JP4110601B2 - Method for producing silicon carbide single crystal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a silicon carbide single crystal, and more particularly to a method for producing a silicon carbide single crystal having few crystal defects and excellent quality stability with a high yield.
SiC has the characteristics that it is very stable thermally and chemically and has a wide electron energy band gap, and can be used even under high temperature and high pressure. Environment-resistant element material, radiation-resistant element material, power element material and short wavelength light-emitting element material As expected.
[0002]
[Prior art]
A silicon carbide single crystal expected as a semiconductor material is usually produced by a sublimation method using silicon carbide powder as a raw material. In the sublimation method, the raw material silicon carbide powder and the single crystal seed crystal are placed facing each other in a graphite crucible and heated to 2000 to 2400 ° C. in an inert atmosphere. The sublimation vapor generated by the decomposition and sublimation of the silicon carbide raw material powder by heating reaches the seed crystal surface held in the growth temperature range and grows epitaxially as a single crystal. In general, the gas composition deviates from the state at the time of generation due to the interaction between the inner wall of a graphite crucible used as a reaction vessel and the sublimation gas and the dissipation from the graphite wall. The sublimation gas component tends to fluctuate and greatly affects the crystallinity of the grown single crystal. As a method for suppressing and correcting these fluctuations, a method of adding a Si component and a C component has been proposed. However, crystal quality and stability are not sufficient, and further improvements are desired.
[0003]
In addition, a graphite crucible used in the prior art from the viewpoint of impurity concentration control is one of large impurity contamination sources. Japanese Laid-Open Patent Publication No. 5-306199 has been proposed as a method for preventing impurities from entering from the crucible wall, but the atmosphere gas flow is made to avoid contact with the reaction chamber wall. However, the effect is not sufficient.
On the other hand, using silicon as a raw material, the silicon vapor is heated and evaporated in a graphite crucible, the carbon vapor evaporated from the inner wall carbon of the graphite crucible reacts, moves to the silicon carbide precipitation chamber, and the inner wall has a single silicon carbide layer. A method for precipitating crystals is also known (Japanese Patent Publication No. 51-8400).
[0004]
[Problems to be solved by the invention]
Decomposition from SiC raw material powder, as sublimation gas, Si, Si ₂ C, SiC ₂ , SiC, etc. are generated, and the partial pressure of these sublimation gases is the reaction, incorporation, and component of the reaction system from the inner wall of the graphite crucible. It fluctuates from the state of decomposition sublimation due to uneven deviation or the like. The change in the sublimation gas component is likely to be incorporated into the crystal as a change in the stoichiometric ratio in the crystal precipitation process, which is the reverse reaction of the sublimation process, and further as an inclusion, an impurity element, and a crystal defect.
The fluctuation of the sublimation gas component during the single crystal growth process is considered to be taken into the crystal as a crystal defect and a cause of crystallinity deterioration such as polymorphism. It is important how to control these fluctuation factors. In the process of crystallizing as SiC from the components in the various sublimation gases described above, the respective reaction paths are necessarily different. It is considered that the reaction route strongly depends on various factors such as the temperature of the raw material, the temperature distribution change, the decomposition reaction form of the raw material SiC, the change in the raw material composition, and the like.
[0005]
Moreover, it is difficult to obtain a high-purity SiC raw material powder for obtaining a high-purity, high-quality single crystal for semiconductor use, and it is expensive. It is important how to reduce the fluctuations of these factors to achieve high purity.
An object of this invention is to provide the method of manufacturing a high quality silicon carbide single crystal with few crystal defects and inclusions.
[0006]
[Means for Solving the Problems]
Analyze and analyze the deviation and variation factors of the decomposition and sublimation composition of the raw materials, and the factors that cause damage to the substrate seed crystals, and identify substances that interact with sublimation gases, such as graphite materials, and that have adverse effects on impurities and substrate crystals. As a result of diligent research on how it can be removed or reduced from the system, a metal carbide-coated crucible was used, and the silicon evaporation gas from the silicon raw material in the crucible was brought into contact with the heated carbon material before reaching the seed crystal substrate. The present invention was completed by confirming that the above object was achieved by precipitating a SiC single crystal.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be specifically described below.
