JP4184622B2 - Method for producing silicon carbide single crystal ingot - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a large silicon carbide single crystal having low defects and good crystallinity by a sublimation recrystallization method.
[0002]
[Prior art]
Silicon carbide (SiC) has been attracting attention as a substrate wafer material for various devices including power devices for electric power because of its excellent physical properties, heat resistance and mechanical strength as a semiconductor material. SiC single crystals are generally manufactured by a sublimation recrystallization method, but because it was difficult to obtain high-quality large single crystals with few crystal defects that can withstand use as semiconductor devices, For many years, its industrialization has been hindered. In recent years, an improved Rayleigh method (Yu. M. Tairov and VF Tsvetkov, Journal of Crystal Growth, vol. 52 (1981) pp. 146), which improved the conventional sublimation recrystallization method, has been proposed, and a single crystal ingot A dramatic progress has been made in improving the quality and size. Although it is at the research and development level, device application research such as GaN-based blue light-emitting diodes and Schottky barrier diodes is being promoted, and at the same time, large single crystal wafers with a maximum diameter of 4 inches (100 mm) can be realized. (CH Carter, et al., FED Journal, vol.11 (2000) pp.7).
[0003]
The modified Rayleigh method is to produce a single crystal by applying SiC sublimation / recrystallization. The SiC single crystal is preliminarily placed in a relatively low temperature part by heating and sublimating the raw material mainly composed of SiC. This is a method for obtaining a large SiC single crystal ingot by recrystallization on a seed crystal composed of Since the sublimation temperature of SiC itself is high, crystal growth generally needs to be performed at a high temperature of 2000 ° C. For this reason, a crucible mainly composed of a heat-resistant material typified by graphite is used for a crystal growth container. In order to obtain a high-quality SiC single crystal ingot free of crystal defects, etc., the optimum growth conditions are maintained by controlling the temperature distribution in the crucible, the sublimation SiC gas distribution, etc., and the conditions are maintained over the entire growth time. There is a need to. However, since it is extremely difficult to monitor the inside of the graphite crucible in real time at such a high temperature, there is no effective method other than guessing from information such as temperature measurement of the outer surface of the crucible, etc. For these reasons, there are still unknown control factors in the crystal growth conditions at present, and the situation is that the stable crystal growth conditions have not been completely established. For this reason, there has been a problem in that the production yield of single crystal ingots is reduced due to frequent occurrences such as disorder in part of the grown crystal resulting in polycrystallization and the occurrence of different polytypes.
[0004]
[Problems to be solved by the invention]
When manufacturing SiC single crystal ingots by sublimation recrystallization, it is known that there are SiC polytypes that tend to form at relatively low temperatures during the temperature rise process during crystal growth (Knippenberg, Phillips Res Reports, vol.18 (1963) pp.161). For example, an SiC polytype called 3C is said to be easily formed in a low temperature range of 2000 ° C. or lower, particularly under non-equilibrium conditions, depending on the growth apparatus. By the way, since the semiconductor characteristics are relatively good, SiC polytypes that are attracting attention as device applications are 4H and 6H. In the sublimation recrystallization method, single crystal ingots composed of these polytypes stably crystallize in a high temperature range of 2000 ° C. or higher. Therefore, when producing 4H and 6H polytype single crystals, the temperature near the seed crystal is The crucible temperature must be controlled so that it falls within the temperature range. For this reason, the atmosphere is basically used for the purpose of suppressing the crystallization of different types of SiC polytypes at low temperatures, except in the case of heat treatment under reduced pressure for different purposes such as degassing for raw material purification. A technique is generally used in which the temperature is raised while increasing the pressure, and the pressure is decreased after reaching the vicinity of the desired growth temperature to start the growth (N. Ohtani, et al., Electronics and Communications in Japan, Part 2, vol.81 (1998) pp.8). When the atmospheric pressure is increased, the diffusion rate of the SiC sublimation gas in the crucible is remarkably reduced. Therefore, the basic principle of this method is that the sublimation rate is suppressed and the crystal growth on the seed crystal hardly progresses. ing. However, even if such atmospheric pressure control is carried out, there are still frequent occurrences such as polycrystal growth and mixing of different types of SiC polytypes, and the yield of crystal production is effectively improved. It is hard to say that there is.
