JP5293732B2 - Method for producing silicon carbide single crystal - Google Patents

Description

  The present invention relates to a method for manufacturing a high-quality silicon carbide single crystal used for manufacturing a power device or the like.

  Silicon carbide (SiC) is a semiconductor material having excellent thermal and chemical characteristics, a forbidden band width larger than that of silicon (Si), and having excellent electrical characteristics. In particular, since electron mobility and saturated electron velocity are large, it is being put into practical use as a semiconductor material for power devices. In order to produce a silicon carbide power device, it is preferable to obtain a silicon carbide single crystal of higher quality, that is, a low crystal defect density. If impurities exist in the crystal, it causes crystal defects during crystal growth. Therefore, in order to obtain a silicon carbide single crystal having a low crystal defect density, it is preferable to manufacture a high-purity silicon carbide single crystal.

  In conventional silicon carbide single crystal manufacturing methods, a silicon carbide single crystal or polycrystal grown separately by a sublimation recrystallization method using the high-purification action of silicon carbide crystals possessed by the sublimation recrystallization method (modified Rayleigh method) itself. A silicon carbide single crystal was produced by sublimation recrystallization using a pulverized material as a raw material. (For example, see Patent Document 1)

JP-A-2005-239396 (pages 4-6)

  In such a method for producing a silicon carbide single crystal, since a material obtained by pulverizing a silicon carbide single crystal or a polycrystal is used as a raw material for producing a silicon carbide single crystal, for example, contamination with a pulverizing tool, etc. It is inevitable that impurities are mixed during grinding. And there was a problem that it was very difficult to remove impurities mixed at the time of grinding.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a method for producing a silicon carbide single crystal capable of obtaining a higher-purity silicon carbide single crystal.

  A method for producing a silicon carbide single crystal according to the present invention includes a step of forming a silicon carbide ingot by a sublimation recrystallization method using silicon and carbon as raw materials in a crucible for forming a silicon carbide ingot, and a seed crystal attachment portion with a seed. And a step of sublimating a silicon carbide ingot by a sublimation recrystallization method to form a silicon carbide single crystal in a crucible for forming a silicon carbide single crystal to which a crystal is attached.

  According to the method for producing a silicon carbide single crystal according to the present invention, a silicon carbide single crystal with higher purity can be obtained.

It is a flowchart which shows the manufacturing method of the silicon carbide single crystal in Embodiment 1 of this invention. It is sectional drawing which shows a part of manufacturing method of the silicon carbide single crystal in Embodiment 1 of this invention. It is sectional drawing which shows a part of manufacturing method of the silicon carbide single crystal in Embodiment 1 of this invention. It is sectional drawing which shows a part of manufacturing method of the silicon carbide single crystal in Embodiment 1 of this invention. It is sectional drawing which shows a part of manufacturing method of the silicon carbide single crystal in Embodiment 1 of this invention. It is a figure which shows the time change of the temperature in a heating furnace and the pressure in the process of forming the silicon carbide polycrystal ingot in Embodiment 1 of this invention. It is sectional drawing which shows the silicon carbide polycrystal ingot in Embodiment 1 of this invention. It is a figure which shows the time change of the temperature in a heating furnace and the pressure in the process of forming the silicon carbide single crystal ingot in Embodiment 1 of this invention.

Embodiment 1 FIG.
FIG. 1 is a flowchart showing a method for manufacturing a silicon carbide single crystal according to Embodiment 1 of the present invention. 2 to 5 are cross sectional views showing a part of the method for manufacturing the silicon carbide single crystal in the first embodiment of the present invention. With reference to FIGS. 1-5, the manufacturing method of the silicon carbide single crystal in Embodiment 1 of this invention is demonstrated.

  First, as shown in FIG. 2, silicon and carbon, which are raw materials 2, are accommodated in a crucible 1 for forming a silicon carbide polycrystalline ingot (S1).

  Here, the crucible 1 for forming a silicon carbide polycrystalline ingot is provided with a main body portion 1a for accommodating the raw material 2 and a lid portion 1b. An ingot growing portion 3 which is a portion where a silicon carbide polycrystal grows and a silicon carbide polycrystal ingot is formed is detachably fixed to the lid portion 1b.

Although the crucible 1 is made of isotropic graphite, the isotropic graphite has innumerable pores. Therefore, when silicon adheres to the surface, silicon soaks into the pores and is cooled during cooling. It may break. In order to prevent this, the ingot growing part 3 of the crucible 1 is formed of high-density isotropic graphite. When the density of the isotropic graphite in the ingot growing part 3 is, for example, about 1.9 to 2.0 g / cm ³ , there are few vacancies, which is effective.

  Moreover, in order to heat efficiently, the outer periphery of the crucible 1 is covered with a heat insulating material (not shown). Furthermore, outside the ingot growth part 3 of the crucible 1 and above the ingot growth part 3, a heat reflecting plate 6 is arranged so that the temperature distribution in the ingot growth part 3 is as uniform as possible. As the heat reflecting plate 6, for example, a graphite plate, a graphite plate coated with pyrolytic carbon, a graphite plate coated with glassy carbon, a graphite sheet (for example, PERMA-FOIL manufactured by Toyo Tanso Co., Ltd.) or the like is used, and heat radiation is used. A rate of 50% or less is preferred. In FIG. 2, two heat reflecting plates 6 are installed. However, the number of heat reflecting plates 6 is not limited to this, but using a plurality of heat reflecting plates 6 is more effective than using a single heat reflecting plate 6.

