JP2018145053A - METHOD FOR MANUFACTURING SiC SINGLE CRYSTAL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a SiC single crystal, capable of stably holding a seed crystal substrate on a seed crystal holding shaft to grow a high quality SiC single crystal.SOLUTION: The method for manufacturing a SiC single crystal, capable of contacting a seed crystal substrate held on the lower end surface of a seed crystal holding shaft to a Si-C solution having a temperature gradient decreasing a temperature toward the surface from the inside to grow the SiC single crystal comprises: preparing sheet-like graphite; exposing the sheet-like graphite to at least one of a high temperature atmosphere and a reduced pressure atmosphere to vaporize water in the sheet-like graphite; bonding the seed crystal substrate on the lower end surface of the seed crystal holding shaft using an adhesive so as to sandwich the sheet-like graphite exposed to the atmosphere therebetween; and heating and curing the adhesive.SELECTED DRAWING: Figure 7

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 defects such as the formation of lattice defects such as hollow through defects called micropipe defects and stacking faults and crystal polymorphism in the grown single crystal. Many of SiC bulk single crystals are 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.

  And the solution method forms Si melt which melt | dissolved Si melt or metals other than Si in a graphite crucible, melt | dissolves carbon C in the melt, and SiC on the seed crystal substrate installed in the low temperature part In this method, a crystal layer is deposited and grown. 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.

  In the growth of a SiC single crystal, if the SiC seed crystal substrate is directly bonded to the graphite seed crystal holding shaft, cracks and cracks may occur in the grown crystal due to the stress due to the difference in thermal expansion between SiC and graphite. In order to relieve the stress due to this thermal expansion difference, there is a method in which sheet-like graphite is disposed as a buffer layer. Patent Documents 1 to 3 include a seed crystal holding shaft positioned on the seed crystal substrate, an adhesive for fixing the seed crystal substrate and the seed crystal holding shaft, and sheet-like graphite sandwiched in the thickness direction by the adhesive. An apparatus for crystal growth is disclosed.

Japanese Patent No. 5734439 JP 2013-136494 A JP 2004-269297 A

  However, in the prior arts such as Patent Documents 1 to 3, the sheet-like graphite contains moisture, and when heat treatment is performed at a temperature of about 200 ° C. in order to cure the adhesive, the moisture in the sheet is vaporized inside. As a result, bubbles were generated on the sheet surface, leading to a problem that the seed crystal substrate dropped off due to a decrease in adhesive strength and the quality of the grown crystal was degraded.

  Therefore, a method for producing a SiC single crystal that can relieve stress due to a difference in thermal expansion between SiC and graphite, and can stably hold a seed crystal substrate on a seed crystal holding shaft and grow a high-quality SiC single crystal. Is desired.

In the present disclosure, a SiC single crystal is grown by bringing a seed crystal substrate held on the lower end face of a seed crystal holding shaft into contact with a Si-C solution having a temperature gradient that decreases in temperature from the inside toward the liquid surface. A method for producing a single crystal comprising:
Preparing sheet-like graphite,
Exposing the sheet-like graphite to at least one of a high-temperature atmosphere and a reduced-pressure atmosphere to vaporize moisture in the sheet-like graphite;
Adhering the seed crystal substrate to the lower end surface of the seed crystal holding shaft with an adhesive so that the sheet-like graphite exposed to the atmosphere is sandwiched therebetween, and curing the adhesive by performing a heat treatment,
The manufacturing method of the SiC single crystal containing is included.

  According to the method of the present disclosure, since moisture contained in the sheet-like graphite is removed before the heat treatment for curing the adhesive, it is possible to suppress the generation of bubbles in the sheet-like graphite in the adhesive curing step. . Therefore, the sheet-like graphite can relax the stress due to the difference in thermal expansion between SiC and graphite, and the seed crystal substrate can be stably held on the seed crystal holding shaft to grow a high-quality SiC single crystal.

