JP2012254892A - Manufacturing method and manufacturing device for single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method that obtains a single crystal with high quality and long size.SOLUTION: In a crucible 1, a raw material 2 of the single crystal 9 and a seed crystal 4 are set oppositely. In the crucible 1, a guide 3 which guides a sublimated gas from the raw material 2 into the seed crystal 4 and a tantalum ring 6 comprising tantalum or tantalum carbide which encloses the surrounding of the seed crystal 4 are set. In a closed space surrounded by the inside of the crucible 1, the guide 3 and the tantalum ring 6, thermal insulation material 5 is arranged. By heating the crucible 1 of the structure described above, the single crystal 9 is developed on the seed crystal 4 by sublimating the raw material 2.

Description

  The present invention relates to a method and apparatus for producing a single crystal such as silicon carbide (SiC).

  A silicon carbide (SiC) semiconductor 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 excellent in electrical characteristics. Yes. In particular, 4H-type SiC is used as a semiconductor material for power devices because of its high electron mobility and saturated electron velocity.

  As a method for obtaining a single crystal as a semiconductor, an improved Rayleigh method (sublimation method) is widely used. The production of SiC single crystal by the sublimation method involves placing a seed crystal (seed substrate), which is an SiC single crystal, and an SiC raw material facing each other in a crucible, and evacuating (evacuating) the inside of the crucible to prevent the use of argon (Ar) or the like. After air substitution with the active gas, the crucible is heated to a high temperature (about 2300 ° C.), and the SiC raw material is sublimated. At this time, by holding the seed crystal at a temperature lower than that of the raw material, the gas (raw material gas) sublimated from the raw material diffuses according to the temperature gradient, reaches the surface of the seed crystal, and an SiC single crystal ingot grows.

  As a method for heating the crucible at this time, an induction heating method using a high frequency is generally used. The induction heating method utilizes the fact that a conductor generates heat due to an induction current generated in the conductor by a high frequency. For this reason, the material of the crucible is required to have conductivity and be able to withstand at high temperatures. Therefore, graphite is generally used as the crucible material. As the shape of the crucible, a cylindrical one is used in order to eliminate temperature non-uniformity due to the skin effect due to high frequency induction heating and to facilitate processing.

  Currently, SiC substrates with a diameter of up to 100 mm are commercially available, but since the crystal defect density is high, it is necessary to further reduce the crystal defect density for use as a semiconductor application. Also, considering the mass productivity of semiconductor devices, it is essential to increase the diameter and length of SiC single crystals.

  For example, Patent Document 1 below discloses a method effective for lengthening a SiC single crystal. In Patent Document 1, a tapered guide is provided in the crucible, and the raw material gas is efficiently collected on the seed crystal by controlling the flow of the raw material gas in the crucible.

  The source gas that has not contributed to the growth of the ingot crystallizes around the pedestal on which the seed crystal is fixed, and becomes polycrystalline. When a polycrystal exists around the single crystal, defects are introduced from the polycrystal into the single crystal. For this reason, in order to produce a single crystal ingot with few defects, it is necessary to grow only the single crystal independently.

  In the method of Patent Document 1, in order to separate and grow a single crystal and a polycrystal, it is necessary to set the guide at a higher temperature than the seed crystal (or growing ingot). However, as the crystal growth progresses and the ingot becomes longer, it is considered that the temperature distribution changes and the temperature of the guide decreases. Alternatively, as a result of the growth of the ingot, the flow of the raw material gas passing between the side surface of the ingot and the guide is hindered, and polycrystal is deposited on the inner wall of the guide, which is integrated with the single crystal and adversely affects the quality of the ingot.

  In order to prevent this, in Patent Document 2 below, a heat insulating material such as graphite felt is disposed on the upper part of the guide in the crucible to suppress the temperature drop of the guide.

