JP2013103848A - METHOD FOR PRODUCING SiC SINGLE CRYSTAL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a single crystal, which grows a high-quality SiC single crystal at a high speed.SOLUTION: The method for producing the SiC single crystal includes steps of: (a) preparing SiC powder 2a and C powder 3 or partially carbonized SiC powder as raw material powder; and (b) rapidly growing the SiC single crystal while suppressing a silicon droplet by a sublimation method using the raw material powder after the step (a). It is preferable that the ratio of carbon to silicon in the raw material powder is 1.04-1.14 in the step (a) and a temperature difference between the neighborhood of a crystal growth surface and the neighborhood of the raw material powder is 200°C or more in the step (b).

Description

  The present invention relates to a method for producing a SiC single crystal.

  Silicon carbide (SiC) is known as a semiconductor material having excellent thermal and chemical characteristics, and having a forbidden band width larger than that of a silicon (Si) semiconductor, and also having excellent electrical characteristics. In particular, 4H—SiC has already been put into practical use as a semiconductor material for power devices because of its high electron mobility and saturated electron velocity. For further practical use of the SiC substrate, it is required to lower the crystal defect density and to improve the mass productivity to reduce the price.

  Currently, the modified Rayleigh method (sublimation method) is widely used as a method for producing SiC single crystals for semiconductor applications, and currently substrates with a diameter of 100 mm are commercially available, but the problem is that the crystal defect density is large. is there. In the sublimation method, the raw material sublimated at a high temperature in the crucible is diffused to the seed crystal side held at a lower temperature than the raw material by the vapor pressure difference of the active species due to the temperature difference, and recrystallized on the seed crystal. This is a method for growing a single crystal.

Non-Patent Document 1 describes that when SiC sublimates in a graphite crucible, active species such as Si, Si ₂ C, and SiC ₂ are generated and sublimate in a state where the partial pressure of Si is higher than the partial pressure of C. Has been. According to Non-Patent Document 2, when the partial pressure of Si in the gas sublimated from the raw material is higher than the saturation vapor pressure of Si near the growth surface where crystal growth is performed, silicon droplets are formed in the crystal. The This causes a hollow defect along the c-axis, which is called a micropipe, and greatly deteriorates the crystal quality. In order to suppress the generation of silicon droplets, Patent Document 1 proposes to dispose polycrystalline SiC around the seed crystal.

Japanese Patent No. 469394

S.K.Lilov et al., Materials Science and Engineering, B21, 1993, pp.65-69. R.V.Drachev et al., Journal of Crystal Growth, 233, 2001, pp.541-547.

  In order to manufacture a SiC wafer at a low price, it is required to increase the crystal growth rate. In order to increase the growth rate by crystal growth using the sublimation method, the temperature difference between the raw material and the seed crystal must be increased. However, if the temperature difference is increased too much, the vapor pressure of Si in the vicinity of the raw material tends to be larger than the saturated vapor pressure of Si in the vicinity of the seed crystal, and even if the method of Patent Document 1 is used, the surface of the seed crystal or the growth. There is a problem in that silicon droplets are generated on the crystal surface and the crystal quality is greatly deteriorated.

  The present invention has been made to solve the above problems, and an object thereof is to provide a method for growing a high-quality SiC single crystal at high speed.

  The SiC single crystal manufacturing method according to the present invention includes (a) a step of preparing SiC powder and C powder or partially carbonized SiC powder as a raw material powder, and (b) a raw material powder after step (a). And a step of growing a SiC single crystal at a high speed while suppressing silicon droplets by a sublimation method using.

  The SiC single crystal manufacturing method according to the present invention includes (a) a step of preparing SiC powder and C powder or partially carbonized SiC powder as a raw material powder, and (b) a raw material powder after step (a). And a step of growing a SiC single crystal at a high speed while suppressing silicon droplets by a sublimation method using a high-quality SiC single crystal.

1 is a cross-sectional view showing a structure of a single crystal manufacturing apparatus according to Embodiment 1. FIG. 6 is a cross-sectional view showing a structure of a single crystal manufacturing apparatus according to Embodiment 2. FIG. It is sectional drawing which shows the lid | cover which attached the seed crystal. It is a figure which shows the relationship between atmospheric pressure and C / Si in sublimation gas.