FIG. 1 is a schematic cross-sectional view of an embodiment in which a sheet-like graphite is sandwiched between a seed crystal substrate and a seed crystal holding shaft and bonded with an adhesive. FIG. 2 shows a state in which bubbles are generated in the sheet-like graphite by heat-treating the seed crystal substrate and the seed-crystal holding shaft sandwiching the sheet-like graphite of FIG. 1 at 200 ° C. in order to cure the adhesive. It is a cross-sectional schematic diagram to represent. FIG. 3 is a schematic cross-sectional view of a seed crystal substrate and a seed crystal holding shaft having a diameter smaller than that of the seed crystal substrate, in which the lower end of the seed crystal holding shaft is covered with sheet-like graphite. FIG. 4 is a schematic cross-sectional view of a seed crystal substrate and a seed crystal holding shaft having a smaller diameter than that of the seed crystal substrate, in which the upper surface of the seed crystal substrate is covered with sheet-like graphite. FIG. 5 is a schematic cross-sectional view illustrating an example of an SiC single crystal manufacturing apparatus that can be used in the method of the present disclosure. FIG. 6 is an appearance photograph of the sheet-like graphite in the example before heat treatment at 200 ° C. FIG. 7 is an appearance photograph of the sheet-like graphite after heat treatment at 200 ° C. in Examples. FIG. 8 is an appearance photograph of the sheet-like graphite in the comparative example before heat treatment at 200 ° C. FIG. 9 is an appearance photograph of the sheet-like graphite in the comparative example after heat treatment at 200 ° C. FIG. 10 is an appearance photograph of the sheet-like graphite in the comparative example before heat treatment at 200 ° C. FIG. 11 is a photograph of the appearance of the sheet-like graphite after the heat treatment at 200 ° C. in the comparative example. FIG. 12 is a graph showing the relationship between the moisture content of sheet-like graphite before heat treatment and the area ratio of bubbles generated after heat treatment.

  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.

  In the prior art, when the sheet-like graphite is used as a buffer layer between the seed crystal substrate and the seed crystal holding shaft, an adhesive is used to sandwich the sheet-like graphite between the seed crystal substrate and the seed crystal holding shaft. Glue. At this time, heat treatment is performed at about 200 ° C. in order to cure the adhesive.

  FIG. 1 shows a schematic cross-sectional view of an embodiment in which a sheet-like graphite 30 is sandwiched between the seed crystal substrate 14 and the seed crystal holding shaft 12 and bonded with an adhesive. The sheet-like graphite 30 and the seed crystal holding shaft 12 are bonded with an adhesive, and the sheet-like graphite 30 and the seed crystal substrate 14 are also bonded with an adhesive. FIG. 2 is a schematic cross-sectional view showing a state when the crystal substrate 14 and the seed crystal holding shaft 12 sandwiching the sheet-like graphite 30 of FIG. 1 are heat-treated at 200 ° C. in order to cure the adhesive. .

  As shown in FIG. 2, in the heat treatment step for curing the adhesive, moisture contained in the sheet-like graphite is vaporized and expanded inside, and bubbles are generated in the sheet. When bubbles are generated in the sheet-like graphite, the adhesive strength and heat conduction of the portion are reduced. As a result, the seed crystal substrate during crystal growth falls off from the seed crystal holding axis, and the quality of the grown crystal is reduced.

  Based on the above findings, the present inventor exposed the sheet-like graphite to at least one of a high-temperature atmosphere and a reduced-pressure atmosphere before bonding the seed crystal substrate to the seed crystal holding shaft. It was found that water was vaporized.

  In the present disclosure, a SiC single crystal is grown by bringing a seed crystal substrate held on the lower end face of a seed crystal holding shaft into contact with a Si-C solution having a temperature gradient that decreases in temperature from the inside toward the liquid surface. A method for producing a single crystal, comprising preparing sheet-like graphite, exposing the sheet-like graphite to at least one of a high-temperature atmosphere and a reduced-pressure atmosphere to vaporize moisture in the sheet-like graphite, an adhesive And bonding the seed crystal substrate to the lower end surface of the seed crystal holding shaft so as to sandwich the sheet-like graphite exposed to the atmosphere, and curing the adhesive by performing a heat treatment, The manufacturing method of a SiC single crystal is an object.

