JP5793815B2 - Seed material for liquid crystal epitaxial growth of single crystal silicon carbide and liquid crystal epitaxial growth method of single crystal silicon carbide - Google Patents

Description

  The present invention relates to a seed material for liquid crystal epitaxial growth of single crystal silicon carbide and a liquid phase epitaxial growth method of single crystal silicon carbide using the seed material.

  Silicon carbide (SiC) can realize high temperature resistance, high voltage resistance, high frequency resistance, and high environmental resistance that cannot be realized by conventional semiconductor materials such as silicon (Si) and gallium arsenide (GaAs). It is believed that. For this reason, silicon carbide is expected as a semiconductor material for next-generation power devices and a semiconductor material for high-frequency devices.

  Conventionally, as a method for growing single crystal silicon carbide, for example, the following Patent Document 1 proposes a sublimation recrystallization method (an improved Rayleigh method). In this improved Rayleigh method, a seed material made of single-crystal silicon carbide is disposed in the low temperature side region in the crucible, and a raw material powder containing Si as a raw material is disposed in the high temperature side region. And after making the inside of a crucible into inert atmosphere, the raw material powder arrange | positioned in the high temperature side area | region is sublimated by heating to the high temperature of 1450 to 2400 degreeC. As a result, silicon carbide can be epitaxially grown on the surface of the seed material disposed in the low temperature region.

  However, the improved Rayleigh method is a method of growing silicon carbide crystals by providing a temperature gradient in the gas phase. For this reason, when the improved Rayleigh method is used, a large apparatus is required for epitaxial growth of silicon carbide, and process control of silicon carbide epitaxial growth becomes difficult. Therefore, there is a problem that the manufacturing cost of the silicon carbide epitaxial growth film is increased. Also, silicon carbide epitaxial growth in the gas phase is non-equilibrium. For this reason, there are problems that crystal defects are likely to occur in the formed silicon carbide epitaxially grown film and that the crystal structure is likely to be rough.

  As an epitaxial growth method of silicon carbide other than the modified Rayleigh method, for example, there is a metastable solvent epitaxy (MSE) method proposed in Patent Document 2 or the like, which is a method of epitaxially growing silicon carbide in a liquid phase. .

  In the MSE method, a seed material made of crystalline silicon carbide such as single crystal silicon carbide or polycrystalline silicon carbide and a feed material made of silicon carbide are opposed to each other with a small interval of, for example, 100 μm or less, and Si is interposed therebetween. A molten layer is interposed. And silicon carbide is epitaxially grown on the surface of the seed material by heat treatment in a vacuum high temperature environment.

  In this MSE method, it is considered that a silicon carbide epitaxial growth film is formed by the concentration gradient of carbon dissolved in the Si melt layer due to the difference between the chemical potential of the seed material and the chemical potential of the feed material. It has been. For this reason, unlike the case of using the improved Rayleigh method, it is not always necessary to provide a temperature difference between the seed material and the feed material. Therefore, when the MSE method is used, the silicon carbide epitaxial growth process can be easily controlled with a simple apparatus, and a high-quality silicon carbide epitaxial growth film can be stably formed.

In addition, an advantage that a silicon carbide epitaxial growth film can be formed on a seed substrate having a large area, and since the Si melt layer is extremely thin, carbon from the feed material is easily diffused, and the temperature of the epitaxial growth process of silicon carbide can be reduced. There is also an advantage.

  Therefore, the MSE method is considered to be an extremely useful method as an epitaxial growth method of single crystal silicon carbide, and research on the MSE method is actively conducted.

Japanese Patent Laid-Open No. 2005-97040 JP 2008-230946 A

  As described above, in the MSE method, it is considered that the feed material and the seed material need to be selected so that the free energy of the feed material is higher than the free energy of the seed material. For this reason, for example, Patent Document 2 describes that the free energy is made different between the feed substrate and the seed substrate by making the crystal polymorph of the feed substrate and the seed substrate different. Specifically, it is described that when the feed substrate is constituted by a polycrystalline 3C-SiC substrate, the seed substrate is constituted by a single crystal 4H-SiC substrate having a lower free energy than that of the 3C-SiC substrate. .

  Here, the polycrystalline 3C-SiC substrate can be easily manufactured by a CVD method. For this reason, as described in Patent Document 2, by using a 3C—SiC substrate as a feed substrate, the formation cost of the silicon carbide epitaxial growth film can be kept low.

  However, among silicon carbide substrates such as 4H—SiC substrates and 3C—SiC substrates, 3C—SiC substrates have the highest free energy. For this reason, it has been considered that a 3C—SiC substrate cannot be used as a seed substrate that requires low free energy. Therefore, in Patent Document 2, a single crystal 4H—SiC substrate that is difficult to manufacture and is expensive is used as a seed substrate, and there is a problem that the formation cost of the silicon carbide epitaxial growth layer is high.

