JP5131262B2 - Silicon carbide single crystal and method for producing the same - Google Patents

Description

  The present invention relates to a high resistivity silicon carbide single crystal and a method for producing the same. The present invention also relates to a high crystal quality silicon carbide single crystal applied to a substrate or the like of a high frequency electronic device, and a method for manufacturing the same.

  Silicon carbide (SiC) has been attracting attention as an environmentally resistant semiconductor material because it has excellent physical and chemical properties such as high heat resistance and mechanical strength and resistance to radiation. In recent years, the demand for SiC single crystals has been increasing as a substrate material for short wavelength optical devices from blue to ultraviolet, high frequency high voltage electronic devices and the like. In the application of SiC single crystal to the semiconductor field, a high-quality single crystal having a large area is required. In particular, in applications such as a substrate for a high-frequency device, it is required to have high electrical resistance in addition to the quality of the crystal. It has been.

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, and impurity carrier concentration. On the other hand, a cubic silicon carbide single crystal is also grown by heteroepitaxial growth on a heterogeneous substrate such as silicon (Si) using chemical vapor deposition (CVD). In this method, a single crystal having a large area can be obtained, but only a SiC single crystal containing many defects (−10 ⁷ cm ⁻² ) is grown due to a lattice mismatch with the Si 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 in which sublimation recrystallization is performed using a SiC single crystal wafer as a seed crystal has been proposed (Non-patent Document 1). By using this improved Rayleigh method, it is possible to grow a SiC single crystal while controlling the crystal polymorphism (6H type, 4H type, 15R type, etc.) and the shape, carrier type and concentration of the SiC single crystal. Currently, SiC single crystal wafers having a diameter of 2 inches (50 mm) to 3 inches (75 mm) are cut out from SiC single crystals manufactured by the modified Rayleigh method, and are used for device manufacture in the field of power electronics and the like.

  On the other hand, in recent years, gallium nitride (GaN) having characteristics superior to silicon (Si) and gallium arsenide (GaAs) has attracted attention as a material for high-frequency semiconductor devices (Non-patent Document 2). In manufacturing a GaN device, it is necessary to form a single crystal thin film of GaN on some single crystal substrate, and one common substrate is a sapphire substrate. Although sapphire has the merit of being able to stably supply a relatively good quality single crystal, the lattice constant difference with GaN is as large as 13.8%, so it is easy to induce deterioration of the quality of the thin film formed on it, In addition, since the thermal conductivity is as low as 0.42 W / cm · K, there is a problem in terms of heat dissipation during device operation, and the GaN high frequency device formed on the sapphire substrate is GaN original in terms of quality and operating characteristics. It is the current situation that it cannot be said that the performance of is fully extracted. On the other hand, SiC single crystal has a small lattice constant difference with GaN of 3.4%, so a high-quality GaN thin film can be formed, and the thermal conductivity is as large as 3.3 W / cm · K, so the cooling efficiency is also high. In recent years, the expectation for a SiC single crystal substrate has been very high in this field as well, since the characteristics of a GaN device can be greatly improved compared to a conventional substrate such as sapphire.

In the above-described high frequency device application of the substrate, in addition to the quality of the crystal, in order to reduce the parasitic capacitance of the element fabricated thereon and to separate the elements, the substrate has a high resistivity (5 × 10 ³ Ωcm or more, 1 × 10 ⁵ Ωcm or more is desirable. At present, such SiC high resistivity substrates are industrially obtained by forming deep levels in the forbidden band of SiC single crystal by some method. For example, vanadium forms a deep level in either a donor or an acceptor in a SiC crystal, and compensates for shallow donor or shallow acceptor impurities that are inevitably incorporated into the crystal, thereby increasing the resistivity of the crystal. It has been known. Specifically, for example, as described in (Non-Patent Document 3), in the above-described sublimation recrystallization method, the vanadium or vanadium compound (silicide, oxide, etc.) is contained in the SiC crystal powder as a raw material. And sublimating with the SiC raw material, a vanadium-added crystal is obtained. However, although the SiC single crystal produced in this way has a high resistivity, the crystal quality is poor, and the crystal portion having a high resistivity is an extremely limited portion in the grown crystal. Further, (Patent Document 1) discloses a technique for obtaining a vanadium-doped crystal having a higher resistivity. This technology overcompensates impurity nitrogen in SiC by adding an element having a trivalent shallow acceptor level, changes the conduction type from n-type to p-type, and transition metals such as vanadium to the donor level. By placing, it is intended to obtain higher resistivity. However, it is difficult to add the acceptor element to the SiC crystal while controlling it at an optimum concentration. In addition, the concentration of impurity nitrogen mixed in the SiC crystal in the sublimation recrystallization method is generally from one digit during growth. Since it often changes on the order of several orders of magnitude, it can be said that it is extremely difficult to maintain an optimum acceptor element concentration in the entire area of the SiC single crystal ingot. For this reason, the conduction type of the crystal cannot be converted to the target p-type due to the lack of the acceptor element, or the crystal becomes an extreme p-type due to the excessive addition of the acceptor element, and it is easy to fall into a situation where it is difficult to compensate with vanadium. . The technology of this publication does not solve the essential problems of vanadium-added crystals such as crystal quality and yield.

The solid solution limit of vanadium in SiC is about ³ to 5 × 10 ¹⁷ / cm ^{3. When} the amount of vanadium exceeds the solid solution limit, precipitates are generated as described in (Non-patent Document 4). There is a problem that the crystal quality is lowered. The amount of vanadium added may be limited for these reasons, making it difficult to produce high resistivity vanadium-added crystals with the prior art.