  According to the manufacturing method of the present disclosure, before adhering the seed crystal substrate so as to sandwich the sheet-like graphite between the lower end surfaces of the seed crystal holding shaft using an adhesive, the sheet-like graphite is heated to a high temperature atmosphere and a reduced pressure atmosphere. The moisture in the sheet-like graphite can be vaporized by exposure to at least one of the above-mentioned atmospheres. Therefore, the moisture content contained in the sheet-like graphite can be reduced before the adhesive curing step.

  As shown in FIG. 1, the sheet-like graphite 30 is disposed on the upper surface of the seed crystal substrate 14, and the seed crystal substrate 14 is held on the lower end surface of the seed crystal holding shaft 12 with the sheet-like graphite 30 interposed therebetween. The The sheet-like graphite 30 is fixed to the lower end surface of the seed crystal holding shaft 12 and the upper surface of the seed crystal substrate 14 with an adhesive.

  The curing temperature of the adhesive depends on the type of adhesive, but is generally performed in a high temperature atmosphere of about 180 to 220 ° C. When the moisture content of the sheet-like graphite is large in the adhesive curing step, bubbles can be generated in the sheet-like graphite.

  According to the method of the present disclosure, since the amount of water contained in the sheet-like graphite can be reduced before the adhesive curing step, the amount of water vaporized from the sheet-like graphite in the adhesive curing step is reduced. And generation of bubbles in the sheet-like graphite can be reduced. As a result, dropping of the seed crystal substrate from the seed crystal holding shaft and deterioration of the quality of the grown crystal can be suppressed.

  Since the sheet-like graphite has flexibility, it functions as a buffer material that reduces the stress caused by the difference in linear expansion coefficient between the seed crystal holding shaft and the seed crystal substrate, and the strain of the grown crystal is reduced. Therefore, the generation of cracks and cracks in the grown crystal can be suppressed, and cracks and cracks are less likely to occur even when processing such as slicing is performed after crystal growth.

  Commercial sheet-like graphite contains about 0.5% by mass of water. In order to reduce the moisture content, the sheet-like graphite is exposed to at least one of a high temperature atmosphere and a reduced pressure atmosphere.

  The high temperature atmosphere to which the sheet-like graphite is exposed may be a temperature at which moisture can be vaporized without generating bubbles in the sheet-like graphite, and is preferably 80 to 120 ° C, more preferably 90 to 110 ° C. The reduced-pressure atmosphere that exposes the sheet-like graphite may be any pressure that can vaporize moisture without generating bubbles in the sheet-like graphite, and is preferably 1 to 100 Pa, more preferably 5 to 20 Pa. The exposure time to at least one of the high temperature atmosphere and the reduced pressure atmosphere is preferably 30 to 600 minutes, more preferably 60 to 200 minutes. Sheet graphite is exposed to a high temperature atmosphere at a temperature in the above range, a reduced pressure atmosphere at a pressure in the above range, or a high temperature atmosphere at a temperature in the above range and a reduced pressure atmosphere at a pressure in the above range for the above time, The amount of moisture contained in the sheet-like graphite can be further reduced. Preferably, a high temperature atmosphere and a reduced pressure atmosphere are combined.

  The moisture content of the sheet-like graphite exposed to at least one of a high temperature atmosphere and a reduced pressure atmosphere is preferably 0.2% by mass or less, more preferably 0.1% by mass or less. When the moisture content is within this range, the generation of bubbles in the sheet-like graphite can be further reduced.

  The bubble area ratio in the sheet-like graphite is preferably 10% or less, more preferably 5% or less, still more preferably 1% or less, and even more preferably 0%.

