JP2013032254A - Method for manufacturing single-crystal silicon carbide substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for forming a high-quality, uniform epitaxial film of single-crystal silicon carbide by suppressing the generation of sticking, thermal strain, and dislocation.SOLUTION: A method for manufacturing a single-crystal silicon carbide substrate includes: a step of forming a silicon thin film on one side of a carbon material or a single-crystal silicon-carbide substrate; a step of putting a silicon thin film between a carbon material and a single-crystal silicon carbide substrate, and of arranging a silicon substrate, a support, and the single-crystal silicon carbide substrate as laminated in a crucible in this order from its bottom and arranging a carbon material support and the carbon material, which are bonded, in the crucible in this order from the side of its lid so that the arrangement satisfies a predetermined formula; a step of melting the silicon substrate and the silicon thin film by heating the crucible that is lidded with its lid at a temperature equal to or higher than the melting point of silicon, and further lowering the crucible lid to the height of the inner wall of the crucible; and a step of forming an epitaxial film of single-crystal silicon carbide on the single-crystal silicon carbide substrate that is suspendedly held by the surface tension of the molten silicon, by heating the crucible at a temperature equal to or higher than the growth temperature of the epitaxial film of the single-crystal silicon carbide.

Description

  The present invention relates to a method for producing a single crystal silicon carbide substrate using a metastable solvent epitaxy method (Metastable Solvent Epitaxy method: MSE method).

  In recent years, development of a semiconductor material having higher withstand voltage characteristics has been promoted under the severe user demand for higher efficiency of electrical equipment. In particular, a semiconductor using single crystal silicon carbide is expected to be applied to a device capable of operating at a high temperature with low loss as compared with silicon because of its physical properties.

  A single crystal silicon carbide device uses a single crystal silicon carbide substrate processed from a bulk crystal manufactured using a sublimation method or the like, and a single crystal silicon carbide epitaxial film serving as an active region of a semiconductor device is formed thereon. Conventionally, a vapor phase growth method in which a desired epitaxial film is formed by supplying a raw material from a vapor phase has been mainly used.

  In contrast to such a vapor phase growth method, there is a liquid phase growth method in which raw materials are supplied from a liquid phase and epitaxial growth is performed, which has been adopted for compound semiconductors such as GaAs. Therefore, it is difficult to form a high quality single crystal silicon carbide epitaxial film by using the liquid phase growth method.

  Therefore, the present applicant firstly melted silicon by sandwiching a silicon raw material between a single crystal silicon carbide substrate and a carbon supply raw material and heating the crucible at a high temperature as a method for forming a single crystal silicon carbide epitaxial film. Thus, a metastable solvent epitaxy method (MSE method) for forming a high-quality single-crystal silicon carbide epitaxial film on a single-crystal silicon carbide substrate at high speed has been proposed (Patent Document 1).

  The formation of a single crystal silicon carbide epitaxial film by the conventional MSE method will be specifically described with reference to FIG. As shown in FIG. 2, a support base 16, a carbon raw material 12, a spacer 20, a single crystal silicon carbide substrate 11, and a silicon substrate 18 are sequentially laminated in a crucible 14, and a weight stone 19 is disposed thereon. .

  Here, the spacer 20 is provided to control the thickness of the single crystal silicon carbide epitaxial film.

  Then, after covering the crucible lid 15, the silicon substrate 18 is melted by heating and flows into the space between the single crystal silicon carbide substrate 11 formed by the spacer 20 and the carbon raw material 12, and the silicon melt layer Form. Then, a single crystal silicon carbide epitaxial film is formed on single crystal silicon carbide substrate 11 by reacting with carbon dissolved from carbon raw material 12 in the silicon melt layer.

  In the above, the silicon melt layer is formed by melting the silicon substrate 18, but the silicon raw material is previously formed in the space between the single crystal silicon carbide substrate 11 formed by the spacer 20 and the carbon raw material 12. The silicon melt layer may be formed by being disposed.

JP 2005-126249 A

  However, when the single crystal silicon carbide epitaxial film is formed using the above-described conventional MSE method, the single crystal silicon carbide substrate 11 and the spacer 20 or the spacer 20 is formed because the spacer 20 is formed of polycrystalline silicon carbide or carbon. Since the carbon raw material 12 and the spacer 20 are fixed, there is a problem that the fixed part must be removed by cutting or the like.

  In addition, since the single crystal silicon carbide substrate 11 is loaded with the weight 19, thermal strain is generated during heating, causing the single crystal silicon carbide substrate 11 to warp, and a large stress is generated in the vicinity of the fixed portion. As a result, new dislocations are generated in the formed single crystal silicon carbide epitaxial film, which adversely affects the characteristics of the single crystal silicon carbide epitaxial film.

