JP2016179920A - METHOD FOR MANUFACTURING SiC RAW MATERIAL USED FOR SUBLIMATION RECRYSTALLIZATION METHOD AND SiC RAW MATERIAL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new SiC raw material capable of preventing a sublimation gas composition from being varied in a sublimation recrystallization method for sublimating SiC used as a raw material to grow a SiC single crystal on a seed crystal, reducing the variation of the gas permeability and surface area and suppressing the time variation of sublimation velocity.SOLUTION: The method for manufacturing a SiC raw material used for a sublimation recrystallization method includes heating a SiC powder at a temperature of 1500-2200°C in an inert gas atmosphere having a pressure of 1.33×10Pa or more to obtain the SiC raw material consisting of a SiC porous sintered body having a porosity of 20-50% and an effective thermal conductivity of 0.5 W/mK or more at a temperature of 1000°C in the atmospheric pressure. The SiC powder consists of a mixed powder of a fine particle SiC powder having a small average particle size with a coarse particle SiC powder having a large average particle size. The fine particle SiC powder has an average particle size a of 30-200 μm, and the coarse particle SiC powder has an average particle size b of 210-2000 μm. The average particle sizes satisfy the relationship of 7a≤b.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for producing a SiC raw material used for the sublimation recrystallization method, and a SiC raw material for the sublimation recrystallization method.

  SiC (silicon carbide) is a wide band gap semiconductor having a wide forbidden band of 2.2 to 3.3 eV, and research and development as a semiconductor material has been performed for a long time because of its excellent physical and chemical characteristics. ing. Particularly in recent years, SiC has attracted attention as a material for short wavelength optical devices from blue to ultraviolet, high frequency electronic devices, and high withstand voltage / high output electronic devices at a more practical stage. However, SiC is difficult to produce a high-quality large-diameter single crystal, which is one factor that hinders the practical use of SiC devices.

Conventionally, on the scale of a laboratory level, for example, a SiC single crystal having a size capable of producing a semiconductor element by a sublimation recrystallization method (Rayleigh method) has been obtained. However, in this method, the area of the obtained single crystal is small, and it is not easy to control the size, shape, crystal polymorph (polytype), and impurity carrier concentration. On the other hand, a cubic SiC single crystal is also grown by heteroepitaxial growth on a heterogeneous substrate such as silicon (Si) using chemical vapor deposition (CVD). With this method, a single crystal having a large area can be obtained, but only SiC single crystal containing many defects (˜10 ⁷ / cm ² ) is grown because there is about 20% lattice mismatch between SiC and Si. Therefore, a high-quality SiC single crystal has not been obtained.

  In order to solve these problems, an improved Rayleigh method has been proposed in which sublimation recrystallization is performed using a SiC single crystal substrate as a seed crystal (see Non-Patent Document 1). By using this modified Rayleigh method, a SiC single crystal can be grown while controlling the crystal polymorphism (6H type, 4H type, 15R type, etc.) of SiC single crystal, shape, carrier type, and concentration. There are over 200 crystalline polymorphs (polytypes) of SiC, but the 4H polytype is considered to be the most excellent in terms of crystal productivity and electronic device performance. The crystals are often 4H. In addition, the conductivity is that nitrogen is easy to handle as a dopant, and single crystal ingots are mostly grown with n-type conductivity. However, for communication device applications, crystals having a high resistivity and almost no dopant element are also produced.

  At present, a SiC single crystal wafer having a diameter of 51 mm (2 inches) to 100 mm is cut out from a SiC single crystal manufactured by an improved Rayleigh method, and is used for device manufacturing in the field of power electronics and the like. Furthermore, a 150 mm wafer has been put on the market (see Non-Patent Document 2), and a full-scale practical application of a device using a 100 mm or 150 mm wafer is expected. Under such circumstances, technologies for improving the productivity and crystal growth yield of SiC ingots that lead to a reduction in wafer costs are becoming increasingly important.

  The main manufacturing method of the SiC single crystal ingot is the improved Rayleigh method as described above. Solution growth (see Non-Patent Document 3) and high-temperature CVD (see Non-Patent Document 4) are also carried out at the research level, but productivity (the number of wafers that can be taken per ingot and the success rate of high-quality ingot growth) It does not extend to the improved Rayleigh method in terms of quality. However, the improved Rayleigh method is a process performed at an ultra-high temperature of 2000 ° C. or higher, and further, there is a technical difficulty in controlling growth conditions such as supply of raw material by a gas phase. Although the exact figures of SiC wafer manufacturers are not disclosed, it is said that the number of wafers that can be taken per ingot and the growth success rate of high-quality ingots are not as good as those in highly mature industries such as Si. From the viewpoint of pursuing commercial profits, the current situation is that further improvement is required in the productivity of SiC single crystals.

  For the above-mentioned purpose, research and development are actively conducted on the production conditions of SiC single crystal ingots by the sublimation recrystallization method. On the other hand, a SiC raw material for sublimation recrystallization (hereinafter sometimes simply referred to as a raw material) has a great influence on the productivity and quality of a SiC single crystal. Non-Patent Document 5 reports the effect of air permeability in the raw material filling part in which a crucible is filled with a SiC raw material on the sublimation amount (sublimation gas generation amount). In Non-Patent Document 6, sublimation and recrystallization occur in the space filled with the raw material due to the temperature gradient of the raw material powder during the growth process (a phenomenon known as so-called rearrangement of the raw material), which is the growth rate. Has been reported to affect In Non-Patent Document 7, it is pointed out that the gas composition supplied to the growing crystal changes due to the rearrangement of the raw materials.

  Based on the above-mentioned viewpoint, although the contents are various, technical development regarding the raw material in the sublimation recrystallization method is progressing, and there are some report examples. For example, Patent Document 1 discloses a method of using a hot-pressed SiC sintered body as a raw material. This method is intended to improve the space efficiency by increasing the density of the raw materials and to improve the energy efficiency by increasing the thermal conductivity of the raw materials.

  In Patent Document 2, a powder containing SiC is pressure-molded and calcined to produce a raw material having a predetermined hardness. The raw material is placed in the upper part of the crucible and the seed crystal is placed in the lower part of the crucible. A method for performing single crystal growth is disclosed. This method aims to avoid quality deterioration due to the support member by not using a seed crystal support member.

