JP4585359B2 - Method for producing silicon carbide single crystal - Google Patents

Description

  The present invention relates to a method for producing a high-quality silicon carbide single crystal excellent in crystallinity with few defects, which is suitable as a substrate for manufacturing a semiconductor element.

  Silicon carbide (SiC) is also attracting attention as an environmentally resistant semiconductor material because of its excellent heat resistance and mechanical strength and physical and chemical properties such as resistance to radiation. SiC is a typical substance having a crystal polymorphic (polytype) structure having many different crystal structures even though the chemical composition is the same. The polytype is based on the difference in the periodic structure when this unit structure molecule is stacked in the c-axis direction ([0001] direction) of the crystal when the molecule in which the Si and C are bonded is considered as one unit Arise. Typical polytypes include 6H, 4H, 15R or 3C. Here, the first number indicates the repetition period of the lamination, and the alphabet represents a crystal system (H is a hexagonal system, R is a rhombohedral system, and C is a cubic system). Each polytype has different physical and electrical characteristics, and application to various uses is considered using the difference. For example, 6H is recently used as a substrate for short-wavelength optical devices from blue to ultraviolet, and 4H is considered to be used as a substrate wafer for high-frequency, high-voltage electronic devices.

  However, a crystal growth technique that can stably supply a high-quality SiC single crystal having a large area on an industrial scale has not yet been established. Therefore, practical use of SiC has been hindered despite the semiconductor material having many advantages and possibilities as described above.

Conventionally, on a laboratory scale scale, for example, a SiC single crystal was grown by a sublimation recrystallization method (Rayleigh method) to obtain a SiC single crystal of a size capable of producing a semiconductor element. However, with this method, the area of the obtained single crystal is small, and it is difficult to control its size and shape with high accuracy. Moreover, it is not easy to control the crystal polymorphism and impurity carrier concentration of SiC. In addition, a cubic silicon carbide single crystal is grown by heteroepitaxial growth on a heterogeneous substrate such as silicon (Si) using a chemical vapor deposition method (CVD method). In this method, a single crystal having a large area can be obtained, but only a SiC single crystal including many defects (−10 ⁷ cm ⁻² ) is grown due to a lattice mismatch with the substrate of about 20%. It is not easy to obtain a high-quality SiC single crystal.

  In order to solve these problems, an improved Rayleigh method has been proposed in which sublimation recrystallization is performed using a SiC single crystal {0001} wafer as a seed crystal (Non-patent Document 1). In this method, since the seed crystal is used, the nucleation process of the crystal can be controlled, and by controlling the atmospheric pressure to about 100 Pa to 15 kPa with an inert gas, the growth rate of the crystal can be controlled with good reproducibility. . The principle of the improved Rayleigh method will be described with reference to FIG. The SiC single crystal as a seed crystal and the SiC crystal powder as a raw material are stored in a crucible (usually graphite) and heated to 2000 to 2400 ° C. in an inert gas atmosphere such as argon (133 to 13.3 kPa). The At this time, the temperature gradient is set so that the seed crystal has a slightly lower temperature than the raw material powder. After sublimation, the raw material is diffused and transported in the direction of the seed crystal by a concentration gradient (formed by a temperature gradient). Single crystal growth is realized by recrystallization of the source gas that has arrived at the seed crystal on the seed crystal. At this time, the resistivity of the crystal is determined by adding an impurity gas in an atmosphere composed of an inert gas, or by mixing an impurity element or a compound thereof in the SiC raw material powder, thereby adding silicon or carbon in the SiC single crystal structure. It can be controlled by substituting the impurity position with an impurity element (doping). Typical substitutional impurities in the SiC single crystal include nitrogen (n-type), boron, and aluminum (p-type). A SiC single crystal can be grown while controlling the carrier type and concentration.

  Currently, SiC single crystal wafers having a diameter of 2 inches (50 mm) to 3 inches (75 mm) are cut out from the SiC single crystal produced by the above-described improved Rayleigh method, and are used for epitaxial thin film growth and device production.