  The raw material 2 is simple silicon and carbon. It is preferable to use silicon and carbon that contain as little impurities as possible. Since the solubility of carbon in the silicon melt is small, the smaller the carbon particle size, the more the yield of silicon carbide can be increased with respect to the amount of the raw material 2. Further, since silicon has a higher vapor pressure than carbon, silicon becomes vapor during temperature rise, and the amount of silicon that reacts with carbon decreases. Therefore, for example, it is preferable to store silicon in excess of carbon so that the molar ratio is Si: C = 1.2: 1.

  Next, the crucible 1 is installed in a heating furnace (not shown) provided with an induction heating device (not shown) and heated by induction heating. Thereby, the silicon carbide polycrystal is grown on the ingot growth part 3 by the sublimation recrystallization method, and as shown in FIG. 3, the silicon carbide polycrystal ingot 7 is formed (S2). Here, the heating method is induction heating, but resistance heating or other heating methods may be used.

  Next, as shown in FIG. 4, the ingot growing portion 3 in which the silicon carbide polycrystalline ingot 7 is formed is moved from the crucible 1 for forming silicon carbide polycrystalline ingot into the crucible 8 for forming silicon carbide single crystal. Move (S3). Here, the ingot growth part 3 is installed at the bottom of the crucible 8 so that the surface of the silicon carbide polycrystalline ingot 7 closer to the raw material 2 during growth (the lower surface in FIG. 3) faces upward.

  The crucible 8 for forming a silicon carbide single crystal includes a main body portion 8a that houses the ingot growing portion 3, and a lid portion 8b. Lid portion 8b has seed crystal attachment portion 8c for attaching seed crystal substrate 11 which is a silicon carbide single crystal substrate.

The crucible 8 is made of isotropic graphite. However, when a silicon carbide single crystal grows on seed crystal substrate 11, stress acts on seed crystal substrate 11 due to a difference in thermal expansion coefficient between silicon carbide seed crystal substrate 11 and seed crystal attachment portion 8 c of crucible 8. Since the silicon carbide single crystal causes crystal defects, the crucible 8 should have a thermal expansion coefficient close to that of silicon carbide. Specifically, the density is about 1.75 to 1.85 g / cm ³ and the difference in thermal expansion coefficient from silicon carbide at room temperature is 0.2 × 10 ⁻⁶ / K or less. It is preferable to use graphite. Note that the thermal expansion coefficient of silicon carbide at room temperature is about 3.09 × 10 ⁻⁶ / K.

  Moreover, in order to heat efficiently, the outer periphery of the crucible 8 is covered with a heat insulating material (not shown). Further, although not shown in FIG. 4, the heat reflecting plate 6 may be disposed outside the seed crystal attachment portion 8 c of the crucible 8 and above the seed crystal attachment portion 8 c.

  Next, the crucible 8 is installed in a heating furnace (not shown) provided with an induction heating device (not shown) and heated by induction heating. Thereby, silicon carbide polycrystalline ingot 7 is sublimated by a sublimation recrystallization method to grow a silicon carbide single crystal on seed crystal substrate 11, and silicon carbide single crystal ingot 12 is formed as shown in FIG. 5. (S4). Here, the heating method is induction heating, but resistance heating or other heating methods may be used.

  High purity and high quality (low crystal defect density) silicon carbide single crystal ingot 12 can be manufactured by the method for manufacturing a silicon carbide single crystal described above. Moreover, since the filling rate of the raw material is increased by using the silicon carbide polycrystalline ingot 7 instead of the powdery raw material 2 as a raw material for producing the silicon carbide single crystal ingot 12, a crucible for forming a silicon carbide single crystal is obtained. The length of 8 can be shortened.

  Next, the step (S2) of forming the silicon carbide polycrystalline ingot 7 and the step (S4) of forming the silicon carbide single crystal ingot 12 will be described in detail with reference to specific examples.

  First, the step (S2) of forming the silicon carbide polycrystalline ingot 7 will be described. FIG. 6 is a diagram showing temporal changes in temperature and pressure in the heating furnace in the step of forming silicon carbide polycrystalline ingot 7 in the first embodiment of the present invention.

  First, a crucible 1 for forming a silicon carbide polycrystalline ingot containing raw material 2 is installed in a heating furnace (not shown) equipped with an induction heating device (not shown).

  Here, as the raw material 2, flaky silicon having an average particle diameter of about 4 mm and a purity of 99.99999999999% (Eleven Nine) was used. The carbon used was a powder having an average particle diameter of 10 μm and a mixed amount of metal impurities such as aluminum, boron, iron and molybdenum, which are main impurities of silicon carbide, being less than 0.01 ppm. Then, 7500 g of raw material 2 in which silicon and carbon were mixed so that Si: C = 1.2: 1 in terms of molar ratio and silicon in excess of carbon was placed in crucible 1.

