JP2005239465A - Silicon carbide single crystal production device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production device which simply and stably grows a 4H-type silicon carbide single crystal with good crystal qualities. <P>SOLUTION: In the silicon carbide single crystal production device, a raw material for growing a silicon carbide single crystal is housed in a graphite-made crucible; the crucible has a seed-crystal-fixing part which fixes a seed crystal for growing the silicon carbide single crystal and is set at a position facing the raw material; and the raw material is sublimated under heating to grow the silicon carbide single crystal on the seed crystal. The crystal growth is performed by adding 2.0-3.5 wt% scandium to the raw material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a technique for producing a silicon carbide single crystal ingot by a sublimation method. In particular, the present invention relates to a technique for efficiently producing a 4H type silicon carbide single crystal.

  Silicon carbide (SiC) has a large thermal conductivity, a low dielectric constant, a wide band gap, and has thermally and mechanically stable characteristics. Therefore, a semiconductor element using silicon carbide has higher performance than a semiconductor element using conventional silicon. The range of use is expected to be environment-resistant device materials, radiation-resistant device materials, power device materials for power control, high-frequency device materials, etc. used in high-temperature environments. This silicon carbide crystal has more than 200 types of crystal polymorphs (polytypes) due to the difference in stacking of atoms when considering a close packed structure of silicon (Si) and carbon (C) atomic unit layers. Among these crystal polymorphs, 4H-type silicon carbide has a higher electron mobility, band gap, and breakdown electric field than other crystal polymorphs. Therefore, it has the highest utility value. However, 4H-type silicon carbide has a low probability of occurrence during crystal growth and is difficult to grow stably.

  On the other hand, a sublimation method (modified Rayleigh method) is known as a method for growing a silicon carbide single crystal. In this method, a silicon carbide raw material is heated and sublimated, and a silicon carbide single crystal is grown on a silicon carbide seed crystal substrate disposed to face the silicon carbide raw material. However, as described above, since the generation probability of 4H type silicon carbide is low, there is a problem that the probability of growth of 4H type silicon carbide is low even in the sublimation method.

Therefore, several methods for growing 4H-type silicon carbide have been proposed. For example, a 4H type buffer layer of 3 mm or less to which high concentration (3 × 10 ^{18 to} 6 × 10 ²⁰ atoms / cm ³ ) nitrogen is added is formed on a seed crystal substrate, and then a 4H type having a desired carrier density is formed. A method for growing silicon carbide is disclosed (Patent Document 1). As another method, 3C type silicon carbide is grown by doping a third element as an impurity on a silicon single crystal substrate, and then the silicon substrate is removed, and a heat treatment at 2000 ° C. or higher is performed to perform 4H type carbonization. A method for producing a silicon single crystal is disclosed (Patent Document 2). Furthermore, it has been reported that doping silicon carbide grown on a seed crystal substrate with a low concentration of scandium in the early stage of growth is effective for the growth of 4H type SiC single crystal.
Japanese Patent Laid-Open No. 10-0667600 Japanese Patent Laid-Open No. 11-26895 Journal of Crystal Growth 52 (1981) 146-150

  However, in the invention of Patent Document 1, an extra step of forming a buffer layer of 3 mm or less is necessary at the initial stage of growth, which causes an increase in manufacturing process cost.

In the invention of Patent Document 2, a silicon single crystal substrate is used. However, since the melting point of silicon is 1414 ° C., a sublimation method that requires heating at 2000 ° C. or higher to sublimate the silicon carbide raw material is used. I can't. Therefore, unless a known CVD method (chemical vapor deposition method) is used in which silane (SiH ₄ ) and propane (C ₃ H ₈ ) are reacted at about 1400 ° C. to grow silicon carbide on the seed crystal substrate. Don't be. However, the crystal growth rate of silicon carbide by the CVD method is about several μm / hour, which is very slow compared to the sublimation method that can obtain a crystal growth rate of several hundred μm / hour or more, and a desired film thickness (about 20 μm). It is necessary to perform crystal growth for a very long time in order to obtain silicon carbide. Furthermore, an extra step of removing the silicon single crystal substrate and a step of performing a heat treatment at 2000 ° C. or higher are necessary, which increases the cost of the manufacturing process. Further, even when the 4H type silicon carbide single crystal film obtained by this method is used as a seed crystal and grown by the sublimation method, the generation probability of 4H type silicon carbide is higher than that of other crystalline polymorphs of silicon carbide. Therefore, the 4H type silicon carbide single crystal does not grow stably.

  In addition, Non-Patent Document 1 does not clearly indicate the necessary growth conditions and the amount of scandium to be doped into a silicon carbide raw material when growing a silicon carbide single crystal using a sublimation method. It only suggests.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for easily and stably growing 4H-type silicon carbide having good crystal quality in the sublimation method.

  The silicon carbide single crystal manufacturing apparatus of the present invention contains a raw material for growing a silicon carbide single crystal in a crucible, and has a seed crystal fixing portion in the crucible for fixing a seed crystal at a position facing the raw material. A silicon carbide single crystal manufacturing apparatus for growing a silicon carbide single crystal on the seed crystal by heating and sublimating the raw material, wherein scandium is added to the raw material in an amount of 2.0 to 3.5% by weight. It is.