  On the other hand, it is also known that the crystal has a high resistivity by reducing the carrier impurity concentration of the SiC single crystal to a very low level. This is considered to be because deep level point defects existing in the forbidden band of SiC crystal called ID, UD-1, or carbon vacancy trap trap conduction electrons or holes (for example, (Non-patent document 5), (Non-patent document 6)). However, the quality of the high resistivity single crystal thus obtained does not satisfy the high demands in the semiconductor field.

Japanese National Patent Publication No. 9-500861

Yu. M.M. Tailov and V.M. F. Tsvetkov, J.M. Crystal Growth, vol. 52 (1981) pp. 146-150 Rutberg & Co. , Gallium Nitride: A Material Opportunity (2001) S. A. Reshanov et al. , Materials Science Forum, vols. 353-356 (2001) pp. 53-56 M.M. Bickermann et al. , Materials Science Forum, vols. 389-393 (2002) pp. 139-142 M.M. E. Zvanut and V.M. V. Konovalov, Applied Physics Letters, Vol. 80, no. 3, pp. 410-412 (2002) B. Magnussen et al. , Material Science Forum, vols. 389-393 (2002) pp. 505-508

In the prior art, when trying to increase the resistivity of a SiC single crystal by adding vanadium, the vanadium concentration in the crystal is an uncompensated impurity concentration (| n-type impurity concentration other than vanadium−p-type impurity concentration other than vanadium |). Need to be higher. That is, in order to obtain a vanadium-doped crystal having a high resistivity, the vanadium concentration must be controlled so that the uncompensated impurity concentration <vanadium concentration <vanadium solid solution limit (3 to 5 × 10 ¹⁷ / cm ³ ). Don't be. However, the concentration of uncompensated impurities in the SiC single crystal is often 1 × 10 ¹⁷ / cm ³ or more, and the above conditions are very narrow in the allowable range. Furthermore, since the sublimation rate or evaporation rate of vanadium is larger than the sublimation rate of SiC raw material, the region where the vanadium concentration exceeds the solid solution limit and below the uncompensated impurity concentration in the SiC crystal grown by the change in the vanadium concentration during growth. And an area that becomes For this reason, the conventional vanadium-added crystal has a problem that the crystal quality is low, and a crystal part having a high resistivity becomes a limited part of the grown crystal.

  On the other hand, in order to reduce the carrier impurity concentration and achieve high resistivity of the SiC single crystal, it is necessary to purify the crystal to an extremely high level. For this reason, in addition to the use of special raw materials, special processes such as high-temperature growth are also required. These are disadvantageous in terms of cost, and control of crystal growth is extremely difficult as compared with a normal single crystal growth method, and thus there is a problem that high quality crystals cannot be obtained.

  An object of the present invention is to solve the above-mentioned problems and to provide a high-resistivity and high-quality large-diameter Si single crystal and a method for producing the same.

  As a result of carrying out various investigations and researches to solve the above problems, the present inventors can increase the resistivity of the crystal with a much smaller amount of vanadium added than before, and have high quality and high resistivity. A technology for providing a SiC single crystal has been found. The present invention has the following configuration.

(1) Inevitable inclusion of uncompensated impurities in atomic density of 1 × 10 ¹⁵ / cm ³ or more and 1 × 10 ¹⁷ / cm ³ or less, and vanadium of 5 × 10 ¹⁴ / cm ³ or more, Silicon carbide containing less than the compensation impurity concentration, having a concentration difference between the uncompensated impurity and the vanadium of 1 × 10 ¹⁷ / cm ³ or less, and an electrical resistivity measured at a room temperature of 5 × 10 ³ Ωcm or more as a wafer Single crystal.

(2) The silicon carbide single crystal according to (1), wherein the concentration of the inevitable uncompensated impurities is 5 × 10 ¹⁶ / cm ³ or less.

  (3) The silicon carbide single crystal according to (1) or (2), wherein the conductivity type due to uncompensated impurities is n-type.

(4) The silicon carbide single crystal according to (1), wherein the vanadium concentration is 1 × 10 ¹⁵ / cm ³ or more.

(5) The silicon carbide single crystal according to (1), wherein the vanadium concentration is 1 × 10 ¹⁶ / cm ³ or more.

(6) The silicon carbide single crystal according to any one of (1) to (5), wherein a concentration difference between the uncompensated impurity and the vanadium is 5 × 10 ¹⁶ / cm ³ or less.

(7) The silicon carbide single crystal according to any one of (1) to (5), wherein a concentration difference between the uncompensated impurity and the vanadium is 1 × 10 ¹⁶ / cm ³ or less.

  (8) The silicon carbide single crystal according to any one of (1) to (7), wherein a main polytype of the silicon carbide single crystal is 3C, 4H, or 6H.

  (9) The silicon carbide single crystal according to any one of (1) to (7), wherein a main polytype of the silicon carbide single crystal is 4H.

  (10) The method for producing a silicon carbide single crystal according to any one of (1) to (9), wherein a single crystal is grown by a sublimation recrystallization method using a seed crystal, wherein silicon carbide and vanadium or A method for producing a silicon carbide single crystal, wherein a mixture of vanadium compounds is used and the nitrogen-containing concentration of a graphite crucible used for crystal growth is 50 ppm or less as measured by an inert gas melting thermal conductivity method.

  (11) The method for producing a silicon carbide single crystal according to (10), wherein a nitrogen-containing concentration in the graphite crucible is 20 ppm or less.

  (12) The method for producing a silicon carbide single crystal according to (10), wherein the nitrogen-containing concentration in the graphite crucible is 10 ppm or less.