  As described above, the resistivity of the grown crystal is controlled by adding an impurity gas in an atmosphere of an inert gas during growth, or by mixing an impurity element or a compound thereof in the SiC raw material powder. This is performed by replacing the position of silicon or carbon atoms in the SiC single crystal structure with an impurity element (doping). In particular, when an impurity gas is added, the impurity gas is usually introduced from the start of growth so as to obtain a target impurity element concentration, and crystal growth is performed while maintaining a constant introduction amount during the growth.

  Here, the inventor obtained the following knowledge. That is, when an impurity gas is introduced so as to obtain a target impurity element concentration, when the impurity concentration of the SiC single crystal substrate used as a seed crystal and the impurity concentration of the single crystal to be grown are significantly different, Micropipe defects associated with the generation of dislocation defects or polytypes different from seed crystals (a type of large-scale screw dislocations, which are thought to occur due to the dislocation cores becoming hollow in order to relieve large strain caused by dislocations. The crystallinity is degraded.

  The cause of the occurrence of this dislocation defect is considered to be the strain generated by the difference in lattice constant between the seed crystal and the grown crystal due to a significant difference in impurity concentration in the crystal. In general, when the crystal growth substrate and the crystal to be grown have different lattice constants, they have a lattice constant intermediate between both of them for the purpose of relaxing the strain energy caused by the difference between the two. By inserting a crystal (commonly referred to as a buffer layer), strain energy is reduced, and crystallinity deterioration such as dislocation generation in a grown crystal is suppressed.

  Usually, when a buffer layer is used, for example, the difference in lattice constant between a seed crystal or a seed crystal as a crystal growth substrate and the grown crystal is several percent or more.

On the other hand, when an impurity, for example, nitrogen is doped in a silicon carbide single crystal, the nitrogen atom is incorporated into the crystal by replacing the position of the carbon atom in the crystal. At this time, the bonds between atoms in the single crystal are in a tetrahedral arrangement. For example, according to Pauling's “chemical bond theory” (Non-patent Document 2), the radius of the carbon atom is 0.077 nm. On the other hand, nitrogen is 0.070 nm, and this difference is as small as 0.007 nm. Furthermore, even if the atomic density actually doped in the crystal is large, it is 10 ²⁰ cm ⁻³ , which is about 0.1% of the whole. Approximate from this, the difference in lattice constant when nitrogen atoms are doped as impurities (for example, the lattice constant of 4H polytype is 0.3076 nm in the a-axis direction) is 0.000025%. When this value is very small and the strain energy due to the difference in lattice constant is also expected to be small, it is expected that the occurrence of dislocations in the grown crystal is unlikely to occur.

However, as described above, as a knowledge obtained by the inventor, in the SiC single crystal growth at a high temperature of 2000 ° C. or higher by the sublimation recrystallization method, the difference in the impurity concentration as described above is caused in the grown crystal. It was confirmed that the crystallinity of the grown crystal deteriorates due to the occurrence of dislocations.
Yu. M.M. Tailov and V.M. F. Tsvetkov, Journal of Crystal Growth, vol. 52 (1981) pp. 146-150. L. Pauling, “The Nature of the Chemical Bond”, Chapter 4, Cornell Univ. Press, New York (1960).

  For this reason, in SiC single crystal growth by the sublimation recrystallization method, the concentration change in the growth crystal of impurity elements such as nitrogen differs from the seed crystal in that the change rate from the same concentration in the seed crystal is more finely controlled. It has become clear that it is very important in obtaining high-quality silicon carbide having a desired impurity concentration.

