JPH0364480B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a method for manufacturing a silicon carbide (SiC) single crystal substrate.

<Prior Art> SiC has many crystal structures (referred to as polytypes) and has a forbidden band width of 2.2 to 3.3 electron volts (eV) depending on the crystal structure.
In addition, SiC is extremely stable thermally, chemically, and mechanically, and is resistant to radiation damage. Furthermore, it is a rare wide-gap semiconductor material that exists in both p-type and n-type co-stability. Therefore, it is seen as a promising semiconductor material for high-temperature operating devices, high-power devices, high-reliability semiconductor devices, radiation-resistant devices, and the like. 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. Furthermore, it is a semiconductor material that can be used as a photoelectric conversion element material for short wavelength visible light and near ultraviolet light by utilizing its wide energy gap. Unlike other wide-gap semiconductors, which generally contain heavy metals as their main components and are associated with pollution and resource problems, silicon carbide is free from both of these problems, making it an excellent electronic material. This is seen as promising.

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 SiC substrates required for mass production on an industrial scale with productivity in mind.

Conventionally, the method for obtaining SiC single crystal substrates on a laboratory scale is to heat SiC powder in a graphite crucible at 2200°C to 2600°C.
The SiC substrate is sublimated at ℃ and further recrystallized using the so-called sublimation recrystallization method (referred to as the Rayleigh method).
The so-called solution method, in which SiC substrates are obtained by mixing impurities such as iron, cobalt, platinum, etc. into silicon or silicon, or by melting the mixture in a graphite crucible, and the Acheson method, which is generally used industrially to obtain abrasive materials, are used. There are methods that use SiC substrates that can be obtained commercially.

However, although it is possible to obtain a large number of recrystallizations using the sublimation recrystallization method and the solution method, it is difficult to obtain a large SiC single crystal substrate because many crystal nuclei are generated at the initial stage of crystal growth, and it is difficult to obtain a large SiC single crystal substrate. SiC of various polytypes coexist, making it an incomplete method for obtaining large SiC single crystals with a single crystal structure with good reproducibility. In addition, 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, in recent years, with the improvement of semiconductor technology, silicon (Si) has become available as a high-quality, large-sized single crystal substrate.
A single crystal thin film of 3C type SiC (having a crystal structure belonging to the cubic crystal structure, with an energy gap of ~2.2 eV) is grown on a heterogeneous substrate using a heteroepitaxial technique using a vapor phase growth method (CVD method). is now available. The CVD method is a manufacturing technology that excels in mass production on an industrial scale, and allows for large-area, high-quality production.
This is a promising technology for growing SiC single crystal films on Si substrates with good reproducibility. Usually, as a silicon raw material,
SiH ₄ , SiCl ₄ , SiH ₂ Cl ₂ , (CH ₃ ) ₃ SiCl,
(CH ₃ ) ₂ SiCl ₂ In addition, CCl ₄ , CH ₄ ,
Using C ₃ H ₈ , C ₂ H ₆ , hydrogen, argon, etc. as a carrier gas, the Si substrate temperature is set at 1200° C. to 1400° C., and a 3C type SiC single crystal thin film is epitaxially grown.

However, since Si is a foreign substrate, SiC
Si and SiC have poor compatibility (wetting) with each other, and the lattice constants of Si and SiC differ by 20%, so it cannot be directly applied to the Si substrate.
Even if you try to grow SiC as a single crystal, you will not be able to obtain a single crystal film through layered growth, but instead it will become a polycrystalline film with a dendrite structure, or even if you can obtain a very thin single crystal film, the quality of the crystal will deteriorate as it gets thicker. It tends to become polycrystalline.

As one of the improvements to the above CVD method, a method has recently been developed to grow high-quality, large-area SiC single crystals on Si single crystal substrates using two-temperature continuous CVD method (Japanese Patent Application No. 76842/1982). . Another method is to carbonize the surface of a Si single crystal substrate with hydrocarbon gas and then grow a silicon carbide single crystal using the CVD method, which is already a well-known technique (Appl.phys.Lett42 (5), 1March 1983P460~
P462).