  (13) The graphite crucible is a graphite crucible subjected to a purification treatment in which the temperature is maintained at 1400 ° C. or more, 10 hours or more and less than 120 hours in an inert gas atmosphere having a pressure of 1.3 Pa or less. ) A method for producing a silicon carbide single crystal according to any one of the above.

(14) Graphite that is maintained for 10 hours or more and less than 120 hours at a temperature of 1400 to 1800 ° C. in an inert gas atmosphere at a pressure of 1.3 Pa or less in a state where raw material powder mainly composed of silicon carbide is filled in a graphite crucible. After purifying the crucible, the graphite crucible and seed crystal were placed in an inert gas atmosphere adjusted to a pressure of 1.3 × 10 ^{2 to} 1.3 × 10 ⁴ Pa, and heated to 2000 ° C. or higher. The method for producing a silicon carbide single crystal according to any one of (10) to (13), wherein crystal growth is started thereafter.

(15) The method for producing a silicon carbide single crystal according to (13) or (14), wherein the pressure of the purification treatment is 1.3 × 10 ⁻¹ Pa or less.

(16) The method for producing a silicon carbide single crystal according to (13) or (14), wherein the pressure of the purification treatment is 6.5 × 10 ⁻² Pa or less.

  (17) The method for producing a silicon carbide single crystal according to any one of (13) to (16), wherein the graphite crucible is subjected to crystal growth without being exposed to the atmosphere after the purification treatment.

  The SiC single crystal of the present invention achieves high resistivity with a much smaller amount of vanadium than the conventional one, which is less than the concentration of uncompensated impurities. This is considered to be caused by the presence of vanadium and deep level defects in the SiC single crystal at the same time. As a result, it has become possible to achieve high resistivity without inducing the generation of precipitates and deterioration of crystal quality due to excessive addition of vanadium, which has been a problem in the past. At the same time, an excessive increase in manufacturing cost can be avoided because an ultra-high purity process of SiC single crystal, which is extremely difficult industrially, is not required.

  Thus, the novel point of the present invention is that vanadium and deep level defects, which are not conventionally used together, are present in the SiC single crystal at the same time, which is much more than expected from the effect when they exist alone. In particular, a great special effect is obtained. The present invention makes it possible to achieve both high resistivity and high crystal quality, which could not be realized by the prior art. In addition, this invention is not limited by the above-mentioned high resistivity expression mechanism.

  As described above, according to the present invention, it is possible to provide a SiC single crystal and a SiC single crystal wafer having high resistivity and high crystal quality. Moreover, according to the manufacturing method of this invention, the said SiC single crystal with a high yield can be manufactured, suppressing the raise of manufacturing cost.

It is a block diagram which shows an example of the single-crystal manufacturing apparatus used in manufacturing the crystal | crystallization of this invention. It is drawing which shows the analysis position of a SiC single crystal wafer with a diameter of 100 mm.

In the SiC single crystal of the present invention, the concentration of uncompensated impurities is desirably 1 × 10 ¹⁷ / cm ³ or less, and more desirably 5 × 10 ¹⁶ / cm ³ or less. The lower limit value of the vanadium concentration is 5 × 10 ¹⁴ / cm ³ or more, preferably 1 × 10 ¹⁵ / cm ³ or more, more preferably 1 × 10 ¹⁶ / cm ³ or more, and the upper limit value is the above-mentioned uncompensated value. Impurity concentration. By setting the uncompensated impurity concentration and vanadium concentration in the SiC single crystal to the above-described values, an effective combined effect of vanadium and deep level defects can be obtained, and the crystal has a high resistivity. When the concentration of uncompensated impurities in the crystal exceeds 1 × 10 ¹⁷ / cm ³ or when the concentration of vanadium is less than 5 × 10 ¹⁴ / cm ³ , the combined effect of deep level defects and vanadium is an impurity. Therefore, it is extremely difficult to increase the resistivity of the SiC single crystal. Further, the concentration difference between the uncompensated impurity concentration and the vanadium concentration in the SiC single crystal is 1 × 10 ¹⁷ / cm ³ or less, desirably 5 × 10 ¹⁶ / cm ³ or less, and more desirably 1 × 10 ¹⁶ / cm ^3. By making the following, vanadium and deep level defects are more dominant than uncompensated impurities, and the SiC single crystal can be effectively increased in resistivity. The type of uncompensated impurities is not specifically mentioned, but a typical impurity of SiC is nitrogen which is a donor element. When a SiC single crystal is produced by a sublimation recrystallization method, the conductivity type of the grown crystal is generally used. Is often n-type. When converting the conductivity type to p-type, it is necessary to add an acceptor element such as boron or aluminum to the SiC single crystal. However, the p-type has an optimum uncompensated impurity concentration by avoiding insufficient addition or excessive addition. It is difficult to produce a SiC single crystal. In the present invention, it is not necessary to convert the conductivity type to the p-type, and the technique of the present invention is more effective when applied to an n-type SiC crystal. Since the SiC single crystal of the present invention has a low vanadium concentration as compared with the concentration of the high resistivity condition by vanadium in the prior art, there is no precipitation of vanadium compound in the entire SiC single crystal ingot or the precipitate is Even if it occurs, it is limited to a local region, so that the crystal quality can be kept high. At the same time, since the technique of the present invention can increase the resistivity of the crystal in a wider vanadium concentration range than the conventional technique, all wafers processed from a SiC single crystal ingot or most of the wafers are 5 × 10 5. It can be a high resistivity wafer of ³ Ωcm or more, desirably 1 × 10 ⁵ Ωcm or more. The SiC single crystal of the present invention can be produced in any of the 3C, 4H, and 6H polytypes that are currently considered to be promising for device applications. Among them, inevitably nitrogen mixing is expected while expecting particularly high device characteristics. It is most effective to apply the technique of the present invention to the 4H polytype having a large number of the above. In consideration of application as a device, it is desirable that the SiC single crystal wafer is composed of a single polytype of 3C, 4H, or 6H. As an SiC single crystal ingot for producing such a wafer, the entire ingot does not necessarily have to be a single polytype, but by making the main polytype of the ingot one of the aforementioned polytypes, The yield of polytype wafers can be increased. Although the diameter of the wafer is not particularly limited, the present invention is particularly effective in a large-diameter SiC single crystal in which the in-plane distribution of the dopant concentration tends to be large, and the single crystal has a diameter of 50 mm or more. A great effect is obtained when the thickness is 100 mm or more. Since the SiC single crystal wafer of the present invention has high resistivity and high crystal quality, it can be applied to a device having a high operating frequency. An epitaxial wafer produced by forming a SiC single crystal thin film on the wafer of the present invention by CVD or the like, or an epitaxial wafer formed by epitaxially growing a thin film of gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof, Since the crystallinity of the SiC wafer is good, it has excellent characteristics (surface morphology of the thin film, electrical characteristics, etc.).