  The present invention has been made in view of the above points, and an object thereof is to provide an inexpensive seed material for silicon carbide liquid phase epitaxial growth.

  As a result of diligent research, the present inventor has some polycrystalline silicon carbide materials whose crystal polymorph is 3C, those that are likely to elute into the silicon molten layer and those that are less likely to elute. It has been found that those which are less likely to be eluted can be suitably used as seed materials for liquid phase epitaxial growth of silicon carbide. As a result, the present inventor came to make the present invention.

That is, the seed material for liquid crystal epitaxial growth of single crystal silicon carbide according to the present invention is a seed material used for the liquid phase epitaxial growth method of single crystal silicon carbide. The seed material for single-crystal silicon carbide liquid phase epitaxial growth according to the present invention has a surface layer containing polycrystalline silicon carbide whose crystal polymorph is 3C. A first-order diffraction peak corresponding to at least one of the (111) crystal plane, the (200) crystal plane, the (220) crystal plane, and the (311) crystal plane is observed by X-ray diffraction of the surface layer. The average crystallite diameter calculated from at least one first-order diffraction peak is greater than 700 mm. For this reason, the single crystal silicon carbide liquid phase epitaxial growth seed material according to the present invention is less likely to elute into the silicon melt layer. Therefore, by using the seed material for single crystal silicon carbide liquid phase epitaxial growth according to the present invention, a concentration gradient in the silicon melt layer can be suitably formed, and liquid phase epitaxial growth of silicon carbide can be suitably performed. In addition, when the average crystallite diameter is larger than 700 mm, the elution into the silicon melt layer is less likely to occur because the ratio of the grain boundaries having high reactivity of the polycrystalline silicon carbide crystal in the surface layer decreases. Conceivable.

  In the present invention, the “crystallite diameter” refers to a crystallite diameter calculated based on the Hall formula shown in the following formula (1).

β · (cos θ) / λ = 2η · (sin θ) / λ + 1 / ε (1)
However,
β: half width,
θ: Black angle of diffraction line,
λ: wavelength of X-ray used for measurement,
η: value of non-uniform strain of the crystal,
ε: average size of crystallite diameter,
It is.

  Moreover, the surface layer of the seed material for single crystal silicon carbide liquid phase epitaxial growth according to the present invention contains polycrystalline silicon carbide having a crystal polymorph of 3C. Therefore, unlike the case where the surface layer includes polycrystalline silicon carbide whose crystal polymorph is 4H, 6H, or the like, or is made of single crystal silicon carbide, the surface layer is easily and easily formed by a CVD (Chemical Vapor Deposition) method. It can be manufactured at low cost.

  That is, by using the seed material for single crystal silicon carbide liquid phase epitaxial growth according to the present invention, an epitaxial growth film of single crystal silicon carbide can be formed easily and inexpensively.

  In the present invention, the “liquid phase epitaxial growth method” means that a concentration gradient of graphite that melts in the silicon melt layer is formed by heating the seed material and the feed material in a state of facing each other through the silicon melt layer, A method of epitaxially growing single crystal silicon carbide on a seed material by the concentration gradient.

In the present invention, “X-ray diffraction” refers to diffraction using X-rays (CuK _α- rays) of 8.048 keV.

  In the present invention, a “feed material” refers to a member that supplies a material for epitaxial growth of single crystal silicon carbide such as Si, C, and SiC. On the other hand, the “seed material” refers to a member in which single crystal silicon carbide grows on the surface.

  Ratio of the intensity of the first-order diffraction peak corresponding to the (111) crystal plane to the total intensity of at least one first-order diffraction peak ((the intensity of the first-order diffraction peak corresponding to the (111) crystal plane) / (at least one 1 The total intensity of the next diffraction peak)) is preferably 5 or more. According to this configuration, the epitaxial growth rate of single crystal silicon carbide can be increased. This is considered to be because the concentration gradient in the silicon melt layer increases because the exposure ratio of the (111) crystal plane, which is less likely to elute into the silicon melt layer, increases.

  In addition, an epitaxially grown film of hexagonal single crystal silicon carbide having excellent characteristics can be formed. This is because a (111) crystal plane is equivalent to a hexagonal (0001) crystal plane, and stacking errors easily occur. As a result, when many (111) crystal planes are exposed, it is considered that the epitaxial growth of hexagonal single crystal silicon carbide suitably proceeds.