(A. Embodiment 1)
<A-1. Device configuration>
FIG. 1 is a cross-sectional view showing a configuration of a single crystal manufacturing apparatus according to Embodiment 1 of the present invention. This single crystal manufacturing apparatus for manufacturing a SiC single crystal using a sublimation method has a configuration in which a crucible 1 to which a lid 4 is attached is covered with a heat insulating material 6.

  In the sublimation method, since the crucible 1 is heated using high frequency induction heating, graphite is used as the material of the crucible 1 in consideration of conductivity and heat resistance. In addition, the crucible 1 is formed in a cylindrical shape because the temperature non-uniformity caused by the skin effect is suppressed and processing is easy. The crucible 1 has an outer diameter of 180 mm, an inner diameter of 160 mm, and a height of 203 mm. The height of the inside of the crucible 1 with the lid 4 attached on the crucible 1 is 173 mm.

  Furthermore, in order to suppress the heat radiation from the crucible 1 and to heat the crucible 1 efficiently, the crucible 1 is covered with a heat insulating material 6. Since the heat insulating material 6 is required to withstand a high temperature of 2400 ° C. and to have a higher resistivity than the graphite crucible, a porous graphite heat insulating material is used.

  The crucible 1 is filled with SiC powder 2a and C powder 3, which become raw material powder for crystal growth. The ratio of carbon (C) and silicon (Si) in the raw material powder is adjusted so that the molar ratio is C: Si = 1.1: 1. Specifically, the SiC powder 2a is 90 g while the C powder 3 is 3000 g. Since carbon is 12 g / mol and silicon is 28 g / mol, SiC 3000 g is 75 mol and carbon 90 g is 7.5 mol. SiC powder 2a has an average particle size of 90 μm and an impurity concentration of generally less than 1 ppm. The C powder 3 has an average particle diameter of 10 μm, and an impurity density of metal impurities such as aluminum, boron, iron, or molybdenum, which are main impurities of SiC, is less than 0.01 ppm.

  A convex pedestal 4a is formed in the inner central portion of the lid 4, and a seed crystal 5 of 4 mm-SiC diameter is attached to the pedestal 4a. The seed crystal 5 has a growth surface facing the raw material powder as a carbon surface. In order to reduce the stress on the ingot obtained by crystal growth, the pedestal 4a is preferably made of a material having a thermal expansion coefficient as close as possible to SiC.

  The reason why the C powder 3 is used as a raw material for crystal growth in addition to the SiC powder 2a is to increase the ratio of carbon to silicon in the gas (raw material gas) sublimated from the raw material powder, that is, C / Si. In the sublimation of SiC, the Si partial pressure is higher than the C partial pressure. That is, since Si sublimes more actively than C, when SiC powder is used as a raw material, C becomes excessive from the raw material as crystal growth proceeds. That is, the sublimation gas of the raw material powder becomes the most Si-rich state immediately after the start of growth.

On the other hand, when the vapor pressure of the active species related to Si (Si, Si ₂ C, SiC ₂ ) sublimated from the raw material powder is higher than the saturated vapor pressure of Si on the surface of the seed crystal 5, silicon droplets are formed on the crystal growth surface. Occur. This state occurs when the temperature difference between the raw material and the seed crystal is large.

  However, since the crystal growth rate is determined by the difference between the vapor pressure of the active species near the raw material powder and the vapor pressure of the active species on the growth surface, in order to increase the crystal growth rate, the temperature between the raw material powder and the seed crystal 5 is increased. It is necessary to increase the difference. That is, silicon droplets are likely to be generated under conditions where the growth rate is high.

  Therefore, in the present embodiment, SiC powder sublimated from SiC powder 2a is reacted with C powder 3 by adding C powder 3 to SiC powder 2a to form a raw material powder. Thereby, C / Si in the raw material gas is made higher than in the case where the C powder 3 is not added to the raw material powder, thereby avoiding the situation of being Si-rich at the start of crystal growth. Thereby, even if the temperature difference between the raw material powder and the seed crystal 5 is increased, it is possible to grow at a high growth rate while suppressing the generation of silicon droplets.