  The crucible 1 was made of isotropic graphite in which the amount of impurities such as aluminum, boron, iron, and molybdenum was less than 0.01 ppm. The crucible 1 was purified by heat treatment at about 2300 ° C. for 10 hours in an inert gas atmosphere such as argon at a pressure of less than 1.3 Pa before use. At this time, the carbon powder used as the raw material 2 was accommodated in the crucible 1 and purified at the same time. The inner diameter of the crucible 1 was 160 mm.

Next, as shown in FIG. 6, the inside of a heating furnace is evacuated to less than 6.5 × 10 ⁻⁴ Pa. Thereafter, the inside of the heating furnace is filled with argon gas, the pressure in the heating furnace is set to 80 kPa, and then evacuated again to less than 6.5 × 10 ⁻⁴ Pa.

  Next, in a state in which the inside of the heating furnace is evacuated without flowing gas, it is heated to 1100 ° C. and held for 10 hours. Thereby, the purification which removes the impurities adsorbed on the crucible 1 or the heat insulating material (not shown) is performed.

  Next, the pressure in the heating furnace is increased to 93 kPa, and while maintaining the pressure, the temperature is increased to 1800 ° C. and held for 20 hours. Thereby, silicon and carbon react.

  Next, heating is performed so that the bottom of the crucible 1 containing the raw material 2 is 2400 ° C. and the top of the crucible 1 to which the ingot growth section 3 is attached is 2200 ° C. In FIG. 6, the temperature at the bottom of the crucible 1 is 2400 ° C. And in order to stabilize the temperature of the crucible 1, it hold | maintains at these temperature for 1 hour. Thereafter, the pressure in the heating furnace is reduced from 93 kPa to 6.7 kPa over 2 hours.

  Here, the temperature in the heating furnace was set to about 2400 ° C., and the pressure was set to 6.7 kPa, under the condition that silicon carbide as a raw material 2 reacted with silicon at the bottom of the crucible 1 and sublimated into silicon carbide. This is because a silicon carbide polycrystal is grown on the ingot growing portion 3 to form a silicon carbide polycrystal ingot 7. Here, if the pressure in the heating furnace is too low, only silicon having a high vapor pressure easily leaks to the outside of the crucible 1, and if the pressure is too high, the growth rate of the silicon carbide polycrystal becomes slow. For this reason, it is preferable to set the pressure in the heating furnace at the time of silicon carbide polycrystal growth to 4.0 to 13.3 kPa, and more preferably to 5.3 to 8.0 kPa. Further, the temperature in the heating furnace and the temperature difference between the bottom of the crucible 1 and the top of the crucible 1 may be appropriately set in consideration of the growth rate and the like.

  When the pressure in the heating furnace reached 6.7 kPa, the growth was started and silicon carbide polycrystal was grown for 100 hours therefrom. At this time, the growth rate of the silicon carbide polycrystal was 50 g / h, and 5000 g of silicon carbide polycrystal ingot 7 was formed. The time for growing the silicon carbide polycrystal may be appropriately adjusted according to the weight of the required silicon carbide polycrystal ingot 7.

  Thereafter, the heating furnace is filled with argon gas, the pressure in the heating furnace is increased to 93 kPa, and the temperature is lowered to room temperature over 15 hours. Then, the obtained silicon carbide polycrystalline ingot 7 is taken out of the crucible 1 together with the ingot growing portion 3.

  FIG. 7 is a cross sectional view showing silicon carbide polycrystalline ingot 7 according to the first embodiment of the present invention. In FIG. 7, the upper surface of silicon carbide polycrystalline ingot 7 is the surface closer to raw material 2 when silicon carbide polycrystalline ingot 7 is grown (lower surface in FIG. 3). As shown in FIG. 7, the shape of the obtained silicon carbide polycrystalline ingot 7 is such that the height h of the outer peripheral portion is lower than the height H of the central portion. This is because there is a difference in the growth rate of the silicon carbide polycrystal because there is a temperature difference between the central part and the outer peripheral part of the ingot growing part 3.

  When there is a difference between the height H of the center portion of the silicon carbide polycrystalline ingot 7 and the height h of the outer peripheral portion, when the silicon carbide polycrystalline ingot 7 is disposed at the bottom of the crucible 8 for forming a silicon carbide single crystal Further, the distance between the upper surface of the silicon carbide polycrystalline ingot 7 and the seed crystal substrate 11 varies. Since seed crystal substrate 11 is mainly heated by radiation from silicon carbide polycrystalline ingot 7 which is a raw material, if the distance between the top surface of silicon carbide polycrystalline ingot 7 and seed crystal substrate 11 varies, radiation heat is generated. Variation occurs, the temperature distribution in the surface of the seed crystal substrate 11 becomes non-uniform, and the seed crystal substrate 11 is distorted. When the seed crystal substrate 11 is distorted, it causes crystal defects in the silicon carbide single crystal grown on the seed crystal substrate 11.

