JP4819069B2 - Method for producing silicon carbide single crystal - Google Patents

Description

  The present invention relates to a method for producing a silicon carbide single crystal by sublimating a silicon carbide raw material, and relates to a method for producing a silicon carbide single crystal excellent in quality stability with few crystal defects at a high yield. Silicon carbide (SiC) has a feature that it is thermally and chemically very stable and has a wide electron energy band gap, and can be used even under high temperature and high pressure. It is expected as a wavelength light emitting device material.

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 general, in the sublimation method, a raw material silicon carbide powder and a single crystal seed crystal are placed facing each other in a graphite crucible and heated to 2000 to 2400 ° C. in an inert atmosphere. Sublimation vapor generated by decomposition and sublimation of the silicon carbide raw material by heating reaches the growth region, precipitates with the crystal orientation aligned on the surface of the seed crystal held at the growth temperature, and grows epitaxially as a single crystal. Generally, the gas composition shifts from the state generated from the raw material due to the interaction between the inner wall of a graphite crucible used as a reaction vessel and the sublimation gas, or the sublimation of carbon or the like from the graphite wall. The sublimation gas component tends to fluctuate, which greatly affects the crystallinity of the grown single crystal. As a method for suppressing and correcting the fluctuation of the sublimation gas component during the crystal growth process, one of Si component and C component is added. For example, there are Patent Document 1 in which Si content is excessively mixed with the raw material and Patent Document 2 in which Si ₃ N ₄ is added. Further, Patent Document 3 is proposed in which introduction of silicon component gas and carbon component gas is used in combination. However, crystal quality and stability are not sufficient, and further improvements are desired. There is also a strong demand for large crystals. The graphite crucible used in the prior art from the viewpoint of impurity concentration control is one of the large impurity contamination sources. As a method for preventing impurities from entering from the crucible wall, Patent Document 4 is proposed in which an atmospheric gas flow is flowed so as to avoid contact with the reaction chamber wall, but the effect is not sufficient.
Japanese Patent Publication No. 51-29518 Japanese Patent Laid-Open No. 6-1698 JP-A-7-82090 JP-A-5-306199

Decomposition from raw material powder, sublimation gas mainly produces Si, Si ₂ C, SiC ₂ etc. in addition to SiC, and the partial pressure of these sublimation gases is the reaction and incorporation with the inner wall of graphite crucible. , And non-uniformity between components from the reaction system will vary from the sublimation state. The fluctuation of 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 considered to be a reverse reaction of the so-called sublimation process, and further as an inclusion, impurity element, and crystal defect. On the other hand, it is known that the substrate is maintained at the growth temperature and generally lower than the raw material temperature, but if a graphite material is present in the vicinity of or in contact with the substrate, etching of the substrate occurs and damages the substrate crystal.

  Further, the change in the sublimation gas component ratio inevitably differs in each reaction path in the process of crystallizing as SiC from the above-mentioned chemical species in the various sublimation gases. Therefore, it is also an incentive to grow a crystal having a polymorphism different from that of the seed substrate crystal. As a result, the obtained single crystal has a low quality with many crystal defects and polymorphs. An object of the present invention is to obtain a silicon carbide single crystal that eliminates the above-mentioned drawbacks and has few inclusions, impurity elements, and crystal defects.

As a result of intensive investigations on deviations and fluctuation factors in the sublimation composition of the raw materials and the effects of these on the single crystal produced, the present inventors achieved the object by using a specific crucible containing the silicon carbide raw material. The present invention was completed after confirming that it was possible. That is, according to the present invention, in a method for producing a silicon carbide single crystal on a silicon carbide substrate by a sublimation recrystallization method, a graphite crucible whose inner surface in contact with the silicon carbide raw material is coated with tantalum carbide is used as a crucible for containing the silicon carbide raw material. It is the method characterized by using.

  When a single crystal is grown on a silicon carbide substrate from the raw material silicon carbide by sublimation recrystallization, a graphite crucible whose inner surface is coated with tantalum carbide is used to stably produce a high-quality SiC single crystal with few crystal defects. Epitaxial growth can be efficiently performed on the SiC seed substrate. Large crystals can also be easily grown.

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.

  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.

The thickness of the metal carbide coating may be as long as it is necessary to prevent the reaction between the metal, graphite, etc. of the base material and the sublimation gas during the production of the silicon carbide single crystal, and generally 10 μm or more. . If the above-described metal carbide reaction crucible is used, decomposition from the raw material powder, the main sublimation gas is SiC, Si, Si ₂ C, SiC ₂ or the like, but unlike the case of using a graphite crucible, a metal crucible, Interaction with the inner wall of these sublimation gases and uniformity among components from the reaction system are maintained, and fluctuations from the state during decomposition sublimation can be remarkably suppressed. Further, the SiC single crystal substrate maintained at the growth temperature can be hardly suppressed by using the crucible of the present invention because the carbon material is in contact with or near the SiC material. As a result, in the crystal precipitation process, which is considered to be the reverse reaction of the decomposition and sublimation process, the negative factors of crystallinity such as fluctuation of stoichiometry, inclusion, impurity element contamination, crystal defect, polymorphism contamination, etc. can be greatly reduced. A high quality SiC single crystal can be epitaxially grown on a seed substrate crystal.

