JP4048606B2 - Single crystal manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a single crystal such as silicon carbide by a sublimation method.
[0002]
[Prior art]
As a method for producing a single crystal such as silicon carbide (SiC), a sublimation method is widely known. The sublimation method is a method of growing a silicon carbide single crystal by supplying a sublimation gas of a raw material on a seed crystal. As shown in FIG. 4, a SiC raw material powder is accommodated in a graphite crucible 1 to form a raw material part 2, The crucible 1 is heated, and the generated sublimation gas of the raw material powder is recrystallized on the seed crystal 4 arranged on the top. In addition, various methods for controlling the growth of single crystals by the sublimation method have been proposed. As one of the methods, Japanese Patent Publication No. 3-501118 discloses the composition, particle size distribution, temperature gradient, etc. of the raw material powder. It is disclosed that, by controlling, a larger single crystal having a desired crystal form can be obtained. For example, by defining the composition of the SiC raw material powder, the ratio of chemical species in the generated sublimation gas can be made constant, and by defining the particle size distribution, the specific surface area in the unit volume can be made constant. It is described that the crystallinity of the generated sublimation gas can be increased to enable constant crystal growth.
[0003]
[Problems to be solved by the invention]
Thus, the growth amount and quality of the SiC single crystal by the sublimation method are greatly influenced by the generation amount of sublimation gas and its change with time. However, the SiC raw material powder tends to sublime from the raw material surface portion in contact with the crucible space. FIG. 4 shows the sublimation efficiency of each part of the raw material part 2 in light and shade, and it can be seen that the sublimation efficiency is distributed in the depth direction of the raw material part 2 and lower in the lower part. Moreover, since the raw material powder on the surface of the raw material sublimates before the bottom and carbonizes and sinters, when the crystal growth progresses, the surface is covered with the carbonized layer and the sintered layer. There was a problem that sublimation of the raw material powder was hindered. This is particularly noticeable when the amount of raw materials is large. In such a state, the generation amount of sublimation gas is reduced, and efficient crystal growth may be hindered.
[0004]
The present invention has been made in view of the above circumstances, and an object of the present invention is to perform uniform sublimation throughout the raw material part, efficiently generate sublimation gas, and reduce the change with time, thereby achieving high-quality single unit. The object is to provide a method for efficiently producing crystals.
[0005]
[Means for Solving the Problems]
According to claim 1 of the present invention, a method for producing a single crystal is provided in which a seed crystal and a silicon carbide raw material powder are arranged in a single crystal production vessel, the raw material powder is sublimated, and a silicon carbide single crystal is grown on the seed crystal. When the raw material powder is accommodated in the lower part of the container, the particle diameter of the raw material powder disposed on the surface part in contact with the space in the container is larger than the particle diameter of the raw material powder disposed on the bottom part . The gap between the large-diameter particles is used as a passage for sublimation gas generated on the bottom side .
[0006]
When the particle size of the raw material powder is small, the particles are likely to sinter, the space between the particles becomes small, and the sublimation gas is difficult to pass. Also, the carbonized layer that has undergone sublimation is similarly difficult to pass sublimation gas, and the sublimation at the bottom is inhibited when the raw material powder is sintered or carbonized in the vicinity of the surface portion in contact with the inner space of the container and in the vicinity thereof, It became clear by experiment. Therefore, in the present invention, the surface powder and the raw material powder in the vicinity thereof have more large-diameter particles than other portions, and the gaps between the particles are made larger than other portions. This facilitates the passage of sublimation gas generated at the bottom of the raw material, and the large-diameter particles are less likely to be sintered or carbonized, so that the passage of the sublimation gas can be prevented from being blocked. Therefore, sublimation at the bottom of the raw material is not hindered, and uniform sublimation can be performed on the entire raw material part to increase the amount of sublimation per weight of the raw material. It can be manufactured efficiently.
[0007]
In the method of claim 2, the raw material powder in the surface portion in contact with the inner space of the container mainly contains large-diameter particles having a particle diameter of 500 to 1000 μm and does not contain small-diameter particles having a particle diameter of 250 μm or less. Preferably, when mainly composed of large-diameter particles having a particle diameter of 500 to 1000 μm, the above-described effect of forming a space and suppressing sintering or the like is large. In addition, since small particles having a particle size of 250 μm or less are not included, the small particles do not enter the gaps between the large particles, and the effect of increasing the space between the particles is high.