  In the present invention, it is preferable that the proportion of the (111) crystal planes observed by surface X-ray diffraction with the orientation angle of 67.5 ° or more is 80% or more. According to this configuration, the epitaxial growth rate of single crystal silicon carbide can be further effectively increased. This is because the degree of exposure of the surface having a lower stability than the (111) crystal face of the crystal exposing the (111) crystal face can be lowered, so that the crystal exposing the (111) crystal face is exposed. It is thought that this is because the elution of can be suppressed.

  In the present invention, the surface layer preferably contains polycrystalline silicon carbide having a crystal polymorphism of 3C as a main component, and is preferably substantially composed of polycrystalline silicon carbide having a crystal polymorphism of 3C. According to this configuration, the epitaxial growth rate of single crystal silicon carbide can be further effectively increased.

  In the present invention, the “main component” refers to a component contained by 50% by mass or more.

  In the present invention, “substantially consists of polycrystalline silicon carbide whose crystal polymorph is 3C” means that it contains no components other than impurities other than polycrystalline silicon carbide whose crystal polymorph is 3C. To do. Usually, the impurity contained in the case of “substantially consisting of polycrystalline silicon carbide whose crystal polymorph is 3C” is 5% by mass or less.

  The seed material for single-crystal silicon carbide liquid phase epitaxial growth according to the present invention may include a support material and a polycrystalline silicon carbide film that is formed on the support material and forms a surface layer. In that case, the thickness of the polycrystalline silicon carbide film is preferably in the range of 30 μm to 800 μm.

  Moreover, the seed material for single crystal silicon carbide liquid phase epitaxial growth according to the present invention may be composed of a polycrystalline silicon carbide substrate containing polycrystalline silicon carbide having a crystal polymorph of 3C.

  In the method of liquid crystal epitaxial growth of single crystal silicon carbide according to the present invention, the surface layer of the seed material for liquid crystal epitaxial growth of single crystal silicon carbide according to the present invention and the surface layer of the feed material having a surface layer made of silicon carbide are fused with silicon. The single crystal silicon carbide is epitaxially grown on the surface layer of the seed material by heating in a state of being opposed to each other. According to this method, an epitaxially grown film of single crystal silicon carbide can be formed at low cost. Further, it is not always necessary to provide a temperature difference between the seed material and the feed material. Therefore, the single crystal silicon carbide epitaxial growth process can be easily controlled with a simple apparatus, and a high-quality single crystal silicon carbide epitaxial growth film can be stably formed.

  According to the present invention, an inexpensive seed material for silicon carbide liquid phase epitaxial growth can be provided.

It is a schematic diagram for demonstrating the epitaxial growth method of the single crystal silicon carbide in one Embodiment of this invention. It is a schematic sectional drawing of the feed board | substrate in one Embodiment of this invention. 1 is a schematic cross-sectional view of a seed substrate in an embodiment of the present invention. It is a schematic sectional drawing of the feed board | substrate in a modification. It is schematic-drawing sectional drawing of the seed substrate in a modification. It is an X-ray diffraction chart of samples 1 to 4. It is a schematic diagram for demonstrating the measuring method of the orientation of a (111) crystal plane. 4 is a graph showing the orientation of (111) crystal plane in Sample 1. 4 is a graph showing the orientation of (111) crystal plane in Sample 2. 4 is a graph showing the orientation of (111) crystal plane in Sample 3. 6 is a graph showing the orientation of a (111) crystal plane in Sample 4. It is a graph which shows the growth rate of the single crystal silicon carbide epitaxial growth film in samples 1, 2 and 4. 5 is a graph showing the growth rate of single crystal silicon carbide epitaxial growth films in samples 3 and 4. FIG. It is a SEM photograph of a seed substrate (sample 3) after execution of a liquid phase epitaxial growth experiment in an example. It is a SEM photograph of a seed substrate (sample 2) after execution of a liquid phase epitaxial growth experiment in a comparative example.

  Hereinafter, an example of the preferable form which implemented this invention is demonstrated. However, the following embodiments are merely examples. The present invention is not limited to the following embodiments.

  FIG. 1 is a schematic diagram for explaining an epitaxial growth method of single crystal silicon carbide in the present embodiment.

  In the present embodiment, an example of forming an epitaxially grown film of single crystal silicon carbide using the MSE method will be described.

