JPS6120518B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing silicon carbide (SiC) crystals, and in particular, the present invention relates to a method for manufacturing silicon carbide (SiC) crystals, in particular, growing silicon carbide using a silicon substrate at a temperature below the melting point of silicon, and then melting or etching the silicon substrate. The present invention relates to a method for further forming a second silicon carbide layer on the back surface (the surface that was in contact with the silicon substrate).

Silicon carbide has excellent heat resistance, corrosion resistance, and radiation resistance, and has high hardness and a large forbidden band width (2.4
to 3.3 electron volts) and easily p
Although silicon carbide is a semiconductor material that can be doped with impurities in both the shape and n-type, silicon carbide was used because it was not possible to supply wafer-shaped crystals with sufficient size and manufacturing reproducibility to industrially form semiconductor devices. Semiconductor devices have only been manufactured on a trial basis and have not yet been widely put into practical use.

The inventors previously developed SiC single crystals with ○a SiC single crystals, ○b polycrystals with grains oriented at the ○b interface, ○c polycrystals containing grains with crystal orientation oriented at the ○c interfaces, or ○ A seed layer consisting of a mixture of Si and SiC is formed, and the Si substrate is melted with a carbon material present on the back surface of the Si substrate, and SiC (2 We proposed a method of liquid-phase growth of the next layer (referred to as the next layer) and epitaxy from a molten substrate.
(abbreviated as Epitaxy from Molten Substrate, EMS). According to this EMS method, the SiC secondary layer can be produced in the size of the initial Si substrate and in the form of a thin plate (wafer shape), so the so-called planer technology and mesa technology, which are currently mainstream in the semiconductor industry, can be applied, and carbonization This will greatly contribute to the industrialization of silicon semiconductor devices.

The present invention relates to improvements in the above-mentioned EMS method, and more specifically, its purpose is to improve the layer that serves as a raw material during the liquid phase growth process.

As the carbon raw material for the EMS method, silicon carbide or a carbon layer is placed on the back side of the Si substrate. Among these, the method using carbon is to deposit a carbon thin film on the back side of the Si substrate.
A CVD deposition method has already been proposed by the present inventors, but it has the disadvantage that it increases the number of CVD steps, making the process complicated. The present invention is also characterized by using a raw material plate obtained by impregnating a carbon plate with silicon in a separate process. Silicon impregnation is extremely simple and can be processed simultaneously in large quantities, making it a material that can contribute to cost reduction.

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

Example FIG. 1 shows an example of a reaction apparatus used in this example. A silicon carbide-coated graphite sample stand 26 supported by a graphite support rod 24 is placed inside a water-cooled vertical double quartz reaction tube 22 , and a high-frequency current is passed through a work coil 28 wound around the outer body of the reaction tube 22 . Then, the sample stage 26 is heated by induction. The lower end of the reaction tube 22 is sealed with a stainless steel flange 30 and an O-ring. A joint 32 serving as a gas outlet and a support stand 34 are provided on the flange 30. A pillar 36 made of quartz is held on a pillar stand 34,
The support rod 24 is attached to the support column 36. An exhaust pipe is connected to the joint 32 on the outlet side and led to a waste gas treatment device (not shown). Reaction tube 2
A branch pipe 38 serving as a gas inlet is provided at the upper end of the reaction tube 22, and a carrier gas is supplied into the reaction tube 22. A silicon-impregnated carbon stand 64 is placed on the sample stand 26,
A silicon substrate 2 serving as a base substrate is placed thereon.

Next, we will discuss the silicon carbide growth method of this example in the second section.
This will be explained with reference to Figures A, B, C, and D.

(1a) The reaction tube 22 is evacuated and replaced with hydrogen, and the silicon-impregnated carbon stand 6 is heated with a known hydrogen chloride/hydrogen mixed gas.
4, the surface of the silicon substrate 2 having the {111} plane as its main surface is removed by etching (see FIG. 2A).
reference).