[0008]
In the method of claim 3, the raw material powder is disposed so that the average particle diameter decreases from the surface portion in contact with the space in the container toward the bottom. When the particle size is small, the surface area per unit weight increases, and as the surface area per unit weight increases, the amount of sublimation gas generated increases, so that sublimation at the bottom of the raw material is promoted and efficient sublimation becomes possible. .
[0009]
In the method of claim 4, the raw material powder is arranged so that the particle size distribution of the raw material powder increases from the surface part in contact with the inner space of the container to the bottom part. The packing is made dense by increasing the particle size distribution, the amount of raw material per unit volume is increased, the amount of sublimation from the bottom of the raw material is increased, and efficient sublimation is enabled.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the first embodiment of the present invention will be described by taking the growth of a silicon carbide (SiC) single crystal as an example. FIG. 1A is a schematic diagram of a single crystal production apparatus used in the present embodiment. A graphite crucible 1 serving as a single crystal production container has a raw material part 2 formed by filling SiC powder in the lower half part. It is. Above the raw material portion 2 is a space portion 3 for growing a single crystal. An SiC single crystal that is supported by a pedestal (not shown) and serves as a seed crystal 4 is disposed at the center of the top surface of the crucible 1 facing the raw material portion 2. The SiC single crystal constituting the seed crystal 4 is composed of, for example, a single crystal by the Atchison method, or a sublimation single crystal grown from the Atchison crystal. After processing this into a pedestal shape into a wafer shape, for example, bonding It is joined to the pedestal using an agent.
[0013]
In the present invention, as schematically shown in FIG. 1 (b), when the SiC powder is filled in the crucible 1, the upper part including the surface part of the raw material part 2 in contact with the space part 3 is larger than the other parts. A large number of particles having a diameter are included so that the gap between the particles is larger than that of other portions. Preferably, the SiC powder is preferably filled so as to mainly include large-diameter particles having a particle diameter of 500 to 1000 μm and not including small-diameter particles having a particle diameter of 250 μm or less in the upper part including the surface part in contact with the space part 3. By having many large particles having a particle size in the range of 500 to 1000 μm, sintering and carbonization of the particles are suppressed, particle size distribution is small, and in particular, small particles having a particle size of 250 μm or less are not included. By making it, it can make it easy to form a space between particles.
[0014]
In the region below the upper part including the surface part in contact with the space part 3, the particle size or particle size distribution is not particularly defined, and may include small-diameter particles. In FIG. 1 (b), the upper part of the raw material part 2 is composed only of large-diameter particles having substantially the same particle diameter, and the lower part is composed of smaller-diameter particles, and the particle size distribution is increased. When the particle size distribution is large, the packing becomes dense, the porosity is reduced, and the surface area per unit weight is increased. That is, if the specific surface area of the bottom part is larger than that of the surface part of the raw material part 2, sublimation of the bottom part is promoted, so that uniform sublimation in the depth direction is possible. In FIG. 1B, the filling method of the SiC powder is changed between the upper part and the lower part of the raw material part 2, but the average particle diameter may be decreased continuously or stepwise from the surface part to the bottom part. Good. Alternatively, the average particle size may be the same, and the particle size distribution may be increased continuously or stepwise, and the same effect can be obtained.
[0015]
When a single crystal is manufactured using the apparatus of FIG. 1A, the SiC powder is filled in the crucible 1 having the seed crystal 4 fixed on the top as described above. This crucible 1 is disposed in a heating device and heated to a predetermined temperature with a heater (not shown). When the atmosphere in the crucible 1 is an inert gas atmosphere such as argon gas and heated to a predetermined temperature under reduced pressure, the SiC powder in the raw material part 2 is sublimated and supplied to the seed crystal 4 as a sublimation gas. The temperature of the raw material part 2 is usually set to 2000 ° C. to 2500 ° C., and the temperature of the seed crystal 4 is held at a low temperature of about 10 ° C. to 100 ° C. A temperature gradient is formed. At this time, the sublimation gas flows from the high temperature raw material portion 2 to the low temperature seed crystal 4 according to the temperature gradient in the crucible 1 and recrystallizes on the surface of the seed crystal 4 to grow a SiC single crystal.