  In the present embodiment, as shown in FIG. 1, in a container 10, a seed substrate 12 as a seed material and a feed substrate 11 as a feed material are combined with a main surface 12 a of the seed substrate 12 and a main surface of the feed substrate 11. It arrange | positions so that 11a may oppose through a silicon plate. In this state, the seed substrate 12 and the feed substrate 11 are heated to melt the silicon plate. By doing so, the seed substrate 12 and the feed substrate 11 are opposed to each other with the silicon melt layer 13 therebetween. By maintaining this state, raw materials such as silicon, carbon and silicon carbide are eluted from the seed substrate 12 side into the silicon melt layer 13. As a result, a concentration gradient is formed in the silicon melt layer 13. As a result, single crystal silicon carbide is epitaxially grown on main surface 12a of seed substrate 12, and single crystal silicon carbide epitaxial growth film 20 is formed. In addition, the thickness of the silicon molten layer 13 is very thin, for example, can be about 10 μm to 100 μm.

(Seed substrate 12)
The seed substrate 12 has a surface layer containing polycrystalline silicon carbide whose crystal polymorph is 3C. Specifically, as shown in FIG. 3, in the present embodiment, the seed substrate 12 includes a support material 12b made of graphite and a polycrystalline silicon carbide film 12c. The support 12b made of graphite has high heat resistance that can sufficiently withstand the epitaxial growth process of silicon carbide. The support material 12b made of graphite has a thermal expansion coefficient similar to that of the single crystal silicon carbide epitaxial growth film 20. Therefore, silicon carbide epitaxial growth film 20 can be suitably formed by using support material 12b made of graphite.

  Specific examples of graphite include natural graphite, artificial graphite, petroleum coke, coal coke, pitch coke, carbon black, and mesocarbon. Examples of the method for producing the support material 12b made of graphite include the production method described in JP-A-2005-132711.

  Polycrystalline silicon carbide film 12c is formed to cover the main surface and side surfaces of support material 12b. Polycrystalline silicon carbide film 12c includes polycrystalline silicon carbide. The surface layer of the seed substrate 12 is formed by the polycrystalline silicon carbide film 12c. Note that the polycrystalline silicon carbide film 12c in the present embodiment preferably includes polycrystalline 3C—SiC as a main component, and is preferably substantially composed of polycrystalline 3C—SiC. That is, in the present embodiment, the surface layer of the seed substrate 12 preferably includes polycrystalline 3C—SiC as a main component, and is preferably substantially composed of polycrystalline 3C—SiC. By doing so, the growth rate of the single crystal silicon carbide epitaxial growth film 20 can be increased.

  Thickness t12 of polycrystalline silicon carbide film 12c is preferably in the range of 30 μm to 800 μm, more preferably in the range of 40 μm to 600 μm, and still more preferably in the range of 100 μm to 300 μm. If the thickness t12 of the polycrystalline silicon carbide film 12c is too thin, the support material 12b made of graphite is exposed when the single crystal silicon carbide epitaxial growth film 20 is formed, and suitable single crystal carbonization due to elution from the support material 12b. The silicon epitaxial growth film 20 may not be obtained. On the other hand, if the thickness t12 of the polycrystalline silicon carbide film 12c is too thick, cracks may easily occur in the polycrystalline silicon carbide film 12c.

  The method for forming polycrystalline silicon carbide film 12c is not particularly limited. The polycrystalline silicon carbide film 12c can be formed by, for example, a CVD (Chemical Vapor Deposition) method or a sputtering method. In particular, in this embodiment, since the polycrystalline silicon carbide film 12c contains polycrystalline 3C-SiC, a dense polycrystalline silicon carbide film 12c can be easily and inexpensively formed by the CVD method.

  The polycrystalline silicon carbide film 12c constituting the surface layer of the seed substrate 12 is at least one of (111) crystal plane, (200) crystal plane, (220) crystal plane, and (311) crystal plane by X-ray diffraction. A first order diffraction peak corresponding to is observed, and an average crystallite diameter calculated from at least one of the first order diffraction peaks is larger than 700 mm.

  By the way, conventionally, as described above, it is necessary to select the feed material and the seed material so that the free energy of the feed material is higher than the free energy of the seed material, and the 3C-SiC substrate having a low free energy is used as the feed substrate. When used as a substrate, a 3C-SiC substrate cannot be used as a seed substrate, and a silicon carbide substrate having another crystal polymorphism such as a 4H-SiC substrate or a 6H-SiC substrate must be used as a seed substrate. It was thought.

  However, as a result of earnest research, the present inventor has some 3C-SiC substrates that are likely to be eluted into the silicon molten layer and those that are less likely to be eluted into the silicon molten layer. It has been found that those that are less likely to be eluted can be suitably used as seed materials for liquid phase epitaxial growth of silicon carbide. As a result of further diligent research, the present inventor has found that elution into the silicon melt layer is less likely to occur as the average crystallite size is larger. In accordance with this finding, the present inventor used a substrate having a surface layer containing polycrystalline silicon carbide having a crystal polymorph of 3C and having an average crystallite diameter of 700 mm or less as the seed substrate 12. By doing so, silicon carbide could be suitably grown by liquid phase epitaxy even when using the seed substrate 12 whose surface layer contains polycrystalline 3C-SiC and can be produced at low cost by the CVD method. The reason for this is that as the average particle size increases, the proportion of polycrystalline silicon carbide crystals with high reactivity in the surface layer decreases, and elution of the surface layer into the silicon melt layer is less likely to occur. It is done.

