JPH11209198A - Synthesis of silicon carbide single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To grow a large-size high-quality SiC epitaxial film at a fast rate. SOLUTION: Two temps. regions T1 , T2 are formed in a gas containing carbon while the temps. of the regions are controlled to T1 <T2 . A solid Si source 8 and a substrate 13 of a SiC seed crystal or a SiC single crystal are arranged in the low temp. region T1 and the high temp. region T2 , respectively. Si is vaporized from the low temp. region T1 , and the vaporized Si is reacted with the carbon component in the gas to produce a SiC forming gas. The SiC forming gas is introduced onto the substrate 13 of a seed crystal or SiC single crystal in the high temp. region T2 to synthesize a SiC single crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synthesizing a SiC single crystal, and more particularly to a high-quality SC suitable for semiconductor electronic parts.
The present invention relates to a method for synthesizing an SiC single crystal for efficiently growing iC.

[0002]

2. Description of the Related Art SiC is a material which has excellent resistance to chemicals such as acids and alkalis, is hardly damaged by high energy rays, has excellent durability, and is also used as a semiconductor material.

By the way, in order to use SiC as a semiconductor material, it is necessary to obtain a high-quality single crystal having a certain size. For this reason, conventionally, a method using a chemical reaction called the Acheson method, a method using a sublimation recrystallization method called the Rayleigh method, or using a single crystal of SiC obtained by these methods as a substrate, A method of growing a SiC single crystal of a target scale by a vapor phase epitaxial growth method or a liquid phase epitaxial growth method is used.

In particular, as a method of epitaxial growth, there is a method in which an SiC single crystal of an appropriate size is used as a substrate in a double-structure water-cooled quartz reaction furnace, and silane and propane are flowed using hydrogen as a carrier gas. General.

[0005]

However, as described in, for example, Nishino et al., J. Crytal Grwoth Vol. 45, p. 144 (1978), the conventional epitaxial growth method has a growth rate of several μm / h. It is known to be small. this is,
It is for controlling the supply of Si, and 1 mm /
This is a great difference compared to the rapid growth rate of about h.
Therefore, in order to increase the growth rate, WO9713013A
Attempts have been made to obtain a high growth rate by blowing a high-speed jet of silane gas onto a SiC substrate in a high-temperature hot wall. However, this method has a problem that the silane gas forms particles in the gas phase in the hot wall and contaminates the device. Further, supply of Si by gas causes a problem that hydrogen etches SiC in a high-temperature hot wall.

FIG. 2 shows that the thermal CVD of SiC
It shows the temperature dependence of the Si partial pressure of the main reaction in which C grows. In this reaction, it can be seen that when the hydrogen partial pressure is increased, the reverse reaction of SiC growth proceeds, and SiC is etched.

As shown in WO9617112A, a liquid phase epitaxial method (LPE method)
There is an attempt to produce a thick film epitaxial substrate by performing high-speed epitaxial. However, the liquid phase epitaxial method has problems such as controllability of film thickness and residual droplets on the surface.

On the other hand, in order to achieve high-speed epitaxial growth, SU913762 performs epitaxial growth by sublimating a SiC raw material using lead, tin, germanium or the like as a transport material. However, this method has a problem that the above-mentioned transport material is mixed into the film.

As a high-speed epitaxial utilizing the sublimation method, a method called a sandwich method has been proposed by Yu.A. Vodakov.
and ENMokhov, Patent GB No. 1458445. This method uses SiC as a raw material and S as a seed crystal.
By placing the iC substrate at a distance of several mm or less and raising the temperature on the raw material side to be higher than that on the seed crystal side, the raw material is transported from the high-temperature part to the low-temperature part, and epitaxial growth proceeds. Things. In this sandwich method,
Since the distance between the raw material and the substrate is short, the driving force for diffusion is large, and a high growth rate can be expected. However, since the distance between the raw material and the substrate is short, if the growth is performed for a long time, the distance between the raw material and the substrate changes, and there is a problem that the growth conditions are not constant. In any case, it is difficult to make the distance between the raw material and the substrate accurately constant at a distance of several mm or less.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a method for synthesizing a SiC single crystal capable of growing a large-sized, high-quality SiC epitaxial film at a high speed. .

