JPS623117B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing silicon carbide (SiC) crystals, and in particular to a method for growing a silicon carbide layer on a substrate by introducing a liquid phase method into epitaxial growth.

Silicon carbide has many crystal structures (referred to as polytypes) and has a forbidden band width of 2.4 to 3.3 electron volts eV depending on the crystal structure. In addition, silicon carbide is extremely stable thermally, chemically, and mechanically, and is resistant to radiation damage. It is also a rare material for wide-cap semiconductors, and is a p-type and n-type co-stable material, making it suitable for high-temperature operation. It is seen as a promising semiconductor material for devices, high-power devices, high-reliability semiconductor devices, and radiation-resistant devices. Furthermore, it is a material that can be used even in environments difficult for elements using conventional semiconductor materials, and can significantly expand the range of applications of semiconductor devices. In addition, considering its energy cap value, it is also an interesting semiconductor material as a photoelectric conversion element material between visible short wavelengths and near ultraviolet light, and other wide-gap semiconductors generally contain heavy metals as their main components. However, silicon carbide is free from both of these problems and is expected to be put to practical use as an electronic material in the future.

Despite this material having many advantages and possibilities, practical application has been hindered due to the following reasons:
The reason for this is that reproducible crystal growth technology has not been established to obtain high-quality, large-area substrates necessary for mass production on an industrial scale with productivity in mind.

Conventionally, the method for obtaining SiC substrates on a laboratory scale is the so-called sublimation recrystallization method (referred to as the Rayleigh method), in which SiC powder is sublimated in a graphite crucible at 2200°C to 2600°C, and then recrystallized to obtain a SiC substrate. ), the so-called solution method to obtain a SiC substrate by melting silicon or a mixture of silicon with impurities such as iron, cobalt, platinum, etc. in a graphite crucible, and the Acheson method, which is generally used to obtain polishing materials industrially. There is a method using a SiC substrate obtained by accident. However, although it is possible to obtain a large number of re-crystallizations using the sublimation recrystallization method and the solution method, it is difficult to obtain large-sized SiC substrates because many crystal nuclei are generated at the initial stage of crystal growth. The crystal structure of (poly
type) SiC is mixed, and it has a single crystal structure and a large size.
This is an incomplete method for obtaining SiC single crystals with better reproducibility. Furthermore, SiC substrates obtained accidentally by the Acheson method have problems in terms of purity and crystallinity when used as semiconductor materials, and even if relatively large ones can be obtained, they are obtained accidentally. , it is not suitable as a method for industrially obtaining SiC substrates.

On the other hand, with the improvement of semiconductor technology in recent years, 3C-type SiC (having a cubic crystal structure That energy gap is ~
2.4eV) single crystal thin films can now be obtained. As a heteroepitaxial growth method on a silicon substrate, (1) SiH ₄ , SiCl ₄ , (CH ₃ ) ₃ SiCl,
Using (CH ₃ ) ₂ SiCl ₂ , CCl ₄ as a carbon raw material, hydrocarbon gas (C ₂ H ₂ , C ₂ H ₆ , CH ₄ , C ₃ H _8, etc.) and hydrogen, argon, etc. as a carrier gas, Si A method of obtaining a 3C-type SiC single crystal thin film by vapor phase growth technology (CVD technology) with the substrate temperature set at 1200°C to 1400°C. (2) Graphite on the Si substrate surface, carbon produced by thermal decomposition of hydrocarbons. (3) Argon activated by direct current or alternating current glow discharge of Si vapor, Passed through hydrocarbon gas and onto Si substrate
There is a method of vapor depositing a SiC single crystal thin film (vapor deposition method), etc. However, the thickness of the 3C type SiC thin film single crystal obtained by heteroepitaxial technology on a Si foreign substrate such as (1), (2), and (3) above is as thin as 1 to 10 μm; In general, it is difficult to say that the integrity of the crystal is good. The reason for this is
Due to the large difference in lattice constant between the Si substrate and the 3C type SiC crystal, many misfit dislocations occur especially near the interface between the SiC substrate and the epitaxial 3C type SiC, and the influence extends to the inside of the epitaxial layer. This is also thought to be because strain is accumulated in the SiC epitaxial layer during the cooling process from the growth temperature to room temperature due to the difference in thermal expansion coefficient between the Si substrate and the SiC crystal. Also, if such a method were used to produce large area and high quality
Even if 3C type SiC (energy gap Eg is ~2.4eV) is obtained, SiC with a crystal structure with an even larger energy gap, such as 6H (Eg ~3.02eV)
a such as 4H (Eg is ~3.26eV) 8H (Eg is ~2.8eV)
When trying to obtain SiC type SiC by epitaxial growth, the growth temperature is generally higher than 1600℃, and it is difficult to grow SiC on a Si substrate or the aforementioned Si substrate (3C type SiC/Si structure). Since the melting point of Si is 1410°C, it cannot be used as a substrate for a-type SiC heteroepitaxial growth.