The inner surface of the crucible used in the present invention is coated with a refractory metal carbide. This metal carbide preferably has a melting point or decomposition temperature of 1900 ° C. or higher. Specifically, it is possible to use a material selected from TaC, ZrC, NbC, Ta ₂ C, TiC, Nb ₂ C, MoC, WC, Mo ₂ C, etc. as a metal carbide, or a combination of these materials. .
Even though the elemental metal constituting these carbides has heat resistance, it gradually undergoes a carbonization reaction during the crystal growth process, and the gas composition changes at that time, which is not desirable.
[0008]
The crucible is only required to have the inner surface coated with the carbide, and the base material of the crucible may be a metal element or graphite constituting the carbide.
When the base material is a metal, the metal carbide can be coated by carbonizing the crucible. Specifically, high purity graphite powder is filled in the crucible and heat treatment is performed in an inert gas atmosphere or in a vacuum, or a carbon compound such as hydrocarbon is introduced into the crucible and heat treatment is performed. I can do it.
Further, when the base material is a crucible made of graphite, the inner surface of the crucible can be formed by using an electron beam heating vapor deposition method or the like.
[0009]
The Si raw material is heated to a temperature equal to or higher than the melting point, and the evaporated Si gas comes into contact with the heated carbon material, and the generated components are lower than the carbon material because the mutual collision reaction and the contact reaction process with the carbon material are repeated. It is considered that SiC crystals are deposited on the substrate surface maintained at a temperature, and as a result, epitaxial bulk SiC crystals with few crystal defects can be obtained at a relatively high rate.
[0010]
The carbon material needs to have a structure in which the contact reaction of Si vapor occurs efficiently and can pass through, and can be composed of a porous structure or a deposited layer of carbon particles. The carbon material of the present invention is a carbonaceous material including amorphous carbon to graphitized carbon. Further, silicon carbide may coexist in advance in the carbon material. Specific examples of the carbon material include the following. The structure is plate-like and fits the inner wall of the crucible, and has through holes as shown in Fig. 1, but the through holes of the carbon plate are arranged so that their centers are shifted from each other and the gas flow does not pass linearly. It can be set to reach the vicinity of the substrate while colliding with the material. In the case of carbon powder particles, it is possible to increase the collision contact area with the gas phase molecules by setting a plurality of stages of the particles deposited on the plate.
[0011]
As SiC to be contained in the carbon material, highly purified αSiC can be used, but βSiC having a high purity and a fine particle size can be relatively easily prepared by CVD of silane gas and hydrocarbon gas. High purity β SiC fine powder prepared by CVD is preferable for carrying out the method of the present invention because stable reaction and high purity can be obtained if it is contained in a carbon body.
The total pressure of the reaction system in the crucible can be in the range of 0.01 to 1000 torr. The total pressure can be controlled by the amount of inert gas introduced.
[0012]
The vapor pressure of Si can be in the range of 0.01 to 1000 torr which is the same as the total pressure without using an inert gas, but is preferably 0.1 to 100 torr. If it is less than 0.01 torr, if the temperature setting is too close to the melting point of Si, the amount of Si vapor is small and the reaction and SiC deposition rate become too slow. If it exceeds 1000 torr, the temperature of the Si melt must be set to 2450 ° C. or higher, which is difficult due to the predetermined temperature distribution in the apparatus, that is, the temperature of the carbon material or silicon carbide single crystal substrate.
Although the Si vapor pressure is controlled by controlling the temperature of the Si raw material part, the Si amount existing in the raw material part can also be controlled temporally, that is, by the Si feed amount. In general, Si is supplied by heating and evaporating Si particles or the like deposited in the crucible. The Si vapor pressure may be a combination of both temperature control and feed amount.