  From this finding, when the growth is performed with the impurity gas flow rate to obtain a growth crystal having a desired impurity concentration from the start of growth as in the conventional case, the same impurity concentration as the target is always used in order not to generate crystal defects. It is necessary to use a seed crystal substrate having an impurity concentration. However, in this case, it is very troublesome to prepare a seed crystal according to the target impurity concentration every time, and there is a problem in terms of productivity from an industrial point of view. In a strict sense, the stability of crystal growth may differ depending on the difference in impurities.For example, in the case of growth in which nitrogen is added in a certain concentration range, the highest quality crystal growth is always obtained with good reproducibility. It is desirable that the highest quality seed crystal having this nitrogen concentration can always be used for the seed crystal. For these reasons, it is desirable to be able to use a seed crystal having any impurity concentration at all times. At the same time, the concentration is changed to the target impurity concentration during growth, and the generation of crystal defects due to the concentration change is suppressed. A technology that can be used is necessary.

Accordingly, the present invention is to solve the problems of the above prior art, and an object thereof is to provide a manufacturing how silicon carbide single crystal can be extracted the silicon carbide single crystal wafer having excellent low crystallinity defect.

The present invention
(1) A method for producing a silicon carbide single crystal by a sublimation recrystallization method, comprising a step of growing a silicon carbide single crystal ingot on a crystal, wherein an additive gas flow rate in an inert atmosphere during crystal growth is changed. The concentration of the additive element in the growth crystal is within the range of the concentration change rate from 1% / 100 μm to 200% / 100 μm with respect to the crystal growth direction from the same concentration as in the seed crystal from the seed crystal. A method of producing a silicon carbide single crystal, characterized by gradually increasing or decreasing the concentration to a desired concentration;
(2) The method for producing a silicon carbide single crystal according to (1), wherein the concentration change rate is in the range of 5% / 100 μm or more and 100% / 100 μm or less with respect to the crystal growth direction,
(3) The method for producing a silicon carbide single crystal according to (1), wherein the additive element is any one of nitrogen, boron, and aluminum ,
It is.

  According to the present invention, a high-quality SiC single crystal having a desired impurity concentration can be grown with good reproducibility by an improved Rayleigh method using a seed crystal. By using a SiC single crystal wafer cut out from such a crystal, it is possible to manufacture a semiconductor element having excellent high-frequency operating characteristics and a high-performance power control semiconductor element with extremely low power loss.

  In the manufacturing method of the present invention, the gas flow rate for impurity addition during crystal growth is gradually increased or decreased over a predetermined time and controlled until a desired impurity concentration is obtained, so that a region where crystallinity has deteriorated in the crystal (various types) A region in which dislocations, crystal grain boundaries, micropipe defects and the like are present) is extremely small, and a high-quality single crystal SiC ingot having a desired impurity concentration can be manufactured.

  First, the sublimation recrystallization method will be described. The sublimation recrystallization method is a method for producing SiC crystals by sublimating SiC powder at a high temperature exceeding 2000 ° C. and recrystallizing the sublimation gas into a low temperature part. In this method, a method for producing an SiC single crystal using a seed crystal composed of an SiC single crystal is called an improved Rayleigh method, and is used for producing a bulk SiC single crystal. The modified Rayleigh method uses a seed crystal to control the nucleation process of the crystal, and the atmosphere pressure is controlled to about 100 Pa to 15 kPa with an inert gas to control the crystal growth rate with good reproducibility. it can. The principle of the improved Rayleigh method will be described with reference to FIG. The SiC single crystal used as a seed crystal and the SiC crystal powder used as a raw material (usually used after cleaning and pretreatment of an abrasive prepared by the Acheson method) are stored in a crucible (usually made of graphite). In an inert gas atmosphere such as argon (133 Pa to 13.3 kPa), it is heated to 2000 to 2400 ° C. At this time, the temperature gradient is set so that the seed crystal has a slightly lower temperature than the raw material powder. After sublimation, the raw material is diffused and transported in the direction of the seed crystal by a concentration gradient (formed by a temperature gradient). Single crystal growth is realized by recrystallization of the source gas that has arrived at the seed crystal on the seed crystal.