  In Patent Document 3, in the method for producing a SiC single crystal, when the raw material is stored in the lower part of the single crystal production container, the particle diameter of the raw material powder arranged on the surface part in contact with the space in the container is reduced to a lower part. A method of efficiently sublimating a raw material by making the gap between the particles of the raw material powder to be arranged and the gap between the large-diameter particles be a passage for sublimation gas generated on the lower side. Is disclosed.

Patent Document 4, the average particle size is sintered 200μm or less of primary particles more than 5 [mu] m, or less average particle size 100μm above 700 .mu.m, and a specific surface area of 0.05 m ² / g or more 0.30 m ² / g or less A method for realizing a high and stable sublimation rate (a reduced amount of raw material per heating time) using the secondary particles described above as SiC powder for producing a SiC single crystal is disclosed.

  In Patent Document 5, the inside of a crucible filled with raw material SiC powder is heated to 500 ° C. or higher and 2000 ° C. or lower in a reducing atmosphere, thereby breaking the chemical bond of nitrogen on the crucible or the raw material surface to obtain high purity. A method for making a simple SiC single crystal is disclosed.

  Patent Document 6 discloses a method of obtaining a high-quality SiC single crystal by using a raw material obtained by preliminarily sublimating 2% or more of the mass of SiC powder and suppressing inclusion of inclusions in the single crystal. ing.

Japanese Patent No. 4619567 JP 2012-36035 A Japanese Patent No. 4048606 JP 2012-101996 A Japanese Patent No. 5336307 JP 2013-95632 A

Yu. M. Tairov and V. F. Tsvetkov, Journal of Crystal Growth, vols. 52 (1981) pp.146-150 A.A.Burk et al. , Mater.Sci. Forum, 717-720, (2012) pp75-80 K. Kusunoki1 et al. , Mater.Sci. Forum, 778-780, (2014) pp79-82 Y. Tokuda et al. , Mater.Sci. Forum, 778-780, (2014) pp51-54 X.wang et al. , Journal of Crystal Growth, vols.305 (207) pp.122-132 A.V.Kulik et al. , Mater.Sci. Forum, 457-460, (2004) pp67-70 T. Fujimoto et al. , Mater.Sci. Forum, 457-460, (2004) pp67-70

  Although it is obvious that SiC is a material for high-performance and energy-saving devices due to its excellent characteristics, as described above, there are problems in productivity and quality due to the difficulty in producing single crystals, which is an obstacle to the practical development. It was.

  Here, in terms of the SiC raw material used in the sublimation recrystallization method, for example, in the above-mentioned Patent Document 1, although the bulk density of the hot press sintered body is not mentioned, the heat transfer between the solid and the gas is not described. (See paragraph 0017 etc.), it can be seen that this is a dense sintered body with very few pores and a small surface area. If such a material is used as a raw material, it is presumed that the space utilization efficiency inside the crucible is improved and the rearrangement of the raw material is also suppressed due to the high thermal conductivity. However, since the surface area is extremely small, the sublimation rate is lowered, and it is difficult to obtain a growth rate of a level necessary for industrial production, and boron, which is a p-type dopant, is used as a sintering aid. Therefore, problems of contamination of the obtained single crystal and deterioration of electrical characteristics are inevitable.

  Patent Document 2 discloses a technique for heat-treating SiC powder after pressure forming, but does not describe heat treatment conditions, porosity, etc. of the sublimation recrystallization raw material. In order to hold the raw material in the crucible upper portion, which is the object of the present invention, it can be presumed that the raw material for sublimation is more advantageous as the porosity is smaller and stronger. Therefore, it can be said that this technology does not fully consider the growth rate and quality improvement.

  In addition, by using the raw material arrangement as in Patent Document 3 or using SiC powder as in Patent Document 4 as a raw material, it is possible to realize an efficient and high sublimation rate in the initial stage of SiC single crystal growth. However, it is not a method that considers reducing the rearrangement of raw materials due to sublimation and recrystallization that occurs during the growth process, so the growth rate is expected to decrease during the latter half of the growth period. There is concern about quality degradation.

  Patent Documents 5 and 6 have the content of heat-treating the raw material powder prior to SiC single crystal growth, but the purpose is to increase the purity of the raw material and not to improve the sublimation conditions.

  The present invention has been made in view of the above-mentioned problems, and improves the productivity of SiC single crystal production by using an unprecedented new sublimation raw material as the SiC raw material used in the sublimation recrystallization method. It is another object of the present invention to obtain a high-quality SiC single crystal.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have set the void ratio of the raw material to an appropriate value (moderately high bulk density), thereby limiting the space in the limited crucible (raw material filling chamber). Can be filled with a sufficient amount of raw materials, ensuring good air permeability, sufficient sublimation rate due to surface area, and growth rate, and having moderately high thermal conductivity, reducing the rearrangement of raw materials, The inventors have found that the change in sublimation gas composition can be prevented and the change in air permeability and surface area can be reduced to suppress the change in sublimation rate over time, thereby completing the present invention.

That is, the gist of the present invention is constituted as follows.
(1) A method for producing a SiC raw material used in a sublimation recrystallization method in which SiC as a raw material is sublimated to grow a SiC single crystal on a seed crystal,
The SiC powder is heat-treated in an inert gas atmosphere at a pressure of 1.33 × 10 ⁴ Pa or more at a temperature of 1500 ° C. or more and 2200 ° C. or less, and the porosity is 20% or more and 50% or less and 1000 ° C. at atmospheric pressure. A SiC raw material for use in a sublimation recrystallization method, characterized in that an SiC raw material comprising an SiC porous sintered body having an effective thermal conductivity of 0.5 W / mK or more is obtained.
(2) the SiC powder, a cumulative distribution of the particle size by volume basis, with a particle size _{D 20} corresponding to cumulative 20% particle size is 200μm or less, a particle the particle diameter _{D 20} falls on the cumulative 50% particle size method for manufacturing a SiC raw material used in the sublimation recrystallization method described in (1) to be one having a particle size distribution of less than 0.2 times the diameter D _50.
(3) The SiC powder is a mixed powder of a fine SiC powder having a small average particle diameter and a coarse SiC powder having a large average particle diameter, and the average particle diameter a of the fine SiC powder is 30 μm or more. 200 μm or less, the average particle diameter b of the coarse SiC powder is 210 μm or more and 2000 μm or less, and these average particle diameters satisfy the relationship of 7a ≦ b. A method for producing an SiC raw material used in a crystallization method.
(4) The SiC raw material used in the sublimation recrystallization method according to (3), wherein the fine SiC powder is mixed in a mixed powder at a ratio of 30% by mass to 50% by mass. Production method.
(5) SiC raw material used in a sublimation recrystallization method in which SiC as a raw material is sublimated to grow a SiC single crystal on a seed crystal, and the porosity is 20% or more and 50% or less, and 1000 ° C. A SiC raw material for a sublimation recrystallization method, comprising an SiC porous sintered body having an effective thermal conductivity at atmospheric pressure of 0.5 W / mK or more.