  In addition, in FIG. 1, a mode that C powder 3 is filled in the bottom part of raw material powder is shown. In the sublimation method, a temperature distribution in which the bottom of the crucible 1 is the highest temperature is employed in order to efficiently sublimate the raw material powder. Since SiC sublimation occurs from the bottom of the raw material powder having the highest temperature, the sublimation gas from C powder 3 and SiC powder 2a can be efficiently reacted by filling the C powder 3 into the raw material bottom.

<A-2. Manufacturing process>
A crystal growth process using the single crystal manufacturing apparatus shown in FIG. 1 will be described below.

  First, the C powder 3 and the SiC powder 2a are put into the crucible 1 and the lid 4 is attached. Then, the periphery is covered with a heat insulating material 6 and installed in the furnace.

Next, the inside of the furnace is evacuated (exhaust) to a level of 10 ⁻⁴ Pa to remove residual nitrogen and oxygen, and then the inside of the furnace is filled with argon as an inert gas, and the pressure is maintained at 800 hPa. In this state, the crucible 1 is heated by induction heating until the bottom temperature reaches 2400 ° C., which is the SiC growth temperature. The frequency of the oscillator of the heating means is 10 kHz.

  Subsequently, while maintaining the temperature of the crucible 1, the pressure in the furnace is reduced to 3.3 hPa, which is the SiC growth pressure, over 90 minutes. When the pressure in the furnace reaches the growth pressure, the growth of the SiC single crystal from the seed crystal 5 starts. At this time, the upper temperature of the crucible 1, that is, the temperature near the crystal growth surface is 2100 ° C. This state is maintained for 50 hours, and crystal growth is performed.

  Thereafter, the furnace is filled with argon, the pressure is increased to 900 hPa, and crystal growth is terminated. After the temperature of the crucible 1 is lowered to room temperature over 28 hours, the crucible 1 is taken out from the furnace, and the ingot is taken out from the crucible 1.

The ingot thus produced had a diameter of 112 mm, a growth height of 52.4 mm, and a very high growth rate of 1.048 mm / h. This large growth rate was obtained by setting the temperature of the crucible to 2400 ° C. at the bottom and 2100 ° C. at the top, and realizing a temperature difference of 300 ° C. or more. A growth rate of 0.7 mm / h or more can be obtained when the temperature difference is 200 ° C. or more. The ingot was peripherally ground to a diameter of 100 mm, sliced into a wafer with a wire saw, the silicon surface was polished with diamond abrasive grains, and then subjected to chemical mechanical polishing (CMP). Then, etching was performed with molten KOH heated to 500 ° C. to make etch pits appear, and the number of etch pits caused by micropipes was counted. The number of micropipes was 8, and crystals with a very low micropipe density of 0.10 / cm ² were obtained. Moreover, when mapping of the X-ray rocking curve measurement was performed on the entire wafer surface, the average value of the full width at half maximum was 18 seconds or less, and it was confirmed that the crystal orientation was excellent.

  In the present embodiment, the raw material C / Si is set to 1.1, but C / Si is preferably in the range of 1.04 to 1.14. When C / Si is smaller than 1.04, the vapor pressure of Si in the gas sublimated from the raw material at the initial stage of crystal growth tends to be higher than the saturated vapor pressure of Si on the growth surface. For this reason, silicon droplets are formed on the crystal growth surface, and many defects such as micropipes are generated to deteriorate the crystal quality. On the other hand, if C / Si is larger than 1.14, C / Si becomes too large when crystal growth proceeds, so that carbon inclusion is easily formed. As a result, defects such as micropipes are formed and the crystal quality deteriorates.

<Effect>
In the method for producing a SiC single crystal according to the present embodiment, since the ratio of carbon to silicon of the raw material powder is 1.04 to 1.14, the sublimation gas of the raw material powder should not be silicon-rich. , Silicon droplets can be suppressed.

  In addition, the SiC single crystal manufacturing method according to the present embodiment forms a SiC single crystal while suppressing a silicon drop by a sublimation method after setting the temperature difference between the crystal growth surface and the raw material powder to 200 ° C. or more. Therefore, a high-quality SiC single crystal can be formed at high speed.