  As the raw material SiC, an abrasive grade by the Atchison method can be used, but it is a fine powder that has been highly purified, and a fine particle size is preferable in order to obtain a sublimation reaction area. Further, it may be used as a porous green compact or a sintered body. On the other hand, β-SiC has a high purity and can be prepared relatively easily by CVD in a hydrogen atmosphere of silane gas and hydrocarbon gas, and is suitable as a high purity raw material. It is desirable to use it in the form of a green compact in order to increase the packing density of the raw material. In order to obtain a large single crystal bulk having a high quality and a large area using the crucible material according to the present invention, if the SiC raw material is intermittently or continuously supplied to the portion where the raw material SiC is disposed, the inner wall of the crucible, the sublimation gas, From the fact that the interaction is extremely small, the decomposition and sublimation balance of the raw material staying in the sublimation region is good, and the growth of the single crystal can be sustained with good time stability.

  The configuration of the raw material supply system can be relatively easily performed by, for example, constructing a crucible and a raw material feeder with the metal component of the metal carbide described above and then carbonizing the inner surface by carbonization. In order to supply raw material SiC intermittently or continuously during crystal synthesis, it is connected to the raw material part of the crucible, and is continuously or intermittently powdered from the raw material feeder in a supply pipe maintaining the inert gas pressure equal to the crucible internal pressure. Or it may carry in with the form of a compact and a sintered grain. In order to further improve the quality, if a seed crystal cut out from a single crystal once grown is newly placed and the operation is repeated under the same conditions, a higher quality single crystal with further reduced crystal defects is grown. Can be. Other heating devices, temperature conditions, and the like may be the same as those of a conventionally known sublimation recrystallization method. That is, a high-frequency heating device can be used as the heating device, and the temperature is 2000 to 2400 ° C. in the raw material zone and 1800 to 2300 ° C. in the substrate.

Detailed explanation is given below with reference to schematic diagrams and reference examples. FIG. 1 is a schematic view showing an example of arrangement in the crucible. In FIG. 1, 1 is a Ta crucible whose inner surface is coated with tantalum carbide, 2 is a silicon carbide seed crystal, 3 is a raw material SiC powder, 4 is a raw material powder supply pipe (only a part is shown), 5 is a grown single crystal, 6 is It is a feedstock guide plate.
[ Reference example]

First, the Ta crucible 120 × 46φ (thickness 0.5 mm) is carbonized. First, 68 g of high-purity graphite powder is filled in the Ta crucible, and the graphite crucible having a size capable of accommodating this is 30 in a vacuum of 2E-3. After degassing for 5 minutes, 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 crucible wall X-ray analysis, Ta ₂ C, TaC, and Ta peaks were observed (here, the raw materials were not continuously supplied, and therefore the crucibles 4 and 6 in FIG. 1 were not installed).

A seed crystal having a diameter of 250 mm and a thickness of 1.5 mm with a 6H—SiC single crystal (0001) plane as a growth surface was mechanically held and installed at the center of the lid of the Ta crucible whose inner wall was carbonized. In the crucible, 220 g of industrially purified SiC 400 mesh with high purity as shown in FIG. 1 was accommodated. The crucible was housed in a graphite mantle tube, and a heat insulating material was further arranged outside the crucible tube and set in the quartz tube. This was operated for 5 hours using a high-frequency heating furnace at a raw material temperature of 2300 ° C., a seed crystal temperature of 2250 ° C. and an argon atmosphere pressure of 100 torr. At this time, the tip of the crystal had a cross-sectional shape close to a circle, a diameter of 45.3 mm, and a height of 10.6 mm. As a result of cutting and polishing the cross section in the crystal growth direction and observing under a microscope, there was no inclusion and the crystal defect density was 1.3E2 / cm ² . Also, an electron microscope sample was prepared by ion etching, and as a result of high-resolution observation, it was confirmed that both the interface and the growth edge had 6H—SiC lattice spacing, and epitaxial growth was maintained.

(Comparative example)
Single crystals were grown under the same conditions as in the reference example except that the crucible in the reference example was replaced with a graphite crucible. The growth crystal size was about 30% smaller in volume than the reference example. In the microscopic observation of the crystal cross section, an inclusion was scattered and the defect density was about three times that of the reference example. Furthermore, in high-resolution observation with an electron microscope, 15R was rarely mixed with the 4H type. Many stacking faults were also observed.

It is sectional drawing which shows the state which grew the silicon carbide single crystal using the crucible of this invention.

Explanation of symbols

1 Tantalum crucible whose inner surface is coated with tantalum carbide 2 Silicon carbide seed crystal 3 Raw material SiC powder 4 Raw material powder supply tube 5 Growing single crystal 6 Feed material guide plate

Claims (1)

In a method for producing a silicon carbide single crystal on a silicon carbide substrate by a sublimation recrystallization method, a graphite crucible having an inner surface in contact with the silicon carbide raw material coated with tantalum carbide is used as a crucible for containing the silicon carbide raw material. A method for producing a silicon carbide single crystal.

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