  According to the present invention, by using the obtained SiC raw material to grow a single crystal by the sublimation recrystallization method, an appropriate sublimation rate is maintained over the entire growth time, and the fluctuation of the sublimation gas composition is small. Therefore, the success rate of crystal growth is high, and a high-quality SiC single crystal can be manufactured.

FIG. 1 is a schematic diagram showing a crystal growth apparatus used in an example of the present invention. FIG. 2 is a schematic diagram showing an outline of a heat treatment and crystal manufacturing part process for obtaining a SiC raw material according to the present invention.

The present invention will be described in detail below.
First, in this invention, the raw material used for the sublimation recrystallization method is comprised with SiC, and the porosity when it is set as a SiC porous sintered compact is 20% or more and 50% or less. When the porosity is less than 20%, the area of the pores, which are passages through which the sublimation gas passes, is too small, the surface area of the raw material that is the sublimation gas generation interface in the sublimation recrystallization method is reduced, and the sublimation rate is significantly reduced. As a result, the growth rate also decreases, and the productivity of the single crystal deteriorates. On the other hand, when the porosity exceeds 50%, the raw material filling amount in the crucible decreases, the height of the obtained single crystal ingot inevitably decreases, and the productivity also deteriorates. In addition, since the thermal conductivity contribution of the solid portion is reduced, the thermal conductivity of the porous sintered body is reduced, and the temperature gradient of the SiC porous sintered body during the growth process is increased. As the temperature gradient of the raw material is larger, the so-called relocation phenomenon of the raw material, in which the generated sublimation gas is recrystallized at a low temperature portion near the generation point, is promoted. Under such conditions that the SiC raw material can be easily rearranged, the amount of sublimation gas reaching the grown crystal decreases, and the sublimation gas after the reaction becomes Si-rich and the composition of the gas fluctuates. Undesirable in terms of quality. In addition, the porosity of the SiC raw material in this invention is calculated | required from following formula (1) in the case of SiC powder and a SiC porous sintered compact.
Porosity [%] = [(SiC raw material volume [cm ³ ]) − (SiC raw material mass [g] /3.215 [g / cm ³ ])] / SiC raw material volume [cm ³ ] × 100 (1)
(However, 3.215 represents the theoretical density [g / cm ³ ] of SiC)

  In addition, the effective thermal conductivity of the SiC raw material according to the present invention is preferably higher in principle, and should be 0.5 W / mK or more under the conditions of atmospheric pressure and 1000 ° C., desirably 1.0 W / mK or more, more desirably 1.5 W / mK or more. In addition, as a measuring method of thermal conductivity, the unsteady hot wire method was employ | adopted in this invention, and the measurement based on JISR2616 was performed. Further, when the size of the test piece is limited as in the case where the shrinkage due to sintering is significant and the SiC porous sintered body becomes small, the laser flash method conforming to JIS R1611-1997 was used.

  Here, no upper limit is set for the effective thermal conductivity of the obtained SiC porous sintered body, but in order to obtain an effective thermal conductivity exceeding 10 W / mK, the effect of the thermal conductivity of the solid is made by using the raw material as a dense body. However, since the excessively densified raw material is not preferable in terms of productivity and quality of the SiC single crystal ingot, the effective thermal conductivity of the SiC porous sintered body is 10 W / mK or less. Is desirable. On the other hand, it is difficult to obtain the physical property values of the present invention simply by filling the crucible with raw material powder (ie, SiC powder) for obtaining a SiC porous sintered body. For example, simply filling a crucible with a GC abrasive or a chemically synthesized commercially available SiC powder material does not result in an effective thermal conductivity of 0.5 W / mK or more. The filled powder consists of minute solids (powder particles) and minute spaces (pores between the powder particles), and thermal energy is frequently converted between the energy of lattice vibration and light energy. The reason for this is that the conduction resistance increases. In order to increase the effective thermal conductivity, it is effective to heat the filled powder under appropriate conditions to obtain a sintered body. In the SiC porous sintered body according to the present invention, a network-like structure is formed by the grain growth and neck growth of the SiC powder, and on the other hand, the volume change until the filled powder reaches the sintered body. Since there is no, the size of one pore is increasing. In such a structure, the thermal energy is effectively transmitted by the heat conduction by the network structure and the radiation conduction through the pores whose size is increased, so that the effective thermal conductivity is improved.

Therefore, the heat treatment for obtaining the SiC porous sintered body needs to be performed in an inert gas atmosphere with the SiC powder at a pressure of 1.33 × 10 ⁴ Pa or more. This is because a sublimation reaction preferentially occurs over a sintering reaction at a pressure of less than 1.33 × 10 ⁴ Pa. Also, the atmosphere must be inert to prevent oxidation of the surface of the SiC powder. The maximum temperature during the heat treatment is 1500 ° C. or higher and 2200 ° C. or lower. If the temperature is lower than 1500 ° C., a sufficient sintering reaction cannot be obtained. On the other hand, if it exceeds 2200 ° C., a sublimation reaction occurs even in the aforementioned pressure range, and the intended SiC porous sintered body (sintered simply) This is because the body may not be generated. The pressure during the heat treatment is not limited as long as the SiC powder can proceed with the sintering reaction without sublimation, and the upper limit is not particularly limited, but the pressure is determined in consideration of the workability and the specifications of the apparatus used for the heat treatment. It is desirable to set it as 1.33 * 10 < ⁵ > Pa or less.