  Moreover, in the manufacturing method of the SiC single crystal which concerns on this Embodiment, when using SiC powder 2a and C powder 3 for raw material powder, the sublimation method is performed in the state which filled C powder 3 in the bottom part in raw material powder. In the sublimation method, a temperature distribution in which the bottom of the crucible 1 is the highest temperature is employed in order to efficiently sublimate the raw material powder. Since SiC sublimation occurs from the bottom of the raw material powder having the highest temperature, the sublimation gas from C powder 3 and SiC powder 2a can be efficiently reacted by filling the C powder 3 into the raw material bottom.

  Further, in the method for manufacturing a SiC single crystal according to the present embodiment, the SiC single crystal is grown at a rate of 0.7 mm / h or more, so that the mass productivity of the SiC single crystal is improved while suppressing silicon droplets. I can do it.

(Embodiment 2)
In the first embodiment, C / Si in the sublimation gas of the raw material powder is increased by adding C powder 3 to SiC powder 2a. In Embodiment 2, only SiC powder 2a is used as a raw material powder, and C / Si in the sublimation gas of the raw material powder is increased by sublimating part of SiC powder 2a by performing preheating.

  Hereinafter, the manufacturing method of the SiC single crystal which concerns on Embodiment 2 is demonstrated using FIG. In FIG. 2, the same components as those in FIG. 1 are denoted by the same reference numerals.

  First, when the SiC powder 2 a is put into the crucible 1 and the preheating lid 7 on which the seed crystal is not attached is attached, the heat insulating material 6 is installed around the crucible 1. The preheating lid 7 is detachably attached to the crucible 1 without being fixed with an adhesive or the like.

These are installed in an induction heating furnace, and the pressure in the furnace is evacuated to a level of 10 ⁻⁴ Pa to remove residual nitrogen and oxygen. Thereafter, after filling the furnace with argon as an inert gas, the furnace pressure is again evacuated to 1.0 Pa. And it heats over 1 hour until the temperature of the crucible 1 becomes 1500 degreeC, and hold | maintains in the state of 1500 degreeC for 1 hour. Thereafter, the furnace is filled with argon and held at 800 hPa, the temperature of the crucible 1 is lowered to room temperature, and the crucible 1 is taken out.

  Next, the preheating lid 7 is removed from the crucible 1, and instead the lid 4 shown in FIG. 3 in which the pedestal 4 a and the seed crystal 5 are installed in advance is attached to the crucible 1. And the heat insulating material 6 is again installed around these, and it installs in a furnace.

  Thereafter, the crystal is grown from the seed crystal 5 in the same process as described in the first embodiment.

By carrying out crystal growth for 50 hours, a crystal having a diameter of 112 mm and a growth height of 51.5 mm was obtained, and the growth rate was a very large value of 1.03 mm / h. The micropipe density measured by the same method as in the first embodiment is 0.11 / cm ² , and the average half-value width of the X-ray rocking curve is 18 seconds or less, so that a very high quality crystal can be obtained. It was.

  In the second embodiment, the SiC powder 2a is slightly sublimated by performing the preheating treatment before crystal growth, so that C / Si of the sublimation gas can be made larger than 1. Therefore, it is possible to prevent the Si-rich state at the initial stage of growth, and it is possible to advance the crystal growth without generating silicon droplets even if the crystal growth is performed under the condition that the growth rate is increased. Become.

  FIG. 3 shows a simulation result of C / Si at the active species vapor pressure when the atmospheric pressure in the furnace is changed. This result shows that C / Si decreases when the atmospheric pressure is lowered, that is, the desorption of Si from SiC is promoted.

  Therefore, from the viewpoint of promoting the effect of preheating, it is desirable to lower the atmospheric pressure during preheating, and it may be less than 20 Pa. For example, preliminary heating may be performed while evacuating with an oil rotary vacuum pump. The pressure in the furnace during preheating depends on the pumping capacity.

