TW201726568A - Solution growth method, pedestal, and method for producing single crystal SiC - Google Patents

Abstract

In this solution growth method, an epitaxial layer is grown on a SiC seed crystal with the SiC seed crystal, which comprises a single crystal SiC, being supported on a pedestal and being in contact with a solution that includes at least Si and C. At least the part of the pedestal that comes into contact with the SiC seed crystal is made of graphite. This prevents fine SiC crystals from being generated on the pedestal compared to when, for example, a SiC pedestal is used. Thus, growth of the epitaxial layer does not tend to be inhibited which allows the epitaxial layer to grow quickly.

Description

Solution growth method, susceptor, and method for producing single crystal SiC

The present invention is mainly directed to a technique for growing a single crystal SiC by a solution growth method.

Compared with Si and the like, SiC has been attracting attention as a novel semiconductor material because of its excellent electrical properties and the like. In the production of a semiconductor element, a seed crystal (single crystal SiC substrate) composed of SiC is first used to produce a SiC substrate, a SiC bulk crystal, or the like. Among them, an MSE method (meta-stable solvent epitaxy method) is known as one of methods for growing a single crystal SiC by using a seed crystal.

Patent Document 1 discloses a method of growing single crystal SiC by the MSE method. The MSE method uses a SiC seed crystal composed of single crystal SiC, a carbon-feeding substrate having a higher free energy than the SiC seed crystal, and a Si melt. Further, by arranging the SiC seed crystals opposed to the carbon-implanted substrate and placing the Si melt therebetween, heating under vacuum allows the single crystal SiC to grow on the surface of the SiC seed crystal.

Patent Document 2 discloses a method of growing SiC seed crystals by sublimation recrystallization. Patent Document 2 describes that sublimation recrystallization is used. The method is mounted on the shape of a sub-mount of the SiC seed crystal or the like.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Laid-Open Patent Publication No. 2008-230946

Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-263539

However, in Patent Document 1, there is no description of the material of the susceptor or the like in the case of performing the MSE method. Further, Patent Document 2 only describes the susceptor when performing the sublimation recrystallization method, and does not describe the susceptor when the solution growth method is performed. Here, in the case where the single crystal SiC is grown by the solution growth method, the growth rate is slowed depending on the material and shape of the susceptor.

The present invention has been made in view of the above circumstances, and a main object thereof is to provide a susceptor which is attached to an SiC seed crystal during a solution growth method and which can increase the growth rate of single crystal SiC.

(Technical means and effects of solving problems)

The problem to be solved by the present invention is as described above, and the means for solving the problem and the effects thereof will be described below.

According to a first aspect of the present invention, a solution growth method is provided in which a crystal growth layer is grown in a state in which a seed crystal composed of SiC is supported on a susceptor and a solution containing at least Si and C is brought into contact with each other. Seed on the seed And a method in which at least the portion of the susceptor that is in contact with the seed crystal is made of graphite.

Thereby, it is difficult to produce minute crystals of SiC on the susceptor as compared with the case of using a SiC base. Thereby, the growth of the epitaxial layer becomes difficult to be hindered, so that the epitaxial layer can be rapidly grown.

In the above solution growth method, it is preferred that the graphite portion of the susceptor has a thermal conductivity of more than 130 W/(m.K).

Thereby, by using graphite having a high thermal conductivity as a material of the susceptor, it is possible to prevent the seed crystal from becoming high temperature. Thereby, growth is preferentially performed as compared with the decomposition of SiC, so that the epitaxial layer can be rapidly grown.

In the above solution growth method, it is preferable that an area of the surface of the susceptor supporting the seed crystal is the same as or larger than the seed crystal.

Thereby, the heat of the seed crystal can be efficiently conducted to the susceptor, so that the seed crystal can be prevented from becoming high temperature. Thereby, growth is preferentially performed as compared with the decomposition of SiC, so that the epitaxial layer can be rapidly grown.

In the above solution growth method, preferably, the solution growth method is a metastable solvent epitaxy method, that is, because the seed crystal and the free energy are higher than the seed crystal and at least the carbon supply of C is supplied. A method in which a material having a Si melt is heated between the materials to grow an epitaxial layer on the surface of the seed crystal.

Thereby, the single crystal SiC can be grown by the difference in free energy without adding a temperature gradient or the like.