The ratio of the intensity of the first-order diffraction peak corresponding to the (111) crystal plane to the total intensity of at least one first-order diffraction peak observed by X-ray diffraction of the polycrystalline silicon carbide film 12c (((111) crystal plane The intensity of the first-order diffraction peak corresponding to) / (total intensity of at least one first-order diffraction peak)) is preferably 5 or more. In this case, the epitaxial growth rate of single crystal silicon carbide can be increased. This is considered to be because the exposure ratio of the (111) crystal plane is less likely to be eluted into the silicon melt layer. In this case, it is possible to form the hexagonal single crystal silicon carbide epitaxially grown film 20 having excellent characteristics. This is because the (111) crystal face is equivalent to the (0001) crystal face of hexagonal crystal, and when many (111) crystal faces are exposed, the epitaxial growth of hexagonal single crystal silicon carbide suitably proceeds. This is probably because of this.

  A typical example of the hexagonal single crystal silicon carbide is single crystal silicon carbide whose crystal polymorph is 4H or 6H. Single crystal silicon carbide (4H-SiC, 6H-SiC) whose crystal polymorph is 4H or 6H has a wide band gap and excellent heat resistance compared to other crystal polymorphs of silicon carbide. There is an advantage that a semiconductor device can be realized.

  The polycrystalline silicon carbide film 12c preferably has a ratio of 80% or more of the (111) crystal plane observed by X-ray diffraction having an orientation angle of 67.5 ° or more. . In this case, the growth rate of the single crystal silicon carbide epitaxial growth film 20 can be further effectively increased. This is because the degree of exposure of the surface having a lower stability than the (111) crystal face of the crystal exposing the (111) crystal face can be lowered, so that the crystal exposing the (111) crystal face is exposed. It is thought that this is because the elution of can be suppressed.

(Feed substrate 11)
In the present embodiment, the feed substrate 11 is not particularly limited as long as it is less likely to elute into the silicon molten layer 13 than the seed substrate 12. For this reason, as the feed substrate 11, for example, it has a surface layer containing polycrystalline silicon carbide whose crystal polymorph is 3C, and (111) crystal plane, (200) crystal plane, ( 220) A first-order diffraction peak corresponding to at least one of the crystal plane and (311) crystal plane is observed, and a substrate having an average crystallite diameter calculated from at least one first-order diffraction peak of 700 mm or less is preferable. Can be used.

  FIG. 2 shows a schematic cross-sectional view of the feed substrate 11 of the present embodiment. As shown in FIG. 2, in this embodiment, specifically, the feed substrate 11 includes a support material 11b made of graphite and a polycrystalline silicon carbide film 11c. The support material 11b made of graphite has high heat resistance that can sufficiently withstand the epitaxial growth process of silicon carbide. The support material 11b made of graphite has a thermal expansion coefficient similar to that of the single crystal silicon carbide epitaxial growth film 20. Therefore, the single crystal silicon carbide epitaxial growth film 20 can be suitably formed by using the support material 11b made of graphite.

  Specific examples of graphite include natural graphite, artificial graphite, petroleum coke, coal coke, pitch coke, carbon black, and mesocarbon. Examples of the method for producing the support material 11b made of graphite include the production method described in JP-A-2005-132711.

Polycrystalline silicon carbide film 11c is formed so as to cover the main surface and side surfaces of support material 11b. Polycrystalline silicon carbide film 11c includes polycrystalline silicon carbide. The surface layer of the feed substrate 11 is formed by the polycrystalline silicon carbide film 11c. The polycrystalline silicon carbide film 11c preferably contains polycrystalline 3C—SiC as a main component, and is preferably substantially made of polycrystalline 3C—SiC. That is, the surface layer of the feed substrate 11 is polycrystalline 3C-S.
It is preferable that iC is contained as a main component, and it is preferable that it substantially consists of polycrystalline 3C-SiC. By doing so, the growth rate of the single crystal silicon carbide epitaxial growth film 20 can be increased.