  Since the sintered body obtained in this way has a strength sufficient to be self-supporting, it can be handled by hand and stored in a crucible for SiC single crystal growth and used for a crystal growth process. Therefore, when obtaining a SiC porous sintered body, there is no particular limitation as long as it is a heat treatment apparatus capable of heat treating SiC powder at the above pressure and temperature in an inert gas atmosphere. In view of the fact that heat treatment under the above conditions can be performed using a furnace (crystal growth apparatus) for producing a SiC single crystal by the sublimation recrystallization method, it is possible to save time and labor for transferring the SiC raw material, etc. Preferably, the raw material powder sintering process is incorporated as a pre-stage of the manufacturing process of the SiC single crystal, and the SiC powder is heat-treated as a continuous process continuous with the manufacturing of the SiC single crystal.

On the other hand, even if the above-mentioned heat treatment is performed on a general SiC powder, it is difficult to form a SiC porous sintered body as in the present invention. In order to generate an appropriate sintering reaction, as the first embodiment, preferably, the particle size D ₂₀ corresponding to 20% of the cumulative particle size distribution of the SiC powder is 200 μm or less, and the same 50 it is necessary than 0.2 times the particle diameter _{D 50} smaller particle size _{D 20} corresponding to%. Here, in the present invention, the particle size of the SiC powder was measured using a laser diffraction method.

Here, when the particle diameter D ₂₀ of SiC powder for which heat treatment is more than 200 [mu] m, sintering reaction does not proceed as an object in the present invention. On the other hand, just as the particle size D ₂₀ is at 200μm or less, only the powder made up of small particles, it is difficult to control in order to cause rapid sintering reaction in a short time. Therefore, as the particle diameter D ₂₀ is 0.2 times less than the particle size D _50, if the powder having a broad particle size distribution, because that will contain the loose grit sintering reaction, The reaction rate of the sintering due to the heat treatment is appropriately reduced, and an excessive increase in the bulk density of the sintered body can be suppressed. Also, common SiC powder used in such GC abrasives, as compared with the SiC powder of the present invention is standing histogram of particle size sharp, 0 particle size D ₂₀ is the particle diameter D ₅₀ Since it is much larger than 2 times, the void ratio exceeds 50% when it is simply contained in the crucible. Therefore, in order to obtain a SiC porous sintered body having a porosity of 20% to 50% as defined in the present invention, it is usually necessary to take a technique such as compression molding. Since SiC powder having a particle size distribution has a structure in which fine grains enter into gaps between coarse grains, SiC porous sintering having a porosity specified in the present invention without performing compression molding or the like. You can get a body.

For particle size D ₂₀ of the SiC powder according to the present invention, for example considering the workability at the time of filling the raw material of the crucible, the lower limit may be between 30 [mu] m. Similarly, for the particle size D _50, in order to increase the packing density, it is necessary D ₂₀ is less than 0.2 times the D _50, also the like that moderate sintering reactivity is also required , and it is preferably a particle size _{D 50} is 150μm or more 2000μm or less.

  Further, in obtaining the SiC powder for producing the SiC porous sintered body as described above, a mixed powder of two or more kinds of powders having different average particle diameters may be used as the second embodiment. It is effective. In that case, preferably, the average particle diameter a of the SiC powder A having the smallest average particle diameter and the average particle diameter b of the SiC powder B having the largest average particle diameter are in a relationship of 7a ≦ b. In addition, it is preferable to select a combination of particles satisfying 30 μm ≦ a ≦ 200 μm and 210 μm ≦ b ≦ 2000 μm. More specifically, a mixed powder of two kinds of powders having different average particle diameters is used, and the average particle diameter a of the fine SiC powder having a small average particle diameter is 30 μm ≦ a ≦ 200 μm, and the coarse powder having a large average particle diameter is used. The average particle diameter b of the granular SiC powder is 210 μm ≦ b ≦ 2000 μm, and these satisfy the relationship of 7a ≦ b.

Here, in obtaining the SiC porous sintered body in the present invention, it is the SiC powder that contributes to the sintering reaction among the particles of the particle diameter D ₂₀ or less in the first embodiment or in the second embodiment. This is a fine SiC powder having an average particle diameter a. The particle size D ₂₀ or the average particle diameter a of the fine SiC powder is steep sintering reaction is less than 30 [mu] m, is not preferred since the control of the sintered body physical properties is difficult. Furthermore, also not preferred because hardly occurs sintering reaction in this case the particle size D ₂₀ or the average particle diameter a of more than 200 [mu] m. On the other hand, the particle size _{D 20} of the SiC powder in the first embodiment and 0.2 times less than the particle size _{D 50,} or the coarse SiC powder having an average particle size of b in the second embodiment fine By setting the average particle size a of the granular SiC powder to 7 times or more, the filling rate of the SiC powder can be increased and an optimum bulk density can be obtained.

  From such a viewpoint, the lower limit value of the average particle diameter b in the second embodiment described above is 210 μm, which is seven times the lower limit value of the average particle diameter a. Similarly, the upper limit of the average particle diameter b is 2000 μm. Coarse particles exceeding 2000 μm are not preferred because they significantly reduce the sintering reaction. In addition, the average particle diameter of SiC powder A and B is calculated | required by the measuring method described above.

  In the case of a mixed powder containing SiC powders A and B, preferably, SiC powder A, which is a fine SiC powder, is mixed at a mass ratio of 30% to 50% in the total mass of the mixed powder. It is better. When the mass ratio of the fine SiC powder is less than this, the sintering reaction is excessively small, and when it is large, the sintering reaction is excessively undesirable.

  The SiC porous sintered body obtained by the present invention can grow a SiC single crystal on a seed crystal using a known crystal growth apparatus based on a sublimation recrystallization method. By using such a SiC porous sintered body as a SiC raw material, an appropriate sublimation rate is maintained over the entire growth time, fluctuations in the sublimation gas composition are small, and the success rate of crystal growth is improved. It becomes possible to manufacture a SiC single crystal of a high quality.