  The bubble area ratio in the sheet-like graphite is a ratio of the area of the bubbles to the area of the sheet-like graphite, and can be calculated using an image processing apparatus according to appearance observation and as desired.

  The thickness of the sheet-like graphite may be any thickness as long as the effect of reducing the stress caused by the difference in linear expansion coefficient between the seed crystal holding shaft and the seed crystal substrate is obtained. For example, 0.01 mm or more, 0.05 mm or more, or 0 .2 mm or more. Although the upper limit of the thickness of sheet-like graphite is not specifically limited, For example, it can be 10 mm or less, 5 mm or less, or 1 mm or less.

  The type of sheet-like graphite is not particularly limited as long as it can reduce the stress caused by the difference in linear expansion coefficient between the seed crystal holding shaft and the seed crystal substrate, and a commercially available one can be used. Sheet-like graphite can be obtained by dehydrating carbon fibers on a roller.

  The shape of the sheet-like graphite 30 is not particularly limited as long as it is disposed between the upper surface of the seed crystal substrate and the lower end surface of the seed crystal holding shaft 12. For example, as shown in FIG. 3, a sheet-like graphite 30 is formed between a lower end surface of the seed crystal holding shaft 12 and a seed crystal substrate 14 having a larger diameter than the lower end surface of the seed crystal holding shaft 12. The entire lower end surface of the holding shaft 12 may be covered, but the entire upper surface of the seed crystal substrate 14 may be disposed so as not to be covered. Alternatively, as shown in FIG. 4, a sheet-like graphite 30 is formed between the lower end surface of the seed crystal holding shaft 12 and the seed crystal substrate 14 having a larger diameter than the lower end surface of the seed crystal holding shaft 12. You may arrange | position so that the whole upper surface of the board | substrate 14 may be covered.

  The adhesive is preferably a carbon adhesive. Examples of the carbon adhesive include phenolic adhesives and epoxy adhesives.

  An adhesive layer composed of an adhesive or mainly composed of an adhesive is disposed on both sides of the sheet-like graphite to form a layer structure of seed crystal holding shaft / adhesive layer / sheet-like graphite / adhesive layer / seed crystal substrate. May be.

  The sheet-like graphite may be composed of a plurality of layers of sheet-like graphite.

  A solution method is used in the manufacturing method of the SiC single crystal of the present disclosure. 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 substrate into contact with a Si—C solution having a temperature gradient that decreases from the inside toward the surface. By forming a temperature gradient in which the temperature decreases from the inside of the Si-C solution toward the surface of the solution, the surface region of the Si-C solution is supersaturated, and the SiC single crystal is removed from the seed crystal substrate in contact with the Si-C solution. Can grow.

  In FIG. 5, 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 an Si—C solution 24 in which carbon C is dissolved in an Si-based melt, and the Si—C solution 24 is formed from the inside of the Si—C solution 24. A seed crystal substrate 14 is held via a sheet-like graphite 30 on the lower end surface of the seed crystal holding shaft 12 that forms a temperature gradient that decreases in temperature toward the surface (liquid surface) and can be raised and lowered in the vertical direction. A SiC single crystal can be grown from the seed crystal substrate 14 by bringing the substrate 14 into contact with the Si—C solution 24.

  As the seed crystal substrate 14, a SiC single crystal of a quality generally used for the production of an SiC single crystal can be used as the seed crystal substrate. For example, a SiC single crystal generally prepared by a sublimation method can be used as a seed crystal substrate. In addition, the seed crystal substrate 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 holding shaft 12 is an axis that holds the seed crystal substrate 14 via the sheet-like graphite 30 on its end face. The seed crystal holding shaft 12 can be a graphite shaft, and can have any shape such as a cylindrical shape or a prismatic shape. The seed crystal holding shaft 12 preferably includes a lower end surface having an area equal to or smaller than the area of the upper surface of the seed crystal substrate 14, more preferably the seed crystal substrate 14. The lower end surface which has an area smaller than the area of the upper surface of is provided.