According to a second aspect of the present invention, a susceptor having the following configuration is provided. That is, the susceptor is grown by using a solution growth method to form an epitaxial layer composed of SiC. When the seed crystal is seeded, the seed crystal is supported. Further, at least a portion of the susceptor that is in contact with the seed crystal is made of graphite.

Thereby, it is difficult to produce minute crystals of SiC on the susceptor as compared with the case of using a SiC base. Thereby, the growth of the epitaxial layer becomes difficult to be hindered, so that the epitaxial layer can be rapidly grown.

Preferably, in the above susceptor, the thermal conductivity of the graphite portion is greater than 130 W/(m.K).

Thereby, by using graphite having a high thermal conductivity, the seed crystal can be prevented from becoming high temperature. Thereby, growth is preferentially performed as compared with the decomposition of SiC, so that the epitaxial layer can be rapidly grown.

According to a third aspect of the present invention, a method for producing a single crystal SiC, comprising: supporting a seed crystal composed of SiC on a susceptor, wherein a portion of the susceptor in contact with the seed crystal is made of graphite And allowing the epitaxial layer to grow on the seed crystal in a state in which the solution containing at least Si and C is brought into contact with the seed crystal supported on the susceptor.

Thereby, by using a susceptor made of graphite, the growth rate of the epitaxial layer is increased, so that single crystal SiC can be efficiently produced.

10‧‧‧High temperature vacuum furnace

30‧‧‧坩埚

33‧‧‧Base

40‧‧‧ SiC substrate

41‧‧‧SiC seed crystal

42‧‧‧Si board

43‧‧‧Feed carbon substrate (feeding carbon material)

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view showing the outline of a high temperature vacuum furnace used for MSE growth of SiC seed crystals of the present invention.

Fig. 2 is a view showing a constitution example in which SiC seed crystals are grown by the MSE method.

Figure 3 shows the MSE method using a SiC base, and A microscope photograph comparing the surface shape of the susceptor in the case of the MSE method using a graphite base.

Fig. 4 is a view showing the surface shape of the single crystal SiC after growth by performing the MSE method using a susceptor made of graphite having different thermal conductivity.

Fig. 5 is a graph comparing the size of a susceptor with the growth rate of single crystal SiC.

Next, an embodiment of the present invention will be described with reference to the drawings. First, a high-temperature vacuum furnace 10 used in the heat treatment of the present embodiment will be described with reference to Fig. 1 .

As shown in FIG. 1, the high temperature vacuum furnace 10 is provided with the main heating chamber 21 and the preliminary heating chamber 22. The main heating chamber 21 can heat at least a SiC substrate 40 (single crystal SiC substrate) having a surface composed of single crystal SiC or a SiC seed crystal 41 to be described later to a temperature of 1000 ° C or more and 2300 ° C or less. The preliminary heating chamber 2 is a space for preliminary heating of the SiC substrate 40, the SiC seed crystal 41, and the like before the main heating chamber 21 is heated.

A vacuum forming valve 23, an inert gas injecting valve 24, and a vacuum gauge 25 are connected to the main heating chamber 21. The vacuum forming valve 23 adjusts the degree of vacuum of the main heating chamber 21. The inert gas injection valve 24 can adjust the pressure of an inert gas (such as Ar gas) in the main heating chamber 21. The vacuum gauge 25 measures the degree of vacuum in the main heating chamber 21.

A heater 26 is provided inside the main heating chamber 21. In addition, heat-reflecting metal (not shown) is fixed to the side wall and the ceiling of the main heating chamber 21 The plate, the heat reflective metal plate, is configured to reflect the heat of the heater 26 toward the central portion of the main heating chamber 21. Thereby, the SiC substrate 40 can be heated strongly and uniformly, and the SiC substrate 40 can be heated to a temperature of 1000 ° C or more and 2300 ° C or less. Further, as the heater 26, for example, a resistance heating type heater or a high frequency induction heating type heater can be used.

Further, the SiC substrate 40 is heated while being housed in a crucible (storage container) 30 made of carbon carbide. The 坩埚30 series is placed on a suitable support table or the like, and is configured to move at least from the preliminary heating chamber to the main heating chamber by the support table. The crucible 30 is provided with a container 31 and a lower container 32 that can be fitted to each other.