Hereinafter, based on an Example and a comparative example, this invention is demonstrated concretely.
FIG. 1 shows an apparatus for growing a single crystal by an improved Rayleigh method used for manufacturing SiC single crystal ingots according to examples of the present invention and comparative examples. Crystal growth is performed by sublimating a sublimation raw material (SiC raw material) 3 by induction heating and recrystallizing on the seed crystal 1. The seed crystal 1 is attached to the inner surface of the crucible lid 6, and the sublimation raw material 3 is filled inside the graphite crucible 4. The graphite crucible 4 and the crucible lid 6 are coated with a heat insulating material 5 for heat shielding, and are placed on a graphite support base 7 inside the double quartz tube 8. After evacuating the inside of the quartz tube 8 to less than 1.0 × 10 ⁻⁴ Pa using the vacuum exhaust device and the pressure control device 12, high purity Ar gas having a purity of 99.9999% or more is supplied through the pipe 10. The high pressure current is supplied to the work coil 9 while keeping the pressure in the quartz tube at 80 kPa using the vacuum exhaust device and the pressure control device 12, and the lower part of the graphite crucible is set to a target temperature of 2400 ° C. Raise to. In the case of a process in which the SiC raw material sintering and the crystal growth performed in advance are performed together, the pressure and temperature at this stage are different, which will be described later. Similarly, nitrogen gas (N ₂ ) was allowed to flow through the pipe 10 while being controlled by the mass flow controller 11, and the nitrogen partial pressure in the atmospheric gas was controlled to adjust the concentration of the nitrogen element taken into the SiC crystal. . The crucible temperature is measured by the radiation thermometers 13a and 13b with an optical path having a diameter of 2 to 15 mm provided in the heat insulating material 5 at the upper and lower parts of the crucible. The crucible upper temperature was the seed crystal temperature, and the crucible lower temperature was the raw material temperature. Thereafter, the pressure inside the quartz tube was reduced from 0.8 kPa to 3.9 kPa, which is the growth pressure, over about 15 minutes, and this state was maintained for a predetermined time to perform crystal growth.

(Examples 1-3)
First, one kind of SiC powder according to the first embodiment having a broad particle size distribution was prepared for one example. Table 1 shows the particle diameter D ₅₀ , particle diameter D ₂₀ , porosity and effective thermal conductivity of each SiC powder. Prior to crystal growth of the SiC single crystal on the seed crystal, the SiC powder was heat-treated. Each SiC powder was filled in a heat treatment crucible made of graphite having the same size as the 100 mm crystal production crucible used for growth. At that time, a sheet of high-purity graphite having a thickness of 1 mm was inserted between the SiC powder and the crucible for heat treatment in order to facilitate separation of the SiC porous sintered body obtained after the heat treatment and the crucible. Next, a crucible filled with SiC powder was placed in a commercially available resistance heating furnace having a graphite heater, and heat treatment was performed. Before the heat treatment, the inside of the resistance heating furnace is evacuated to less than 1.0 × 10 ⁻⁴ Pa, and then introduced from the room temperature over a period of 4 hours while introducing Ar, which is an inert atmosphere gas, and controlling to a predetermined pressure Heating was performed up to the heat treatment temperature and maintained at the predetermined temperature for 6 hours. Thereafter, furnace cooling was performed, and after cooling to near room temperature, the crucible was taken out. The pressure and temperature for the heat treatment are shown in Table 1.

Moreover, regarding the SiC powder used in each Example and its heat treatment conditions, an SiC porous sintered body of 84 mm × 200 mm × 65 mm was prepared in advance, and its physical property values were measured. Table 1 shows the effective thermal conductivity and the porosity calculated from the volume and mass of the SiC porous sintered body. Although the sintered body was strong enough to be lifted by hand, there was no volume change in the process from the powder to the sintered body, so the calculated porosity was the same as the SiC powder before heat treatment. It was. Here, the particle diameter D ₂₀ and the particle diameter D ₅₀ of the SiC powder are obtained by measuring the particle diameter using a laser diffraction method and creating a histogram from the converted particle volume. The effective thermal conductivity was measured by heating the specimen in an air atmosphere using the unsteady hot wire method for both the SiC powder and the SiC porous sintered body. Furthermore, the porosity was calculated using the above equation (1) for both the SiC powder and the SiC porous sintered body. Here, the volume of the SiC raw material was obtained from the direct measurement of the raw material dimensions or the internal volume of the portion filled with the raw material in the graphite crucible (the same applies to the following examples and comparative examples).

Next, using the SiC porous sintered body obtained above, a SiC single crystal was manufactured three times for each example by a crystal growth apparatus as shown in FIG. The conditions for producing a single crystal will be described. The graphite crucible 4 and the crucible lid 6 used in Examples 1 to 3 have a size and a structure for manufacturing a 100 mm ingot. As the seed crystal 1, an SiC single crystal substrate composed of a single polytype of 4H with a diameter of 101 mm, with the (0001) plane as the principal plane and the <0001> axis tilted by 4 ° in the <11-20> direction is used. did. The micropipe density of the seed crystal is 1 piece / cm ² or less. As the sublimation raw material 3, the above-mentioned SiC porous sintered body was used. The growth pressure is 1.33 kPa, and the partial pressure of nitrogen gas is 180 Pa to 90 Pa. The nitrogen partial pressure was varied to maintain optimum conductivity throughout the resulting ingot. Then, a high-frequency current was passed through the work coil 9, and the lower part of the graphite crucible was set to a target temperature of 2400 ° C. to grow a SiC single crystal.

  The SiC single crystal ingot obtained by the above production method had a diameter of about 105 mm, and the height was different depending on conditions, as shown in Table 1. In appearance observation, no crystal defects were observed in the obtained ingot. Also, when the crucible after growth was disassembled and the state of the raw material was observed, the carbon residue remaining after sublimation maintained most of the network structure of the sintered body before sublimation. The resulting dense SiC polycrystal or dense carbon remained only slightly in the center of the raw material.

  The obtained ingot is processed into a 0.4 mm-thick mirror surface wafer having a (0001) surface with an off angle of 4 ° by a known processing technique, using a known processing technique, and transmitted light observation is performed. Were counted using a CS10 Optical Surface Analyzer manufactured by Candela. The observation results are shown in Table 1. The quality of the obtained crystals was all the same or better than that of the seed crystals.