[0016]
In the above configuration, since the upper half of the raw material portion 2 is composed of large-sized particles not containing small-sized particles, the space between the particles is large, and even if crystal growth proceeds, the particles are sintered or carbonized or grown. It is difficult to cause sublimation gas passage. Furthermore, since the lower half of the raw material part 2 is composed of particles having a smaller diameter and the particle size distribution is increased to increase the specific surface area, the sublimation of the SiC powder in the lower half is promoted and uniform in the depth direction. Sublimation can be performed. Therefore, sublimation of the raw material in the lower half is not hindered, and uniform sublimation can be performed throughout the raw material portion, so that the sublimation amount per raw material weight can be increased. Thus, it is possible to efficiently generate a sublimation gas and to reduce the change with time, and to efficiently produce a large single crystal with good quality.
[0017]
FIG. 2 shows a second embodiment of the present invention. In the present embodiment, the SiC powder is filled so that the surface portion of the raw material portion 2 has an uneven shape. Sublimation depends on the surface area of the raw material part 2 in contact with the space part 3, and the larger the surface area, the greater the amount of sublimation. By increasing the surface area by providing irregularities, the amount of sublimation gas generated is higher than when the surface is flat. The crystal growth can be promoted by increasing. Further, as in the third embodiment of the present invention shown in FIG. 3, a rod-like or flat plate-like member 5 made of a material that hardly causes a chemical reaction with SiC powder, such as TaC or graphite, is used as the surface portion of the raw material portion 2. It can also be embedded in Also in this case, the surface of the raw material portion 2 in contact with the space portion 3 or the rod-like or flat plate-like member 5 has an uneven shape, and the same effect can be obtained that the surface area is increased and the amount of sublimation gas generated is increased.
[0018]
In each of the above embodiments, the manufacture of the SiC single crystal has been described. However, the single crystal that can be manufactured based on the present invention is not limited to SiC. For example, ZnSe, ZnS, CdS, CdSe, AlN, The present invention may be applied to any of single crystals that can be grown by vapor phase methods such as sublimation methods such as GaN and BN.
[Brief description of the drawings]
FIG. 1 (a) is an overall schematic cross-sectional view of a single crystal manufacturing apparatus used in the first embodiment of the present invention, and FIG. 1 (b) is an enlarged cross-sectional view of a main part of FIG. 1 (a). is there.
FIG. 2 is an enlarged cross-sectional view of a main part of a single crystal manufacturing apparatus used in the second embodiment of the present invention.
FIG. 3 is an enlarged cross-sectional view of a main part of a single crystal manufacturing apparatus used in a third embodiment of the present invention.
FIG. 4 is an overall schematic cross-sectional view of a single crystal production apparatus showing the sublimation efficiency of a raw material part in a conventional single crystal production method.
[Explanation of symbols]
1 Crucible (single crystal production container)
2 Raw material part 3 Space part 4 Seed crystal 5 Bar-shaped or flat plate-shaped member

Claims (4)

The single crystal production vessel by disposing a silicon carbide raw material powder and the seed crystal, sublimated the raw material powder, the method for producing a single crystal to grow a silicon carbide single crystal on the seed crystal, the above container bottom When containing the raw material powder , the particle diameter of the raw material powder disposed on the surface portion in contact with the space in the container is larger than the particle diameter of the raw material powder disposed on the bottom portion , and between these large-diameter particles A method for producing a single crystal, wherein the gap is a passage for sublimation gas generated on the bottom side . 2. The method for producing a single crystal according to claim 1, wherein the raw material powder in the surface portion in contact with the inner space of the container mainly contains large-diameter particles having a particle diameter of 500 to 1000 μm and does not contain small-diameter particles having a particle diameter of 250 μm or less. .   The method for producing a single crystal according to claim 1 or 2, wherein the raw material powder is arranged so that an average particle diameter of the raw material powder decreases from a surface part in contact with the space in the container toward a bottom part.   The method for producing a single crystal according to claim 1 or 2, wherein the raw material powder is arranged so that a particle size distribution of the raw material powder increases from a surface portion in contact with the space in the container toward a bottom portion.

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