When the SiC substrate 40 or the SiC seed crystal 41 or the like is heat-treated, first, the crucible 30 is placed in the preheating chamber 22 of the high-temperature vacuum furnace 10 as indicated by a chain line in FIG. 1 at a suitable temperature (for example, about 800). °C) Perform preparatory heating. Next, the crucible 30 is moved to the main heating chamber 21 which is previously heated to a set temperature (for example, about 1800 ° C). Then, the SiC substrate 40 is heated while adjusting the pressure or the like. Further, the preliminary heating may be omitted.

Next, a method of producing a SiC substrate by growing a single crystal SiC (epitaxial layer) from a SiC seed crystal using the MSE method which is one of the methods of the solution growth method will be described. Fig. 2 is a view showing a constitution example in which SiC seed crystals are grown by the MSE method.

As shown in FIG. 2, an SiC seed crystal 41, a Si plate 42, and a carbon-feeding substrate (carbon-feeding material) 43 are disposed inside the crucible 30. Further, the SiC seed crystal 41 is supported by the susceptor 33.

SiC seed crystal 41 is used as a substrate for liquid phase epitaxial growth (seed side) use. The SiC seed crystal 41 is produced, for example, by cutting (cutting) 4H-SiC of a predetermined size. In addition, it is also possible to replace 4H-SiC and switch to 6H-SiC. A Si plate 42 is disposed above the SiC seed crystal 41.

The Si plate 42 is a plate-shaped member made of Si. Since the melting point of Si is about 1400 ° C, the Si plate 42 is melted by heating in the above high temperature vacuum furnace 10 to become a Si melt. A carbon feeding substrate 43 is disposed above the Si plate 42.

The carbon substrate 43 is used as a carbon supply side, that is, a carbon supply side. The carbon substrate 43 is fed to a substrate having a higher energy than the SiC seed crystal 41 (for example, a substrate made of polycrystalline 3C-SiC).

When the SiC seed crystal 41, the Si plate 42, and the carbon-feeding substrate 43 are disposed as described above and heated at, for example, 1800 ° C, the Si plate 42 disposed between the SiC seed crystal 41 and the carbon-importing substrate 43 is melted to become a Si-melt. body. This Si melt acts as a solvent for moving carbon.

Specifically, a concentration gradient is generated in the Si melt according to the difference in free energy between the SiC seed crystal 41 and the carbon-implanted substrate 43, and this concentration gradient becomes a driving force, and C is eluted from the carbon substrate 43 toward the Si melt. C which is taken into the Si melt moves toward the lower side (the SiC seed crystal 41 side), and is deposited as a single crystal SiC onto the surface of the SiC seed crystal 41.

According to the above description, single crystal SiC can be grown on the surface of the SiC seed crystal 41 by the MSE method. Thereby, a micropipe or an atomic-scale flat SiC substrate 40 (single crystal SiC) having few crystal defects can be produced. The step of growing the epitaxial layer by the CVD method (chemical vapor deposition method) or the solution growth method (such as the MSE method) or the step of implanting ions is performed on the SiC substrate. The semiconductor element is fabricated by a tempering step (heating step) or the like for activating the ions.

Next, a material of the susceptor 33 when the single crystal SiC is grown by the MSE method will be described with reference to FIG. 3. Fig. 3 is a photomicrograph comparing the case where SiC is used for a susceptor and the case where graphite is used for a susceptor.

Fig. 3(a) is a photomicrograph of the surface of the susceptor 33 in the case where the MSE method is performed using the susceptor 33 made of SiC. As shown in FIG. 3(a), when the susceptor 33 made of SiC is used, minute crystals of SiC are generated in a large amount on the susceptor 33. This tiny crystal can hinder the growth of single crystal SiC.

Fig. 3(b) is a photomicrograph of the surface of the susceptor 33 in the case where the MSE method is performed using the susceptor 33 made of graphite. As shown in Fig. 3(b), when the base 33 made of graphite is used, it is difficult to produce minute crystals of SiC on the susceptor 33 as compared with Fig. 3(a). Therefore, by using the susceptor 33 made of graphite without using SiC, the growth rate of the single crystal SiC in the case of performing the MSE method can be improved. As can be seen from the above description, graphite is more suitable as a material of the susceptor 33 than SiC.

Next, the thermal conductivity of the susceptor 33 when the single crystal SiC is grown by the MSE method will be described with reference to FIG. Fig. 4 is a view showing the surface shape of the single crystal SiC after growth by performing the MSE method using the susceptor 33 made of graphite having different thermal conductivity.