  In the first embodiment of the present invention, the outer periphery of the crucible 1 for forming a silicon carbide polycrystalline ingot is covered with a heat insulating material (not shown), and the heat reflecting plate 6 is disposed above the ingot growing portion 3, whereby the ingot The temperature difference between the central portion and the outer peripheral portion of the growth portion 3 can be reduced, and the difference in the rate of silicon carbide polycrystal growth between the central portion and the outer peripheral portion of the ingot growth portion 3 can be reduced. Thereby, the shape of the silicon carbide polycrystalline ingot 7 is such that (height H of the central portion / height h of the outer peripheral portion) is in the range of 0.95 to 1.1, more preferably 1.0 to 1. .05.

Here, a preliminary experiment is performed under the same conditions as the method described above, and the result of analyzing impurities in the formed silicon carbide polycrystalline ingot 7 will be described. Silicon carbide polycrystalline ingot 7 obtained in the preliminary experiment was sliced into a wafer and analyzed for impurities by secondary ion mass spectrometry (SIMS). The concentrations of nitrogen, aluminum, and boron, which are main impurities of silicon carbide, were all less than 3 × 10 ¹⁶ cm ⁻³ . Thereby, it has confirmed that the high purity silicon carbide polycrystal grew by the process (S2) of forming the silicon carbide polycrystal ingot 7 in Embodiment 1 of this invention.

  Next, the step (S4) of forming silicon carbide single crystal ingot 12 will be described. FIG. 8 is a diagram showing temporal changes in temperature and pressure in the heating furnace in the step of forming silicon carbide single crystal ingot 12 according to Embodiment 1 of the present invention.

  First, before the step (S4) of forming the silicon carbide single crystal ingot 12, the ingot growth portion 3 in which the silicon carbide polycrystalline ingot 7 is formed is removed from the crucible 1 for forming the silicon carbide polycrystalline ingot from the silicon carbide. A step (S3) of moving into the crucible 8 for forming a single crystal is performed.

  Ingot growth portion 3 is installed at the bottom of crucible 8 so that the surface of silicon carbide polycrystalline ingot 7 on the side close to raw material 2 during growth (the lower surface in FIG. 3, the upper surface in FIG. 7) faces upward. To do. Before the silicon carbide single crystal was grown, the silicon carbide polycrystal ingot 7 was installed such that the distance between the center portion of the upper surface of the silicon carbide polycrystalline ingot 7 and the surface of the seed crystal substrate 11 was 110 mm.

The crucible 8 is made of isotropic graphite in which the amount of impurities such as aluminum, boron, iron, and molybdenum is less than 0.01 ppm, the density is 1.82 g / cm ³ , and the thermal expansion coefficient is substantially equal to silicon carbide. What was done was used. The crucible 8 was purified by heat treatment at about 2300 ° C. for 10 hours in an inert gas atmosphere such as argon at a pressure of less than 1.3 Pa before use. The crucible 8 had an inner diameter of 160 mm and a length L of 230 mm. Here, the length L of the crucible 8 is the length in the thickness direction of the seed crystal substrate 11 attached to the seed crystal attachment portion 8c, as shown in FIG. It is the total length.

  As seed crystal substrate 11, a silicon carbide single crystal substrate having a diameter of 100 mm and a polytype of 4H was used. As described above, the raw material is the silicon carbide polycrystalline ingot 7 formed in the step (S2) of forming the silicon carbide polycrystalline ingot 7, and its weight is 5000 g.

  After performing the process (S3) of moving the ingot growth part 3 into the crucible 8 for silicon carbide single crystal formation, the process (S4) of forming the silicon carbide single crystal ingot 12 is performed. First, the crucible 8 for forming a silicon carbide single crystal in which the ingot growing section 3 is installed is installed in a heating furnace (not shown) provided with an induction heating device (not shown).

Next, as shown in FIG. 8, the inside of the heating furnace is evacuated to less than 6.5 × 10 ⁻⁴ Pa. Thereafter, the inside of the heating furnace is filled with argon gas, the pressure in the heating furnace is set to 80 kPa, and then evacuated again to less than 6.5 × 10 ⁻⁴ Pa.

  Next, in a state in which the inside of the heating furnace is evacuated without flowing gas, it is heated to 1350 ° C. and held for 10 hours. Thereby, the purification which removes the impurities adsorbed on the crucible 8 and the heat insulating material (not shown) is performed.

  Next, the inside of the heating furnace is filled with argon gas, the pressure in the heating furnace is set to 80 kPa, and while maintaining the pressure, the flow rate of argon gas is set to 200 sccm, and the crucible 8 containing the silicon carbide polycrystalline ingot 7 as a raw material is accommodated. Heating is performed so that the bottom is 2400 ° C. and the upper part of the crucible 8 to which the seed crystal substrate 11 is attached is 2300 ° C. In FIG. 8, the temperature at the bottom of the crucible 8 is 2400 ° C. And in order to stabilize the temperature of the crucible 8, it hold | maintains at these temperature for 1 hour. Thereafter, the pressure in the heating furnace is reduced from 80 kPa to 0.33 kPa over 90 minutes.

  Here, the temperature in the heating furnace was set to about 2400 ° C., and the pressure was set to 0.33 kPa under the condition that the silicon carbide polycrystalline ingot 7 as a raw material was sublimated, and a 4H type silicon carbide single crystal was formed on the seed crystal substrate 11. This is to form crystals. The temperature and pressure in the heating furnace during the growth of the silicon carbide single crystal may be appropriately set in consideration of the polytype of the silicon carbide single crystal and the growth rate.