(Examples 4 to 6)
The crystal growth of Examples 4 to 6 was carried out as a continuous process continuous with crystal production incorporating a SiC powder sintering process. The prepared SiC powder is a mixed powder of fine particles and coarse particles according to the second embodiment, and one kind of SiC powder made of mixed powder of fine particles and coarse particles is prepared for each example. . Table 2 shows the average particle diameter of the fine SiC powder and the coarse SiC powder used, the mixing ratio thereof, the porosity, and the effective thermal conductivity.

  For each example, SiC powder consisting of a mixture of fine and coarse particles was filled into the raw material filling chamber in the crystal growth crucible, and the following three production experiments of SiC single crystal ingot were conducted. It was. Here, as a filling method of the SiC powder into the crucible, a method in which the powder is sufficiently mixed with a rocking mixer or the like in advance and then charged into the crucible, or a predetermined amount of coarse particles are first filled and then shaken. For example, there is a method in which a predetermined amount of fine particles are put on the coarse particles while the crucible is shaken at a predetermined frequency with a vessel. The present invention is not limited to the method of filling the SiC powder, nor is it intended to create a particle size distribution in the crucible.

Next, a description will be given of a part process of heat treatment of SiC powder and single crystal production using the crystal growth apparatus as shown in FIG. The graphite crucible 4 and the crucible lid 6 used in Examples 4 to 6 have a size and a structure for producing a 150 mm ingot. The seed crystal 1 has a diameter of 152 mm, a SiC single crystal substrate composed of a single polytype of 4H with a <0001> axis tilted by 4 ° in the <11-20> direction as a principal plane (0001) plane It was used. The micropipe density of the seed crystal is 1 piece / cm ² or less. A crucible loaded with SiC powder and seed crystal was placed in a quartz tube of a crystal growth furnace, and after evacuation in the same way as in normal growth, high purity Ar gas with a purity of 99.9999% or more was connected to pipe 10 The high-frequency current is passed through the work coil 9 while keeping the pressure in the quartz tube at a predetermined pressure of the heat treatment using the vacuum exhaust device and the pressure control device 12, and the SiC powder is supplied in a predetermined manner. Heating was done until the temperature was reached. The heat treatment temperature at that time is a value obtained by numerical calculation based on the measured values of the radiation thermometers above and below the crucible. The heat treatment pressure and temperature are shown in Table 2. Then, the work coil 9 was driven up and down with respect to the graphite crucible 4 in order to uniformly sinter the SiC powder while maintaining a predetermined temperature. At that time, the work coil 9 is driven vertically with a width corresponding to the height of the raw material filling chamber of the graphite crucible around the coil position set at the time of crystal growth, and positioned at a speed of about 1 mm to 10 mm per hour. The heat treatment was performed for 12 hours while changing.

  After obtaining the SiC porous sintered body according to each example as described above, the work coil 9 is moved to a position where it is used for the growth of the SiC single crystal, and the lower part of the crucible is raised to the target temperature of 2400 ° C. The pressure in the quartz tube was reduced from the heat treatment pressure to the growth pressure of 1.33 kPa over about 15 minutes to start the growth of the SiC single crystal. The partial pressure of nitrogen gas is 180 Pa to 90 Pa. The nitrogen partial pressure was varied to maintain optimal conductivity throughout the ingot. An outline of the operating conditions of the above-described part process is shown in FIG.

  Here, as for the physical properties of the SiC porous sintered body, a test piece of 84 mm × 200 mm × 65 mm was processed from the SiC porous sintered body that had undergone the same heat treatment process as described above, and each physical property value was measured. Table 2 shows the thermal conductivity and the porosity calculated from the above equation (1). As in Examples 1 to 3, there was no volume change in the process from the SiC powder to the sintered body, and the porosity was the same as that of the powder.

  The SiC single crystal ingots obtained by the above production methods all had a diameter of about 155 mm, and the height was different depending on conditions, as shown in Table 2. In appearance observation, no crystal defects were observed in the obtained ingot. When the state of the raw material after completion of growth was observed, the carbon residue remaining after sublimation maintained most of the network structure of the sintered body before sublimation as in Examples 1 to 3, and the rearrangement of the raw material The dense SiC polycrystal or the dense carbon resulting from is left only in the center of the raw material.

  The obtained ingot was processed into a mirror wafer having a thickness of 0.4 mm having a (0001) surface with an off angle of 4 ° in the same manner as in Examples 1 to 3, and the transmitted light was observed and the micropipes were counted. The observation results are shown in Table 2. The quality of the obtained crystals was all the same or better than that of the seed crystals.

(Comparative Examples 1-2)
Next, the manufacture of the single crystal of the comparative example will be described. In Comparative Examples 1 and 2, the particle size _{D 20} commercial SiC powder of 13μm and a particle size _{D 50} of 32 [mu] m (Comparative Example 1), the particle size _{D 20} is 568μm and particle size _{D 50} of commercial SiC powder 710μm Growth was performed using each of the bodies (Comparative Example 2). The SiC raw material was filled in the crucible in a powder state, and without performing heat treatment to obtain a sintered body, the growth of the SiC single crystal was started in the same manner as in Examples 1 to 3. Similar to Examples 1 to 3, physical property values of SiC powder are measured. The results are shown in Table 3. The crucible structure and the crystal growth process are the same as in Examples 1-3. For these Comparative Examples 1 and 2, ingot production was performed three times under the same conditions. In the appearance observation of the obtained SiC single crystal ingot, there was also an ingot that could clearly confirm that crystal defects were generated. The evaluation results of the crystals are also shown in Table 3. The height of the ingot is low compared to the examples. This is because, although the porosity of the powder filled in Comparative Examples 1 and 2 is higher than that of the example, large-scale rearrangement occurred during the growth process, and the porosity and surface area after the rearrangement are rather examples. This is probably because the sublimation reaction after that became difficult to proceed. In addition, the micropipe density is higher than that of the seed crystal. This is due to the change of the gas composition induced by the rearrangement and the change of the gas supply amount. This is considered to be due to the formation of a foreign phase such as carbon particles, and the occurrence of foreign polytypes starting from the foreign phase.