[0005]
Based on a detailed investigation on the temperature of the crucible at the time of temperature rise and an analysis based on numerical analysis simulation, the inventors have found that, for example, in the case of crystal growth in a graphite crucible, depending on the pressure drop speed, It was found that the temperature rises by about 50 to 100 ° C. even in the vicinity of the exothermic part. When the atmospheric pressure is lowered, the contribution of heat conduction by the atmosphere gas is reduced among the heat flow controlling factors such as radiation and heat conduction that determine the temperature distribution of the entire system including the crucible. It is considered that the temperature distribution in the crucible rises because the heat insulation is improved. In such a case, the crystal growth rate is not stabilized due to the temperature change when the atmospheric pressure is lowered, and the crystallinity of the grown crystal is likely to be disturbed. In some cases, crystal grains having different crystal orientations are generated. , It will be polycrystallized. Alternatively, the growth temperature shifts to a temperature range where other heterogeneous polytypes are likely to be generated, making it impossible to obtain a desired single polytype single crystal. In such a case, from the vicinity of the interface with the heterogeneous polytype. hollow micro defects called micropipe occurs (N. Ohtani, et al., 1 st International Workshop on Ultra-Low-Loss Power Device Technology, (2000)). In any case, it has been strongly desired to propose a heat treatment process that realizes stable crystal growth because it causes a decrease in the production yield of high-quality SiC single crystal ingots.
[0006]
The present invention has been made in view of the above circumstances, and provides a method for producing a SiC single crystal ingot that enables stable production of a large-diameter single crystal wafer having good crystallinity.
[0007]
[Means for Solving the Problems]
The method for producing a SiC single crystal according to the present invention heats and sublimates a raw material mainly composed of SiC, and the sublimation gas is preliminarily placed on a seed crystal composed of a SiC single crystal placed at a relatively low temperature part from the raw material part. A method for obtaining a SiC single crystal ingot by supplying and sublimating and recrystallizing the seed crystal;
(1) A method for producing a silicon carbide single crystal ingot characterized by lowering the crucible temperature when the atmospheric pressure is reduced (2) The crucible temperature drop is 5 ° C. or more and 100 ° C. or less ( 1) The method for producing a silicon carbide single crystal ingot according to 1), wherein the crucible temperature is lowered when the atmospheric pressure is reduced, and the temperature is raised again to the crystal growth temperature after the pressure is reduced (1) or (2) (4) The method for producing a silicon carbide single crystal ingot according to (3), wherein the temperature increase is performed within a period of 40 hours or less.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
By the production method of the present invention, it is possible to suppress a temporary temperature rise in the crucible that occurs when the atmospheric pressure is reduced, without causing unstable disturbance to stable growth dominating factors such as crystal growth rate, and as a result, A large-sized single crystal ingot having good crystallinity can be stably manufactured, and a large-diameter SiC single crystal wafer can be stably manufactured.
[0009]
FIG. 1 shows an example of a basic growth processing pattern proposed by the inventors. In the temperature rising process, the atmospheric pressure is increased to suppress the generation of heterogeneous SiC polytypes that are likely to occur at relatively low temperatures. Before the temperature rise, degassing treatment may be performed under reduced pressure in a sufficiently low temperature range where crystal growth does not occur. However, when the temperature is raised to the growth temperature, it is necessary to increase the atmospheric pressure. It is sufficient that the pressure during the temperature raising process is 0.8 × 10 ⁵ Pa or more. After reaching the desired growth temperature, the temperature is decreased simultaneously with the start of the decrease in the atmospheric pressure. The temperature drop at this time is desirably 5 ° C. or more and 100 ° C. or less. If it is smaller than this temperature range, the temperature rise in the crucible cannot be suppressed and stable growth cannot be realized. On the other hand, if the temperature is lowered beyond this temperature range, the temperature will drop abnormally when the pressure drops, resulting in polycrystallization without realizing stable growth, or generation of different SiC polytypes. End up. Note that the growth pressure may be 1.3 × 10 ⁴ Pa or less. Further, the temperature drop speed is almost equal to the pressure drop speed and is not particularly problematic. If there is no possibility of mixing different types of SiC polytypes after the atmospheric pressure has decreased to the specified pressure, growth may be continued at that temperature, but the growth rate will decrease and a sufficiently large single crystal ingot will be obtained. Therefore, it is desirable to quickly return to the vicinity of the growth temperature before the drop. The rate of temperature rise at this time is preferably within 40 hours or less. If the temperature is exceeded, crystal growth cannot be continued due to factors such as deterioration of the heat insulating material under high-temperature exposure. The temperature cannot be recovered in time.
[0010]
【Example】
Examples of the present invention will be described below.