  The preheating temperature is preferably 1300 ° C. or higher and lower than 1800 ° C. At a temperature of 1300 ° C. or lower, the raw material SiC does not sublime and the effect of preheating cannot be obtained. Moreover, when preheating is performed at a high temperature of 1800 ° C. or higher, the raw material is excessively sublimated, and C / Si at the initial growth stage becomes too large. In this case, carbon inclusions are likely to be formed in the crystal, causing deterioration of crystal quality.

  Since the temperature and pressure at the time of preheating affect the crystal quality, it is required to optimize the crystal growth conditions according to each crystal growth furnace.

  Further, by performing preheating, it is possible to remove impurities adhering to the raw material and the crucible, so that a single crystal having a high purity and a low defect density can be obtained in a short time.

<Effect>
The SiC single crystal manufacturing method according to the present invention includes (a) a step of preparing SiC powder 2a and C powder 3 or a partially carbonized SiC powder 2b as a raw material powder, and (b) after step (a). And a step of growing a SiC single crystal at a high speed while suppressing silicon droplets by a sublimation method using a raw material powder, so that a high-quality SiC single crystal can be formed at a high speed.

  In the method for producing an SiC single crystal according to the second embodiment, the step of preparing partially carbonized SiC powder 2b as a raw material powder in step (a) includes (a1) crucible 1 filled with SiC powder 2b. The step (b) includes a step of heat treatment without disposing the seed crystal, and after the step (b1) (a1), the gas in the crucible 1 is exhausted and then the seed crystal 5 is disposed in the crucible 1, A step of crystal growth from the seed crystal 5 is provided. In the step (a1), a certain amount of Si is desorbed from the SiC powder 2b to increase C / Si as a raw material, and then crystal growth is performed by a sublimation method, so that silicon droplets can be suppressed.

  Further, in the step (a1), the raw material powder is heat-treated at 1300 ° C. or higher and lower than 1800 ° C., so that C / Si of the raw material can be increased to such an extent that no carbon inclusion is formed in the step (b).

  In the step (a1), Si can be efficiently desorbed from the raw material powder by heat-treating the raw material powder at an atmospheric pressure of 20 Pa or less.

  In the present invention, the embodiments can be appropriately modified and omitted within the scope of the invention.

  1 crucible, 2a, 2b SiC powder, 3C powder, 4 lid, 4a pedestal, 5 seed crystal, 6 heat insulating material, 7 lid for preheating.

Claims (8)

(A) a step of preparing SiC powder and C powder or partially carbonized SiC powder as a raw material powder;
(B) After the step (a), a step of growing a SiC single crystal at a high speed while suppressing silicon droplets by a sublimation method using the raw material powder.
A method for producing a SiC single crystal. The step (a) is a step in which the ratio of carbon to silicon in the raw material powder is 1.04 to 1.14.
The manufacturing method of the SiC single crystal of Claim 1. In the step (b), the temperature difference between the vicinity of the crystal growth surface and the raw material powder is set to 200 ° C. or more.
The manufacturing method of the SiC single crystal of Claim 1 or 2. When preparing the SiC powder and C powder as the raw material powder in the step (a),
The step (b) is a step of executing the sublimation method in a state where the bottom portion in the raw material powder is filled with the C powder.
The manufacturing method of the SiC single crystal in any one of Claims 1-3. The step of preparing the partially carbonized SiC powder as the raw material powder in the step (a),
(A1) comprising a step of heat-treating without placing a seed crystal in a crucible filled with SiC powder;
The step (b)
(B1) After the step (a1), the method includes the steps of evacuating the gas in the crucible, placing a seed crystal in the crucible, and growing crystals from the seed crystal.
The manufacturing method of the SiC single crystal in any one of Claims 1-3. The step (a1) is a step of heat-treating the raw material powder at 1300 ° C. or more and less than 1800 ° C.,
The manufacturing method of the SiC single crystal of Claim 5. The step (a1) is a step of heat-treating the raw material powder at an atmospheric pressure of 20 Pa or less.
The manufacturing method of the SiC single crystal of Claim 5 or 6. The step (b) is a step of growing the SiC single crystal at a rate of 0.7 mm / h or more.
The manufacturing method of the SiC single crystal in any one of Claims 1-7.

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