  The Si-C solution 24 is a solution in which carbon using a Si-based melt as a solvent is dissolved. The Si-based melt is preferably a Si or Si / X melt. X is one or more metals other than Si, 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, Ge, Al and the like.

  The Si-based melt is more preferably a Si / Cr / X melt. X is one or more metals other than Si and Cr. Examples of suitable metals X include Ti, Mn, Ni, Ce, Co, V, Fe, Ge, Al and the like. A Si—C solution using a melt of Si: Cr: X = 30 to 80:20 to 70: 0 to 20 in terms of atomic composition percentage as a solvent is more preferable because of less variation in the amount of dissolved carbon. For example, in addition to Si, a raw material such as Cr can be introduced into the crucible to form a Si—C solution in which carbon is dissolved in a Si / Cr melt.

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

  The temperature of the Si—C solution 24 refers to the surface temperature of the Si—C solution 24. The surface temperature of the Si—C solution 24 is preferably 1900 to 2100 ° C. at which carbon solubility suitable for SiC single crystal growth is obtained.

  The temperature measurement of the Si—C solution 24 can be performed 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 contact of the seed crystal substrate 14 with the Si—C solution 24 causes the seed crystal holding shaft 12 holding the seed crystal substrate 14 on the lower end surface to descend toward the liquid surface of the Si—C solution 24, The lower surface can be made parallel to the liquid surface of the Si—C solution 24 and brought into contact with 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 holding position of the seed crystal substrate is such that the position of the lower surface of the seed crystal substrate coincides with the Si-C solution surface, is below the Si-C solution surface, or is relative to the Si-C solution surface. It may be on the upper side. 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. 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 crystal growth.

  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. 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 temperature of the Si-C solution 24 usually has a temperature distribution in which the surface temperature is lower than the inside of the Si-C solution 24 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 By adjusting the positional relationship with the height direction 10 and the output of the high-frequency coil 22, the upper part of the solution where the seed crystal substrate 14 contacts the Si-C solution 24 becomes low temperature, and the lower part of the solution (inside) becomes high temperature. In addition, a vertical temperature gradient can be formed on the surface of the Si-C 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 temperature gradient can be formed in the Si—C solution 24 such that the upper part of the solution is cold and the lower part of the solution is hot.

  The carbon 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 inside of the Si—C solution 24 due to output control of the heating device, heat radiation from the surface of the Si—C solution 24, heat removal through the seed crystal holding shaft 12, and the like. A temperature gradient is formed. When the carbon dissolved in the solution having high solubility at high temperature reaches the vicinity of the seed crystal substrate having low solubility at low temperature, it becomes supersaturated, and SiC crystals can be grown on the seed crystal substrate 14 by using this supersaturation as a driving force. .

(Example 1-1)
As the sheet-like graphite, a sheet-like graphite having a thickness of 0.2 mm and an outer shape of 2 inches (50.8 mm) in diameter (manufactured by Sakai Kogyo, GRAFOIL (registered trademark)) was prepared. The moisture content of the sheet-like graphite was 0.5% by mass.

  The sheet-like graphite was exposed to a high temperature atmosphere at 100 ° C. for 2 hours. The moisture content of the sheet-like graphite after exposure to a high temperature atmosphere was 0.1% by mass.

The sheet-like graphite after exposure to a high temperature atmosphere was heat-treated at 200 ° C. for 2 hours. In FIG. 6, the external appearance photograph before the heat processing of 200 degreeC of sheet-like graphite is shown. In FIG. 7, the external appearance photograph after 200 degreeC heat processing of sheet-like graphite is shown. The bubble area ratio in the sheet-like graphite after the heat treatment was 0%.
(Example 1-2)
A SiC single crystal having a diameter of 2 inches (50.8 mm) and a thickness of 350 μm and having a disk-like 4H—SiC single crystal produced by a sublimation method having a (000-1) bottom surface is prepared as a seed crystal. Used as a substrate.

  A cylindrical graphite shaft having a diameter of 12 mm and a length of 40 cm was prepared as a seed crystal holding shaft.