In the above-described sublimation recrystallization method, impurity doping into a single crystal to be produced is performed in the form of an additive gas in an inert gas atmosphere such as argon during crystal growth (nitrogen gas for nitrogen atoms, trimethylaluminum for aluminum (Al (CH ₃ ) ₃ ), trimethylboron (B (CH ₃ ) ₃ ) in the case of boron is introduced by introducing a predetermined amount, however, for any element, the addition density in the seed crystal used for growth Thus, in order to realize a growth crystal having a higher density or a lower density, it is necessary to increase or decrease the additive gas flow rate.

  What has the greatest influence on the crystal quality is the dopant that exhibits the highest concentration. Therefore, when a plurality of elements are included, the dopant may be controlled with a gas containing the element that exhibits the highest concentration.

  When the impurity concentration is changed in the growth direction, distortion due to the difference in crystal lattice spacing due to the impurity concentration difference occurs between the crystal grown so far and the newly grown crystal. The strain energy increases as the impurity concentration difference increases. For this reason, when the impurity concentration change rate (impurity concentration gradient) is steep, crystal growth proceeds and the crystal thickness increases (the strain energy is proportional to the thickness), and the strain energy reaches a critical value. When it exceeds, various defects such as dislocations occur in the grown crystal and the crystallinity deteriorates. In order to prevent this, it is necessary to keep the impurity concentration change rate in the growth direction below a predetermined value so that the strain energy is kept below the critical value that induces the above-described defect generation.

  In the present invention, by controlling the rate of change in the growth direction of the impurity concentration during crystal growth, the strain energy on the surface of the grown crystal is suppressed to a critical value or less that leads to the occurrence of defects, thereby preventing the occurrence of crystal defects during crystal growth. Suppress. In this case, when the crystal growth is actually confirmed, the upper limit value of the concentration change rate at which the crystal growth can be performed without generating defects is 200% / 100 μm as an average at a fixed distance with respect to the crystal growth direction. is there. On the other hand, as the lower limit, from an industrial point of view, even though it is effective to suppress the occurrence of defects, extremely reducing the growth rate is extremely difficult to apply, so it cannot be actually applied. A change rate of at least 1% / 100 μm or more with respect to the direction is required. The upper limit value and the lower limit value are as described above, but in actual application, a more desirable range is a range of 5 to 100% / 100 μm. While maintaining this concentration gradient condition, by changing the impurity concentration to a desired concentration, a grown crystal having good crystallinity similar to the seed crystal is obtained without generating new crystal defects during the growth. be able to.

In addition, by using a seed crystal taken out from a crystal having good crystallinity obtained in this way, and using a crucible having a structure in which the diameter of the crystal expands during growth, the diameter is larger than the seed crystal diameter. Can be obtained. By repeating this method, a silicon carbide single crystal having a diameter of 50 mm to 300 mm can be obtained.
Further, by cutting and polishing these single crystals, a silicon carbide single crystal wafer having a diameter of 50 mm or more and 300 mm or less can be taken out.

  Moreover, a silicon carbide single crystal epitaxial wafer can be produced by epitaxially growing a SiC single crystal thin film on these single crystal wafers by using a chemical vapor deposition method (CVD method). This epitaxial wafer inherits the good crystallinity of the silicon carbide single crystal wafer used as the substrate, and a device that exhibits excellent characteristics when an electronic device is produced can be obtained.

  Examples of the present invention will be described below.

Example 1
First, the single crystal growth apparatus shown in FIG. 2 will be briefly described. Crystal growth is performed by sublimating SiC crystal powder 2 and recrystallizing on SiC single crystal 1 used as a seed crystal. The seed crystal SiC single crystal 1 is attached to the inner surface of the lid 4 of the high-purity graphite crucible 3. The raw material SiC crystal powder 2 is filled in a high-purity graphite crucible 3. Such a graphite crucible 3 is installed inside a double quartz tube 5 by a support rod 6 made of graphite. Around the graphite crucible 3, a graphite felt 7 for heat shielding is installed. The double quartz tube 5 can be highly evacuated (10 ⁻³ Pa or less) by an evacuation apparatus, and the internal atmosphere can be pressure controlled by Ar gas introduced through the gas flow rate controller 10. it can. Various doping gases (nitrogen, trimethylaluminum, trimethylboron) can also be introduced through the gas flow controller 10. In addition, a work coil 8 is provided on the outer periphery of the double quartz tube 5, and the graphite crucible 3 can be heated by flowing a high-frequency current to heat the raw material and the seed crystal to a desired temperature. The temperature of the crucible is measured using a two-color thermometer by providing an optical path having a diameter of 2 to 4 mm at the center of the felt covering the upper and lower parts of the crucible, and extracting light from the upper and lower parts of the crucible. The temperature at the bottom of the crucible is the raw material temperature, and the temperature at the top of the crucible is the seed temperature.

