JP2012162439A - METHOD FOR MANUFACTURING SiC SINGLE CRYSTAL BY SOLUTION METHOD - Google Patents

Abstract

The present invention provides a method for producing a SiC single crystal by a solution method by preventing the occurrence of cracks at the edge of a grown crystal.
In a method for producing an SiC single crystal by a solution method in which an SiC single crystal is grown on the lower surface of an SiC seed crystal brought into contact with the Si-C solution surface, the grown SiC single crystal is formed when the crystal growth is completed. A method for producing an SiC single crystal by a solution method, wherein the grown SiC single crystal is pulled up from the solution surface after the C concentration of the Si-C solution in the vicinity of the solution surface in contact is lowered. It is desirable to reduce the C concentration of the Si—C solution in the vicinity of the solution surface in contact with the grown SiC single crystal to 7 at% or less.
[Selection] Figure 2

Description

  The present invention relates to a method for producing a SiC single crystal by a solution method, and particularly to prevention of cracks at the edge of a grown crystal.

  The manufacturing method of the SiC single crystal by the solution method is a method of growing the SiC single crystal on the lower surface of the SiC seed crystal brought into contact with the Si—C solution surface. When the growth crystal is pulled up and the end portion is separated from the solution surface when the crystal growth is completed, the Si—C solution adheres to the growth end portion. There was a problem that cracks occurred at the end due to the stress when the adhesion solution solidified.

  In the production method of the Si single crystal by the solution method, even if the solution adheres, the problem of crack generation as in the SiC single crystal does not occur because the compressive stress acts because it expands at the time of solidification. In addition, there is a method of controlling the diameter of the growth end portion so as to make it convex so that the end portion having a risk of occurrence of cracks is not used, but there is a problem that the yield decreases. In particular, in the case of a SiC single crystal having a slow growth rate, a yield reduction that cannot be ignored is inevitable.

  As a countermeasure, Patent Document 1 proposes that when the growth crystal is pulled up, the growth solution is rotated at a high speed to disperse the adhesion solution. However, with this method, it is difficult to completely remove the adhesion solution at the center of the crystal because no centrifugal force is applied, and there is a problem that the adhesion solution remains at the end portion to be polycrystallized and cause cracks. .

  In Patent Document 2, a Si melt container not containing C is further housed in a furnace containing a Si—C solution container used for crystal growth, and the SiC single crystal is pulled up from the Si—C solution. After that, it has been proposed to wash away the adhering solution by immersing in Si melt. However, in this method, it is necessary to expand the hot zone of the furnace by considerably increasing the capacity of the crystal growth apparatus including the furnace in order to accommodate the container for washing out in addition to the growth container. Furthermore, when a high temperature is required as in the growth of a SiC single crystal, there is a problem that it is difficult to form a temperature distribution necessary for crystal growth.

Japanese Patent Laid-Open No. 06-048897 JP-A-61-202411

  An object of the present invention is to provide a method for producing a SiC single crystal by a solution method by solving the above-described drawbacks of the prior art, preventing cracks from occurring at the edge of the grown crystal.

  In order to achieve the above object, according to the present invention, in the method for producing an SiC single crystal by a solution method, an SiC single crystal is grown on the lower surface of an SiC seed crystal in contact with the Si-C solution surface. When the step is completed, the grown SiC single crystal is pulled up from the solution surface after the C concentration of the Si-C solution in the vicinity of the solution surface in contact with the grown SiC single crystal is lowered. A method for producing a SiC single crystal by a solution method is provided.

  According to the present invention, since the C concentration of the Si—C solution adhering to the grown crystal edge is reduced, the stress generated during solidification is reduced, and the generation of cracks is prevented.

The apparatus for growing a SiC single crystal by a solution method is shown. When the C concentration of the Si—C solution is 17 at%, (1A) the as-grown and (1B) state after the acid treatment at the edge of the grown crystal, and the C concentration of the Si—C solution is 2 at. The state of (2A) as grown (as-grown) and (2B) after the acid treatment at the edge of the grown crystal in the case of% is shown by photographs.

  In the growth method of the SiC single crystal by the solution method, when the C concentration of the solution is low, the growth rate of the SiC single crystal is slow (about 70 μm / hr at the maximum), so the third element (Cr or the like) that increases the C solubility of the solution It is common to increase the C concentration by adding. However, if the C concentration is high, cracks occur due to bonding with the grown crystals when the adhesion solution is solidified. In the present invention, the C concentration necessary for securing the growth rate is maintained during the crystal growth, and the C concentration is lowered when the crystal growth is completed to prevent the generation of cracks.