  Thickness t11 of polycrystalline silicon carbide film 11c is preferably in the range of 30 μm to 800 μm, more preferably in the range of 40 μm to 600 μm, and still more preferably in the range of 100 μm to 300 μm. If the thickness t11 of the polycrystalline silicon carbide film 11c is too thin, the support material 11b made of graphite is exposed when the single crystal silicon carbide epitaxial growth film 20 is formed, and suitable single crystal carbonization due to elution from the support material 11b. The silicon epitaxial growth film 20 may not be obtained. On the other hand, if the thickness t11 of the polycrystalline silicon carbide film 11c is too thick, cracks may easily occur in the polycrystalline silicon carbide film 11c.

  The method for forming polycrystalline silicon carbide film 11c is not particularly limited. The polycrystalline silicon carbide film 11c can be formed by, for example, a CVD method or a sputtering method. In particular, in this embodiment, since the polycrystalline silicon carbide film 11c contains polycrystalline 3C-SiC, a dense polycrystalline silicon carbide film 11c can be formed easily and inexpensively by the CVD method.

  The polycrystalline silicon carbide film 11c constituting the surface layer of the feed substrate 11 is at least one of (111) crystal plane, (200) crystal plane, (220) crystal plane and (311) crystal plane by X-ray diffraction. 1 is observed, and the average crystallite diameter calculated from at least one of the first diffraction peaks is 700 mm or less. Therefore, in this embodiment, the single crystal silicon carbide epitaxial growth film 20 can be formed at a high growth rate. This is considered to be because the smaller the average particle size, the greater the proportion of polycrystalline silicon carbide crystals in the surface layer, which has high reactivity, and the elution of the surface layer into the silicon melt layer is more likely to occur. It is done.

  The polycrystalline silicon carbide film 11c is preferably such that the proportion of the (111) crystal plane observed by X-ray diffraction with the orientation angle of 67.5 ° or more is less than 80%. . In this case, the growth rate of the single crystal silicon carbide epitaxial growth film 20 can be further effectively increased. This is because the degree of exposure of the crystal having the (111) crystal plane exposed is higher because the degree of exposure of the surface having a lower stability than the (111) crystal plane is high. It is thought that this is because

  In the above-described embodiment, an example in which each of the feed substrate 11 and the seed substrate 12 is configured by the support materials 11b and 12b and the polycrystalline silicon carbide films 11c and 12c has been described. However, the present invention is not limited to this configuration. For example, as shown in FIG. 4, feed substrate 11 may be formed of a silicon carbide substrate containing silicon carbide. Further, as shown in FIG. 5, the seed substrate 12 may be constituted by a polycrystalline silicon substrate containing polycrystalline silicon carbide whose crystal polymorph is 3C.

  The silicon carbide substrate can be produced, for example, by coating a graphite base material with polycrystalline silicon carbide by a CVD method and then mechanically or chemically removing the graphite. The silicon carbide substrate can also be produced by reacting a graphite material with a silicate gas to convert the graphite material into silicon carbide. The silicon carbide substrate can also be produced by adding a sintering aid to silicon carbide powder and sintering at a high temperature of 1600 ° C. or higher.

  Hereinafter, the present invention will be further described based on specific examples, but the present invention is not limited to the following specific examples.

(Production Example 1)
A graphite material (15 mm × 15 mm × 2 mm) made of high purity isotropic graphite material having a bulk density of 1.85 g / cm ³ and an ash content of 5 ppm or less was used as a base material. This base material was put in a CVD reactor, and a polycrystalline silicon carbide film having a thickness of 30 μm was formed on the base material by a CVD method to prepare Sample 1. Note that silicon tetrachloride and propane gas were used as the source gas. Film formation was performed at normal pressure and 1200 ° C. The deposition rate was 30 μm / h.

(Production Example 2)
A sample 2 was produced by forming a 50 μm polycrystalline silicon carbide film on the surface of the graphite material in the same manner as in Production Example 1 except that the reaction temperature was 1400 ° C. and the film formation rate was 60 μm / h. .

(Production Example 3)
Polycrystalline 50 μm on the surface of the graphite material in the same manner as in Preparation Example 1 except that the reaction temperature was 1250 ° C., the film formation rate was 10 μm / h, and CH ₃ SiCl ₃ was used instead of silicon tetrachloride. A silicon carbide coating was formed to prepare Sample 3.

(Production Example 4)
Graphite was prepared in the same manner as in Preparation Example 1 except that dichlorosilane (SiH ₂ Cl ₂ ) and acetylene were used instead of silicon tetrachloride and propane gas, the reaction temperature was 1300 ° C., and the film formation rate was 10 μm / h. A sample 4 was prepared by forming a 50 μm polycrystalline silicon carbide coating on the surface of the material. In Sample 4, the thickness of the polycrystalline silicon carbide film was about 1 mm.