In order to produce the SiC single crystal of the present invention, a vanadium compound such as vanadium metal, silicide, carbide or the like is used as a source of vanadium, and is mixed with an SiC raw material in a predetermined composition in consideration of uptake efficiency. For example, a known single crystal growth method can be used. In that case, a commercially available raw material can be used as a SiC raw material. In order to reduce the concentration of uncompensated impurities in the sublimation recrystallization method, it is important to reduce nitrogen, which is a typical impurity of SiC crystals. The present inventors paid attention to the fact that the nitrogen concentration is often locally high in the vicinity of the seed crystal of the SiC single crystal grown by the sublimation recrystallization method, and investigated the cause. As a result, it has been found that the incorporation of nitrogen generated from a crucible made mainly of graphite into the SiC single crystal is one of the main causes of the decrease in purity. When the SiC single crystal of the present invention is produced by a sublimation recrystallization method using a seed crystal, the nitrogen-containing concentration is 50 ppm or less, desirably 20 ppm or less, more desirably 10 ppm or less, as measured by an inert gas melting thermal conductivity method. By using this graphite crucible, nitrogen taken into the SiC single crystal from the crucible can be reduced, and the uncompensated impurity concentration of the SiC single crystal can be reduced. Further, such a graphite crucible can be obtained by subjecting the graphite crucible to a purification treatment in which the temperature is maintained at 1400 ° C. or more for 10 hours or more and less than 120 hours in an inert gas atmosphere. In this case, the pressure of the inert gas atmosphere is 1.3 Pa or less, desirably 1.3 × 10 ⁻¹ Pa or less, and more desirably 6.5 × 10 ⁻² Pa or less. Although there is no upper limit for the processing time, if the processing pressure exceeds 1.3 Pa or the processing temperature is less than 1400 ° C., the nitrogen removal efficiency is remarkably lowered, the heating and holding time is prolonged, and particularly in terms of manufacturing cost. Disadvantages arise. There is no particular upper limit on the processing temperature, but if the processing temperature is 3000 ° C. or higher, there is a problem in terms of durability of the processing apparatus, which is not preferable. Moreover, the above processing can also be performed by incorporating it into the SiC crystal growth process. That is, in the sublimation recrystallization method using a seed crystal, the pressure in the inert gas atmosphere is 1.3 Pa or less, preferably 1.3 × 10 ⁻¹ in a state where a graphite crucible is filled with a sublimation material mainly composed of SiC. The graphite crucible is purified by holding at Pa or lower, more preferably 6.5 × 10 ⁻² Pa or lower, and holding at a temperature of 1400 ° C. or higher and 1800 ° C. or lower for 10 hours or more and less than 120 hours. At this time, if the pressure exceeds 1.3 Pa, the purification treatment cannot be performed efficiently. Even if the processing temperature is 1400 ° C. or lower, the purification treatment cannot be performed efficiently. On the other hand, if the processing temperature exceeds 1800 ° C., crystal growth is started during the purification processing to generate polycrystals, and in the subsequent SiC single crystal growth process. Normal single crystal growth cannot be realized. Following this purification treatment, the growth furnace is not opened in the atmosphere, the inert gas pressure is adjusted to 1.3 × 10 ^{2 to} 1.3 × 10 ⁴ Pa, heated to 2000 ° C. or higher, and then the SiC crystal Implement growth. There is no particular upper limit for the crystal growth temperature, but if it is 3000 ° C. or higher, there is a problem in terms of durability of the growth apparatus, which is not preferable. If the graphite crucible purification process is performed without incorporating it into the SiC crystal growth process, if the graphite crucible after the purification process is exposed to the atmosphere, nitrogen in the atmosphere is re-adsorbed on the graphite surface, reducing the effect of the purification process. End up. In order not to expose the crucible after treatment to the atmosphere, it is possible to avoid the influence of re-adsorption of nitrogen by preparing for sublimation raw material filling in a vacuum glove box filled with inert gas. is there.

  Hereinafter, the present invention will be specifically described with reference to examples.

(Example 1, Comparative Examples 1-3)
Example 1 and Comparative Examples 1 to 3 were manufactured using the crystal growth apparatus of FIG. As a seed crystal, an SiC single crystal wafer composed of a 4H single polytype having a (0001) plane with a diameter of 50 mm was prepared. The seed crystal 1 is attached to the inner surface of the graphite lid 4. As sublimation raw material 2, for Example 1 and Comparative Example 1, a mixture of commercially available SiC crystal powder and vanadium compound was filled. The vanadium compound was mixed in such an amount that the mass concentration in the sublimation raw material was 0.042% in terms of vanadium atoms. For Comparative Examples 2 and 3, only commercially available SiC crystal powder was filled as a sublimation raw material. Next, the crucible 3 filled with the raw material is closed with a graphite lid 4 fitted with a seed crystal, covered with a graphite felt 7, placed on a graphite support rod 6, and installed inside the double quartz tube 5. Then, crystal growth was performed by the following process.