  According to the method for growing a silicon carbide single crystal of the present invention, 4H type silicon carbide having good crystallinity can be stably grown without mixing other crystal polymorphs. In addition, although the subject of patent document 1 mentions that adding a heavy metal impurity to a crystal | crystallization is not preferable from a viewpoint of device preparation, since scandium is hardly taken in into the crystal | crystallization of silicon carbide (semiconductor SiC technology and application) : Written by Hiroyuki Matsunami, published by Nikkan Kogyo Shimbun, ISBN 4-526-05096-2), added scandium causes leakage current and does not deteriorate device characteristics.

  Hereinafter, embodiments of a method for growing a silicon carbide single crystal of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic view of a growth apparatus used for growing a silicon carbide single crystal of the present invention. The silicon carbide raw material 2 added with scandium is accommodated in the crucible 1, and the seed crystal substrate 4 is fixed to the convex portion inside the crucible upper lid 3. The growth surface of this single crystal substrate is a (000-1) carbon surface of 4H type silicon carbide crystal. If a (0001) silicon surface is used as the growth surface, the growth of 6H type silicon carbide is dominant, and the growth of 4H type silicon carbide is not observed at all. For this reason, when growing a 4H-type silicon carbide single crystal, it is necessary to use a (000-1) carbon surface as the growth surface of the seed crystal substrate.

  The crucible 1 that houses the silicon carbide raw material 2 uses a temperature of 2000 ° C. or higher necessary for sublimation of silicon carbide. Therefore, the material must be able to withstand the temperature, and for example, a graphite crucible is used. Further, since radiant heat is lost in proportion to the fourth power of the temperature, it is necessary to cover the crucible 1 and the crucible upper lid 3 with the heat insulating material 5 at a high temperature of 2000 ° C. or higher. The crucible 1 and the crucible upper lid 3 covered with the heat insulating material 5 are arranged in a reaction tube 6 made of quartz. The reaction tube 6 has a double tube structure, and is cooled by flowing cooling water 7 during crystal growth. A gas inlet 8 is provided at the upper part of the reaction tube 6, and a gas outlet 9 is provided at the lower part.

  Thereafter, the inside of the reaction tube 6 is replaced with an inert gas, and argon (Ar) is suitable as the inert gas in terms of cost, high purity, and the like. In this inert gas replacement, first, the inside of the reaction tube 6 is evacuated to a high vacuum from the gas exhaust port 9, and then the inert gas is filled from the gas inlet 8 to normal pressure. In order to sufficiently replace the inside of the reaction tube 6 with argon gas, it is better to repeat this process several times.

  Thereafter, by applying a high-frequency current to the coil 10 spirally wound around the reaction tube 6, the crucible 1 and the crucible upper lid 3 are heated at a high frequency to raise the temperature. When raising the temperature, the inside of the reaction tube 6 needs to be kept at a pressure of about several tens of kPa. This is to prevent sublimation of the silicon carbide raw material 2 at low temperatures (below the desired crystal growth temperature) and prevent crystal growth from starting.

  The temperature control at the time of heating is performed by a radiation thermometer 12 through a temperature measuring window 11 made of quartz provided in the upper and lower portions of the reaction tube 6 and a temperature measuring hole provided in the upper and lower portions of the heat insulating material 5. Measure the temperature at the center point (point A in FIG. 1) at the bottom of the crucible 1 and the center point (point B in FIG. 1) at the top of the crucible upper lid 3 and apply feedback to a high-frequency power source (not shown). 10 is carried out by controlling the high-frequency current flowing through 10. Thus, after raising the temperature to a desired temperature, the pressure is gradually reduced to start crystal growth.

  The crystal growth rate of silicon carbide is determined by the temperature of the silicon carbide raw material 2 (proportional to the crucible lower temperature), the temperature gradient in the crucible, and the growth pressure. The growth rate increases as the temperature of the silicon carbide raw material 2 and the temperature gradient in the crucible increase and the growth pressure decreases. However, if the growth rate is too high, the crystallinity of the growing silicon carbide single crystal will deteriorate. On the other hand, when the growth rate is slow, the crystallinity is good, but the growth is slow and there is no industrial practicality. Therefore, the growth rate is preferably in the range of 0.1 to 1.0 mm / hour. Further, the growth pressure during crystal growth is preferably 0.6 to 4.0 kPa, the crucible 1 lower temperature is 2200 to 2350 ° C., and the temperature gradient in the crucible is 5 to 15 ° C./cm.

  The temperature gradient in the crucible is defined as follows from the temperatures of the crucible 1 lower center point A and the crucible upper lid 3 upper center point B.

Temperature gradient in crucible = (temperature of point A−temperature of point B) ÷ crucible height At the end of the growth of the silicon carbide single crystal, the reverse procedure to that at the start of growth is performed. That is, the pressure in the reaction tube 6 is gradually increased to several tens of kPa to stop the sublimation of the raw material from the silicon carbide raw material 2, and then the lower temperature of the crucible 1 is slowly lowered to room temperature.