  When the pressure in the heating furnace reached 0.33 kPa, growth was started, and a silicon carbide single crystal was grown for 130 hours therefrom. At this time, the growth rate of the silicon carbide single crystal is 20 g / h (0.78 mm / h), the weight is 2600 g, and the height (the length in the thickness direction of the seed crystal substrate 11) is 101 mm. Ingot 12 was formed. Note that the time for growing the silicon carbide single crystal may be appropriately adjusted according to the amount of the required silicon carbide single crystal ingot 12.

  After 130 hours from the start of the growth of the silicon carbide single crystal, the heating furnace is filled with argon gas, and the pressure in the heating furnace is increased to 93 kPa over 1 hour. Thereafter, the temperature in the heating furnace is lowered to room temperature over 20 hours. Then, crucible 8 is taken out of the heating furnace, and silicon carbide single crystal ingot 12 is taken out of crucible 8.

The result of analyzing the impurities of the obtained silicon carbide single crystal ingot 12 will be described. Silicon carbide single crystal ingot 12 manufactured using the method for manufacturing a silicon carbide single crystal described above was sliced into a wafer shape, and impurities were analyzed by secondary ion mass spectrometry (SIMS). The concentrations of nitrogen, aluminum, and boron, which are main impurities of silicon carbide, were all less than 1 × 10 ¹⁶ cm ⁻³ . Thereby, it was confirmed that the silicon carbide single crystal of high purity can be manufactured by the method for manufacturing the silicon carbide single crystal in the first embodiment of the present invention.

  Next, the results of experiments conducted as comparative examples will be described.

  First, under the same conditions as the above-described step (S1) of containing silicon and carbon as raw materials 2 in crucible 1 for forming a silicon carbide polycrystalline ingot and the step of forming silicon carbide polycrystalline ingot 7 (S2), A silicon carbide polycrystalline ingot was produced.

  Next, the silicon carbide polycrystalline ingot was pulverized into a powder having an average particle size of about 90 μm. And this powdery silicon carbide was accommodated in the crucible for silicon carbide single crystal formation. Here, in order to store 5000 g of powdered silicon carbide in a crucible having an inner diameter of 160 mm, the length L of the crucible was 320 mm.

  Next, a silicon carbide crystal was grown under the same conditions as in the step (S4) of forming silicon carbide single crystal ingot 12 described above. However, grain boundaries are generated in the grown silicon carbide crystal, and a high-quality silicon carbide single crystal having a low crystal defect density cannot be obtained. This is because when a silicon carbide polycrystalline ingot is pulverized, impurities are mixed into the raw material, for example, due to contamination by a pulverizing tool, etc., so that impurities are also mixed into the grown crystal and single crystal growth is inhibited. This is considered to be due to the fact that the length of the crucible for forming a silicon carbide single crystal has become longer, making it difficult to control the temperature near the seed crystal substrate.

  In Embodiment 1 of the present invention, a silicon carbide single crystal ingot 12 with higher purity can be obtained by performing the above. If impurities exist in the crystal, it causes crystal defects during crystal growth. Therefore, a silicon carbide single crystal ingot 12 having a lower crystal defect density can be obtained by obtaining a higher purity silicon carbide single crystal ingot 12. Can be obtained.

  In addition, by using silicon carbide polycrystalline ingot 7 that has not been crushed as a raw material for forming silicon carbide single crystal ingot 12, the filling rate of the raw material is higher than when a powdery raw material is used. Therefore, the length L of the crucible 8 for forming a silicon carbide single crystal can be shortened. When the length L of the crucible 8 is shortened, the temperature distribution around the seed crystal substrate 11 can be easily controlled, so that the seed crystal substrate 11 is distorted and the growth rate of the silicon carbide single crystal is varied in the plane. This can be suppressed. Therefore, silicon carbide single crystal ingot 12 having a lower crystal defect density can be obtained. Moreover, the cost of the crucible 8 can be reduced by shortening the length L of the crucible 8.

  Specifically, when the seed crystal substrate 11 having a diameter of 100 mm or more is used and the silicon carbide single crystal ingot 12 having a height of 100 mm or more is formed, the length L of the crucible 8 for forming the silicon carbide single crystal is determined. It can be 230 mm or less. That is, a long and large silicon carbide single crystal ingot 12 can be formed with a shorter crucible 8.

  In addition, since the polycrystalline ingot 7 is formed as a raw material for forming the silicon carbide single crystal ingot 12, it is possible to easily form a large amount of raw material ingot compared to a single crystal or amorphous.

  Since the ingot growth part 3 is removable from the crucible 1 for forming a silicon carbide polycrystalline ingot, the ingot growth part 3 formed with the silicon carbide polycrystalline ingot 7 is moved into the crucible 8 for forming a silicon carbide single crystal. The step (S3) to be performed can be easily performed. Further, by moving the ingot growing part 3 into the crucible 8 for forming a silicon carbide single crystal (S3), without moving the ingot growing part 3 without any modification to the silicon carbide polycrystalline ingot 7, The raw material for forming the silicon carbide single crystal ingot 12 can be installed. Therefore, it can suppress that an impurity mixes in the raw material for forming the silicon carbide single crystal ingot 12.

