ratio of 35.7%.

  Table 1 shows ΔTc, ΔTa, ΔTc / ΔTa, and 4H ratios of Examples 1, 2-1, 2-4, and 3 and Comparative Examples 1-1, 1-4, and 2. In FIG. 14, the graph showing 4H rate by (DELTA) Tc / (DELTA) Ta of all the Examples and comparative examples is shown. FIG. 15 is a graph showing the relationship between the temperature at the center of the surface of the Si—C solution and the 4H ratio in Example 1, Examples 2-1 to 2-4, and Comparative Examples 1-1 to 1-4. Show.

DESCRIPTION OF SYMBOLS 100 Single crystal manufacturing apparatus 10 Crucible 12 Seed crystal holding shaft 14 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 28 Opening part of crucible upper part 34 Meniscus

Claims (4)

A method for producing a SiC single crystal, wherein a SiC single crystal is grown by bringing a seed crystal substrate into contact with a Si-C solution having a temperature gradient that decreases from the inside toward the liquid surface,
The seed crystal substrate is 4H-SiC;
Making the (000-1) plane of the seed crystal substrate a growth plane;
The temperature of the central part of the region where the growth surface of the seed crystal substrate is in contact with the surface of the Si-C solution is set to 1900 ° C. or higher, and the central part and a position 10 mm vertically downward from the central part, The ratio ΔTc / ΔTa between the temperature gradient ΔTc between the central portion and the temperature gradient ΔTa between the central portion and a position 10 mm in the horizontal direction from the central portion is 1.7 or more. Production method.   The manufacturing method of the SiC single crystal of Claim 1 including making the temperature of the said center part 1950 degreeC or more.   The manufacturing method of the SiC single crystal of Claim 1 or 2 whose horizontal holding position of the said seed crystal substrate is the surface center part of the said Si-C solution.   A SiC single crystal having a terrace width on the growth surface of 11 μm or less and a 4H ratio of 46% or more.