Japanese Patent No. 3961750 JP 2010-585309 A

  However, in the method of Patent Document 2, the graphite heat insulating material disposed in the crucible is etched by the source gas that has reached the periphery of the pedestal without contributing to the growth of the ingot or by heat. When the carbon particles generated by the etching reach the single crystal, the carbon particles are taken into the single crystal and become carbon inclusion, thereby deteriorating the quality of the single crystal.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a single crystal manufacturing method and a manufacturing apparatus capable of obtaining a high-quality and long single crystal.

  The method for producing a single crystal according to the present invention includes (a) a step of disposing a single crystal raw material and a seed substrate in a crucible, and (b) tantalum or tantalum carbide surrounding the seed substrate in the crucible. And (c) a step of growing a single crystal on the main substrate by heating the crucible and sublimating the raw material.

  According to the present invention, the graphite particles generated by etching the inner wall of the crucible react with the tantalum ring, and tantalum becomes tantalum carbide. As a result, the graphite particles can be prevented from reaching the crystal growth space, so that the inclusion of carbon inclusions in the single crystal can be suppressed. For this reason, a high quality long single crystal can be manufactured.

3 is a cross-sectional view showing a configuration of a crucible of the crystal growth apparatus according to Embodiment 1. FIG. 6 is a cross-sectional view showing the structure of a crucible of a crystal growth apparatus according to Embodiment 2. FIG.

<Embodiment 1>
FIG. 1 is a view for explaining the structure of a single crystal manufacturing apparatus according to Embodiment 1 of the present invention, and shows a cross section of a crucible of the apparatus. The crucible 1 is made of graphite, and includes a raw material storage container 1a for storing the SiC raw material 2 and a lid 1b having a pedestal 7 on which a seed crystal can be attached to face the raw material 2. Further, a guide 3 is provided on the inner side surface of the raw material storage container 1 a so that one end thereof is in contact with the inner wall of the raw material storage container 1 a and guides the gas sublimated from the raw material 2 to the base 7. In FIG. 1, the seed crystal 4 attached to the pedestal 7 and the ingot 9 growing on the surface thereof are also illustrated.

The guide 3 is a cylindrical member extending toward the seed crystal 4 fixed to the pedestal 7, and guides the raw material gas sublimated from the raw material 2 to the pedestal 7. The guide 3 is installed in the crucible 1 by placing a flange portion provided at the lower end thereof on a stepped portion provided on the inner wall of the raw material storage container 1a. As the material of the guide 3, high-density graphite is used in order to prevent the inner wall of the guide 3 from being etched by a raw material gas formed by sublimation of the raw material 2 or heat. Specifically, isotropic orthographite having a density of 1.92 to 1.99 g / cm ³ was used.

  On the outer surface of the guide 3 (the surface facing the inner wall of the crucible 1), a heat insulating material 5 made of graphite is disposed. The guide 3 is heated by the radiant heat from the raw material 2, but heat is prevented from being released to the outside of the guide 3 by the heat insulating material 5.

  A ring-shaped tantalum ring 6 surrounding the seed crystal 4 is provided in the vicinity of the seed crystal 4 fixed to the pedestal 7. The tantalum ring 6 is supported by a step portion provided on the inner wall of the raw material storage container 1 a and the upper end portion of the guide 3. The thickness of the tantalum ring 6 may be 1 to 2 mm.

  In the present embodiment, the space between the outer surface of the guide 3 and the inner wall of the crucible 1 (the space in which the heat insulating material 5 is disposed) is sealed without a gap by the guide 3 and the tantalum ring 6. Thereby, during the growth of the ingot 9, the raw material gas is prevented from flowing outside the guide 3 to etch the heat insulating material 5, and the graphite particles generated by the thermal etching of the heat insulating material 5 are guided by the guide 3. It is prevented that it goes around inside.