By forming the ingot growth part 3 with a high density isotropic graphite having a density of 1.9 to 2.0 g / cm ³ , the ingot growth part 3 has a higher density than that of the low density graphite. The void | hole which has can be reduced. Thereby, it can suppress that silicon penetrate | invades in a void | hole, and when it cools after the silicon carbide polycrystalline ingot 7 formation, it can prevent that the ingot growth part 3 will break.

The crucible 8 for forming a silicon carbide single crystal has a density of 1.75 to 1.85 g / cm ³ and a difference in thermal expansion coefficient from that of silicon carbide at room temperature of 0.2 × 10 ⁻⁶ / K or less. By forming with isotropic graphite, the difference in thermal expansion coefficient between the crucible 8 and the seed crystal substrate 11 is reduced, and it is possible to suppress the stress from acting on the seed crystal substrate 11 due to the difference in thermal expansion coefficient. Thereby, since it can suppress that a seed crystal substrate 11 produces distortion, it can control that a crystal defect arises at the time of growth of a silicon carbide single crystal resulting from distortion of seed crystal substrate 11.

  By disposing the heat insulating material and the heat reflecting plate 6 outside the ingot growth portion 3 of the crucible 1 for forming the silicon carbide polycrystalline ingot, the temperature difference between the central portion and the outer peripheral portion of the ingot growth portion 3 can be reduced. It is possible to reduce the difference in the rate at which the silicon carbide polycrystal grows between the central portion and the outer peripheral portion of the ingot growing portion 3. Thereby, the height of the center part of the silicon carbide polycrystalline ingot 7 is H, the height of the outer peripheral part is h, and H / h is in the range of 0.95 to 1.1, more preferably 1.0. Can be in the range of ~ 1.05.

  If there is a difference between the height H of the central portion of the polycrystalline silicon ingot 7 and the height h of the outer peripheral portion, the distance between the upper surface of the polycrystalline silicon ingot 7 and the seed crystal substrate 11 varies, and the Variations occur in the radiant heat from a certain silicon carbide polycrystalline ingot 7, the temperature distribution in the surface of the seed crystal substrate 11 becomes non-uniform, and the seed crystal substrate 11 is distorted. However, in Embodiment 1 of the present invention, since the upper surface of silicon carbide polycrystalline ingot 7 can be formed more flat as described above, this can be suppressed. Thereby, it is possible to suppress the occurrence of crystal defects in the silicon carbide single crystal grown on seed crystal substrate 11.

  In Embodiment 1 of the present invention, silicon carbide polycrystalline ingot 7 is formed, and this silicon carbide polycrystalline ingot 7 is used as a raw material for forming silicon carbide single crystal ingot 12. However, the raw material for forming silicon carbide single crystal ingot 12 is not limited to silicon carbide polycrystal, and may be single crystal or amorphous.

Moreover, in Embodiment 1 of this invention, the removable ingot growth part 3 was provided in the cover part 1b of the crucible 1 for silicon carbide polycrystalline ingot formation. However, in the step (S3), the entire lid 1b of the crucible 1 is regarded as the ingot growth part 3 without providing the ingot growth part 3 and the ingot growth part 3 is moved into the crucible 8 for silicon carbide single crystal formation. The entire lid portion 1b may be moved into the crucible 8 for forming a silicon carbide single crystal. In this case, the lid 1b may be formed of high-density isotropic graphite having a density of 1.9 to 2.0 g / cm ³ .

In Embodiment 1 of the present invention, the entire ingot growing part 3 is formed of high-density isotropic graphite having a density of 1.9 to 2.0 g / cm ³ . However, even if only the inner surface of the ingot growth portion 3 that is a portion in contact with the silicon carbide polycrystal is formed of the above-described high-density isotropic graphite, a certain effect can be obtained. When the lid portion 1b is used as the ingot growing portion 3, the inner surface of the lid portion 1b may be the above-described high-density isotropic graphite.

Further, it is not limited to isotropic graphite having a density of 1.9 to 2.0 g / cm ³ , and may be formed of isotropic graphite covered with a pyrolytic carbon film. Since pyrolytic carbon is extremely dense, even if silicon adheres, the ingot growth part 3 is difficult to crack during cooling. In this case, the density of the isotropic graphite may be lower. If isotropic graphite having the same density as that of the lid portion 1b of the crucible 1 is used, thermal expansion is caused between the ingot growing portion 3 and the lid portion 1b. Since there is no difference in coefficient, it becomes more difficult to break. Of course, the effect can be obtained if at least the inner surface of the ingot growing part 3 is covered with a pyrolytic carbon film.

The same effect can be obtained by using a glassy carbon film or a silicon carbide film instead of the pyrolytic carbon film. When a silicon carbide film is used, the density of the isotropic graphite to be coated is 1.75 to 1.85 g / cm ³ , and the difference in thermal expansion coefficient from silicon carbide at room temperature is 0. Isotropic graphite of 2 × 10 ⁻⁶ / K or less may be used. In this case, since the difference in thermal expansion coefficient between the silicon carbide polycrystalline ingot 7 formed in the ingot growing part 3 and the ingot growing part 3 becomes small, the ingot growing part 3 becomes difficult to break.