In view of the above-mentioned current situation, the present invention provides a new and useful method for manufacturing a silicon carbide crystal layer, which allows controlling the shape, size, growth layer thickness, etc. of SiC crystal by combining vapor phase growth and liquid phase growth. The purpose is to provide the following.

Hereinafter, the basic configuration of the present invention will be explained with reference to FIG.

A silicon carbide layer (hereinafter referred to as a primary layer) 4 is formed on a silicon substrate 2 . The formation method usually uses a vapor phase chemical precipitation method, but a carbonization method by heat exchange or chemical conversion, molecular beam epitaxy or other vapor deposition method may also be used, or a combination of these methods is also possible. The film needs to have a thickness that will not break during the silicon substrate melting process described below, and although it depends on the size of the silicon substrate, it is desirable to have a thickness of at least about 5 to 10 μm.

A silicon substrate 2 on which a silicon carbide primary layer 4 is formed,
It is immersed in a silicon melt in a crucible containing a carbon raw material, and silicon carbide secondary layer 14 is grown in liquid phase on the back surface of silicon carbide primary layer 4 (the surface that was in contact with silicon substrate 2).

At this time, silicon substrate 2 may be removed from silicon carbide primary layer 4 or left as is without being removed. If the silicon substrate 2 is immersed in the silicon melt in that state, it will naturally melt and mix with the silicon melt. In this case, if a problem arises in controlling impurities in the liquid-phase grown silicon carbide secondary layer 14, it is preferable to remove the silicon substrate in advance by chemical etching or the like.

In general, liquid phase grown crystals have superior crystal integrity compared to vapor phase grown crystals. However, in normal liquid phase growth, spontaneously generated nuclei are used, or substrate crystals (seed crystals) prepared in advance by other methods are used. unable to grow. In contrast, in the present invention, liquid phase growth is performed on the primary layer 4 formed on a silicon substrate, and silicon substrates are advantageous because perfectly crystalline silicon substrates of various sizes and orientations are easily available. . In addition, it is generally known that when silicon carbide is heteroepitaxially grown on a silicon substrate, a thin film of about 1 μm thick can become a single crystal, but if the film is made thicker than that, it becomes polycrystalline. There is. In the primary layer 4 of the present invention, the seed crystal for growing the next silicon carbide secondary layer 14 is not the surface of the growth layer, but the back surface, that is, the side in contact with the silicon substrate 2. Therefore, even if silicon carbide primary layer 4 becomes polycrystalline, no problem will occur during precipitation of silicon carbide secondary layer 14 if the initially grown portion on silicon substrate 2 is maintained as a single crystal.

When using planar technology, which is the mainstream of the current semiconductor electronics industry, the main surface of the wafer-shaped crystal only needs to be a good single crystal, and the thickness can be several μm. In the silicon carbide wafer according to the present invention, portions that function as devices such as diodes and transistors may be formed in the liquid phase grown crystal portion, and other portions may function as reinforcement.