  As shown in FIG. 1, the outer diameter of the flange portion of the guide 3 and the outer diameter of the tantalum ring 6 are equal to the inner diameter of the crucible 1. The tantalum ring 6 is in contact with the upper end of the guide 3 while covering the space between the guide 3 and the inner wall of the crucible 1. Therefore, the space in which the heat insulating material 5 is disposed becomes a sealed space surrounded by the inner wall of the crucible 1, the outer surface of the guide 3, and the lower surface of the tantalum ring 6.

  Further, the position of the opening of the tantalum ring 6 coincides with the position of the opening at the upper end of the guide 3, and the inner diameter of the tantalum ring 6 and the inner diameter of the upper end portion of the guide 3 are equal. Therefore, the source gas guided by the guide 3 is not blocked by the tantalum ring 6. Since the growth temperature of the SiC single crystal is about 2300 ° C., the dimensions of the guide 3 and the tantalum ring 6 must be designed in consideration of the thermal expansion at that temperature.

  The tantalum ring 6 is excellent in etching resistance due to a source gas and heat, and moreover, graphite particles generated by etching the inner wall of the crucible 1 in the process of growing the ingot 9, and a source gas (SiC) that has not contributed to the growth of the ingot 9. ) To form tantalum carbide. That is, surplus carbon reacts with the tantalum ring 6, so that it is suppressed from being taken into the growing ingot 9. Therefore, mixing of carbon inclusions into the single crystal of the ingot 9 is suppressed, and a high quality single crystal can be obtained.

  It is considered that the same effect can be obtained even if the tantalum ring 6 is made of tantalum carbide. However, when the tantalum carbide tantalum ring 6 obtained by coating graphite with tantalum is used, the tantalum carbide coat may be peeled off during the growth of the ingot 9 and the graphite may be exposed. When this happens, the exposed graphite is etched, and the resulting particles can cause carbon inclusion. Therefore, when using the tantalum carbide tantalum ring 6, it is preferable to use a tantalum carbide structure obtained by carburizing tantalum.

As a result of growing the SiC single crystal ingot 9 on the seed crystal 4 by the sublimation method using the crucible 1 having the above-described structure, the single crystal ingot having a diameter of 54 mm and a height of 67 mm is obtained independently of the polycrystal. 9 was obtained. As a result of slicing the crystal of this ingot 9 and evaluating it, the micropipe density was 0.5 / cm ² , which was very high quality.

On the other hand, when an experiment for growing a SiC single crystal ingot 9 was performed without the tantalum ring 6 installed, the heat insulating material 5 disposed on the outer surface of the guide 3 was etched by the source gas or heat, and thereby generated. The crystal quality of the ingot 9 deteriorated due to the influence of the particles. When the micropipe density of the crystal of the ingot 9 was measured, it was 100 / cm ² or more and the quality was poor.

  Since tantalum is an expensive metal, the tantalum ring 6 is preferably used a plurality of times in order to reduce the manufacturing cost of the single crystal. The tantalum ring 6 used for crystal growth gradually becomes tantalum carbide from the surface. However, when repeatedly used, carburization proceeds and the entire tantalum ring 6 becomes tantalum carbide, which becomes very brittle and difficult to reuse.

  Therefore, the tantalum ring 6 used for crystal growth is preferably covered with a thin tantalum foil and heated to about 1800 ° C. in an inert gas or vacuum. When this treatment is performed, the carbon in the tantalum carbide reacts with the surrounding tantalum foil, and the thickness of the tantalum carbide layer in the tantalum ring 6 is reduced. By repeating this process and the use for crystal growth, the lifetime of the tantalum ring 6 can be greatly extended, and the manufacturing cost can be saved.

  As described above, the guide 3 is made of high-density graphite having excellent etching resistance. However, if tantalum is disposed on the inner wall of the guide 3, etching can be further suppressed, and generation of carbon inclusion in the ingot 9 can be further suppressed. . In this case, the inner wall of the guide 3 may be coated with tantalum carbide by coating the inner wall of the high-density graphite guide 3 with tantalum. Although the tantalum carbide coat may be peeled off, the etching of the guide 3 is suppressed as compared with the case without the tantalum carbide coat.