[0013]
The temperature of the Si raw material portion can be set in the range of 1450 to 2500 ° C. below the set temperature of the carbon material portion, but is preferably 1500 to 2000 ° C.
Next, the temperature of the carbon material portion is preferably 1600 ° C. or higher and higher than the seed substrate temperature, and the difference does not exceed 300 ° C. If the temperature difference from the seed substrate exceeds 300 ° C., defects and strains are likely to be introduced into the grown SiC crystal, so a desirable set temperature is 1800 to 2600 ° C.
The substrate temperature needs to be higher than the temperature of the Si raw material portion and lower than the temperature of the carbon material portion with a temperature difference within 300 ° C. Specifically, 1700 to 2300 ° C is desirable within the range of 1500 to 2500 ° C. When the substrate temperature is low, the stoichiometry of the precipitated crystals tends to be on the Si-rich side and polymorphism tends to occur. If it is high, introduction of various crystal defects and polymorphism are likely to occur.
[0014]
In order to obtain a high-resistance single crystal for semiconductor use, it is one of the essential conditions to use a high-purity raw material, but a semiconductor grade can be used for a high-purity Si raw material. Impurity doping can also be easily performed if necessary, for example, by mixing a dopant element in the raw material portion.
The growth mechanism of SiC single crystal, that is, the mechanism by which Si vapor from the Si raw material part comes into contact with the carbon material and grows as a SiC single crystal on the seed substrate is uncertain, but the Si vapor from the Si raw material part comes into contact with the carbon material. It is considered that unreacted Si and Si ₂ C, SiC, SiC _{2 and the} like exist mainly in the gas phase, and these gases react or interact with each other and precipitate as SiC on the seed crystal substrate. It is done.
These reaction product gas compositions can be varied depending on conditions such as Si raw material temperature, carbon material temperature, pressure, and inert gas pressure. By combining these conditions, a SiC single crystal can be stably grown on the substrate surface.
[0015]
When silicon carbide is contained in the carbon material, silicon carbide works as an initiator for the reaction between the Si vapor and the carbon material, and at the same time, the pores and reaction active points are dispersed in the carbon material. It is thought that it provides a reaction field with good time stability. The amount of silicon carbide contained in the carbon material can be 0.1 to 10 moles per mole of carbon. When silicon carbide is contained in the carbon material, the ratio of the Si raw material to the carbon material can be 0.1 mol or more of Si with respect to 1 mol of the carbon material. If the amount of Si is less than 0.1 mol, it does not change from the conventional SiC raw material sublimation method.
[0016]
In order to obtain a large single crystal bulk with good quality and a large area according to the present invention, a batch system in which the raw material Si and carbon material are newly exchanged and the operation is repeated can be adopted. The Si raw material and the silicon carbide-containing carbon material can be continuously or intermittently supplied to each part, and the substrate position can be moved according to the single crystal growth, so that the single crystal growth can be continued. Large crystals can be achieved by increasing the growth time. As for the substrate, if a seed crystal cut out from the previously grown single crystal is newly arranged as a substrate and operated, a high-quality single crystal with further reduced crystal defects can be grown.
[0017]
【Example】
The present invention will be specifically described below with reference to examples.
FIG. 1 is a schematic cross-sectional view of the crucible used in the embodiment and the inside thereof.
In the figure, 1 is a seed crystal SiC substrate, 2 is a Si raw material, 3 is a SiC-containing carbon material, 4 is a tantalum carbide-coated crucible, 41 is the same lid, 5 is a grown SiC single crystal, 6 is a funnel shaped plate, 61 is It is a small hole in the same plate. The tantalum carbide-coated crucible used here was manufactured as follows.