Note that technical considerations may be added in this step so that liquid phase grown silicon carbide is deposited on the upper surface side (the surface not in contact with silicon substrate 2) of silicon carbide primary layer 4. Even if silicon carbide is deposited on the top surface of the primary layer 4, the quality of the crystal (crystal perfection) is better in the silicon carbide secondary layer 14 on the back surface, so the parts where diodes and transistors are made are layer 14
Use.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

〔Example〕

FIG. 2 shows a cross section of an example of a crucible. Graphite crucible 40 is supported by graphite struts 42 . Silicon is placed in the crucible 40, and when the crucible 40 is heated, the silicon melts and becomes a silicon melt 46. The silicon carbide primary layer 4 adhered to the silicon substrate 2 is gripped by the tip of a graphite gripper 44 and immersed in the silicon melt 46 . The crucible 40 is placed in a reaction tube (not shown) made of quartz, for example, and hydrogen, argon, or the like is supplied as an atmospheric gas. A work coil (not shown) is provided outside the reaction tube to heat the crucible 40 with high frequency.

Next, a method for growing a silicon carbide crystal layer according to this embodiment will be explained with reference to the drawings.

(a) Place the silicon substrate 2 on a sample stage in a reaction tube used in a general vapor phase chemical deposition method, replace the inside of the reaction tube with hydrogen, and cover the surface of the silicon substrate 2 with a mixed gas of hydrogen chloride and hydrogen. Remove by etching.

(b) The temperature of the silicon substrate 2 is set to a temperature below the melting point of silicon,
Preferably, the temperature is set at 1100 to 1200° C., and silicon carbide is grown on silicon substrate 2 using a general vapor phase growth method. A rare gas such as argon (Ar), helium (He), or hydrogen gas (H ₂ ) is used as the carrier gas. Silicon raw materials include silicon tetrachloride (SiCl ₄ ), silane dichloride (SiH ₂ Cl ₂ ), and silane (SiH ₄ ), and carbon raw materials include carbon tetrachloride (CCl ₄ ) and propane (C ₃ H _{8 )} . ), methane (CH ₄ ), and other hydrocarbons.

In this example, hydrogen gas at a flow rate of 1/min is used as the carrier gas, and silane dichloride (SiH ₂ Cl ₂ ) and propane (C ₃ H ₈ ) are used as the raw material gases. 1 x 10 ^-4 and propane at 3 x 10 ^-4 , 30 μm growth was achieved in 2 hours of growth.
A 3C type silicon carbide primary layer 4 was formed. Silicon carbide layer 16 is also formed on the side surface of silicon substrate 2 at the same time. (See FIG. 1) (c) Graphite crucible 40 is heated and silicon carbide primary layer 4 with silicon substrate 2 attached is immersed in silicon melt 46 .
This may be done by gripping the silicon carbide layer 16 on the side surface with a graphite gripper 44. In this case, the inner wall of the graphite crucible 40 dissolves into the silicon melt and serves as a carbon raw material. When the temperature of graphite crucible 40 was maintained at 1600° C., a 30 μm thick silicon carbide secondary layer 14 grew on the back side of primary layer 4 (the side that was in contact with silicon substrate 2) in one hour. At the same time, a liquid phase growth layer 18 was also obtained on the upper surface side.

(d) Pull up the gripping tool 44 and remove the remaining solidified silicon melt with a hydrofluoric acid/nitric acid mixture.

Through the above steps, a silicon carbide crystal layer can be obtained.

By introducing the liquid phase method as described above, the present invention mass-produces a silicon carbide crystal layer with good crystallinity with good reproducibility using the single crystal face of the silicon carbide layer on the side that was in contact with the silicon substrate as a seed crystal. It is also possible to control the size of the crystal layer obtained.

[Brief explanation of the drawing]

FIGS. 1 and 2 are main part sectional views schematically illustrating an embodiment of the present invention. 2...Silicon substrate, 4...Silicon carbide primary layer, 14
... Silicon carbide secondary layer, 40 ... Crucible, 46 ... Silicon melt.

Claims (1)

[Scope of Claims] 1. A step of forming a first silicon carbide layer on a silicon substrate, and immersing the first silicon carbide layer in a silicon melt containing a carbon raw material. A method for producing a silicon carbide crystal layer, comprising the step of growing a second silicon carbide layer in a liquid phase using the single crystal plane on the side that was in contact with the silicon substrate as a seed crystal.