[0011]
(Example 1)
FIG. 2 shows a schematic view of the production apparatus of the present invention for growing a SiC single crystal by an improved Rayleigh method using a seed crystal. A graphite crucible was filled with SiC raw material powder, a 6H polytype single crystal seed crystal wafer was installed on the upper facing surface, and then placed in a water-cooled double quartz tube. The inner diameter of the crucible is 25.4 mm. In order to remove impurities from the SiC raw material powder, degassing was performed by heating and holding at about 500 ° C. by high-frequency heating under a high vacuum of about 10 ⁻³ Pa or less. Thereafter, argon gas was charged until the pressure in the quartz tube became 1.0 × 10 ⁵ Pa, and then the temperature was raised to 2150 ° C. over about 1 hour. In addition, although it is the temperature measuring method of a crucible temperature, it provided with the optical path of diameter 2-4mm in the center part of the upper part of a crucible, and measured with the two-color thermometer installed outside the quartz tube. Subsequently, the pressure in the quartz tube was started to be reduced, and at the same time, the power of the high-frequency power source was lowered to reach the state of pressure 1.3 × 10 ³ Pa and temperature 2100 ° C. in about 5 minutes. Thereafter, the crystal was grown at a temperature of 2100 ° C. for 20 hours. In addition, as a comparative experiment of the above example by the production method of the present invention, after degassing treatment, the temperature was raised to 2100 ° C. in about 1 hour, and then the pressure was lowered to 1.3 × 10 ³ Pa and the temperature was increased to 2100 ° C. A crystal growth experiment was carried out for a long time.
[0012]
When the grown crystal was taken out and observed after completion of the growth, the crystal produced by the production method of the present invention was a single crystal ingot of 6H polytype almost completely as a whole. On the other hand, in the case of the comparative example, the single crystal state without the large-angle crystal grains is maintained, but the 4H polytype is mixed in the inside of the grown crystal, and the micropipe shape is formed near the interface with the 6H polytype portion. It has been found that the structural defects of FIG.
[0013]
(Example 2)
A 4H polytype single crystal ingot growth experiment was carried out under growth conditions substantially the same as in Example 1. However, when the pressure inside the quartz tube is 1.3 × 10 ³ Pa, the temperature is raised to 2050 ° C. over about 1 hour. After reaching the pressure 1.3 × 10 ³ Pa and the temperature 2000 ° C. in about 5 minutes, the pressure is reduced to 2050 ° C. under reduced pressure. The temperature was raised over about 1 hour, and the temperature was further maintained for 19 hours. As a comparative experiment, an experiment was performed in which the temperature was raised to 2050 ° C. in about 1 hour, and then the pressure was reduced to 1.3 × 10 ³ Pa and held at 2050 ° C. for 20 hours.
[0014]
The crystal obtained by the production method of the present invention was an ingot in an almost complete single crystal state with no generation of crystal grains. This ingot was cut out in parallel to the growth direction, a thin plate having a thickness of about 1 mm was collected, and the polytype of each part of the thin plate was examined by Raman spectroscopy. As a result, it was found that the entire surface was a 4H polytype. Data were obtained, indicating that stable crystal growth was achieved without the occurrence of different polytypes. On the other hand, as a comparative example, 4H polytype microcrystal grains having greatly different crystal orientations are generated in the peripheral portion of the grown crystal, particularly close to the inner wall of the crucible, and it is a single crystal over the entire crystal surface. A 4H polytype ingot was not obtained. Further, when the polytype of each part of the thin plate was examined by the same method as above, 6H and 15R polytypes were generated in the peripheral part of the crystal, and it was not a single polytype ingot consisting only of 4H. There was found.
[0015]
【The invention's effect】
As described above, according to the present invention, a high-quality silicon carbide single crystal ingot having good crystallinity can be produced by an improved Rayleigh method using a seed crystal. By using such a silicon carbide single crystal wafer, it is possible to produce a blue light-emitting element having excellent optical characteristics and a high voltage / environment resistant electronic device having excellent electrical characteristics.
[Brief description of the drawings]
FIG. 1 shows an example of a temperature pattern of the crystal growth method of the present invention.
FIG. 2 is a configuration diagram showing an example of a single crystal growth apparatus used in the manufacturing method of the present invention.
[Explanation of symbols]
1 ... Seed crystal (SiC single crystal)
2 ... SiC powder raw material 3 ... Graphite crucible 4 ... Double quartz tube (water-cooled)
5 ... Heat insulating material 6 ... Vacuum exhaust device 7 ... High frequency heating coil

Claims (4)

A method for producing a silicon carbide single crystal comprising a step of growing a silicon carbide single crystal on a seed crystal by a sublimation recrystallization method, wherein the crucible temperature is lowered when the atmospheric pressure during crystal growth is reduced. A method for producing a silicon carbide single crystal ingot, which is characterized. 2. The method for producing a silicon carbide single crystal ingot according to claim 1, wherein a fall width of the crucible temperature is 5 ° C. or more and 100 ° C. or less. 3. The method for manufacturing a silicon carbide single crystal ingot according to claim 1, wherein in the method for manufacturing a silicon carbide single crystal ingot, the temperature is increased again to the crystal growth temperature before the decrease after the pressure is reduced. The method for producing a silicon carbide single crystal ingot according to claim 3, wherein the temperature rise after the pressure drop is performed within 40 hours or less.

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