  The method for reducing the C concentration upon completion of crystal growth is as follows.

  (1) The temperature of the Si—C solution is lowered immediately before pulling up the grown crystal.

  (2) An element that does not increase the C solubility of the Si—C solution is added immediately before pulling up the grown crystal.

  (3) The growth crystal is heated to a temperature at which the Si—C solution does not solidify, an element that does not increase the C solubility of the Si—C solution is added, and then the growth crystal is pulled up.

  As the method for lowering the temperature of the Si-C solution (1), any of the following methods is possible.

(A) Decreasing the output of the high-frequency coil (b) Changing the crucible position with respect to the high-frequency coil Si is most suitable as an element used in the above (2) and (3) that does not increase the C solubility of the Si—C solution. However, it is not necessary to limit to Si, and rare earth elements such as Co, Nd, and Py, Al, Ga, In, Ti, P, As, Sb, Bi, Mo, Ni, and the like can also be used.

  When pulling up the growth crystal, it is desirable to rotate the growth crystal in order to reduce the adhesion of the solution to the edge of the growth crystal.

  The additive element can be supplied by introducing a granular element (Si or the like) into the solution via a graphite tube. When providing the additive element, it is desirable not to cause the solution to flow by stopping the step of promoting the stirring of the solute such as the rotation of the solution. Moreover, when lowering the C concentration of the solution, by reducing the C concentration in the vicinity of the solution in contact with the single crystal, it is possible to narrow the target region for lowering the C concentration in the solution. Further, it is desirable that the region to be reduced in C concentration is a region that can adhere to the single crystal in the step of pulling up the grown single crystal. By doing so, the C concentration of the solution adhering at the time of crystal pulling can be more reliably reduced. Further, after the operation of reducing the C concentration, it is desirable not to stir the solution so that the region where the C concentration is reduced does not diffuse.

  The crystal growth apparatus shown in FIG. 1 is used to change the C concentration of the Si—C solution from 2 at% to 17 at% as shown in Table 1, and using a seed crystal 4H—SiC at a growth temperature of 1900 ° C. at a single crystal of SiC. Crystals were grown.

  The presence or absence of cracks at the end of the grown crystal was examined and is shown in Table 1. In Table 1, ◯ indicates that no crack is generated, and × indicates that a crack is generated. For fractions (n1 / n2) such as 0/5, the numerator (n1) indicates the number of cracked samples, and the denominator (n2) indicates the total number of samples.

  FIG. 2 shows (1A) the as-grown and (1B) state after the acid treatment at the edge of the grown crystal when the C concentration of the Si—C solution is 17 at%, and the Si—C solution. When the C concentration is 2 at%, (2A) the as-grown state and (2B) the state after the acid treatment at the edge of the grown crystal are shown by photographs.

  In the case where the C concentration is 17 at%, peeling occurs from the crack generation site due to the acid treatment. On the other hand, when the C concentration is 2 at%, peeling due to acid treatment does not occur at all. Thus, the presence or absence of crack generation could be clearly determined by the acid treatment.

  From this result, it can be seen that by making the C concentration 7 at% or less, the generation of cracks at the edge of the grown crystal can be completely prevented.

  In this example, as a simulation of the method of the present invention, SiC single crystal growth was performed using a Si—C solution in which the C concentration was changed from the beginning. However, the C concentration was changed (lowered) after the completion of crystal growth. In this case, the same effect can be obtained.

  When adding an element that does not increase the C solubility of the Si—C solution in accordance with the present invention, it may be added via a raw material supply cylinder such as graphite as shown by the phantom line in FIG. In this case, the tip of the cylinder is not brought into contact with the Si—C solution to prevent the addition of excess C.

  According to the present invention, there is provided a method for producing a SiC single crystal by a solution method, which eliminates the above-mentioned drawbacks of the prior art, prevents the occurrence of cracks at the edge of the grown crystal. That is, since the C concentration of the Si—C solution adhering to the edge of the grown crystal is reduced, the stress generated during solidification is reduced and the generation of cracks is prevented.

Claims (2)

  In a method for producing a SiC single crystal by a solution method in which a SiC single crystal is grown on a contact surface of a SiC seed crystal brought into contact with a Si-C solution surface, when the crystal growth is completed, the grown SiC single crystal comes into contact A method for producing an SiC single crystal by a solution method, wherein the grown SiC single crystal is pulled up from the solution surface after the C concentration of the Si—C solution in the vicinity of the solution is lowered.   2. The method for producing a SiC single crystal according to claim 1, wherein the C concentration of the Si—C solution in the vicinity of the solution in contact with the grown SiC single crystal is reduced to 7 at% or less.