JP4872283B2 - Single crystal manufacturing apparatus and manufacturing method - Google Patents

Description

  The present invention relates to a crucible for producing a single crystal, and can be suitably used particularly for producing a silicon carbide single crystal.

  Conventionally, a sublimation method has been widely used as a method for growing a silicon carbide single crystal. The sublimation method is also called the modified Rayleigh method. A seed crystal substrate composed of a silicon carbide single crystal and a raw material powder are placed on a graphite pedestal placed in a graphite crucible, and sublimation gas is generated from the raw material powder by heating the graphite crucible, and the raw material powder and the single crystal Since the concentration difference of the sublimation gas occurs between the substrate and the sublimation gas, the sublimation gas diffuses to the single crystal substrate, and the supersaturation in the vicinity of the single crystal substrate serves as a driving force to progress the single crystal growth. The composition of the sublimation gas generated when silicon carbide is used as a raw material is Si, SiC2, Si2C, Si2, Si3, etc. In particular, Si, SiC2, and Si2C are considered to have important equilibrium partial pressures.

  A general sublimation silicon carbide single crystal growth method will be described in detail with reference to FIG. The graphite crucible 1 is composed of a crucible lower member 1a, a crucible middle member 1b, and a crucible upper member 1c. A seed crystal 3 composed of crystals is attached. Single crystal growth proceeds in a single crystal growth space 4 formed by being surrounded by graphite crucible 1, raw material powder 2 and seed crystal 3.

  As a material of the graphite member 1, a substance other than graphite, such as a high melting point substance or a high melting point substance coated graphite, may be partially used. However, since most members are usually made of graphite, This is called a graphite crucible 1. In addition, since there is a degree of freedom in crucible design, the number of crucible members may not be three as shown in FIG. 8, but from the functional aspect, the crucible lower member in which the raw material powder is arranged, and the crucible in which the single crystal growth space is formed The crucible upper member for fixing the member and the seed crystal can be classified as described above. As raw material powder 2, silicon carbide powder is generally used, but silicon, carbon, or a dopant may be added to silicon carbide depending on the purpose.

  The heat insulating material 5 is arranged so as to surround the periphery of the crucible 1, and a high frequency current of 20 kHz, for example, is passed through the high frequency work coil 6 by several hundred A, whereby the graphite crucible 1 is induction heated to 2000 ° C. or higher. The temperature distribution can be controlled by the design of the graphite crucible 1, the design of the heat insulating material 5, the positional relationship with the high frequency work coil 6, the crucible lower member 1 a at 2200 to 2500 ° C., and the crucible upper member 1 c at the crucible. Heat to a temperature 50 to 200 ° C. lower than the lower member 1a. With such a temperature distribution, the sublimation gas is stably transported from the raw material powder 2 to the seed crystal 3, and stable growth is performed. The temperature is measured with a non-contact thermometer.

  FIG. 9 shows a schematic diagram after the single crystal growth. When the single crystal is grown, the grown single crystal 3a grown on the seed crystal 3 and the silicon carbide polycrystal 7 attached to the inner wall of the crucible do not come into contact with each other. (Hereinafter referred to as single crystal separation growth) is important, and it has been conventionally known to produce high quality silicon carbide by performing single crystal separation growth under different crucible designs and conditions. (For example, refer to Patent Document 1 and Patent Document 2).

  FIG. 10 shows a schematic diagram in the case where the single crystal separation growth is not performed. When the grown single crystal 3a grown on the seed crystal 3 comes into contact with the silicon carbide polycrystal 7 attached to the inner wall of the crucible, stress is applied to the grown single crystal 3a to cause dislocations and cracks, or in the silicon carbide polycrystal 7 Since crystal defects easily propagate into the grown single crystal 3a, it becomes difficult to produce high-quality silicon carbide.

  However, the silicon carbide single crystal growth by the sublimation method described above has a problem that the crystal growth rate is slow. The growth rate of the crystal is mainly determined by the growth temperature, growth pressure, and crucible design, but there are optimum conditions for maintaining the crystal polymorphism in the growth temperature and growth pressure. Crystal quality is liable to deteriorate due to the inclusion of polymorphs. For this reason, the growth temperature and pressure need to be almost determined according to the desired crystal polymorphism, and the crucible design has constraints from the standpoint of single crystal separation growth. Difficult to do.

  Therefore, it has been difficult to improve the growth rate of the silicon carbide single crystal with the conventional technique. In particular, the larger the single crystal diameter is, the slower the growth rate becomes. Therefore, the improvement of the crystal growth rate is an important issue. Further, since the temperature of the raw material powder 2 is non-uniform, there is a problem that the method of consumption of the raw material is non-uniform and the generated sublimation gas is non-uniform.