(X-ray diffraction measurement)
X-ray diffraction was performed on the surface layers of Samples 1 to 4 prepared above. X-ray diffraction was performed using Rigak Ultima. The measurement results are shown in FIG. Also, the relative intensities of the diffraction peaks corresponding to each crystal plane when the intensity of the observed diffraction peak and the first-order diffraction peak corresponding to the (111) crystal plane are set to 100 in samples 1 to 4 are summarized.

  Note that the intensity of the first-order diffraction peak corresponding to the (111) crystal plane) / (total intensity of at least one first-order diffraction peak) is 100 / (100 + 13 + 12 + 12) = 0.730 in samples 1 to 4, respectively. 100 / (100 + 40 + 51 + 47) = 0.420, 100 / (100 + 0 + 0 + 1) = 0.990, 100 / (100 + 0 + 0 + 0) = 1.00.

(Calculation of average crystallite size)
Based on the result of the X-ray diffraction measurement, the average crystallite diameter of each of Samples 1 to 4 was calculated using the Hall equation. For the calculation, data of diffraction peaks related to the (111) crystal plane, the (200) crystal plane, the (220) crystal plane, and the (311) crystal plane were used. The results are shown in Table 2 below.

  From the results shown in Table 2, samples 1 and 2 have an average crystallite size of 700 mm or less, more specifically 500 mm or less, while samples 3 and 4 have an average crystallite diameter of more than 700 mm. Was over 1000 kg.

(Evaluation of orientation of (111) crystal plane)
Next, for Samples 1 to 4, as shown in FIG. 7, the angle at which the diffraction peak of the (111) plane appears was measured while rotating the sample. The results are shown in FIGS. In the graphs shown in FIGS. 8 to 11, the horizontal axis is the orientation angle (α) shown in FIG. 7. The vertical axis is intensity.

  Table 3 below shows the ratio of the intensity integral value of the region where the orientation angle (α) is 67.5 ° or more with respect to the intensity integral value of the entire region when the orientation angle (α) is 15 ° to 90 ° ((orientation angle (Α) is the integrated intensity value of the region where 67.5 ° or more) / (intensity integrated value of the entire region when the orientation angle (α) is 15 ° to 90 °)). In addition, ((intensity integrated value of region where orientation angle (α) is 67.5 ° or more) / (intensity integrated value of whole region when orientation angle (α) is 15 ° to 90 °)) is obtained by X-ray diffraction. This corresponds to the proportion of the observed (111) crystal plane with an orientation angle of 67.5 ° or more.

  As shown in FIGS. 8 and 9 and Table 3 above, in Samples 1 and 2, there is a large intensity distribution even in the region where the orientation angle (α) is less than 67.5 °, and among the (111) crystal planes, The ratio of those having an orientation angle (α) of 67.5 ° or more was less than 80%. On the other hand, in samples 3 and 4, as shown in FIGS. 10 and 11 and Table 3 above, there is no large intensity distribution in the region where the orientation angle (α) is less than 67.5 °, and the orientation angle ( The ratio of α) being 67.5 ° or more was 80% or more.

(Growth rate evaluation of single crystal silicon carbide liquid phase epitaxial growth film)
Using the liquid phase epitaxial growth method described in the above embodiment, a single crystal silicon carbide epitaxial growth film 20 was produced under the following conditions using Samples 1 to 4 as a feed substrate. Then, the thickness of the single crystal silicon carbide epitaxial growth film 20 was measured by observing a cross section of the single crystal silicon carbide epitaxial growth film 20 using an optical microscope. The growth rate of the single crystal silicon carbide epitaxial growth film 20 was determined by dividing the measured thickness by the time during which the silicon carbide epitaxial growth was performed.

  The results are shown in FIGS. 12 and 13, the vertical axis represents the growth rate of the single crystal silicon carbide epitaxial growth film 20, and the horizontal axis represents the reciprocal (1 / L) of the thickness (L) of the silicon melt layer 13.

  From the results shown in FIGS. 12 and 13, when samples 1 and 2 having an average crystallite diameter of 700 mm or less in the polycrystalline silicon carbide film 11c constituting the surface layer of the feed substrate 11 are used, single crystal silicon carbide The growth rate of the epitaxial growth film 20 was high. On the other hand, when samples 3 and 4 having an average crystallite diameter larger than 700 mm in polycrystalline silicon carbide film 11c constituting the surface layer of feed substrate 11 were used, the growth rate of single crystal silicon carbide epitaxial growth film 20 was low. . From this, it can be seen from Samples 3 and 4 that elution into the silicon melt layer 13 hardly occurs.