  In addition, the crucible after the growth was disassembled and the state of the raw material was observed. Regarding the carbon residue remaining after sublimation, the portion that maintained the powder form before sublimation is less than half of the raw material volume, and the dense SiC polycrystal or dense carbon resulting from the rearrangement of the raw material is the raw material. It existed in a large volume in a columnar shape in the center.

(Comparative Examples 3-4)
Comparative examples 3 to 4 will be described. In Comparative Examples 3 to 4, the same commercially available SiC powder as in Comparative Examples 1 and 2 was used, and the SiC powder was grown in advance after heat-treating the SiC powder in advance. The graphite crucible used in Comparative Examples 3 to 4 is the same 100 mm crystal manufacturing crucible as the crucible used in Examples 1 to 3, and the seed crystal 1 is the same as in Examples 1 to 3. Crystal growth was carried out as a continuous continuous process of heat treatment and crystal production of SiC powder. The conditions of the partial process of Comparative Examples 3 to 4 will be described below.

  A crucible loaded with SiC powder and seed crystal was placed in a quartz tube of a crystal growth furnace, and after evacuation in the same way as in normal growth, high purity Ar gas with a purity of 99.9999% or more was connected to pipe 10 The SiC powder is allowed to flow through the work coil 9 while keeping the pressure inside the quartz tube at a predetermined pressure by using the vacuum exhaust device and the pressure control device 12 to control the SiC powder. Heated until reached. At that time, in Comparative Examples 3 to 4, the coils were moved up and down with the same settings as in Examples 4 to 6. The heat treatment was completed after the predetermined movement was completed. The heat treatment conditions are shown in Table 4.

  After heat-treating the SiC powder as described above, the work coil 9 is moved to a position where it is used for the growth of the SiC single crystal, the crucible lower part is raised to the target temperature of 2400 ° C., and the pressure in the quartz tube is increased. The pressure was reduced from 9 kPa to a growth pressure of 1.33 kPa over about 15 minutes to start growth. The partial pressure of nitrogen gas is 180 Pa to 90 Pa. The nitrogen partial pressure was varied to maintain optimal conductivity throughout the ingot.

  Here, the SiC powder used in Comparative Examples 3 to 4 was subjected to a heat treatment experiment in advance under the same conditions as described above, and the physical properties of the powder after the heat treatment were evaluated. Although the heat treatment conditions of Comparative Examples 3 to 4 were within the scope of the present invention, the powder was not sintered because the porosity was high, and the change in physical properties before the heat treatment was within the error range. Since the effect of sintering is not acquired as above-mentioned, the height of the ingot obtained in Comparative Examples 3-4 is equivalent to Comparative Examples 1-2. Therefore, it can be said that the state of the raw material after completion of the growth and the crystal quality are equivalent to those of Comparative Examples 1 and 2.

(Comparative Examples 5-7)
Comparative Examples 5 to 7 were carried out as a part process continuous with crystal production, incorporating a sintering process of SiC powder. The heat treatment process is the same as in Examples 4-6. One kind of SiC powder was prepared for one comparative example. Table 5 shows the particle diameters D ₅₀ and D ₂₀ , the porosity, the effective thermal conductivity, and the heat treatment pressure and maximum temperature of each SiC powder.

  About each comparative example, SiC powder was filled in the raw material filling chamber in the crucible for crystal growth, and the production experiment of the SiC single crystal ingot was performed three times. The structures of the graphite crucible 4 and the crucible lid 6 used in these comparative examples 5 to 7, the diameter and specification of the seed crystal, and the conditions of the one-piece process are the same as those in the examples 4 to 6.

Here, the SiC powder used in Comparative Examples 5 to 7 was heat-treated in advance under the same conditions as described above, and the sinterability was investigated. The ratio between the heat treatment condition in the comparative example the powder particle size D ₅₀ of 5 and D ₂₀ while within the scope of the present invention, a low sinterability for the particle size D ₂₀ is greater. Comparative Example 6 is a particle size _{D 50} and _{D 20,} the ratio also while within the scope of the present invention, the low heat treatment temperatures. Therefore, in the comparative examples 5-6, the sintered compact was not obtained and it was the form of the powder filler after heat processing. In addition, the effective thermal conductivity was measured again for the powder after the heat treatment, but the difference from that before the heat treatment was within an error range. Table 5 shows the effective thermal conductivity of the SiC powder after the heat treatment and the porosity calculated from the previous equation (1). There was no volume change during the heat treatment, and the calculated porosity was unchanged before and after the heat treatment.

  On the other hand, Comparative Example 7 is the SiC powder in the range of the first embodiment, but the heat treatment temperature is very high. For this reason, the SiC powder put in the crucible generated sublimation and recrystallization inside thereof, and the volume was remarkably reduced due to firing shrinkage, and the porosity was lowered. Since a test piece of 84 mm × 200 mm × 65 mm could not be produced due to shrinkage, a test piece of φ10 mm × 5 mm was separately processed, and the effective thermal conductivity was measured by a laser flash method. That is, using Nd glass laser, heat was applied to one side of the sample, and the effective thermal conductivity of the test piece of φ10 mm × 5 mm was measured by analyzing the data obtained by capturing the temperature change of the opposite side with an infrared sensor.

  A SiC single crystal was grown in the same manner as in Examples 4 to 6 using each SiC raw material as described above. The heights of the obtained ingots of Comparative Examples 5 to 7 are lower than the ingot heights of Examples 4 to 6 having the same crystal diameter. In particular, the height of the ingot of Comparative Example 7 is low, and even in the appearance observation of the ingot, the resulting ingot has a large number of radial streaks and dimples reflecting the presence of different polytypes and the presence of micropile (MP). It was. When the crucible after the growth was disassembled and the state of the raw material was observed, a dense SiC polycrystal or dense carbon resulting from the rearrangement of the raw material was present in a columnar large volume in the center of the raw material. It was. Since the raw materials of Comparative Examples 5 and 6 were not sintered, it was assumed that phenomena such as extreme heating and rearrangement of the raw materials occurred and the crystal growth conditions became unstable. On the other hand, the raw material of Comparative Example 7 undergoes sublimation, recrystallization, and firing shrinkage inside the raw material filling chamber due to the heat treatment before growth, and the porosity was significantly reduced before the growth started. For this reason, although rearrangement during the growth hardly occurs, it can be inferred that the sublimation amount was extremely small from the start of the growth to the end. The obtained ingot was processed into a mirror wafer in the same manner as in the example, and the transmitted light was observed and the micropipes were counted. The observation results are shown in Table 5. All wafers had higher MP density than the seed crystal.