To solve these problems, as shown in FIG. 11, by installing a substantially axisymmetric heat conductor in the graphite crucible, the temperature of the central portion in the graphite crucible is increased, and the material consumption is made uniform and used. A technique for improving the efficiency is described (for example, see Patent Document 3).
In addition, by installing a hollow heat transfer body with a thin upper part and a thick lower part in the graphite crucible, the temperature inside the graphite crucible is made uniform, and even when the material is grown for a long time while suppressing changes in raw material consumption, A technique for ensuring uniformity and improving the use efficiency of raw materials is described (for example, see Patent Document 4).
Japanese Unexamined Patent Publication No. 01-108200 Japanese Patent Laid-Open No. 05-319998 JP-A-5-58774 Japanese Patent Laid-Open No. 2001-72491

  However, with the conventional configuration, it is difficult to improve the problem of non-uniform raw material consumption and the growth rate at the same time. For example, the technique described in Patent Document 3 cannot improve the crystal growth rate. Further, in the technique described in Patent Document 4, since the inside of the heat transfer body is hollow, the raw material powder filling amount is greatly reduced, so that the growth rate is likely to be lowered. Furthermore, it is difficult to respond to the increase in size and length of single crystals, and it is not suitable for general mass production equipment.

  The present invention solves the above-described conventional problems, and satisfies the growth rate improvement and uniform material consumption at the same time, and aims to provide a single crystal manufacturing apparatus capable of efficiently manufacturing a high-quality single crystal. To do.

In order to solve the above-described conventional problems, the single crystal production apparatus of the present invention includes a graphite crucible, a seed crystal fixed inside the graphite crucible, and a raw material powder disposed in the graphite crucible. And a single crystal manufacturing apparatus provided with a high frequency work coil for heating the graphite crucible and the raw material powder , a cylindrical heat having an outer diameter in the range of 2/15 to 2/3 of the crucible inner diameter. The conductive member is arranged at the center of the graphite crucible where the raw material powder is arranged so as not to contact the inner wall of the graphite crucible .

According to the single crystal manufacturing apparatus of the present invention, it is possible to simultaneously improve the growth rate and make the material consumption uniform, and to manufacture a high quality single crystal efficiently.

Embodiments of a single crystal production apparatus of the present invention will be described below in detail with reference to the drawings.

  FIG. 1 shows a schematic diagram of a single crystal manufacturing apparatus in a first embodiment of the present invention. In FIG. 1, a graphite crucible 1 includes a crucible upper member 1c, a crucible middle member 1b, and a crucible lower member 1a, and has a height of 150 mm and an outer diameter of 60 mm. The diameter of the seed crystal attachment portion 1d is 10 mm, the inner diameter of the crucible lower member 1a is 30 mm, the height direction of the raw material powder 2 is 76 mm, and the diameter of the seed crystal 3 is approximately 10 mm. The vertical position of the high-frequency work coil 6 is adjusted so that the center thereof is within a range of plus or minus 20 mm from the center of the graphite crucible 1, and large Joule heat is generated in the crucible middle member 1b and the crucible lower member 1a. The diameter of the heat conductor 10 was 6 mm, the height was 50 mm, and the material was graphite. In addition to graphite, a refractory metal such as tantalum or a refractory material such as refractory carbide may be used, but graphite is selected from the viewpoint of cost.

  A method for accurately placing the heat conductor 10 in the raw material powder 2 at a desired position will be described. First, as shown in FIG. 2 (a), when a predetermined amount of the first raw material powder 2a, 26.3g in this case, was charged into the crucible lower member 1a, the crucible lower member 1a was filled with 21 mm in the height direction. Next, a heat conductor placement jig 11 shown in FIG. 3 is prepared. Here, the heat conductor placement jig 11 is approximately rotationally symmetric, such as a combination of a disk and a cylinder. The cylindrical part is referred to as a guide part 11a, and an area where a part of a disk is cut out is referred to as a raw material powder input part 11b. The inner diameter of the guide portion 11a was 6.1 mm. As shown in FIG. 2B, the heat conductor placement jig 11 is placed on the crucible lower member 1a, and the heat conductor 10 is placed on the upper part of the first raw material powder 2a through the guide portion 11a. The body 10 can be accurately arranged at the axial center of the crucible lower member 1a.