(Measurement conditions of growth rate of single crystal silicon carbide epitaxial growth film 20)
Seed substrate: silicon carbide substrate with crystal polymorph 4H atmosphere pressure: 10 ⁻⁶ to 10 ⁻⁴ Pa
Atmospheric temperature: 1900 ° C

(Example)
Using the sample 1 prepared as the feed substrate 11 and the sample 3 prepared as the seed substrate 12, a liquid crystal epitaxial growth experiment of single crystal silicon carbide was performed under the same conditions as the growth rate evaluation experiment. Thereafter, a scanning electron microscope (SEM) photograph of the surface of the sample 3 as the seed substrate 12 was taken. An SEM photograph of the surface of Sample 3 is shown in FIG. From the photograph shown in FIG. 14, Sample 3 whose average crystallite diameter is larger than 700 mm and whose intensity of the first-order diffraction peak corresponding to the (111) crystal plane) / (total intensity of at least one first-order diffraction peak) is 25. It can be seen that a hexagonal single crystal silicon carbide epitaxial growth film can be obtained by using as a seed substrate 12.

(Comparative example)
Using the sample 1 prepared as a feed substrate and the sample 2 prepared as a seed substrate, a liquid crystal epitaxial growth experiment of single crystal silicon carbide was performed under the same conditions as the growth rate evaluation experiment. Thereafter, a scanning electron microscope (SEM) photograph of the surface of sample 2 as a seed substrate was taken. An SEM photograph of the surface of Sample 2 is shown in FIG. From the photograph shown in FIG. 15, it can be seen that when sample 2 having an average crystallite diameter of 700 mm or less is used as a seed substrate, epitaxial growth hardly proceeds.

DESCRIPTION OF SYMBOLS 10 ... Container 11 ... Feed substrate 11a ... Main surface 11b ... Support material 11c ... Polycrystalline silicon carbide film 12 ... Seed substrate 12a ... Main surface 12b ... Support material 12c ... Polycrystalline silicon carbide film 13 ... Silicon molten layer 20 ... Single crystal Silicon carbide epitaxial growth film

Claims (9)

Oite the liquid phase epitaxial growth method of a single crystal silicon carbide, a seed material used to face the feed material through the silicon melt layer,
Having a surface layer comprising polycrystalline silicon carbide having a crystalline polymorph of 3C;
A first-order diffraction peak corresponding to at least one of (111) crystal plane, (200) crystal plane, (220) crystal plane and (311) crystal plane is observed by X-ray diffraction of the surface layer,
A seed material for single-crystal silicon carbide liquid phase epitaxial growth, wherein an average crystallite diameter calculated from the at least one first-order diffraction peak is greater than 700 mm.
  Ratio of the intensity of the first-order diffraction peak corresponding to the (111) crystal plane to the total intensity of the at least one first-order diffraction peak ((intensity of the first-order diffraction peak corresponding to the (111) crystal plane) / (at least one The seed material for single-crystal silicon carbide liquid phase epitaxial growth according to claim 1, wherein the total intensity of two first-order diffraction peaks)) is 5 or more.   3. The single crystal carbonization according to claim 1, wherein a proportion of the (111) crystal planes observed by X-ray diffraction of the surface layer, whose orientation angle is 67.5 ° or more, is 80% or more. Seed material for silicon liquid phase epitaxial growth.   The seed material for liquid crystal epitaxial growth of a single crystal silicon carbide according to any one of claims 1 to 3, wherein the surface layer includes polycrystalline silicon carbide having a crystal polymorph of 3C as a main component.   The seed material for liquid crystal epitaxial growth of a single crystal silicon carbide according to claim 4, wherein the surface layer is substantially made of polycrystalline silicon carbide having a crystal polymorph of 3C.   The single-crystal silicon carbide liquid phase according to any one of claims 1 to 5, comprising a support material and a polycrystalline silicon carbide film that is formed on the support material and forms the surface layer. Seed material for epitaxial growth.   The seed material for single-crystal silicon carbide liquid phase epitaxial growth according to claim 6, wherein the polycrystalline silicon carbide film has a thickness in a range of 30 μm to 800 μm.   The seed material for single-crystal silicon carbide liquid phase epitaxial growth according to any one of claims 1 to 5, wherein the seed material is composed of a polycrystalline silicon carbide material containing polycrystalline silicon carbide having a crystal polymorph of 3C.   The state in which the surface layer of the seed material for single-crystal silicon carbide liquid phase epitaxial growth according to any one of claims 1 to 8 and the surface layer of the feed material having a surface layer made of silicon carbide are opposed to each other through a silicon melt layer A liquid crystal epitaxial growth method of single crystal silicon carbide, in which single crystal silicon carbide is epitaxially grown on a surface layer of the seed material by heating at a temperature.

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