For Example 1 and Comparative Example 3, a crystal growth process including purification of a graphite crucible was used. The contents are as follows. First, after the inside of the quartz tube 5 was evacuated to less than 1.0 × 10 ⁻⁴ Pa, a current was passed through the work coil 8 while continuing the evacuation, and the temperature of the graphite crucible was raised to 1600 ° C., which is a purification treatment temperature. . At this time, the internal pressure of the quartz tube temporarily increased to 1.3 Pa or more, but the internal pressure of the quartz tube became 1.0 × 10 ⁻¹ Pa or less which is a purification treatment pressure while maintaining the temperature. The evacuation was performed, and impurity nitrogen removal processing in the crucible was started. The processing time was 48 hours, and during that time, the vacuum evacuation device 11 was always operated, and the internal pressure of the quartz tube was maintained at a value lower than the aforementioned value. After the crucible purification process is completed, high-purity Ar gas having a purity of 99.9999% or more is introduced as the atmospheric gas while being controlled by the Ar gas mass flow controller 10 through the pipe 9, and the pressure in the quartz tube is the growth pressure. While maintaining 1.3 × 10 ³ Pa, the temperature of the graphite crucible was raised to the target temperature of 2400 ° C., and then the growth was continued for about 20 hours. At this time, the temperature gradient in the crucible was 14.5 to 15.5 ° C./cm, and the growth rate was about 0.8 to 0.9 mm / hour. The diameter of the obtained crystal was about 52 mm, and the height was about 16 mm for the crystal of Example 1 and about 17 mm for the crystal of Comparative Example 3.

In Comparative Example 1 and Comparative Example 2, crystal growth was performed by a normal crystal growth process not including purification treatment of the graphite crucible. The contents are as follows. After the inside of the quartz tube is evacuated to 1.0 × 10 ⁻⁴ Pa, high purity Ar gas having a purity of 99.9999% or more is introduced, and the pressure in the quartz tube is increased to 1.3 × 10 ³ Pa which is the growth pressure. While maintaining, a current was passed through the work coil 8 to raise the temperature of the graphite crucible to 2400 ° C. Thereafter, the growth continued for about 20 hours. At this time, the temperature gradient in the crucible was 14.5 to 15.5 ° C./cm, and the growth rate was about 0.8 to 0.9 mm / hour. The diameter of the obtained crystal was about 52 mm, and the height was about 16 mm for the crystal of Comparative Example 1 and about 18 mm for the crystal of Comparative Example 2.

Prior to the analysis of the obtained SiC single crystal, the nitrogen concentration of the graphite crucible subjected to the purification treatment was measured. First, a graphite crucible having the same material and shape as that used for crystal growth is used and held for 48 hours at a temperature of 1600 ° C. and a pressure of 1.0 × 10 ⁻¹ Pa or less, as in Example 1 and Comparative Example 3. A purification treatment was performed. At this time, the graphite crucible was not filled with the sublimation raw material. After the purification treatment, the graphite crucible is cooled, and a test piece having a diameter of about 5 mm and a length of 10 mm is processed from the crucible after the purification treatment in a vacuum glove box filled with an inert gas to obtain a measurement test piece. It was measured by the active gas melting thermal conductivity method. The measurement was performed as follows. First, a large current is passed through the heating crucible in the analyzer without loading the sample, the inside of the heating crucible is maintained at a high temperature of 2500 ° C. or higher for 30 seconds, and the impurity nitrogen near the surface of the heating crucible and the surface layer is removed. The measurement space was sufficiently purified. After cooling the heating crucible, the test piece that had been waiting outside the heating zone of the measuring apparatus was moved into the heating crucible without being exposed to the atmosphere, and the inside of the crucible was held at a high temperature of 2500 ° C. or higher for 30 seconds. In this state, nitrogen generated from the test piece was transported by a helium carrier gas, and the nitrogen concentration was determined by measuring the thermal conductivity of this mixed gas. As a result of the measurement, the nitrogen concentration in the purification crucible was about 9 ppm. Further, the graphite crucible that was not subjected to the purification treatment was measured by the same method, and as a result, the nitrogen concentration was about 59 ppm.

When the SiC single crystals of Example 1 and Comparative Examples 1 to 3 thus obtained were analyzed by X-ray diffraction and Raman scattering, it was confirmed that SiC single crystals having a main polytype of 4H were grown in all ingots. It was. In order to measure the impurity concentration and resistivity of the crystal, three wafers having a thickness of 1 mm and a diameter of 51 mm were produced from the grown single crystal ingot. The plane orientation of the wafer is (0001) plane just. The vanadium concentration and impurity concentration in the wafer corresponding to the upper, middle and lower portions (near the seed crystal) of the grown crystal (the distance from the seed crystal growth start surface to the wafer bottom surface, 12 mm, 8 mm and 4 mm, respectively) Investigation was performed using ion mass spectrometry (Secondary Ion Mass Spectrometry, SIMS). R. G. Wilson et al. , Secondary Ion Mass Spectrometry: According to A Practical Handbook For Depth Profiling And Bulk Impurity Analysis (1989), the measurement lower limit of 1.5 × ¹⁰ 14 / cm ³ is obtained for the analysis of vanadium. In the present invention, analysis was performed by a method based on this, and the lower limit of measurement of vanadium was less than 5 × 10 ¹⁴ / cm ³ . The room temperature resistivity of each wafer was examined by the Van der Pauw method. The results shown in Tables 1 to 4 were obtained by the above analysis.