In Embodiment 1 of the present invention, the crucible 8 for forming a silicon carbide single crystal has a density of 1.75 to 1.85 g / cm ³ and a difference in thermal expansion coefficient from that of silicon carbide at room temperature. The isotropic graphite was 0.2 × 10 ⁻⁶ / K or less. However, if at least the seed crystal attachment portion 8c of the crucible 8 is formed of the above isotropic graphite, a certain effect can be obtained.

  In the first embodiment of the present invention, the heat insulating material and the heat reflecting plate 6 are arranged outside the ingot growing portion 3 of the crucible 1 for forming a silicon carbide polycrystalline ingot. However, even if only one of the heat insulating material and the heat reflecting plate 6 is arranged, a certain effect can be obtained.

Embodiment 2. FIG.
A method for manufacturing a silicon carbide single crystal according to Embodiment 2 of the present invention forms a p-type silicon carbide polycrystalline ingot 7 and uses the p-type silicon carbide polycrystalline ingot 7 as a raw material to produce a p-type silicon carbide single crystal. The point that the crystal ingot 12 is formed is different from the first embodiment of the present invention.

  With reference to FIGS. 1-5, the manufacturing method of the silicon carbide single crystal in Embodiment 2 of this invention is demonstrated in detail.

  First, in the step (S1) of storing the raw material 2 in the crucible 1 for forming a silicon carbide polycrystalline ingot, a carbide containing an element that becomes a p-type impurity in addition to silicon and carbon is used as the raw material 2 in the crucible 1. Accommodate.

For example, a group III element such as boron or aluminum is used as an element that becomes a p-type impurity, and boron carbide (B ₄ C), aluminum carbide (Al ₄ C ₃ ), or the like is used as the carbide. By using a group III element and carbon compound, impurities other than p-type impurities can be prevented from being mixed.

  Since boron carbide is more thermally stable than aluminum carbide and has a smaller difference in melting point from silicon carbide, boron carbide is more p-type at a uniform concentration by silicon carbide polycrystalline ingot 7. It is possible to add the impurities. Further, instead of using a carbide containing a group III element, a group III element alone may be used.

  Then, using the raw material 2 described above, a p-type silicon carbide polycrystalline ingot 7 is formed (S2). Thereafter, the ingot growing portion 3 in which the p-type silicon carbide polycrystalline ingot 7 is formed is moved into the crucible 8 for forming a silicon carbide single crystal (S3), and the p-type silicon carbide polycrystalline ingot 7 is used as a raw material. A silicon carbide single crystal ingot 12 of a type is formed (S4). Since S2 to S4 are the same as in the first embodiment of the present invention, description thereof is omitted.

If the amount of impurities added to the silicon carbide single crystal ingot 12 is too large, crystal defects are likely to be formed, and if the amount added is too small, the resistivity of the silicon carbide single crystal ingot 12 increases, so the silicon carbide single crystal ingot 12 The amount of impurities added to 12 is preferably in the range of 5 × 10 ¹⁸ to 8 × 10 ¹⁹ cm ⁻³ . In order to set the addition amount to the silicon carbide single crystal ingot 12 within the above range, the addition amount of impurities to the silicon carbide polycrystalline ingot 7 is within the range of 5 × 10 ¹⁹ to 2 × 10 ²⁰ cm ⁻³ . It is preferable that In the step (S1) of storing the raw material 2 in the crucible 1 for forming the silicon carbide polycrystalline ingot, the raw material 2 is adjusted so that the amount of impurities added to the silicon carbide polycrystalline ingot 7 is within the above range. deep.

Boron carbide is added to the raw material 2 and S1 to S4 are performed under the same conditions as in the example described in the first embodiment of the present invention. The obtained silicon carbide single crystal ingot 12 is sliced into a wafer shape to obtain secondary ions. Impurities were analyzed by mass spectrometry (SIMS). As a result, the concentration of boron was 1 × 10 ¹⁹ cm ⁻³ , and the concentrations of nitrogen and aluminum were both less than 1 × 10 ¹⁶ cm ⁻³ .

  In the second embodiment of the present invention, the p-type silicon carbide single crystal ingot 12 having a smaller amount of impurities other than the p-type impurities and a lower crystal defect density can be obtained as described above.

In the second embodiment of the present invention, silicon carbide polycrystalline ingot 7 is formed by adding a single element of p-type impurity element or a carbide containing an element that becomes p-type impurity to raw material 2. However, instead of adding a single element that becomes a p-type impurity or a carbide containing an element that becomes a p-type impurity to the raw material 2, the raw material 2 uses only silicon and carbon to form a silicon carbide polycrystalline ingot 7. In the step (S2), a gas containing a group III element that becomes a p-type impurity may be mixed in the atmosphere. As the gas containing a Group III element, for example, diborane (B ₂ H ₆ ), trimethylaluminum (Al (CH ₃ ) ₃ ), or the like is used.