Next, an example of manufacturing a SiC single crystal using this crystal growth apparatus will be described. First, a hexagonal SiC single crystal wafer having a (0001) plane with a diameter of 50 mm was prepared as a seed crystal. The micropipe defect density of the same type crystal was as small as 5 pieces / cm ² or less and good crystallinity, and the concentration of nitrogen as a doping element was 1 × 10 ¹⁹ cm ⁻³ . Next, the seed crystal 1 was attached to the inner surface of the lid 4 of the graphite crucible 3. The inside of the graphite crucible 3 was filled with SiC crystal raw material powder produced by the Atchison method. Next, the graphite crucible 3 filled with the SiC raw material was closed with the lid 4 and covered with the graphite felt 7, and then placed on the graphite support rod 6 and installed inside the double quartz tube 5. And after evacuating the inside of a quartz tube, the electric current was sent through the work coil and the raw material temperature was raised to 2000 degreeC. Thereafter, high-purity Ar gas (purity 99.9995%) was introduced as the atmospheric gas, and the raw material temperature was raised to the target temperature of 2400 ° C. while maintaining the pressure in the quartz tube at about 80 kPa. The growth pressure was reduced to 1.3 kPa over about 30 minutes, and then the growth was continued for about 20 hours. During this growth time, the nitrogen flow rate is 0.5 × 10 ⁻⁶ m ³ / sec at the start of growth (at the same flow rate, the nitrogen concentration in the growth crystal is 1 × 10 ¹⁹ cm ^−3, which is equivalent to the concentration in the seed crystal). Therefore, after the start of growth, the nitrogen flow rate was increased at a constant rate, and 5.0 × 10 ⁻⁶ m ³ / sec over 5 hours (at the same flow rate, the nitrogen concentration in the grown crystal) Is increased to 2 × 10 ²⁰ cm ⁻³ ). Thereafter, the pressure was kept constant at 5.0 × 10 ⁻⁶ m ³ / sec and kept until the end of growth. The temperature gradient in the crucible at this time was 15 ° C./cm. The growth rate is about 0.8 mm / hour, and the concentration change rate in the growth crystal with respect to the nitrogen concentration in the seed crystal is 50% / 100 μm (= 2000% / (0.8 mm / hour × 5 hours)). Met. The diameter of the obtained crystal was 51 mm, and the height was about 16 mm.

When the silicon carbide single crystal thus obtained was analyzed by Raman scattering, it was confirmed that a hexagonal SiC single crystal having the same polytype as the seed crystal was grown over the entire surface. For the purpose of measuring the crystallinity, a wafer having a thickness of 1.0 mm was cut out from the uppermost portion of the grown single crystal ingot (the portion grown near the end of growth). When the wafer was directly observed with an optical microscope, it was confirmed that the through-hole defect density was 10 / cm ² or less, which was as low as the seed crystal. For further confirmation, etching was performed in a potassium hydroxide solution melted at 520 ° C. for 5 minutes. When this etching process is performed, the penetrating hollow defects can be observed as hexagonal etch pits. When the number density of etch pits on the wafer was examined, through-hole defects having the same number density as in the visual observation were detected. In addition, in order to confirm whether a high-quality crystal equivalent to the seed crystal is obtained, the X-ray topography imaging data of the seed crystal measured in advance and the X-ray topography imaging data of the wafer cut out from the grown crystal are obtained. As a result of comparison, it was confirmed that the product had the same high quality as the seed crystal and no new defects were generated due to the growth.