  As the sheet-like graphite 30, the same sheet-like graphite as used in Example 1-1 was prepared and exposed to a high-temperature atmosphere under the same conditions as in Example 1-1.

  As schematically shown in FIG. 4, the sheet-like graphite 30 exposed to the high temperature atmosphere is bonded to the upper surface of the seed crystal substrate using a phenol-based carbon adhesive so as to completely cover the upper surface of the seed crystal substrate. Further, the lower end surface of the seed crystal holding shaft was bonded to the central portion of the upper surface of the seed crystal substrate coated with the sheet-like graphite 30 using a phenol-based carbon adhesive. Next, heat treatment was performed in an air atmosphere at 200 ° C. for 2 hours to cure the adhesive.

  Using a single crystal manufacturing apparatus 100 shown in FIG. 5, Si / Cr was charged as a melt raw material at a ratio of Si: Cr = 60: 40 in atomic composition percentage into a graphite crucible 10 containing an Si—C solution.

After the inside of the single crystal manufacturing apparatus 100 was evacuated to 1 × 10 ⁻³ Pa, argon gas was introduced to 1 atm, and the air inside the single crystal manufacturing apparatus 100 was replaced with argon. A high frequency coil 22 serving as a heating device disposed around the graphite crucible 10 was energized to melt the raw material in the graphite crucible 10 to form a Si / Cr alloy melt. Then, a sufficient amount of C was dissolved from the graphite crucible 10 in the Si / Cr alloy melt to form a Si—C solution 24.

  The graphite crucible 10 is heated by adjusting the outputs of the upper coil 22A and the lower coil 22B, the temperature on the surface of the Si—C solution 24 is increased to 2000 ° C., and within the range of 1 cm from the surface of the Si—C solution 24. It controlled so that the average temperature gradient which temperature falls toward the solution surface from the inside of a solution might be 30 degrees C / cm. The surface temperature of the Si—C solution 24 was measured with a radiation thermometer, and the temperature gradient of the Si—C solution 24 was measured using a thermocouple movable in the vertical direction.

  A position where the lower surface of the seed crystal substrate 14 bonded to the seed crystal holding shaft 12 is parallel to the liquid surface of the Si-C solution 24 and the position of the lower surface of the seed crystal substrate 14 coincides with the liquid surface of the Si-C solution 24. Then, the seed touch was performed in which the lower surface of the seed crystal substrate was brought into contact with the Si—C solution, and the crystal was grown at that position for 15 hours.

  After completion of the crystal growth, the seed crystal holding shaft 12 is raised and cooled to room temperature, and the seed crystal substrate 14 and the SiC crystal grown from the seed crystal substrate are separated from the Si-C solution 24 and the seed crystal holding shaft 12. And recovered.

  A high-quality SiC single crystal free from cracks and cracks could be grown without dropping the seed crystal substrate from the seed crystal holding shaft.

(Example 2-1)
The same sheet-like graphite as used in Example 1-1 was prepared and exposed to a reduced pressure atmosphere at room temperature and 10 Pa for 2 hours. The moisture content of the sheet-like graphite after exposure to a reduced-pressure atmosphere was 0.1% by mass.

  The sheet-like graphite after exposure to a reduced pressure atmosphere was heat treated at 200 ° C. for 2 hours. The bubble area ratio in the sheet-like graphite after the heat treatment was 0%.

(Example 2-2)
Except that the same sheet-like graphite as used in Example 2-1 was prepared and exposed to a reduced-pressure atmosphere under the same conditions as in Example 2-1, and the sheet-like graphite exposed to this reduced-pressure atmosphere was used. A SiC crystal was grown under the same conditions as in Example 1-2.

  A high-quality SiC single crystal free from cracks and cracks could be grown without dropping the seed crystal substrate from the seed crystal holding shaft.