  Next, as shown in FIG. 2C, 60 g of the second raw material powder 2 b was charged from the raw material powder charging portion 11 b of the heat conductor arranging jig 11. Here, if the raw material powder is charged by rotating the heat conductor placement jig 11 a plurality of times with respect to the central axis, the raw material powder can be uniformly filled while suppressing the bias of the raw material powder. Next, as shown in FIG. 2 (d), the heat conductor placement jig 11 is removed from the crucible lower member 1a, a predetermined amount of the third raw material powder 2c is charged, the second raw material powder 2b and the third raw material powder 2c. By making the total weight of 66.3 g, the total height of the first, second, and third raw material powders could be filled to 76 mm. Thus, by using the heat conductor placement jig 11, the heat conductor 10 can be accurately placed on the central axis of the crucible lower member 1a.

  The heat conductor placement jig 11 may be other than the one shown in FIG. 3 as long as it has the guide portion 11a and the raw material powder input portion 11b. For example, even the one shown in FIG. 4 can be arranged with high accuracy.

After arranging the heat conductor 10 as described above, the crucible middle member 1b, the crucible upper member 1c, and the like were attached, arranged inside the heat insulating material 5, and arranged in the reaction tube. After reducing the pressure in the reaction tube to 3.0 × 10 ⁻⁴ Pa, the graphite crucible 1 is heated to 1200 ° C. or higher, and argon gas is charged to 8.0 × 10 ⁴ Pa, the graphite crucible 1 is heated, The current was controlled so that the lower temperature of the crucible was 2300 ° C. Thereafter, the argon atmosphere pressure was reduced to 2.7 × 10 ³ Pa to grow a silicon carbide single crystal. The crystal growth time was 12 hours.

(Comparative Example 1)
For comparison, crystals were grown without arranging a heat conductor as shown in FIG. Other conditions such as the dimensions of the graphite crucible 1, the position of the high frequency coil, the growth temperature, the growth pressure, and the growth time are the same as those in the first embodiment. The growth rate was derived by dividing the amount of vertical crystal growth by the growth time.

  Comparing Example 1 and Comparative Example 1, the growth rate of 304 μm / h in Example 1 is 195 μm / h in Comparative Example 1, and the crystal growth in Example 1 grows about 56% faster. This is presumably because the temperature of the raw material powder was increased and the use efficiency of the raw material was improved by arranging the heat conductor in the raw material powder.

  The thermal conductivity of the thermal conductor (graphite) used in this experiment is about 70 W / m · K, and the thermal conductivity of polycrystalline silicon carbide is about 0.1 W / m · K. In order to show temperature dependence, the thermal conductivity at a high temperature around 2300 ° C. is larger by two digits or more. For this reason, it is considered that the temperature of the raw material powder 2 becomes more uniform than before, and the consumption of the raw material and generation of sublimation gas become uniform. As a result, the single crystal growth conditions are more stable, and the flying of the soot-like substance from the locally carbonized raw material powder is reduced, so that the single crystal quality is improved.

  As described above, according to the present invention, it is possible to simultaneously improve the growth rate and make the material consumption uniform, and to produce a high-quality single crystal efficiently.

  As Example 2, as shown in FIG. 5, the upper end of the heat conductor 10 was arranged to be exposed in the single crystal growth space 4. In order to arrange the heat conductor 10 at a predetermined position, the heat conductor 10 was arranged in the same manner using the above-described heat conductor arranging jig 11. Other growth conditions such as the dimensions, growth temperature, growth pressure, and growth time of the graphite crucible 1 and the heat conductor 10 are the same as those in the first embodiment.

  The crystal growth rate in Example 2 was 290 μm / h, and the growth rate was improved by 49% compared with Comparative Example 1 which is a conventional technique. Further, it is considered that the consumption of the raw material becomes more uniform than in the past due to the arrangement of the heat conductor, and the generated sublimation gas is also uniform. Thus, the present invention is also effective in this embodiment. Therefore, it is desirable that the surface of the heat conductor 10 is in contact with the raw material powder as shown in Example 1, but it is effective even if the upper end of the heat conductor 10 is exposed to the growth space as in Example 2. can get.

  As shown in FIG. 6, a ring-shaped heat conductor 12 having an outer diameter of 20 mm, an inner diameter of 16 mm, and a height of 70 mm was disposed in the graphite crucible described above. Other growth conditions such as dimensions, growth temperature, growth pressure, and growth time of the graphite crucible 1 are the same as those in the first embodiment.

  The crystal growth rate in Example 3 was 238 μm / h, and the crystal growth rate was improved by 22% compared with Comparative Example 1 which is a conventional technique. Further, it is considered that the consumption of the raw material becomes more uniform than in the past due to the arrangement of the heat conductor, and the generated sublimation gas is also uniform. Thus, the present invention is effective even with a ring-shaped heat conductor.