  In order to measure the resistivity of the wafer, the wafer was cut into 12 mm squares, washed, and then nickel electrodes (circular with a diameter of 1 mm) were formed at the four corners by vacuum deposition. Hole measurement was performed using the wafer piece to which this electrode was attached, and when the resistivity of the wafer was determined, it was confirmed that it had a low resistivity of 0.009 Ωcm.

  A silicon carbide single crystal epitaxial wafer is produced by epitaxially growing a SiC single crystal thin film by using a chemical vapor deposition method (CVD method) on a wafer produced by cutting and processing the crystal having good crystallinity thus obtained. did. In order to investigate the crystallinity of the epitaxial wafer, the surface of the epitaxial wafer was etched in the molten potassium hydroxide solution described above. As a result, it was confirmed that the good crystal quality of the silicon carbide single crystal wafer as the substrate was inherited.

On the other hand, when the crystal growth is carried out at a flow rate of 5.0 × 10 ⁻⁶ m ³ / sec, which is the final required flow rate from the start of the growth, the seed is reached when the crystal thickness reaches about 1 mm. A 3C polytype having a different atomic arrangement (trigonal form) than a crystal (hexagonal form) is generated, and as a result of the generation of a polycrystal or a heterogeneous polytype, crystal grain boundaries, micropipe defects, etc. occur, resulting in crystallinity. Deteriorated. It was estimated that the distortion due to the markedly different impurity concentration between the seed crystal and the grown crystal increased as the crystal grew and the thickness increased, causing deterioration of crystallinity.

(Example 2)
In the same manner as in Example 1, a hexagonal SiC single crystal 1 having a (0001) plane was prepared as a seed crystal. The micropipe defect density of the same type crystal was as small as 5 pieces / cm ² or less and good crystallinity, and the concentration of nitrogen as a doping element was 1 × 10 ¹⁹ cm ⁻³ . Next, the seed crystal 1 was attached to the inner surface of the lid 4 of the graphite crucible 3. The graphite crucible 3 was filled with high-purity SiC crystal powder 2 obtained by a CVD method (a high-purity raw material with few impurities is necessary to achieve high resistivity). Next, the graphite crucible 3 filled with the SiC raw material was closed with the lid 4 and covered with the graphite felt 7, and then placed on the graphite support rod 6 and installed inside the double quartz tube 5. And after evacuating the inside of a quartz tube, the electric current was sent through the work coil and the raw material temperature was raised to 2000 degreeC. Thereafter, high-purity Ar gas (purity 99.9995%) was introduced as the atmospheric gas, and the raw material temperature was raised to the target temperature of 2400 ° C. while maintaining the pressure in the quartz tube at about 80 kPa. The growth pressure was reduced to 1.3 kPa over about 30 minutes, and then the growth was continued for about 20 hours. At this time, the temperature gradient in the crucible was 15 ° C./cm, and the growth rate was about 0.75 mm / hour. The diameter of the obtained crystal was 51 mm, and the height was about 15 mm. During this growth time, at the start of growth, the nitrogen flow rate is 0.5 × 10 ⁻⁶ m ³ / sec (at the same flow rate, the nitrogen concentration in the grown crystal becomes 1 × 10 ¹⁹ cm ⁻³ , which is equivalent to the concentration in the seed crystal). Therefore, after the start of growth, the nitrogen flow rate was reduced at a constant rate and decreased to 0 m ³ / sec (valve closed state) in 5 hours. Since the nitrogen concentration in the grown crystal obtained when the nitrogen flow rate is 0 m ³ / sec (andop) is 1 × 10 ¹⁸ cm ⁻³ , the concentration change rate in the grown crystal is 26.7% / 100 μm (= 1000% / (0.75 mm / hour × 5 hours)).