  The application of the present invention is not limited to the production of SiC single crystals, and can be widely applied to the production of single crystals that are grown at high temperatures using graphite crucibles or heat insulating materials such as AlN and GaN. is there.

<Embodiment 2>
FIG. 2 is a cross-sectional view of a crucible of a crystal growth apparatus according to Embodiment 2 of the present invention. In the figure, elements having the same functions as those shown in FIG. As shown in FIG. 2, in this embodiment, a ring-shaped heat insulating material 8 having a hole in the center is disposed on the lid 1b of the crucible 1 shown in FIG.

  Tantalum carbide has a thermal conductivity that is two orders of magnitude greater than that of the graphite heat insulating material, and the tantalum ring 6 cannot be expected to have an effect as a heat insulating material. Therefore, in the case where the tantalum ring 6 is arranged around the seed crystal 4 as in the first embodiment and the case where the heat insulating material is arranged around the seed crystal 4 (for example, Patent Document 2 above), the latter It is considered that the temperature of the guide 3 can be increased. That is, when the tantalum ring 6 is provided, the temperature of the guide 3 is not sufficiently high, and there is a concern that polycrystals that cause deterioration of the quality of the single crystal are likely to precipitate on the inner wall of the guide 3. This problem can be solved by increasing the temperature gradient in the radial direction of the crucible 1 (increasing the temperature toward the outside of the crucible 1).

  In addition, when manufacturing a long ingot, it is conceivable to repeat the growth step a plurality of times. In that case, the temperature gradient in the radial direction in the crucible 1 can be increased as the growth step is performed later. preferable.

  For example, when performing growth twice, the radial temperature gradient in the crucible 1 is made larger in the second growth step than in the first growth step. Most of the source gas formed by sublimation of the source material 2 is recrystallized on the seed crystal 4, but the source gas that has not contributed to the growth passes between the base 7 and the guide 3 and surrounds the base 7. And then crystallizes to become polycrystalline. In the second growth step, since the ingot 9 has a certain size as shown in FIG. 2, the resistance of the passage through which the source gas passes to the lid 1 b increases, and polycrystals are likely to precipitate on the guide 3. . The reason why the temperature gradient in the radial direction of the crucible 1 is increased in the second growth process is to suppress the precipitation.

  As described above, if the radial temperature gradient of the crucible 1 is increased, the precipitation of polycrystals on the guide 3 can be suppressed, but if it becomes excessively large, the temperature difference in the ingot 9 during the growth increases, Another problem arises that thermal distortion occurs and the crystal quality deteriorates.

  Thus, since the radial temperature gradient of the crucible 1 greatly affects the crystal quality of the ingot 9, it is desirable to adjust it appropriately.

  The ring-shaped heat insulating material 8 in FIG. 2 is for adjusting the radial temperature gradient of the crucible 1. For example, when the thickness of the ring-shaped heat insulating material 8 is increased (or the number is increased), heat radiation upward is reduced in the outer peripheral portion of the crucible 1 covered with the ring-shaped heat insulating material 8, and relatively in the center portion. Since heat dissipation occurs intensively, the radial temperature gradient increases. On the other hand, when the thickness of the ring-shaped heat insulating material 8 is reduced, the difference in the upward heat radiation between the central portion and the outer peripheral portion of the crucible 1 is reduced, so that the radial temperature gradient is reduced.

  For example, when manufacturing the ingot 9 in two growth steps, a thin ring-shaped heat insulating material 8 (for example, 7 mm thick) is provided in the first growth step, and a thick ring-shaped heat insulating material 8 (for example, in the second growth step) (for example, 14 mm thick), the radial temperature gradient of the crucible 1 in the second growth step can be made larger than that in the first time, and a high-quality single crystal can be obtained. Alternatively, if the ring-shaped heat insulating material 8 is not provided in the first growth step and the ring-shaped heat insulating material 8 is provided only in the second growth step, the same effect can be obtained.