(Comparative Example 2)
As shown in FIG. 11, the graphite crucible was processed so that the lower end of the heat conductor 10 was in contact with the crucible lower portion 1a, and the raw material powder was filled to a height of 76 mm. Thereafter, the same growth as in Example 1 was performed. Other growth conditions such as growth temperature, growth pressure, and growth time are the same as those in the first embodiment.

  The crystal growth rate in Comparative Example 2 was 214 μm / h, an improvement of 9% compared to Comparative Example 1, and a great effect was not obtained. Therefore, in the case of the prior art in which the heat conductor is disposed in contact with the bottom of the crucible, uniform consumption of the raw material can be achieved, but the effect of improving the growth rate is considered to be limited. This is because heat transfer from the upper part of the raw material powder to the lower part of the raw material powder is difficult because the heat transfer between the thermal conductor 10 and the crucible lower part 1a is easy in Comparative Example 2, and the temperature of the raw material powder is unlikely to rise. . If the temperature distribution is changed so that the temperature of the lower part of the raw material powder is higher than that of the upper part of the raw material powder by changing the high-frequency coil, etc., there is a possibility that a large increase in the growth rate can be obtained with this conventional technique. There is a problem that the silicon carbide polycrystal 7 adhering to the silicon oxide tends to adhere to the grown single crystal 3a, and the crystal defects easily increase.

  As described in Examples 1 to 3, the shape of the heat conductor is preferably a columnar shape, but may be a cylindrical shape. In addition, if it is generally axially symmetric, the effect can be obtained with other shapes. Further, a plurality of heat conductors may be used in combination, for example, a rod-like heat conductor 10 and a ring-like heat conductor 12 may be used in combination as shown in FIG. If the outer diameter of the heat conductor is too small, a sufficient effect cannot be obtained, so 4 mm or more is preferable, and if it is too large, it may be an obstacle to transport of sublimation gas generated from the raw material powder, so 20 mm or less is preferable. .

  The method for producing a silicon carbide single crystal according to the present invention can simultaneously improve the growth rate and make the material consumption uniform, and can efficiently produce a high-quality single crystal, and particularly a high-quality silicon carbide single-crystal substrate. It is useful as a method for efficiently producing.

  The method for producing a silicon carbide single crystal according to the present invention can also be applied to other material materials produced by a sublimation method.

The schematic diagram which shows the silicon carbide single crystal manufacturing apparatus in Example 1 of this invention The schematic diagram which shows the arrangement | positioning method of the heat conductor in Example 1 of this invention. The schematic diagram of the heat conductor arrangement | positioning jig | tool in Example 1 of this invention. Schematic diagram showing another form of heat conductor placement jig Schematic diagram of a silicon carbide single crystal manufacturing apparatus in Example 2 of the present invention Schematic diagram of a silicon carbide single crystal growth apparatus in Example 3 of the present invention Schematic diagram showing another embodiment of the present invention Schematic diagram showing a conventional silicon carbide single crystal manufacturing device Schematic diagram showing the silicon carbide single crystal manufacturing equipment after growth Schematic diagram showing a silicon carbide single crystal manufacturing device that is not single crystal separate growth Schematic diagram showing a conventional silicon carbide single crystal growth apparatus

Explanation of symbols

1 graphite crucible 1a crucible lower member 1b crucible middle member 1c crucible upper member 1d seed crystal mounting portion 1e gas guide portion 2 raw material powder 2a first raw material powder 2b second raw material powder 2c third raw material powder 3 seed crystal 3a Growth single crystal 4 Single crystal growth space 5 Heat insulating material 6 High frequency work coil 7 Silicon carbide polycrystal 10 Thermal conductor 11 Thermal conductor placement jig 11a Guide portion 11b Raw material powder input portion 12 Ring-shaped thermal conductor

Claims (3)

A graphite crucible;
A seed crystal fixed inside the graphite crucible;
Raw material powder disposed in the graphite crucible,
In the single crystal manufacturing apparatus provided with a high frequency work coil for heating the graphite crucible and the raw material powder,
The center of the graphite crucible in which the raw material powder is arranged so that a cylindrical heat conducting member whose outer diameter is in the range of 2/15 to 2/3 of the crucible inner diameter does not contact the inner wall of the graphite crucible An apparatus for producing a single crystal, wherein The single crystal manufacturing apparatus according to claim 1, wherein the heat conducting member is a metal or a metal carbide having a melting point higher than a growth temperature of the single crystal. The single crystal manufacturing apparatus according to claim 1, wherein the heat conducting member is graphite.

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