The uncompensated impurity concentration of the crystal of Example 1 (Table 1) is 1.65 to 2.24 × 10 ¹⁶ / cm ³ . The main component of the impurity is nitrogen which is a donor element, and conduction by the impurity is n-type. The nitrogen concentration minus the compensation by the impurity acceptor element is the uncompensated impurity concentration. As a result of the purification treatment of the graphite crucible, the concentration of uncompensated impurities was also reduced because the nitrogen concentration at the lower part of the ingot was particularly low as compared with Comparative Example 1 and Comparative Example 3. The vanadium concentration is 3.99 × 10 ^{15 to} 3.87 × 10 ¹⁶ / cm ^3, which is lower than the aforementioned uncompensated impurity concentration. Since the vanadium concentration does not exceed the solid solution limit throughout the ingot, no precipitate is generated and the crystallinity is excellent. On the other hand, the resistivity of all the upper to lower wafers is as high as 10 ¹⁰ Ωcm or more.

Comparative Example 1 (Table 2) is a crystal having substantially the same vanadium concentration as the Example, but has a high uncompensated impurity concentration because no technique for removing impurities is used. The main component of the impurity is nitrogen, and the conduction by the uncompensated impurity is n-type. Particularly in the initial growth region below the ingot, the influence of nitrogen generated from the graphite crucible is large, and the uncompensated impurity concentration is 1 × 10 ¹⁸ / cm ³ or more. The resistivity is as low as less than 1 × 10 ⁰ Ωcm throughout the ingot.

Comparative Example 2 (Table 3) is a crystal in which vanadium was not mixed with the sublimation raw material. The main impurity is nitrogen, and conduction by uncompensated impurities is n-type. Since the same graphite crucible purification treatment technology as in Example 1 was introduced, the incorporation of nitrogen was reduced, and the uncompensated impurity concentration was within the scope of the present invention. However, since vanadium was not added, the resistivity was 1 Although it is less than × 10 ³ Ωcm and higher resistivity than Comparative Example 1, it does not reach the required high level.

Comparative Example 3 (Table 4) is a crystal in which vanadium is not mixed in the sublimation raw material and a technique for reducing the impurity concentration is not used. The concentration of nitrogen, the main impurity, is high throughout the ingot, especially in the lower part. Conduction due to uncompensated impurities is n-type. The resistivity is as low as less than 1 × 10 ⁰ Ωcm throughout the ingot.

(Example 2)
Next, an example of a process for crystal growth after purifying the graphite crucible in advance will be described. First, the graphite crucible was purified using the apparatus excluding the seed crystal and the sublimation material shown in FIG. The graphite crucible 3 and the lid 4 are covered with a felt 7 and installed inside the double quartz tube 5. After the vacuum inside of the quartz tube is evacuated to less than 1.0 × 10 ⁻⁴ Pa, the workpiece is continuously evacuated. An electric current was passed through the coil 8 to raise the temperature of the graphite crucible and the lid to 2500 ° C. The purification treatment time was 20 hours, and during that time, the evacuation apparatus 11 was always operated, and the internal pressure of the quartz tube was maintained at a value lower than 1.3 × 10 ⁻² Pa which is the purification treatment pressure. After the purification treatment, the graphite crucible 3 and the lid 4 were cooled, taken out from the double quartz tube 5 in a vacuum glove box filled with an inert gas, and prepared for crystal growth without exposing the crucible to the atmosphere. A SiC single crystal wafer composed of a 6H single polytype having a (0001) face with a diameter of 50 mm is attached to the inner surface of the lid 4 as a seed crystal 1, and a commercially available mixture of SiC crystal powder and vanadium compound is sublimated raw material 2. The graphite crucible 3 was filled as follows. The vanadium compound was mixed in such an amount that the mass concentration in the sublimation raw material was 0.032% in terms of vanadium atoms. The crucible filled with the raw material was closed with the lid 4 and placed inside the double quartz tube 5 again, and crystal growth was performed by the following process. After the inside of the quartz tube is evacuated to less than 1.0 × 10 ⁻⁴ Pa, high purity Ar gas having a purity of 99.9999% or more is introduced, and the pressure inside the quartz tube is 1.3 × 10 ³ Pa which is the growth pressure. The graphite crucible temperature was raised to 2400 ° C. while passing a current through the work coil 8. Thereafter, the growth continued for about 20 hours. At this time, the temperature gradient in the crucible was 14.5 to 15.5 ° C./cm, and the growth rate was about 0.8 mm / hour. The diameter of the obtained crystal was about 52 mm, and the height was about 16 mm.

  Prior to the evaluation of the crystals, the nitrogen concentration of the graphite crucible treated under the same conditions as the purification treatment of Example 2 was measured by an inert gas melting thermal conductivity method for the purpose of confirming the effect of the graphite crucible purification treatment. did. The measurement was performed in the same manner as in Example 1 described above, and the nitrogen concentration was about 7 ppm.

  When the silicon carbide single crystal thus obtained was analyzed by X-ray diffraction and Raman scattering, it was confirmed that an SiC single crystal having a main polytype of 6H was grown. Three wafers having a plane orientation of (0001) plane corresponding to the upper, middle, and lower portions of the grown crystal (the distance from the growth start surface of the seed crystal are 12 mm, 8 mm, and 4 mm, respectively) are produced. The same analysis was performed. The results are shown in Table 5.