  The radial temperature gradient of the crucible 1 can also be adjusted by the size (diameter) of the hole provided in the central portion of the ring-shaped heat insulating material 8.

<Embodiment 3>
When the heating method of the crucible 1 is the induction heating method, the radial temperature gradient of the crucible 1 is increased even if the output of the induction heating oscillator is increased and the induction current density at the outer periphery of the crucible 1 is increased. be able to. When the output of the oscillator increases, the current flowing through the induction heating coil increases, and the induction current density on the outer wall of the crucible 1 increases. The guide 3 is heated mainly by heat conduction from the crucible 1 and radiant heat from the raw material 2, but the raw material is considered to be heated by heat conduction from the outer wall of the crucible. Therefore, when the current density of the outer wall of the crucible 1 increases, the outer periphery of the raw material 2 becomes higher in temperature, the radiant heat from the outer peripheral portion of the raw material 2 increases, and the guide 3 becomes higher in temperature. The temperature gradient increases.

  However, in the method of increasing the radial temperature gradient by the induced current density, there is a possibility that the temperature of the entire crucible 1 rises and the crystal growth conditions are affected. Therefore, when this method is adopted, it is desirable to adjust the thickness, density, and thermal conductivity of the heat insulating material provided around the crucible 1 so that a predetermined growth temperature is maintained.

  1 crucible, 1a raw material storage container, 1b lid, 2 raw materials, 3 guide, 4 seed crystal, 5 heat insulating material, 6 tantalum ring, 7 pedestal, 8 ring-shaped heat insulating material, 9 ingot.

Claims (9)

(A) a step of disposing a single crystal raw material and a seed substrate oppositely in a crucible;
(B) installing a tantalum ring containing tantalum or tantalum carbide surrounding the seed substrate in the crucible;
(C) A method for producing a single crystal comprising: a step of growing the single crystal on the main substrate by heating the crucible and sublimating the raw material. (D) before the step (c), a step of installing a cylindrical guide that has one end in contact with the inner wall of the crucible and guides the gas sublimated from the raw material to the seed substrate;
(E) before the step (c), further comprising a step of installing a heat insulating material between the guide and the inner wall of the crucible,
In the step (b), the tantalum ring is installed so as to cover between the other end of the guide and the crucible, and a space in which the heat insulating material is disposed is an inner wall of the crucible, the guide, and the tantalum ring. The method for producing a single crystal according to claim 1, wherein the single crystal is hermetically sealed. The method for producing a single crystal according to claim 1 or 2, wherein the step (c) is performed a plurality of times, and the radial temperature gradient in the crucible is set larger as the step is performed later. The method for producing a single crystal according to any one of claims 1 to 3, further comprising a step of performing a heat treatment after the step (c) is performed by covering the tantalum ring with a tantalum foil. A crucible having a pedestal capable of storing a single crystal raw material and a seed substrate facing the raw material,
An apparatus for producing a single crystal, comprising: a tantalum ring including tantalum or tantalum carbide, disposed in the crucible so as to surround the periphery of the pedestal. A cylindrical guide that has one end in contact with the inner wall of the crucible and guides the gas obtained by sublimation of the raw material to the pedestal;
A heat insulating material disposed between the guide and the inner wall of the crucible;
The tantalum ring is disposed so as to cover between the other end of the guide and the crucible,
The single crystal manufacturing apparatus according to claim 5, wherein a space in which the heat insulating material is disposed is sealed by an inner wall of the crucible, the guide, and the tantalum ring. The single-crystal manufacturing apparatus according to claim 5, wherein the tantalum ring includes a layer in which tantalum is carburized. The single crystal manufacturing apparatus according to any one of claims 5 to 7, wherein an inner wall of the guide is coded by tantalum or tantalum carbide. The single-crystal manufacturing apparatus according to any one of claims 5 to 8, further comprising a ring-shaped heat insulating material placed on the crucible.

Images