(1b) The temperature of silicon substrate 2 is set to a temperature below the melting point of silicon, preferably 1100 to 1200° C., and silicon carbide is grown on silicon substrate 2 by 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 respective source gases. The concentration was set to 7.5 x 10 ^-4 for dichlorosilane and 1.5 x 10 ^-3 for propane in atomic ratio, and 30μ was grown for 30 minutes.
A mixed layer 4 of m thickness of silicon and 3C type silicon carbide was formed. A mixed layer 16 of silicon and silicon carbide is also formed on the side surface of silicon substrate 2 at the same time.

At this time, the SiC grains (estimated to have a grain size on the order of 1000 Å) existing at the interface of the mixed layer 4 with the silicon substrate 2 are oriented in accordance with the orientation of the silicon substrate. That is, Si<111>SiC<111>
And Si<110>SiC<110>. However, the symbol represents parallel.

(1c) Stop feeding the raw material gas and reduce the flow rate to 1/
Create only a hydrogen atmosphere for 1 minute.

The high frequency output applied to the work coil 28 is increased to raise the temperature of the silicon-impregnated carbon stand 64 to about 1500° C., and the silicon substrate 2 is melted. After melting, the temperature is set at a constant temperature of about 1450°C to 1650°C and this state is maintained. In this example, the silicon-impregnated carbon table 64 was set to 1500° C., and a 10 μm thick single-crystal silicon carbide secondary layer 14 was formed by growth for 2 hours.

Since the heating method uses a high frequency heating method, the sample stage 26 becomes a heater and the silicon-impregnated carbon stage 64
There is a natural temperature difference between the surface of the mixed layer 4 and the mixed layer 4, resulting in liquid phase growth.

The mixed layer 16 on the side surface acts as a spacer to maintain a distance between the mixed layer 4 and the sample stage 26, and has the effect of preventing the mixed layer 4 from tilting with respect to the sample stage 26. (See Figure 2C) (1d) Stop the high-frequency output, lower the temperature, immerse the silicon-impregnated carbon base 64 in a hydrofluoric acid/nitric acid mixture to remove silicon, and remove the silicon-impregnated carbon base 64 from the growth layers 4, 14. Remove. (See FIG. 2D.) According to this embodiment, the silicon-impregnated carbon stand 64 is placed in the reaction tube from the beginning, so that the steps can be performed continuously. On the other hand, if there is no problem with the temperature dropping even more between steps (1b) and (1c), the silicon-impregnated carbon stand is not inserted at first, but it is inserted between steps (1b) and (1c). It doesn't matter.

According to the present invention, since the raw material layer (silicon-impregnated carbon stand) is provided separately, there is no need to replace an expensive sample stand every time, and productivity is improved.

Further, in the above embodiment, a silicon-impregnated carbon stand is placed on the sample stand, but the silicon-impregnated carbon stand may be used as a sample stand and directly heated by induction.

If a thick carbon plate is used as the raw material layer, the silicon substrate 2
When the silicon melt 12 is melted, it is sucked into the carbon plate and liquid phase growth becomes impossible.However, according to the present invention, since the carbon plate is impregnated with silicon in advance, the silicon melt 12
can be grown in liquid phase without being absorbed.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a cross section of a main part of a reaction apparatus used for implementing the present invention, and FIGS. 2A, B, C, and D are cross-sectional views illustrating the manufacturing process of an embodiment of the present invention. 2...Silicon substrate, 4...Lamination, 12...Silicon melt, 14...Silicon carbide secondary layer, 64...Silicon-impregnated carbon base.

Claims (1)

[Scope of Claims] 1. A first step of forming a seed layer containing a silicon carbide seed crystal that will become a seed for silicon carbide crystal growth in the next step on a silicon substrate, and a side opposite to the layer formation surface of the silicon substrate. A silicon carbide substrate comprising the steps of: melting the silicon substrate with its surface in contact with a silicon-impregnated carbon plate, and forming a silicon carbide layer from the silicon melt on the surface of the seed layer in contact with the silicon melt. manufacturing method.