The main impurity of the crystal of Example 2 (Table 5) was nitrogen, and the impurity conduction was n-type. As a result of the crucible purification process, the nitrogen concentration is greatly reduced, and as a result, the uncompensated impurity concentration is reduced to 9.76 × 10 ^{15 to} 3.01 × 10 ¹⁶ / cm ³ . On the other hand, the resistivity at room temperature is as high as 1 × 10 ¹⁰ Ωcm or more.

(Example 3)
Next, the Example which manufactures the SiC single crystal of this invention with a diameter of 100 mm or more is described. Example 3 was also manufactured using the crystal growth apparatus of FIG. As the seed crystal 1, an SiC single crystal wafer composed of a 4H single polytype having a (0001) plane with a diameter of 100 mm was attached to the inner surface of the graphite lid 4. Sublimation raw material 2 was filled with a mixture of commercially available SiC crystal powder and vanadium compound as in Example 1. The vanadium compound was mixed in such an amount that the mass concentration in the sublimation raw material was 0.042% in terms of vanadium atoms. Next, the crucible 3 filled with the raw material is closed with a graphite lid 4 fitted with a seed crystal, covered with a graphite felt 7, placed on a graphite support rod 6, and installed inside the double quartz tube 5. Then, crystal growth was performed by a crystal growth process including purification treatment of the graphite crucible. The contents are as follows. First, after the inside of the quartz tube 5 was evacuated to less than 1.0 × 10 ⁻⁴ Pa, a current was passed through the work coil 8 while continuing the evacuation, and the temperature of the graphite crucible was raised to 1600 ° C., which is a purification treatment temperature. . At this time, the internal pressure of the quartz tube temporarily increased to 1.3 Pa or more, but the internal pressure of the quartz tube became 1.0 × 10 ⁻¹ Pa or less which is a purification treatment pressure while maintaining the temperature. The evacuation was performed, and impurity nitrogen removal processing in the crucible was started. The treatment time was 72 hours, and during that time, the evacuation device 11 was always operated, and the internal pressure of the quartz tube was maintained at a value lower than the aforementioned value. After the crucible purification process is completed, high-purity Ar gas having a purity of 99.9999% or more is introduced as the atmospheric gas while being controlled by the Ar gas mass flow controller 10 through the pipe 9, and the pressure in the quartz tube is the growth pressure. While maintaining 1.3 × 10 ³ Pa, the temperature of the graphite crucible was raised to the target temperature of 2400 ° C., and then the growth was continued for about 20 hours. At this time, the temperature gradient in the crucible was 14.5 to 15.5 ° C./cm, and the growth rate was about 0.8 to 0.9 mm / hour. The diameter of the obtained crystal was about 104 mm and the height was about 15 mm.

  Prior to the evaluation of the crystals, the nitrogen concentration of the graphite crucible treated under the same conditions as the purification treatment of Example 3 was measured by an inert gas melting thermal conductivity method. The measurement was performed in the same manner as in Example 1 described above, and the nitrogen concentration was about 8 ppm.

  When the silicon carbide single crystal thus obtained was analyzed by X-ray diffraction and Raman scattering, it was confirmed that a SiC single crystal having a main polytype of 4H was grown. Three wafers having a plane orientation of (0001) plane corresponding to the upper, middle, and lower portions of the grown crystal (the distance from the growth start surface of the seed crystal are 12 mm, 8 mm, and 4 mm, respectively) are produced. The same analysis was performed. In Example 3, for the purpose of examining the in-plane distribution of characteristics, an analysis was performed on a total of five points including one point at the wafer center and four points at the periphery as shown in FIG. Table 6 shows the maximum value of the analysis result in the central portion and the maximum value of the dispersion, that is, | analysis value in the central portion−analysis value in the peripheral portion |.

The main impurity of the crystal of Example 3 (Table 6) was nitrogen, and the impurity conduction was n-type. Since the crucible volume increases with the increase in the diameter of the ingot, the amount of nitrogen generated in the crucible without purification treatment increases, but in Example 3, the nitrogen in the crucible is significantly reduced by the purification treatment, and the result As a result, the uncompensated impurity concentration of the grown SiC single crystal is as low as 8.97 × 10 ^{15 to} 3.54 × 10 ¹⁶ / cm ³ at the center of the wafer. Both the uncompensated impurity and vanadium have a high room temperature resistivity of 1 × 10 ¹⁰ Ωcm or more over the entire wafer surface, although a slight concentration difference is observed in the plane.

Example 4
Next, from a SiC single crystal ingot manufactured by the same process as in Example 3, a mirror wafer having a diameter of 100 mm and a thickness of 360 μm having a plane orientation of 4 degrees off from the (0001) plane in the <11-20> direction. Produced. Using this mirror wafer as a substrate, SiC was epitaxially grown. The growth conditions of the SiC epitaxial thin film are as follows: the growth temperature is 1500 ° C., and the flow rates of silane (SiH ₄ ), propane (C ₃ H ₈ ), and hydrogen (H ₂ ) are 5.0 × 10 ⁻⁹ m ³ / sec, 3 It was ^{.3 × 10 -9 m 3 /sec,5.0×10 -5} m 3 / sec. The growth pressure was atmospheric pressure. The growth time was 2 hours, and the film was grown to a thickness of about 5 μm. When the epitaxial thin film thus obtained was observed with a normalsky optical microscope, it was found that a high-quality SiC epitaxial thin film having excellent surface morphology with very few surface defects such as pits was formed over the entire wafer surface. It could be confirmed.