  Accordingly, in view of the above problems, the present invention prevents the occurrence of sticking by spacers in the formation of a single crystal silicon carbide epitaxial film, and sufficiently suppresses the occurrence of thermal strain and new dislocations, thereby achieving high quality. It is an object of the present invention to provide a method for manufacturing a single crystal silicon carbide substrate capable of forming a uniform single crystal silicon carbide epitaxial film.

  The present inventor has intensively studied to solve the above problems, paying attention to the surface tension of the silicon melt, has found that the above problems can be solved by the following method, and has completed the present invention.

That is, the invention described in claim 1
A silicon thin film forming step for forming a silicon thin film having a predetermined thickness on one surface of a carbon raw material or a single crystal silicon carbide substrate in advance,
A silicon substrate, a support base, and a single crystal silicon carbide substrate are stacked in order from the bottom in the crucible so that the silicon thin film is disposed between the carbon raw material and the single crystal silicon carbide substrate and satisfies the following formula. And arranging the carbon raw material support base and the carbon raw material in order from the crucible lid side, inside the crucible lid,
A silicon melting step of heating the crucible covered with the crucible lid to a temperature equal to or higher than a melting point temperature of silicon to melt the silicon substrate and the silicon thin film, and lowering the crucible lid to the height of the inner wall of the crucible;
The single-crystal silicon carbide substrate is further suspended and held on the carbon raw material by the surface tension of a silicon melt formed by melting the silicon thin film by further heating the crucible above the growth temperature of the single-crystal silicon carbide epitaxial film. A method for producing a single crystal silicon carbide substrate, further comprising a single crystal silicon carbide epitaxial film forming step for forming a single crystal silicon carbide epitaxial film.

  According to the present invention, it is possible to prevent the occurrence of sticking in the formation of a single crystal silicon carbide epitaxial film, and to sufficiently suppress the occurrence of thermal strain and new dislocations, thereby producing a high quality and uniform single crystal silicon carbide epitaxial film. Can be formed.

It is a schematic diagram explaining formation of the single crystal silicon carbide epitaxial film by this invention. It is a figure explaining formation of the conventional single crystal silicon carbide epitaxial film.

  Hereinafter, based on an embodiment, the present invention will be specifically described with reference to the drawings.

  In view of the fact that the occurrence of sticking and thermal strain in the conventional MSE method is due to the use of spacers and the influence of the weight of the heavy stone, the present inventor does not use the spacer and does not affect the weight of the heavy stone. As a method for forming the epitaxial film, it was considered that the single crystal silicon carbide epitaxial film was formed while the single crystal silicon carbide substrate was held by the surface tension of the silicon melt. This will be specifically described below.

1. Silicon Thin Film Forming Process First, the silicon thin film forming process will be described.

  This step is a step of forming a silicon thin film in advance on one surface of a single crystal silicon carbide substrate or a carbon raw material. Specifically, a silicon deposition method in a vacuum or a plasma is generated on a silicon target. Then, it can be formed using a sputtering deposition method in which silicon as a target material is attached to a facing substrate. As will be described later, the formed silicon thin film is melted by heating to form a silicon melt.

2. Material Arrangement Step Next, the material arrangement step will be described.

  FIG. 1 is a schematic diagram for explaining the formation of a single crystal silicon carbide epitaxial film according to the present invention, and schematically shows a state before silicon is melted.

In FIG. 1, reference numeral 14 denotes a crucible, and reference numeral 15 denotes a crucible lid. The crucible lid and the crucible lid 15 are produced in a small volume within a range where a single crystal silicon carbide epitaxial film can be formed so that a temperature difference hardly occurs inside. In the crucible 14 (inner wall height: l ₁ ), in order from the bottom, a silicon substrate 18 (thickness: t ₁₈ ), a carbon support 16 (height: l ₃ ), and a single crystal silicon carbide substrate 11 (thickness). : T ₁₁ ) are laminated. On the other hand, a carbon raw material support 17 (height: l ₂ ) and a carbon raw material 12 (thickness: t ₁₂ ) are joined to the crucible lid 15 in this order from the crucible lid 15 side. The silicon thin film 13 (thickness: t ₁₃ ) formed in the silicon thin film forming step is arranged so as to be positioned between the single crystal silicon carbide substrate 11 and the carbon raw material 12.

  At this time, the relationship shown by the following formula is satisfied between the thickness and height of each material and the height of the inner wall of the crucible.