  A more specific embodiment of the present invention using the above apparatus will be described with reference to FIG. First, nine kinds of silicon carbide raw materials 2 (samples 1 to 9) to which 0 to 4.0 wt% of scandium is added are put in the crucible 1, and the convex portion inside the crucible upper lid 3 so as to face the silicon carbide raw material 2. A seed crystal substrate 4 was fixed to the substrate. The crystal growth surface of the single crystal substrate 4 was a (000-1) carbon surface of 4H type silicon carbide. Thereafter, the crucible 1 and the crucible upper lid 3 on which the silicon carbide raw material 2 and the seed crystal substrate 4 were placed were covered with a heat insulating material 5 and placed in a reaction tube 6 made of quartz.

Thereafter, the inside of the reaction tube 6 is evacuated to a high pressure of 10 ⁻⁷ kPa using a rotary pump and a turbo molecular pump from the gas exhaust port 9, and then argon gas is supplied from the gas inlet 8 to normal pressure. Filled. In order to sufficiently replace the argon gas inside the reaction tube 6, this process was repeated three times, and the pressure inside the reaction tube 6 was adjusted to 80 KPa when the last argon gas was introduced.

  Thereafter, the crucible 1 and the crucible upper lid 3 were heated by flowing a high-frequency current through a coil 10 wound spirally around the reaction tube 6. The temperature control at the time of heating is performed by a radiation thermometer 12 through a temperature measuring window 11 made of quartz provided in the upper and lower portions of the reaction tube 6 and a temperature measuring hole provided in the upper and lower portions of the heat insulating material 5. The temperature at the center point (point A in FIG. 1) at the bottom of the crucible 1 and the center point (point B in FIG. 1) at the top of the crucible upper lid 3 are measured, and feedback is applied to a high-frequency power source (not shown) This was carried out by controlling the high-frequency current flowing through 10.

  In this way, the temperature at the lower center point A of the crucible 1 was slowly raised from room temperature to 2250 ° C. over 2 hours and 30 minutes, and then the pressure in the reaction tube was reduced from 80 kPa to 4 kPa over 1 hour. Crystal growth was started. At this time, the positions of the coil 10 and the crucible 1 are adjusted so that the temperature gradient in the crucible becomes 10 ° C./cm. In this state, crystal growth was performed for 40 hours.

  At the end of growth, contrary to the start of growth, the pressure in the reaction tube 6 was increased to 80 kPa over 1 hour to stop the sublimation of the raw material from the silicon carbide raw material 2 and then slowly cooled to room temperature. .

As described above, the polymorphism of the obtained silicon carbide single crystal was measured and determined by Raman spectroscopy. The results are shown in Table 1.

  As is clear from the results in Table 1, when the silicon carbide raw material 2 of Sample 1 was used, 6H-type silicon carbide single crystals were all obtained. Moreover, when the silicon carbide raw material 2 of the samples 2-4 was used, the silicon carbide single crystal in which 4H type and 6H type were mixed was obtained. When the silicon carbide raw material 2 of samples 5 to 8 was used, 4H type silicon carbide single crystals were obtained in all cases. When the silicon carbide raw material 2 of the sample 9 was used, 4H type silicon carbide crystals were obtained, but polycrystals were mixed, all became single crystals, and good quality silicon carbide crystals were not obtained.

  From the above results, it is understood that scandium may be added to the silicon carbide raw material 2 in the range of 2.0 to 3.5 wt% in order to grow a 4H type silicon carbide single crystal having good crystallinity.

  The silicon carbide single crystal manufacturing apparatus according to the present invention is useful as a manufacturing apparatus capable of selectively manufacturing a 4H type silicon carbide single crystal without adding an extra step.

Diagram of silicon carbide single crystal growth equipment used in the examples

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crucible 2 Silicon carbide raw material 3 Crucible top cover 4 Seed crystal substrate 5 Heat insulating material 6 Reaction tube 7 Cooling water 8 Gas inlet 9 Gas exhaust 10 Coil 11 Temperature measurement window 12 Radiation thermometer

Claims (3)

A raw material for growing a silicon carbide single crystal is housed in a crucible, and a seed crystal fixing portion for fixing a seed crystal at a position facing the raw material is provided in the crucible, and the raw material is heated and sublimated to form the seed crystal. A silicon carbide single crystal manufacturing apparatus for growing a silicon carbide single crystal thereon, wherein 2.0 to 3.5 wt% of scandium is added to the raw material. 2. The silicon carbide single crystal manufacturing apparatus according to claim 1, wherein the growth surface of the seed crystal is a (000-1) carbon surface of 4H type silicon carbide. The growth pressure for growing the silicon carbide crystal is 0.6 to 4 kPa, the temperature of the lower part of the crucible containing the raw material is 2200 to 2350 ° C., and the temperature gradient in the crucible is 5 to 15 ° C./cm. The silicon carbide single crystal manufacturing apparatus according to claim 1, wherein:

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