(Comparative Examples 8 to 10)
In Comparative Examples 8 to 10, heat treatment was performed to sinter SiC powder prior to growth in the same manner as in Examples 1 to 3. In one embodiment, one kind of mixed powder composed of fine SiC powder and coarse SiC powder is prepared, and a heat treatment made of graphite having the same size as a crucible for producing 100 mm crystal used for growing a SiC single crystal. The crucible for filling was filled and heat-treated at a predetermined pressure and temperature. In addition to the average particle diameter of the fine SiC powder and the coarse SiC powder used and the mixing ratio thereof, the particle diameter D ₅₀ and particle diameter D _{20 of} the SiC powder made of the mixed powder, and the heat treatment conditions are Table 6 shows. For each comparative example, a fine SiC powder and a coarse SiC powder were filled into a raw material filling chamber in a crystal growth crucible, subjected to heat treatment, and then a SiC single crystal ingot was manufactured three times each. It was. Table 6 shows the heat treatment conditions, the effective thermal conductivity of the raw material before and after the heat treatment, and the porosity calculated from the previous equation (1).

  The particle size of the fine SiC powder of Comparative Example 8 and the relationship between the average particle size of the fine SiC powder and the coarse SiC powder (7a ≦ b) are within the range shown in the second embodiment. The proportion of fine particles in the mixed powder is very large. For this reason, while the heat treatment conditions were within the scope of the present invention, the material contracted significantly due to high sintering reactivity, and the volume of the raw material after the heat treatment was greatly reduced. The effective thermal conductivity of the SiC powder after the heat treatment in Comparative Example 8 was measured by the laser flash method as in Comparative Example 7. In Comparative Example 9, the particle size of the fine SiC powder and the relationship between the average particle size of the fine SiC powder and the coarse SiC powder (7a ≦ b) are within the range shown in the second embodiment. The ratio of fine particles in the mixed powder is small. For this reason, a sintered body was not obtained even when heat treatment was carried out under the conditions of the present invention, and no significant difference was observed in the physical property values of the powder before and after the heat treatment. In the SiC powder of Comparative Example 10, the mixing ratio of the fine SiC powder and the coarse SiC powder is in the range shown in the second embodiment. However, since the average particle size of the fine SiC powder is excessive, the sintering reactivity is lowered, and a sintered body cannot be obtained even if heat treatment is performed under the conditions of the present invention. No significant difference was observed in the physical properties of the powder.

  When SiC single crystals were grown in the same manner as in Examples 1 to 3 using these SiC raw materials, the SiC single crystal ingots obtained in Comparative Examples 8 to 10 had a diameter of about 105 mm. Although it was equivalent to 1-3, the height of the ingot was lower than the Example and crystallinity was greatly inferior. Table 6 shows the ingot height and crystal quality.

  In addition, the state of the raw material after completion of the growth was also observed. In the raw materials of Comparative Examples 9 to 10, a dense SiC polycrystal or dense carbon resulting from the rearrangement of the raw materials was present in a large volume in a columnar shape in the center of the raw material. This is a result of the raw material moving to the center due to rearrangement during the growth process. In Comparative Example 8, the form of the dense sintered body formed by the heat treatment was almost maintained, and the change before and after the growth process was small.

1: Seed crystal (SiC single crystal)
2: SiC single crystal ingot 3: Sublimation material (SiC material)
4: graphite crucible 5: heat insulating material 6: crucible lid 7: graphite support base (crucible support base and shaft)
8: Double quartz tube 9: Work coil 10: Piping 11: Mass flow controller 12: Vacuum exhaust device and pressure control device 13a: Radiation thermometer (for crucible upper part)
13b: Radiation thermometer (for crucible lower part)

Claims (5)

A method for producing a SiC raw material used in a sublimation recrystallization method in which SiC as a raw material is sublimated to grow a SiC single crystal on a seed crystal,
The SiC powder is heat-treated in an inert gas atmosphere at a pressure of 1.33 × 10 ⁴ Pa or more at a temperature of 1500 ° C. or more and 2200 ° C. or less, and the porosity is 20% or more and 50% or less and 1000 ° C. at atmospheric pressure. A SiC raw material for use in a sublimation recrystallization method, characterized in that an SiC raw material comprising an SiC porous sintered body having an effective thermal conductivity of 0.5 W / mK or more is obtained. The SiC powder, a cumulative distribution of the particle size by volume basis, with a particle size _{D 20} corresponding to the particle size of cumulative 20% is 200μm or less, the particle diameter _{D 50} the particle diameter _{D 20} falls on the particle size of cumulative 50% The manufacturing method of the SiC raw material used for the sublimation recrystallization method of Claim 1 which has a particle size distribution of 0.2 times less than this.   The SiC powder is a mixed powder of a fine SiC powder having a small average particle diameter and a coarse SiC powder having a large average particle diameter, and the average particle diameter a of the fine SiC powder is 30 μm or more and 200 μm or less, 2. The sublimation recrystallization method according to claim 1, wherein the average particle diameter b of the coarse SiC powder is 210 μm or more and 2000 μm or less, and the average particle diameter satisfies a relationship of 7a ≦ b. The manufacturing method of the SiC raw material to be used.   The method for producing a SiC raw material for use in the sublimation recrystallization method according to claim 3, wherein the fine SiC powder is mixed in the mixed powder at a ratio of 30% by mass or more and 50% by mass or less.   A SiC raw material used in a sublimation recrystallization method in which SiC, which is a raw material, is sublimated to grow a SiC single crystal on a seed crystal, and has a porosity of 20% or more and 50% or less and 1000 ° C. at atmospheric pressure An SiC raw material for a sublimation recrystallization method, comprising an SiC porous sintered body having an effective thermal conductivity of 0.5 W / mK or more.

Images