That is, the height (l ₁ ) of the inner wall of the crucible is the height of the support 16 (l ₃ ), the thickness of the silicon thin film 13 (t ₁₃ ), the thickness of the single crystal silicon carbide substrate 11 (t ₁₁ ), and the carbon raw material support. The height (l ₂ ) of the base 17 and the total thickness (l ₂ + l ₃ + t ₁₁ + t ₁₂ + t ₁₃ ) of the thickness (t ₁₂ ) of the carbon raw material 12 are larger than the total thickness of the silicon substrate 18. It is set to be smaller than the thickness plus the thickness _{(t 18) (l 2 +} l 3 + t 11 + t 12 + t 13 + t 18).

3. Silicon melting step Next, the silicon melting step will be described.

First, the crucible lid 15 is put on the crucible 14. At this time, as described above, the height (l ₁ ) of the inner wall of the crucible 14 is such that the support base 16, the silicon substrate 18, the silicon thin film 13, the single crystal silicon carbide substrate 11, the carbon raw material support base 17, and the carbon raw material 12. Is set to a value smaller than the total thickness (l ₂ + l ₃ + t ₁₁ + t ₁₂ + t ₁₃ + t ₁₈ ), so that the crucible lid 15 is separated from the upper end of the inner wall of the crucible 14 and the respective members are in close contact with each other. It has become.

  For this reason, in the state where the crucible lid 15 is covered, the carbon raw material support base 17 and the carbon raw material 12 joined to the crucible lid 15 and the carbon raw material 12 function in the same manner as the weight stone in the conventional MSE method, It is possible to sufficiently suppress the displacement of the arrangement of each member that occurs due to the inclination during the crucible installation.

  Here, in the arrangement of the material of the conventional MSE method, a method of using a deposited silicon film having a predetermined thickness, for example, 100 μm, instead of arranging the silicon raw material on the single crystal silicon carbide substrate is also conceivable. In this case, the arrangement may be shifted due to an inclination during conveyance or crucible installation. However, according to the present embodiment, as described above, since it functions as a relatively heavy weight in spite of a small volume including the crucible lid, the occurrence of these deviations can be suppressed.

  Next, with the crucible lid 15 covered, the entire crucible is placed in the MSE apparatus and heated. When the temperature in the crucible exceeds the melting point of silicon (about 1410 ° C.), the silicon thin film 13 and the silicon substrate 18 are melted. At this time, as described above, the volume of the crucible is made small as long as the single crystal silicon carbide epitaxial film can be formed. Therefore, there is almost no temperature difference inside the production crucible, and the silicon thin film 13 and the silicon substrate 18 are not generated. Both melt at about the same time.

  The melted silicon thin film 13 forms a silicon melt layer between the single crystal silicon carbide substrate 11 and the carbon raw material 12.

On the other hand, when the silicon substrate 18 is melted, the support 16 is lowered by its own weight, and the crucible lid 15 is lowered accordingly. However, as described above, the height (l ₁ ) of the inner wall of the crucible 14 is the total thickness (l ₂ ) of the support base 16, the silicon thin film 13, the single crystal silicon carbide substrate 11, the carbon raw material support base 17, and the carbon raw material 12. + L ₃ + t ₁₁ + t ₁₂ + t ₁₃ ), and the crucible lid 15 is prevented from descending beyond the inner wall height of the crucible 14, so that the crucible lid 15 lowered to the inner wall height of the crucible 14. And the crucible 14 seals the inside of the crucible.

  Furthermore, when heating is continued as it is, the silicon substrate 18 is further melted and the support base 16 is lowered. However, since the crucible lid 15 is held by the inner wall of the crucible 14 and no longer descends, the gap between the support base 16 stacked on the crucible 14 and the carbon raw material 12 joined to the crucible lid 15 via the carbon raw material support base 17 is provided. A gap is formed in this, and this gap gradually widens.

  At this time, the single crystal silicon carbide substrate 11 does not descend together with the support 16 and is suspended from the carbon raw material 12 by the surface tension of the silicon melt layer formed between the single crystal silicon carbide substrate 11 and the carbon raw material 12. It is held in the state.

  This is because the surface tension of the silicon melt layer is large, and the single crystal silicon carbide substrate 11 can be held (lifted) with a force much larger than the gravity applied to the single crystal silicon carbide substrate 11.

Specifically, the surface tension of the silicon melt is about 760 mN / m. For example, the force f that the surface tension of the silicon melt holds (lifts) the single crystal silicon carbide substrate 11 having a thickness of 350 μm and a diameter of 3 inches is F = 4πrγ (γ: surface tension of the silicon melt, r: radius of the single crystal silicon carbide substrate), and is calculated to be about 0.36N. On the other hand, the gravity applied to single crystal silicon carbide substrate 11 is calculated to be about 0.05 N if the density of single crystal silicon carbide substrate 11 is expected to be 3.22 g / cm ³ . From this result, the force f for holding (lifting) the single crystal silicon carbide substrate 11 is 7 times or more the gravity applied to the single crystal silicon carbide substrate 11, and the single crystal silicon carbide substrate 11 is made of carbon raw material by the silicon melt layer. As can be seen from FIG.