  As a method for adding a p-type impurity, when a gas containing a group III element is used, instead of mixing a gas containing a group III element into the atmosphere in the step (S2) of forming the silicon carbide polycrystalline ingot 7, In the step (S4) of forming the crystal ingot 12, a gas containing a group III element may be mixed into the atmosphere.

  In the second embodiment of the present invention, portions different from the first embodiment of the present invention are described, and descriptions of the same or corresponding portions are omitted.

Embodiment 3 FIG.
A method for manufacturing a silicon carbide single crystal according to Embodiment 3 of the present invention forms an n-type silicon carbide polycrystalline ingot 7 and uses the n-type silicon carbide polycrystalline ingot 7 as a raw material to produce an n-type silicon carbide single crystal. The point that the crystal ingot 12 is formed is different from the first and second embodiments of the present invention.

  The raw material 2 uses only silicon and carbon, and in the step (S2) of forming the silicon carbide polycrystalline ingot 7, a gas containing a group V element serving as an n-type impurity is mixed into the atmosphere. As the gas containing a group V element, for example, nitrogen or the like is used. Since S3 to S4 are the same as in the first embodiment of the present invention, description thereof will be omitted.

  In the third embodiment of the present invention, the n-type silicon carbide single crystal ingot 12 having a small amount of impurities other than the n-type impurities and a lower crystal defect density can be obtained by the above process.

  Instead of mixing a gas containing a group V element in the atmosphere in the step (S2) of forming the silicon carbide polycrystalline ingot 7, a gas containing a group V element in the step (S4) of forming the silicon carbide single crystal ingot 12 May be mixed in the atmosphere.

  In the third embodiment of the present invention, portions different from the first and second embodiments of the present invention are described, and descriptions of the same or corresponding portions are omitted.

DESCRIPTION OF SYMBOLS 1 Crucible for forming silicon carbide polycrystalline ingot 1b Crucible lid for forming silicon carbide polycrystalline ingot 2 Raw material 3 Ingot growing part 6 Heat reflector 7 Silicon carbide polycrystalline ingot 8 Crucible for forming silicon carbide single crystal 8c Crystal mounting portion 11 Seed crystal substrate 12 Silicon carbide single crystal ingot

Claims (9)

Forming a silicon carbide ingot by a sublimation recrystallization method using silicon and carbon as raw materials in a crucible for forming a silicon carbide ingot;
A step of sublimating the silicon carbide ingot by a sublimation recrystallization method to form a silicon carbide single crystal in a crucible for forming a silicon carbide single crystal having a seed crystal attached to the seed crystal attachment portion;
A method for producing a silicon carbide single crystal comprising:   2. The method for producing a silicon carbide single crystal according to claim 1, wherein, in the step of forming the silicon carbide ingot, a silicon carbide polycrystal ingot is formed. The crucible for forming the silicon carbide ingot is detachable from the ingot growth part which is a part where the silicon carbide ingot is formed,
3. The silicon carbide single unit according to claim 1, further comprising a step of moving the ingot growth portion on which the silicon carbide ingot is formed into a crucible for forming a silicon carbide single crystal. 4. Crystal production method. The surface on which the silicon carbide polycrystalline ingot of the ingot growth part is formed has a layer formed of isotropic graphite having a density of 1.9 to 2.0 g / cm ³ . A method for producing a silicon carbide single crystal. The ingot growth part is formed of isotropic graphite,
4. The method for producing a silicon carbide single crystal according to claim 3, wherein the surface on which the silicon carbide polycrystalline ingot of the ingot growing part is formed is covered with pyrolytic carbon, glassy carbon, or silicon carbide. The seed crystal mounting portion is made of isotropic graphite having a density of 1.75 to 1.85 g / cm ³ and a difference in thermal expansion coefficient from that of silicon carbide at room temperature of 0.2 × 10 ⁻⁶ / K or less. The method for producing a silicon carbide single crystal according to any one of claims 1 to 5, wherein the silicon carbide single crystal is formed. A seed crystal substrate having a diameter of 100 mm or more is attached to the seed crystal attachment part,
The length in the thickness direction of the seed crystal substrate of the crucible for forming a silicon carbide single crystal is 230 mm or less,
7. The silicon carbide single crystal according to claim 1, wherein in the step of forming the silicon carbide single crystal, the silicon carbide single crystal having a length in the thickness direction of the seed crystal substrate of 100 mm or more is formed. The manufacturing method of the silicon carbide single crystal of description. On the outside of the ingot growth portion of the crucible for forming the silicon carbide ingot, at least one of a heat insulating material and a heat reflecting member is disposed,
In the step of forming the silicon carbide ingot, the height of the center of the silicon carbide ingot is H, the height of the outer periphery of the silicon carbide ingot is h, and the silicon carbide so that H / h is 1 to 1.05. An ingot is formed, The manufacturing method of the silicon carbide single crystal of any one of Claim 1 thru | or 7 characterized by the above-mentioned.   In the step of forming a silicon carbide ingot, a p-type silicon carbide ingot is formed using, as a raw material, a single element of an element that becomes a p-type impurity or a carbide that contains an element that becomes a p-type impurity in addition to silicon and carbon. The method for producing a silicon carbide single crystal according to any one of claims 1 to 8, wherein:

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