(Example 5)
Further, from another SiC single crystal ingot manufactured by the same process as in Example 3, a mirror wafer having a (0001) plane just and a diameter of 100 mm and a thickness of 360 μm was manufactured. Using this mirror wafer as a substrate, a gallium nitride thin film was epitaxially grown by metal organic chemical vapor deposition (MOCVD). The growth conditions of the gallium nitride thin film are as follows: the growth temperature is 1050 ° C., and the flow rates of trimethylgallium (TMG), ammonia (NH ₃ ), and silane (SiH ₄ ) are 54 × 10 ⁻⁶ mol / min, 4 L / min, and 22 ×, respectively. 10 ⁻¹¹ mol / min. The growth pressure was atmospheric pressure. By growing for 60 minutes, n-type gallium nitride was grown to a thickness of about 3 μm. When the epitaxial thin film thus obtained was observed with a normalsky optical microscope, it was confirmed that a high-quality gallium nitride epitaxial thin film having a very flat morphology over the entire wafer surface was formed.

  Finally, Table 7 will be used to explain the effects of the present invention. Table 7 arranges the above-mentioned Example 1 and Comparative Examples 1 to 3 according to the vanadium concentration and impurity concentration in the crystal. As shown in Table 7, only the high resistivity targeted by Example 1 of the present invention is shown. The present invention, intended for the combined effect of vanadium and deep level defects, is much larger than would be expected from the effect when they act alone, Comparative Examples 1 and 3, or Comparative Examples 2 and 3. A special effect is obtained.

1 seed crystal (SiC single crystal),
2 Sublimation raw materials,
3 graphite crucible,
4 Graphite lid,
5 Double quartz tube,
6 Support rod,
7 Graphite felt,
8 Work coil,
9 High purity Ar gas piping,
10 Mass flow controller for high purity Ar gas,
11 Vacuum exhaust device,
21 100 mm diameter SiC single crystal wafer,
22 Analysis point (1 point) in the center of the wafer,
23 Analysis points (4 points) around the wafer.

Claims (17)

An uncompensated impurity that is inevitably mixed is contained in an atom number density of 1 × 10 ¹⁵ / cm ³ or more and 1 × 10 ¹⁷ / cm ³ or less, and vanadium is contained in an amount of 5 × 10 ¹⁴ / cm ³ or more. A silicon carbide single crystal containing less than, a concentration difference between the uncompensated impurity and the vanadium is 1 × 10 ¹⁷ / cm ³ or less, and an electrical resistivity measured at a room temperature of 5 × 10 ³ Ωcm or more as a wafer. 2. The silicon carbide single crystal according to claim 1, wherein the concentration of the inevitable uncompensated impurities is 5 × 10 ¹⁶ / cm ³ or less.   The silicon carbide single crystal according to claim 1 or 2, wherein the conductivity type due to uncompensated impurities is n-type. The silicon carbide single crystal according to claim 1, wherein the vanadium concentration is 1 × 10 ¹⁵ / cm ³ or more. The silicon carbide single crystal according to claim 1, wherein the vanadium concentration is 1 × 10 ¹⁶ / cm ³ or more. The silicon carbide single crystal according to claim 1, wherein a concentration difference between the uncompensated impurity and the vanadium is 5 × 10 ¹⁶ / cm ³ or less. The silicon carbide single crystal according to claim 1, wherein a concentration difference between the uncompensated impurity and the vanadium is 1 × 10 ¹⁶ / cm ³ or less.   The silicon carbide single crystal according to any one of claims 1 to 7, wherein a main polytype of the silicon carbide single crystal is 3C, 4H, or 6H.   The silicon carbide single crystal according to any one of claims 1 to 7, wherein a main polytype of the silicon carbide single crystal is 4H.   The method for producing a silicon carbide single crystal according to any one of claims 1 to 9, wherein a single crystal is grown by a sublimation recrystallization method using a seed crystal, wherein a mixture of silicon carbide and vanadium or a vanadium compound is used as a sublimation raw material. A method for producing a silicon carbide single crystal, wherein the concentration of nitrogen contained in a graphite crucible used for crystal growth is 50 ppm or less as measured by an inert gas melting thermal conductivity method.   The method for producing a silicon carbide single crystal according to claim 10, wherein a nitrogen-containing concentration in the graphite crucible is 20 ppm or less.   The method for producing a silicon carbide single crystal according to claim 10, wherein a nitrogen-containing concentration in the graphite crucible is 10 ppm or less.   The graphite crucible is a graphite crucible subjected to a purification treatment in which the temperature is maintained at 1400 ° C or higher, 10 hours or longer and less than 120 hours in an inert gas atmosphere at a pressure of 1.3 Pa or lower. The manufacturing method of the silicon carbide single crystal of description. Purification of a graphite crucible that is maintained at a temperature of 1400 to 1800 ° C. for 10 hours or more and less than 120 hours in an inert gas atmosphere at a pressure of 1.3 Pa or less with a raw material powder mainly composed of silicon carbide in a graphite crucible. After the treatment, the graphite crucible and seed crystal are placed in an inert gas atmosphere adjusted to a pressure of 1.3 × 10 ^{2 to} 1.3 × 10 ⁴ Pa, heated to 2000 ° C. or higher, and then crystallized. The method for producing a silicon carbide single crystal according to claim 10, wherein the growth is started. The method for producing a silicon carbide single crystal according to claim 13 or 14, wherein a pressure of the purification treatment is 1.3 × 10 ^-1 Pa or less. The method for producing a silicon carbide single crystal according to claim 13 or 14, wherein a pressure of the purification treatment is 6.5 × 10 ^-2 Pa or less.   The method for producing a silicon carbide single crystal according to any one of claims 13 to 16, wherein after the purification treatment, the graphite crucible is subjected to crystal growth without being exposed to the atmosphere.

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