However, in any of the above CVD methods, a SiC layer is grown on a Si substrate, resulting in a SiC single crystal containing many crystal defects due to the difference in thermal expansion coefficients of Si and SiC by about twice. In order to use SiC single crystal for device fabrication, a crystal with few crystal defects is required.

<Object of the invention> In view of the above-mentioned problems, the present invention has been made to
In CVD growth, by using SOS (Silicon on Sapphire), which has a coefficient of thermal expansion similar to that of SiC, as the base substrate for growth, it is possible to obtain a SiC single crystal with few lattice defects. The purpose is to provide a manufacturing method.

<Example> After carbonizing the Si single crystal surface on an SOS substrate with a hydrocarbon gas such as propane (C ₃ H ₈ ) to form a silicon carbide thin film on the surface, monosilane (SiH ₄ ) and propane were used as raw material gases. An embodiment of the present invention will be described below, taking as an example a method of growing a silicon carbide single crystal by CVD using (C ₃ H ₈ ).

The accompanying drawing is a block diagram of a growth apparatus used in one embodiment of the present invention. A quartz support stand 3 on which a graphite sample stand 2 is placed is installed inside a water-cooled horizontal double quartz tube 1, and a high-frequency current is passed through a work coil 4 wound around the outer body of the reaction tube 1. This sample stage 2 is heated by induction. The sample stage 2 may be installed horizontally or may be appropriately inclined. A branch pipe 5 serving as a gas inlet is provided at one end of the reaction tube 1, and cooling water is supplied to the quartz tube outside the double quartz tube 1 via branch pipes 6 and 7. The other end of the reaction tube 1 is closed with a stainless steel flange 8, and a stop plate 9, a bolt 10, a nut 11, and a rolling 1 are arranged around the flange.
It is sealed at 2. A branch pipe 13 serving as a gas outlet is provided at the center of the flange 8. Using this growth apparatus, the following crystal growth was performed.

The SOS board 14 is placed on the sample stage 2. Hydrogen (H ₂ ) gas was flowed at a rate of 3.0 cc/min as a carrier gas, and propane (C ₃ H ₈ ) gas was flowed at a rate of 1.0 cc/min as a raw material gas for carbonization to convert the silicon surface on the SOS into silicon carbide. A high-frequency current is applied to the graphite sample stage 2 to heat it, and the temperature of the SOS board 14 is approximately
Heating to 1350°C forms a silicon carbide single crystal thin film on the silicon single crystal surface on the SOS. Next, the supply of propane was cut off, the flow rate of propane and monosilane (SiH ₄ ) gas was adjusted to 0.4 to 0.9 cc per minute, and the flow was continued for 1 hour to form a silicon carbide single crystal thin film of approximately 3 μm on the above thin film. can. As a result, a silicon carbide single crystal thin film with a flat surface and few lattice defects was obtained on the entire surface of the SOS substrate 14 by observation using an electron microscope.

The reason for the decrease in lattice defects is thought to be that by using SOS as the base substrate, the lattice defects that were generated due to the difference in thermal expansion coefficient were reduced, resulting in fewer lattice defects in the grown single crystal film.

In the above examples, normal pressure is used as the growth method.
Although the CVD method was used, a reduced pressure CVD method may also be used.

<Effects of the Invention> According to the present invention, a high-quality, large-area silicon carbide single crystal with few lattice defects can be obtained on an SOS substrate and is suitable for mass production. It becomes possible to put it into practical use on a large scale.

[Brief explanation of drawings]

The accompanying drawing is a configuration diagram of a growth apparatus used to explain one embodiment of the present invention. 1...Reaction tube, 2...Sample stand, 3...Support stand,
4... Work coil, 5, 6, 7, 13... Branch pipe, 8... Flange, 14... SOS board.

Claims (1)

[Claims] 1. A method for producing a silicon carbide single crystal, characterized in that a silicon-on-sapphire substrate is used as a base substrate when growing a silicon carbide single crystal thin film by a vapor phase growth method.