  In addition, since the single crystal silicon carbide substrate 11 and the carbon raw material 12 are arranged in a position facing each other due to the surface tension of the silicon melt, the single crystal silicon carbide substrate and the carbon are arranged depending on the inclination at the time of transportation or crucible installation. Even if there is a slight deviation from the raw material, it is automatically corrected to the directly facing position.

4). Single Crystal Silicon Carbide Epitaxial Film Formation Step Next, the single crystal silicon carbide epitaxial film formation step will be described.

  Subsequent to the silicon melting step described above, the temperature was raised from 1600 ° C., which is the growth temperature of the single crystal silicon carbide epitaxial film, to 2000 ° C., and held at this temperature for a predetermined time. A single crystal silicon carbide epitaxial film is formed and grown on single crystal silicon carbide substrate 11. A single crystal silicon carbide epitaxial film having a desired thickness can be formed by appropriately adjusting the temperature holding time.

  Thus, according to the present embodiment, since a single crystal silicon carbide epitaxial film can be formed without using a spacer, sticking does not occur unlike the conventional MSE method.

  At this time, the carbon raw material 12 suspends and holds the single crystal silicon carbide substrate 11 but is bonded to the crucible lid 15 that cannot be lowered, so that no load is applied to the carbon raw material 12. In combination with the absence of the spacer, the occurrence of warpage due to thermal strain is suppressed. For this reason, when a single crystal silicon carbide epitaxial film is formed, a large stress is not generated, and generation of new dislocations in the formed single crystal silicon carbide epitaxial film is sufficiently suppressed.

  As a result, a high quality and uniform single crystal silicon carbide epitaxial film can be formed on single crystal silicon carbide substrate 11.

  Note that the thickness of the silicon thin film 13 that affects the thickness of the single crystal silicon carbide epitaxial film to be formed is about 10 to 100 μm between the spacers in the conventional MSE method by using the above-described vacuum deposition method or the like. The thickness can be easily controlled.

5). Each material Finally, each material used in the present invention will be described. However, these materials are the same materials as those used in the conventional MSE method, and an increase in cost can be suppressed.

  That is, as the single crystal silicon carbide substrate 11, for example, a substrate after being cut from a single crystal silicon carbide ingot produced by a conventionally known method can be used. A commercially available single crystal silicon carbide substrate may also be used.

  The carbon raw material 12 is not particularly limited as long as carbon can be supplied into the silicon melt. For example, a single crystal silicon carbide substrate, a polycrystalline silicon carbide substrate, a carbon substrate, a porous silicon carbide substrate, a sintered material is used. A silicon carbide substrate, an amorphous silicon carbide substrate, or the like can be used.

  In addition, as the crucible 14 and the crucible lid 15, those manufactured using a material having a high temperature resistance such as carbon is used.

  While the present invention has been described based on the embodiments, the present invention is not limited to the above embodiments. Various modifications can be made to the above-described embodiment within the same and equivalent scope as the present invention.

11 Monocrystalline silicon carbide substrate 12 Carbon raw material 13 Silicon thin film 14 Crucible 15 Crucible lid 16 Support base 17 Carbon raw material support base 18 Silicon substrate 19 Weight 20 Spacer

Claims (1)

A silicon thin film forming step for forming a silicon thin film having a predetermined thickness on one surface of a carbon raw material or a single crystal silicon carbide substrate in advance,
A silicon substrate, a support base, and a single crystal silicon carbide substrate are stacked in order from the bottom in the crucible so that the silicon thin film is disposed between the carbon raw material and the single crystal silicon carbide substrate and satisfies the following formula. And arranging the carbon raw material support base and the carbon raw material in order from the crucible lid side, inside the crucible lid,
A silicon melting step of heating the crucible covered with the crucible lid to a temperature equal to or higher than a melting point temperature of silicon to melt the silicon substrate and the silicon thin film, and lowering the crucible lid to the height of the inner wall of the crucible;
The single-crystal silicon carbide substrate is further suspended and held on the carbon raw material by the surface tension of a silicon melt formed by melting the silicon thin film by further heating the crucible above the growth temperature of the single-crystal silicon carbide epitaxial film. A method for producing a single crystal silicon carbide substrate, comprising: a single crystal silicon carbide epitaxial film forming step for forming a single crystal silicon carbide epitaxial film.

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