Figure 4 (a) is a table showing the thermal conductivity of graphite used in the experiment. The thermal conductivity of graphite (1) is 120W/(m.K), the thermal conductivity of graphite (2) is 130W/(m.K), and the thermal conductivity of graphite (3) is 140W/(m.K). . Further, in the present specification, the thermal conductivity is measured by the following method. That is, using processed into diameter A sample of 10 mm and a thickness of 3 mm was obtained by using a laser flash heat quantity measuring device TC-9000 (manufactured by Ulvac Co., Ltd.) to obtain a thermal diffusivity, and the thermal conductivity at room temperature was calculated from the heat capacity and the bulk density.

4(b) is a view showing the surface shape of the single crystal SiC in the case where the single crystal SiC is grown by the MSE method at 1900 ° C and 13.3 kPa in an argon atmosphere using a susceptor 33 made of graphite (2). Figure. In the microscope photograph of FIG. 4(b), the hexagonal shape similar to the SiC seed crystal 41 was clearly confirmed, and thus it was found that the single crystal SiC hardly grew.

Fig. 4 (c) is a view showing the surface shape of the single crystal SiC in the case where the single crystal SiC is grown under the same conditions as described above using the susceptor 33 made of graphite (3). In the micrograph of Fig. 4(c), the hexagon is not clearly confirmed and has a shape with rounded corners, so that compared with Fig. 4(b), it is understood that single crystal SiC is growing. In addition, the scales of FIGS. 4(b) and 4(c) are the same scale, and it is apparent that the single crystal SiC of FIG. 4(b) is larger. According to the above description, the single crystal SiC can be rapidly grown by using the graphite (3) for the susceptor as compared with the case where the graphite (2) is used for the susceptor.

The reason why the above difference occurs depending on the thermal conductivity can be considered as follows. That is, graphite (3) has a high thermal conductivity as compared with graphite (2), so that the heat of the SiC seed crystal 41 can be efficiently conducted to the susceptor 33 and discharged. Therefore, by using the susceptor 33 made of graphite (3), the SiC seed crystal 41 can be prevented from becoming high temperature. Thereby, growth is preferentially performed as compared with the decomposition of SiC, so that single crystal SiC can be rapidly grown.

Further, although the micrograph of the surface shape of the graphite (1) is omitted, the same as the graphite (2), the knot growth rate of the single crystal SiC is insufficient. fruit. In view of the above considerations, it is considered that the MSE method is performed by using the susceptor 33 made of graphite having a thermal conductivity of more than 130 W/(m.K), and there is a possibility that the single crystal SiC can be favorably grown. Further, it is preferable that the susceptor 33 has a thermal conductivity of 140 W/(m.K) or more.

Next, the relationship between the size of the susceptor 33 and the growth rate of the single crystal SiC will be described with reference to FIG. 5.

5 shows the MSE method in an argon atmosphere at 1900 ° C and 13.3 kPa in a susceptor 33 having a larger area than the SiC seed crystal 41 and a smaller pedestal 33 than the SiC seed crystal 41. The growth rate in the a-axis direction in the case of growing single crystal SiC (the growth length in the a-axis direction in the case of the same time MSE method) is compared. Further, the a-axis direction shows a direction (horizontal direction) perpendicular to the thickness direction of the SiC seed crystal 41. As is apparent from the graph of Fig. 5, in the case where the susceptor 33 having a larger area than the SiC seed crystal 41 is used, the growth rate becomes faster as compared with the case where the susceptor 33 having a smaller area than the SiC seed crystal 41 is used.

The reason why the above difference occurs depending on the size of the susceptor 33 can be considered as follows. That is, in the case where the size of the susceptor 33 is large, heat is transmitted from the entire SiC seed crystal 41, so that the SiC seed crystal 41 can be prevented from becoming high temperature. Thereby, growth is preferentially performed as compared with the decomposition of SiC, so that single crystal SiC can be rapidly grown. In view of the above considerations, it is preferable that the size of the susceptor 33 (in detail, the area of the surface supporting the SiC seed crystal 41) is set to be the size of the SiC seed crystal 41 (in detail, the area supported by the surface of the susceptor 33). The same or larger than the size of the SiC seed crystal 41.

As described above, in the solution growth method of the present embodiment, The SiC seed crystal 41 composed of a single crystal SiC is supported in the state of the susceptor 33, and the epitaxial layer is grown on the SiC seed crystal 41 in a state where at least a solution containing Si and C is brought into contact. Further, at least a portion of the susceptor 33 that is in contact with the SiC seed crystal 41 is made of graphite.