First, 165 g of high-purity graphite powder is charged into a Ta crucible 170 × 46φ (thickness: 0.5 mm), and this is removed in a 2E (−3) torr vacuum for 30 minutes in a graphite crucible large enough to accommodate this. After gassing, treatment was performed at 2300 ° C. for 5 hours in an argon atmosphere of 760 torr. The inner wall of the crucible after the treatment was uniformly gold. In the X-ray analysis of the crucible wall, Ta ₂ C, TaC and Ta peaks were observed.
[0018]
(Example 1)
A seed crystal having a diameter of 24 mm and a thickness of 0.4 mm with a 6H—SiC single crystal (0001) plane as the growth substrate 1 was placed in the center of the lid 41 of the tantalum carbide-coated crucible. As shown in FIG. 1, 120 g of semiconductor-grade Si crystal pieces 2 were accommodated in the crucible. The silicon carbide-containing carbon material 3 was set in a two-stage mixed powder of 65 g of high-purity graphite fine powder and 40 g of SiC on a Ta plate (small hole diameter 1.2 mm) whose surface was coated with TaC. This crucible was set in a quartz tube of a high frequency furnace. First, the inside of the reaction apparatus was pulled to 1 × E (−3) torr, and a heat treatment was performed in which the Ta crucible was heated to 1450 ° C. and held for 30 minutes. The seed crystal temperature was raised to 2050 ° C., the argon atmosphere pressure was 120 torr, and the operation was performed for 5 hours. The crystal tip was almost flat and had a circular cross section with a spiral pattern around the center. The average diameter was 39.3 mm and the height was 7.5 mm. As a result of cutting and polishing the cross section in the growth direction of the crystal and performing microscopic observation, no inclusion was observed and the crystal defect density was on the order of 2.8 × 10 / cm ² . In addition, polymorph identification by Raman spectroscopy was 6H-SiC from the peak position, and it was confirmed that the single crystal was a good quality with no other polymorphs mixed.
[0019]
(Comparative example)
Crystal growth was performed under the same conditions as in Example 1 except that a graphite crucible was used as the crucible and no SiC powder was mixed with the carbon material. The crystal size was almost equal, but the crystal surface was rough with unevenness. Although there was no inclusion, the defect density in the microscopic observation of the crystal cross section was about 20% higher than that in the example.
[0020]
【The invention's effect】
A high-quality SiC single crystal with few crystal defects can be efficiently epitaxially grown on a SiC seed substrate stably and at a high speed from the reaction between the Si raw material and the carbon material.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a crucible used as an example in the method of the present invention and its interior.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Seed-crystal SiC substrate 2 Si raw material 3 SiC containing carbon material 4 Tantalum carbide covering crucible 5 Grown SiC single crystal 6 Funnel-shaped eye plate 41 Crucible lid 61 Small hole of eye plate

Claims (6)

In a method for producing a silicon carbide single crystal by a sublimation method in which a SiC single crystal is grown on a seed substrate crystal, a crucible coated with metal carbide is used, and the silicon raw material in the crucible is within a range of 1450 to 2500 ° C. The evaporated gas generated from the silicon raw material was brought into contact with the carbon material heated within the range of 1800 to 2600 ° C. above the heating temperature of the silicon raw material and higher than 300 ° C. above the seed crystal substrate temperature . Then , it reaches on the seed crystal substrate heated within the range of 1500-2500 degreeC , The manufacturing method of the silicon carbide single crystal characterized by the above-mentioned. 2. The method for producing a silicon carbide single crystal according to claim 1, wherein the pressure in the reaction system is 0.01 to 1000 torr. The method for producing a silicon carbide single crystal according to claim 1 or 2, wherein the metal carbide covering the crucible is a carbide of Ta. The method for producing a silicon carbide single crystal according to any one of claims 1 to 3, wherein the carbon material is disposed between the silicon raw material and the seed crystal. The method for producing a silicon carbide single crystal according to claim 1, wherein the carbon material is composed of a plurality of porous structures or a deposited layer of a plurality of carbon material particles. The silicon carbide single crystal according to any one of claims 1 to 5 , wherein the carbon material contains silicon carbide.

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