JPS6120514B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing silicon carbide (SiC) crystals, in particular, by introducing a liquid phase method into epitaxial growth, growing silicon carbide on a substrate, and growing silicon carbide on a substrate during the liquid phase growth period. This invention relates to a new crystal growth technology that simultaneously forms a silicon carbide growth layer that serves as a reinforcing material.

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 material that exists stably in p-type and n-type, which is rare for wide-gap semiconductors. It is seen as a promising semiconductor material for high-power devices, high-reliability semiconductor devices, radiation-resistant devices, etc. 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 gap value, it is an interesting semiconductor material as a photoelectric conversion element material between visible short wavelength and near ultraviolet light, and other wide gap semiconductors generally contain heavy metals as their main components. This brings with it problems of pollution and resources, whereas silicon carbide is free from both of these problems and is therefore 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 for obtaining high-quality, large-area substrates required for heavy production on an industrial scale with productivity in mind has not been established.

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 black-earth crucible, and Acheson, which is generally used to obtain polishing materials industrially. There are methods such as using a SiC substrate accidentally obtained by a method. However, although it is possible to obtain a large number of recrystallizations using the sublimation recrystallization method and solution method, it is difficult to obtain large SiC substrates because many crystal nuclei are generated at the initial stage of crystal growth, and there are several types of SiC substrates. 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 (crystal structure belonging to the cubic crystal structure) has been created using heteroepitaxial technology on a silicon heterogeneous substrate using Si, which is available as a relatively high-quality, large-sized single-crystal substrate. The 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 _3, etc.), 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 Si heterogeneous substrates such as (1), (2), and (3) above is as thin as 1 to 10 μm; In general, it is difficult to say that the quality 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 3C type SiC,
(Eg is 2.4 eV), SiC has a crystal structure with an even larger energy gap, such as 6H (Eg is ~3.02 eV) and 4H (Eg is ~3.02 eV).
3.26eV), 8H (Eg is ~2.8eV), etc., by epitaxial growth, the growth temperature is generally higher than 1600℃, and the growth temperature is generally higher than 1600℃. A substrate on which a SiC thin film is grown (3C type SiC/Si structure) etc. cannot be used as a substrate for α type SiC heteroepitaxial growth because the melting point of Si is 1410°C.

In view of the above-mentioned current situation, the present invention combines the vapor phase growth method and the liquid phase growth method to improve the shape of SiC crystals.
It is an object of the present invention to provide a new and useful method for manufacturing a silicon carbide crystal layer that can control the size, growth layer thickness, etc.

The basic configuration of the present invention will be explained below with reference to FIG.
This will be explained together with B.

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. Film Thickness It is necessary that the film has a thickness that will not break during the silicon substrate melting process described later, 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.

Silicon substrate 2 on which primary layer 4 of silicon carbide is formed
is placed on a sample stage 10 having a silicon carbide surface layer 6, and the sample stage 10 is heated in an atmosphere containing carbon and silicon raw materials to melt the silicon substrate 2 and form a silicon melt 12. . This state is maintained for a certain period of time while the sample stage 10 is held at a higher temperature than the silicon carbide primary layer 4, and a silicon carbide precipitated layer 8 is deposited from the gas phase on the front side of the silicon carbide primary layer 4, and a silicon carbide precipitated layer 8 is deposited from the silicon melt 12 on the back side. A silicon carbide secondary layer 14 is deposited. Since the silicon carbide precipitated layer 8 also plays a reinforcing role in the finished substrate, it may be of a quality in which carbon and silicon are mixed as long as it is mainly silicon carbide.
It is difficult to precipitate high-quality silicon carbide crystals from the gas phase because a portion of the silicon melt 12 may evaporate into the gas phase and become a silicon raw material. Since it is not necessary, materials such as those mentioned above are sufficient.

On the other hand, the silicon carbide secondary layer 14 deposited on the back side of the primary layer 4 is such that the silicon carbide on the surface of the sample stage is the silicon melt 1.
It is believed that the particles were dissolved in the silicon carbide 2 and precipitated on the silicon carbide primary layer 4 on the low temperature side.

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 the silicon substrate 2, and silicon substrates are advantageous because they are easily available in various sizes and orientations with perfect crystallinity. be. Furthermore, it is generally known that when silicon carbide is heteroepitaxially grown on a silicon substrate, a thin film of about 1 μm can become a single crystal, but if the film is made thicker than that, it becomes polycrystalline. 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, silicon substrate 2
If the initially grown portion is maintained as a single crystal, no problem will occur during precipitation of silicon carbide secondary layer 14.

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 its thickness may be several micrometers. 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, that is, the silicon carbide primary layer and the precipitated layer, may serve as reinforcement.