Thereby, compared with the case where the susceptor 33 made of SiC is used, it becomes difficult to generate minute crystals of SiC on the susceptor 33. Therefore, the growth of the epitaxial layer becomes difficult to be hindered, so that the epitaxial layer (single crystal SiC) can be rapidly grown.

Further, in the solution growth method of the present embodiment, the thermal conductivity of the graphite portion of the susceptor 33 is more than 130 W/(m.K).

Thereby, by using graphite having a high thermal conductivity as a material of the susceptor 33, the SiC seed crystal 41 can be prevented from becoming high temperature. Thereby, growth is preferentially performed as compared with the decomposition of SiC, so that the epitaxial layer can be rapidly grown.

Further, in the solution growth method of the present embodiment, the area of the surface of the susceptor 33 supporting the SiC seed crystal 41 is the same as or larger than that of the SiC seed crystal 41.

Thereby, the heat of the SiC seed crystal 41 can be efficiently conducted to the susceptor 33, so that the SiC seed crystal 41 can be prevented from becoming high temperature. Thereby, growth is preferentially performed as compared with the decomposition of SiC, so that the epitaxial layer can be rapidly grown.

Although the preferred embodiments of the present invention have been described above, the above-described configurations can be changed as follows.

As the apparatus for performing the solution growth method, the apparatus described above is an example and can be appropriately changed. For example, you can also use the above high temperature. A heating device other than the empty furnace 10 or a container having a shape or material different from the crucible 30. Further, the shape of the susceptor 33 is also arbitrary. For example, the support surface of the SiC seed crystal 41 may be a circular shape or a hexagonal shape.

In the above embodiment, the susceptor 33 is made of a single material, but it is only required to have at least a portion of the material in contact with the SiC seed crystal 41 (preferably, a thickness required for heat conduction).

As an environment (temperature, pressure, and gas atmosphere) for performing the solution growth method, the above-described cases are merely examples, and can be appropriately changed.

The surface for the growth of the epitaxial layer in the SiC seed crystal 41 is arbitrary, and may be a Si surface or a C surface.

In the above embodiment, the MSE method is employed as the solution growth method, but other solution growth methods (for example, a method of moving C in a solution by setting a temperature gradient) may be employed. Even in other solution growth methods, by using the susceptor 33 made of graphite, it is difficult to generate minute crystals of SiC on the susceptor, so that the growth rate of the epitaxial layer can be increased.

10‧‧‧High temperature vacuum furnace

21‧‧‧Main heating room

22‧‧‧Preparation heating room

23‧‧‧Vacuum forming valve

24‧‧‧Inert gas injection valve

25‧‧‧ Vacuum gauge

26‧‧‧heater

30‧‧‧坩埚

31‧‧‧Upper container

32‧‧‧Under container

40‧‧‧ SiC substrate

Claims (7)

A solution growth method is a method for growing an epitaxial layer on a seed crystal in a state in which a seed crystal composed of SiC is supported on a susceptor and a solution containing at least Si and C is brought into contact with each other, characterized in that The portion of the susceptor that is in contact with the seed crystal is made of graphite. The solution growth method of claim 1, wherein the graphite portion of the susceptor has a thermal conductivity greater than 130 W/(m.K). The solution growth method of claim 1, wherein an area of the surface of the susceptor supporting the seed crystal is the same as or larger than the seed crystal. The solution growth method of claim 1, wherein the solution growth method is a metastable solvent epitaxy method, that is, a carbon feed material having a higher seed crystal and free energy than the seed crystal and supplying at least C There is a method in which a Si melt is heated to grow an epitaxial layer on the surface of the seed crystal. A susceptor is a substrate which is supported by a solution growth method in which a crystal growth layer is grown on a seed crystal composed of SiC, and is characterized in that at least a portion in contact with the seed crystal is made of graphite. The susceptor of claim 5, wherein the graphite portion has a thermal conductivity greater than 130 W/(m.K). A method for producing single crystal SiC, comprising the steps of: supporting a seed crystal composed of SiC on a susceptor, wherein a portion of the susceptor in contact with the seed crystal is made of graphite; The epitaxial layer is grown on the seed crystal in a state in which the solution containing at least Si and C is brought into contact with the seed crystal supported on the susceptor.