When the silicon carbide single crystal thus obtained was analyzed by Raman scattering, it was confirmed that a hexagonal SiC single crystal having the same polytype as the seed crystal grew over the entire surface. For the purpose of measuring the crystallinity, a wafer having a thickness of 1.0 mm was cut out from the uppermost portion of the grown single crystal ingot (the portion grown near the end of growth). When the wafer was directly observed with an optical microscope, it was confirmed that the through-hole defect density was 10 / cm ² or less, which was as low as the seed crystal. For further confirmation, etching was performed in a potassium hydroxide solution melted at 520 ° C. for 5 minutes. When this etching process is performed, the penetrating hollow defects can be observed as hexagonal etch pits. When the etch pit number density of the wafer was examined, through-hole defects having the same number density as in the visual observation were detected. In addition, in order to confirm whether a high-quality crystal equivalent to the seed crystal is obtained, the X-ray topography imaging data of the seed crystal measured in advance and the X-ray topography imaging data of the wafer cut out from the grown crystal are obtained. As a result of comparison, it was confirmed that the product had the same high quality as the seed crystal and no new defects were generated due to the growth.

With respect to the resistivity measurement of this wafer, the dielectric relaxation phenomenon was used to measure the electrical resistivity of a sample having a large insulation, and the measurement was performed using a “dielectric relaxation method”. As a result, the wafer resistivity was as high as 5 × 10 ⁵ Ωcm. It was confirmed to have resistivity.

  A silicon carbide single crystal epitaxial wafer is produced by epitaxially growing a SiC single crystal thin film by using a chemical vapor deposition method (CVD method) on a wafer produced by cutting and processing the crystal having good crystallinity thus obtained. did. In order to investigate the crystallinity of the epitaxial wafer, the surface of the epitaxial wafer was etched in the molten potassium hydroxide solution described above. As a result, it was confirmed that the good crystal quality of the silicon carbide single crystal wafer as the substrate was inherited.

On the other hand, when the growth is performed under the condition of 0 m ³ / sec (the nitrogen gas valve is closed and no nitrogen is flown at all), which is the nitrogen gas flow rate at which the final target concentration is obtained, from the start of the growth, When reaching about 1 mm, a 3C polytype having an atomic arrangement (trigonal crystal) different from the seed crystal (hexagonal crystal) is generated, from which polycrystals are generated or heterogeneous polytypes are generated. The crystallinity deteriorated due to micropipe defects. It was estimated that the distortion due to the markedly different impurity concentration between the seed crystal and the grown crystal increased as the crystal grew and the thickness increased, causing deterioration of crystallinity.

Diagram explaining the principle of the improved Rayleigh method Schematic diagram of crystal growth equipment used in the examples

Explanation of symbols

1 Seed crystal (SiC single crystal)
2 SiC crystal powder raw material 3 Crucible (high melting point metal such as graphite or tantalum)
4 Graphite crucible lid 5 Double quartz tube 6 Support rod 7 Graphite felt (heat insulation)
8 Work coil 9 High purity Ar gas piping 10 Mass flow controller for high purity Ar gas and impurity gas 11 Vacuum exhaust system.

Claims (3)

  A method for producing a silicon carbide single crystal by a sublimation recrystallization method, comprising a step of growing a silicon carbide single crystal ingot on a seed crystal, wherein an additive gas flow rate in an inert atmosphere during crystal growth is changed, The additive element concentration in the growth crystal gradually increases or decreases within the range of the concentration change rate from 1% / 100 μm to 200% / 100 μm with respect to the crystal growth direction from the same concentration as in the seed crystal in the growth crystal. A method for producing a silicon carbide single crystal, wherein the concentration is changed to a desired concentration. The concentration change rate is 5% / 100 μm or more, 100% / 100 μm with respect to the crystal growth direction.
The method for producing a silicon carbide single crystal according to claim 1, which is within the following range. The method for producing a silicon carbide single crystal according to claim 1, wherein the additive element is any one of nitrogen, boron, and aluminum.