A feature of the present invention is that the silicon carbide precipitated layer is deposited and grown as a reinforcing material during the liquid phase growth period, so carbon and silicon raw materials are used throughout the liquid phase growth period. It is not necessary to supply it, and it is sufficient to supply it as needed at any part of the period to obtain the intended layer thickness. Although it depends on the area of the entire substrate, it is usually easier to handle if the overall thickness is 50 to 400 μm.

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

Example FIG. 2 shows an example of a reaction apparatus used in this example. A silicon carbide-coated graphite sample stage 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 applied to a work coil 28 wound around the outer body of the reaction tube 22. , this 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 column 36 made of quartz is held on the column base 34, and the support rod 24 is attached to the 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). 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 substrate 2 serving as a base substrate is placed on the sample stage 26 .

Next, a third section regarding the silicon carbide growth method of this example will be explained.
This will be explained with reference to Figures A, B, C, and D.

(a) The reaction tube 22 is evacuated and replaced with hydrogen, and the surface of the silicon substrate 2 placed on the sample stage 26 is etched away using a known hydrogen chloride/hydrogen mixed gas (see Figure 3A). b) The temperature of the silicon substrate 2 is 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 _{3 )} . ), methane (CH ₄ ), and other hydrocarbons.
In this embodiment, hydrogen gas at a flow rate of 1/min is used as a carrier gas, and silane dichloride (SiH ₂ Cl ₂ ) and propane (C ₃ H ₃ ) are used as source gases. The concentrations were set at an atomic ratio of 1×10 ⁻⁴ for dichlorosilane and 3×10 ⁻⁴ for propane, and a 3C type silicon carbide primary layer 4 having a thickness of about 10 μm was formed by growth for 40 minutes. A silicon carbide layer 16 is also formed on the side surface of silicon substrate 2 at the same time.

(b) Stop feeding the raw material gas, increase the high frequency output to the work coil 28 while flowing only hydrogen at a flow rate of 1/min, and raise the temperature of the sample stage 26 to 1500.
The temperature is raised to about .degree. 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 temperature on the surface of the sample stage was set to 1500°C. Thereafter, propane at a concentration of 1×10 ⁻³ and dichlorosilane at a concentration of 2×10 ⁻³ are added to the hydrogen of the carrier gas to serve as raw materials for forming the silicon carbide precipitation layer 8 . When grown in this state for 2 hours, a 60 μm thick silicon carbide precipitated layer 8 was precipitated and grown on the upper surface of the silicon carbide primary layer 4, and a 10 μm thick silicon carbide secondary layer 14 was precipitated and grown on the lower surface.

Since the heating method is high frequency heating, the sample stage 26 acts as a heater, and a temperature difference is naturally created between the surface of the sample stage 26 and the silicon carbide primary layer 4, resulting in liquid phase growth.

The silicon carbide layer 16 on the side surface is connected to the primary layer 4 and the sample stage 2.
6, and has the effect of preventing the primary layer 4 from tilting with respect to the sample stage 26.

(d) Stop the high-frequency output, lower the temperature, immerse the entire sample stand in a hydrofluoric acid/nitric acid mixture to etch away the silicon, and remove it from the sample stand.

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

As described above, the present invention makes it possible to mass-produce a silicon carbide crystal layer with good crystallinity with good reproducibility by introducing a liquid phase method into epitaxial growth, and also makes it possible to control the size of the obtained crystal layer. It is possible. Furthermore, since the liquid phase growth substrate is reinforced, there are various excellent effects such as no fluctuation in crystal shape, orientation, etc.

[Brief explanation of the drawing]

Figures 1A and B are schematic diagrams for explaining the concept of the present invention, Figure 2 is a perspective view showing a cross section of essential parts of a reactor used in an embodiment of the present invention, Figures 3A, B, C,
D is a sectional view illustrating the manufacturing process of an embodiment of the present invention. 2...Silicon substrate, 4...Silicon carbide primary layer, 6...
...Silicon carbide surface layer of sample stand, 8...Silicon carbide precipitation layer, 10...Sample stand, 12...Silicon melt, 14...
...Silicon carbide secondary layer.

Claims (1)

[Claims] 1. Forming a first silicon carbide layer on a silicon substrate, melting the silicon substrate on a sample stand having a silicon carbide surface layer to form a silicon melt, and melting the silicon carbide surface layer of the sample stand as described above. A second silicon carbide is formed on the silicon melt contact surface of the first silicon carbide layer by holding the silicon carbide layer at a higher temperature than the first silicon carbide layer, and during a part or all of this process. A method for producing a silicon carbide crystal, comprising the step of supplying raw materials of carbon and silicon in an atmosphere to form a third silicon carbide layer on the surface of the first silicon carbide layer. .