JPS6121197B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a silicon carbide (SiC) crystal substrate, in particular, by growing silicon carbide using a silicon substrate at a temperature below the melting point of silicon, and then melting the silicon substrate. The present invention relates to a method of depositing and growing a second silicon carbide layer on the back surface of the silicon carbide (the surface in contact with the silicon melt) from a silicon melt.

Silicon carbide has excellent heat resistance, corrosion resistance, radiation resistance, high hardness, and a wide forbidden band width (approximately 2.4
It is a semiconductor material with an advantage of having a voltage of 3.3eV to 3.3eV (electron volt) and can be easily doped with p-type and n-type impurities. Since it has not been possible to supply wafer-shaped crystals, semiconductor devices using silicon carbide have only been manufactured on a trial basis, and have not been put into widespread practical use.

The inventors previously proposed an epitaxial method using a molten Si substrate (hereinafter referred to as the EMS method). According to this method, SiC crystal can be produced in a thin plate shape (wafer shape) with approximately the same width as the Si substrate, so the so-called planer technology and mesa technology, which are currently mainstream in the semiconductor industry, can be applied. This will greatly contribute to the industrialization of semiconductor devices.

The present inventors previously proposed a method in which a secondary SiC layer is grown using the FMS method, and then a tertiary layer is grown thereon using the CVD method, and the present invention aims to improve this method. This allows the secondary layer growth and the tertiary layer growth to be performed continuously.

Hereinafter, the present invention will be explained in detail according to embodiments with reference to the drawings.

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 work coil 28 wound around the outer body of the reaction tube 22 has a high breaking current. 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 on the upper end side of the reaction tube 22, and the discharge gas is supplied into the reaction tube 22. A silicon substrate 2 serving as a base substrate is placed on the sample stage 26 .

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, D, and E.

(a) The reaction tube 22 is evacuated and replaced with hydrogen, and the surface of the silicon substrate 2 whose main surface is the (111) plane placed on the sample stage 26 is etched away using a known hydrogen chloride/hydrogen mixed gas. (See Figure 2A).

(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 1200 to 1300° 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 are used.

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 at an atomic ratio of silane dichloride (2×10 ⁻³ propane) to 4×10 ⁻³ , and a primary silicon carbide layer 4 made of polycrystalline SiC with a thickness of 50 μm was formed by growth for 100 minutes. Polycrystalline silicon carbide layer 16 is also formed on the side surface of silicon substrate 2 at the same time.

(c) Stop the high frequency liquid current, cool down the temperature, and take out the sample stage 26. Si substrate 2 with SiC primary layer 4 deposited
Take out the sample, place it face down on the original sample stand or another sample stand 26 so that the SiC primary layer 4 is in contact with the sample stand 26, put it into the reaction tube 22, and set the flow rate to 1/min. flowing a hydrogen atmosphere.

A high frequency output is applied to the work coil 28 to raise the temperature of the sample stage 26 to about 1500° C. and melt the silicon substrate 2. 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 temperature was set to 1500° C. on the surface of the sample stage, and a 10 μm thick single crystal silicon carbide secondary layer 14 was formed by growth for 1 hour. SiC1 on the side
6 serves as a barrier to prevent the Si melt 12 from flowing out.

(d) Increase the high frequency output to raise the temperature to approximately 1700°C, and reduce the internal pressure of the reaction tube to approximately 100 torr. The Si melt gradually evaporates and decreases in size. The internal pressure of the reaction tube is approx.
SiH ₂ Cl ₂ :0.1Ncc/min while maintaining 100torr,
C ₃ H ₈ 0.1Ncc/min, H ₂ 100Ncc/min pouring 100
A high-temperature CVD-SiC layer (tertiary layer) 15 with a thickness of about 50 μm was grown in minutes. (See Figure 2D).

Although the details of the mechanism of secondary layer growth in the present invention have not yet been fully elucidated, it is believed that the mechanism is roughly as shown in FIG. 3. After second layer growth
The SiC primary layer 4 is an aggregate of fibrous grains 4', 4' whose boundaries have been removed. accordingly
The SiC primary layer 4 has a dense layered structure after being deposited, and its crystal structure is thought to be a dense aggregate of fibrous grains. When the Si substrate 2 is melted, the center part of the fibrous grains has relatively better crystal perfection than the boundary part, but since the boundary part is extremely imperfect, it is preferentially decomposed from this part. A part of this melts into the Si melt 12, precipitates at the tips of the fibrous grains, and grows in a liquid phase to form the secondary layer 14. The fibrous grains are deposited according to the orientation of the Si substrate (in the previously described embodiment, the (111) plane is the main surface, and the secondary layer 14 is epitaxially deposited on the fibrous grains. Each grain formed has the same orientation.As secondary growth progresses, the secondary layer grains spread laterally and combine to form a layered structure.In this case, after combining, in the case of using a (111) plane, a triangular Although some shaped pores may remain, the entire surface becomes almost single-crystalline.

In the embodiment, in the step (step (b)) of depositing the SiC primary layer 4 on the Si substrate 2, an undesired SiC polycrystalline thin film may be formed also on the back surface of the Si substrate.

At this time, if the present invention is carried out, SiC will also be precipitated from the liquid phase on the SiC thin film on the back surface of the substrate, so the precipitation of the SiC secondary layer on the SiC primary layer will be inhibited and the growth rate will be reduced. Moreover, this SiC thin film hinders the growth of the tertiary layer. Therefore, when a SiC thin film is grown on the back side of the substrate, it is necessary to remove this SiC film after step (b) by, for example, the lapping method.
It is preferable to remove the thin film.

According to the secondary growth of the present invention, the crystal imperfections of the primary layer, which serve as seeds for the growth of the secondary layer, decompose and melt out, and this becomes the raw material for the growth of the secondary layer.
During growth of the next layer, epitaxial growth will occur in areas with good crystal perfection, and good secondary growth can be achieved regardless of the crystal imperfection of the primary layer.

The secondary layer produced by this method sometimes leaves triangular holes and may not be completely smooth. Therefore, in the present invention, following this step, SiC is deposited from the gas phase by the CVD method. Unlike EMS, CVD does not need to maintain a Si melt, so it can grow at a desired temperature, and is advantageous in this respect.

In the present invention, secondary layer growth and tertiary layer growth can be carried out successively, which is effective in shortening manufacturing time and preventing the introduction of undesired thermal distortion.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional perspective view of a main part of a reaction apparatus used for implementing the present invention, FIG. 2 A, B, C, and D are cross-sectional views schematically showing the manufacturing process of an embodiment of the present invention, and FIG. 3 FIG. 2 is a cross-sectional view schematically showing the crystal growth mechanism of the present invention. 2...Silicon substrate, 4...First silicon carbide layer,
4'... Grain of first silicon carbide layer, 12...
Silicon melt, 14...Silicon carbide secondary layer.

Claims (1)

[Claims] 1. A first step of forming a first silicon carbide layer made of polycrystalline silicon carbide on a silicon substrate, and placing the silicon substrate on a base with the surface on which the first silicon carbide layer is formed facing downward. and a second step of increasing the temperature to melt the silicon substrate and growing a second silicon carbide layer on the first silicon carbide layer from this silicon melt; A method for producing a silicon carbide crystal, comprising: a third step of growing a third silicon carbide layer by supplying a raw material from a phase.