(Example 3-1)
The same sheet-like graphite as used in Example 1-1 was prepared and exposed to a high-temperature and reduced-pressure atmosphere of 100 ° C. and 10 Pa for 2 hours. The moisture content of the sheet-like graphite after being exposed to the high temperature and reduced pressure atmosphere was 0.1% by mass.

  The sheet-like graphite after being exposed to a high temperature and reduced pressure atmosphere was heat-treated at 200 ° C. for 2 hours. The bubble area ratio in the sheet-like graphite after the heat treatment was 0%.

(Example 3-2)
Except that the same sheet-like graphite as used in Example 3-1 was prepared, exposed to a high-temperature reduced-pressure atmosphere under the same conditions as Example 3-1, and the sheet-like graphite exposed to this high-temperature reduced-pressure atmosphere was used. The SiC crystal was grown under the same conditions as in Example 1-2.

  A high-quality SiC single crystal free from cracks and cracks could be grown without dropping the seed crystal substrate from the seed crystal holding shaft.

(Comparative Example 1-1)
The same sheet-like graphite as used in Example 1-1 was prepared, and heat-treated at 200 ° C. for 2 hours without being exposed to a high temperature atmosphere or a reduced pressure atmosphere. In FIG. 8, the external appearance photograph before heat processing of 200 degreeC of sheet-like graphite is shown. In FIG. 9, the external appearance photograph after 200 degreeC heat processing of sheet-like graphite is shown. The bubble area ratio in the sheet-like graphite after the heat treatment was 20%.

(Comparative Example 1-2)
The same sheet-like graphite as that used in Comparative Example 1-1 was prepared, and SiC crystals were formed under the same conditions as in Example 1-2, except that they were not exposed to a high temperature atmosphere or a reduced pressure atmosphere before curing the adhesive. Grown up.

  The seed crystal substrate sometimes dropped off from the seed crystal holding axis, and cracks were found in the grown SiC single crystal.

(Comparative Example 2-1)
The same sheet-like graphite as used in Example 1-1 was prepared and exposed to a humid atmosphere. The moisture content of the sheet-like graphite after being exposed to a humid atmosphere was 17% by mass. Next, the sheet-like graphite was heat-treated at 200 ° C. for 2 hours. In FIG. 10, the external appearance photograph before the heat processing of 200 degreeC of sheet-like graphite is shown. In FIG. 11, the external appearance photograph after the heat processing of 200 degreeC of sheet-like graphite is shown. The bubble area ratio in the sheet-like graphite after the heat treatment was 32%.

(Comparative Example 2-2)
The same sheet-like graphite as used in Comparative Example 2-1 was prepared, exposed to a humid atmosphere under the same conditions as Comparative Example 2-1, and not exposed to a high temperature atmosphere or a reduced pressure atmosphere before curing the adhesive. Except for this, an SiC crystal was grown under the same conditions as in Example 1-2.

  The seed crystal substrate sometimes dropped off from the seed crystal holding axis, and cracks were found in the grown SiC single crystal.

  In FIG. 12, the graph showing the relationship between the moisture content of the sheet-like graphite before heat processing and the area ratio of the bubble generated after heat processing is shown.

DESCRIPTION OF SYMBOLS 100 Single crystal manufacturing apparatus 10 Crucible 12 Seed crystal holding shaft 14 Seed crystal substrate 17 Grown crystal 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 Sheet graphite

Claims (1)

Production of a SiC single crystal by growing a SiC single crystal by bringing a seed crystal substrate held on the lower end face of a seed crystal holding shaft into contact with a Si-C solution having a temperature gradient that decreases from the inside toward the liquid surface. A method,
Preparing sheet-like graphite,
Exposing the sheet-like graphite to at least one of a high-temperature atmosphere and a reduced-pressure atmosphere to vaporize moisture in the sheet-like graphite;
Using an adhesive, the seed crystal substrate is bonded to the lower end surface of the seed crystal holding shaft so as to sandwich the sheet-like graphite exposed to the atmosphere, and the adhesive is cured by performing a heat treatment. Letting
The manufacturing method of the SiC single crystal containing this.