[0011]

Means for Solving the Problems In order to solve the above problems, the present invention provides a method of synthesizing a SiC single crystal by forming _two temperature zones T ₁ and T ₂ in a gas containing carbon, The temperature of the region is set to T ₁ <T ₂ , solid Si is used for the low temperature region T ₁ , and a seed crystal or SiC is used for the high temperature region T _2.
Set up a single crystal substrate, respectively, Si from the low temperature area T ₁
Was evaporated, the Si obtained by its evaporation was reacted with carbon component in the gas to form a SiC-forming gas, the SiC forming gas to reach the seed crystal or the SiC single crystal substrate of the high-temperature region T ₂ of the SiC single crystal It is characterized by combining.

That is, according to the present invention, solid Si is heated to a melting point or higher to be melted, and the evaporated Si is transported to the substrate by an inert gas such as Ar. Here, stoichiometry can be adjusted by adjusting the supply balance of the elements.

In the present invention, by using a solid source of Si, the partial pressure of hydrogen in the atmosphere is reduced, and the problem of film etching is eliminated. Further, since an unstable gas such as silane is not used as the Si source, there is no problem of particles due to decomposition of the gas in the gas phase, and sufficient Si can be supplied.
As a result, the problem of controlling the supply of Si in CVD can be solved, and high-speed growth can be achieved.

From the above, it can be seen that in the main reaction of the SiC growth shown in FIG. 2, the reaction proceeds in the direction in which the SiC grows as the hydrogen partial pressure decreases. Since the amount of Si flux (cm ^-1 s ^-1 ) can be calculated from the partial pressure of Si, if this flux is considered to all contribute to growth, several hundred μm /
It can be seen that the growth rate of h can also be expected.

The carbon component is supplied as a gas in order to increase the uniformity of the film thickness.

Since high-purity materials such as solid Si and hydrocarbon as raw materials can be easily obtained, the impurity concentration of the epitaxially grown film can be greatly reduced. Further, solid Si is inexpensive as compared with Si-based gas, and the production cost can be suppressed even when high-speed growth is performed.

In the present invention, a shield made of carbon, quartz or SiC may be provided at the interface between liquid Si and gaseous Si in the low temperature region T ₁ to control the vapor pressure of Si. Here, as the carbon, glassy carbon (glassy carbon) is particularly suitable, and does not react with Si even at a high temperature, and provides an excellent shield.

Further, as the carrier gas of the Si evaporated from the low temperature region T _1, it is preferable to use an argon gas. This is because by-products are not generated when argon gas is used.

Further, the seed crystal or Si in the high temperature region T ₂
The C single crystal substrate may be synthesized while rotating at a high speed of 100 rpm or more. As described above, by rotating the substrate at high speed, the film thickness distribution can be reduced, and high-speed growth can be performed. This is because the rotation causes the diffusion layer on the surface of the substrate to become thinner and the driving force for diffusion to increase. Thus, the growth rate can be increased without using a proximity method such as a sandwich method.

On the other hand, the inner surface of a container made of, for example, carbon, which forms the low temperature region T ₁ and the high temperature region T _2, may be formed of diamond-like carbon or glassy carbon (glassy carbon). By coating the inner surface of the container with diamond-like carbon or glassy carbon, generation of natural nuclei can be suppressed, and a high-quality SiC epitaxial film can be synthesized.

On the other hand, by disposing a heat shield made of graphite outside the container forming the low temperature region T ₁ and the high temperature region T ₂ , heat radiation due to heat radiation can be suppressed.

Further, if the heat shield is formed so that a plurality of strip-shaped graphite plates are arranged adjacent to each other with a gap therebetween so as to have a substantially cylindrical shape, an induction current can be suppressed when high-frequency heating is performed. Arranging a plurality of heat shields in the radial direction of the container is even better in terms of suppressing heat radiation and suppressing induced current.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a synthesizing apparatus used in this embodiment. In this synthesizing apparatus, the cylindrical hot wall 1 made of graphite includes a cylindrical upper hot wall 1a and a lower hot wall 1b. The upper end of the upper hot wall 1a is closed by a disc-shaped lid 2. On the other hand, the lower hot wall 1b has a double structure in which two cylinders are overlapped in the radial direction with a small gap. Each inner peripheral surface of the upper hot wall 1a and the lower hot wall 1b
Each is formed of diamond-like carbon or glassy carbon (glassy carbon) having high smoothness. The surface roughness of each inner peripheral surface of the upper hot wall 1a and the lower hot wall 1b is preferably Rmax <10 μm.

Inside the lower hot wall 1b, a bottomed cylindrical crucible 3 made of graphite and containing Si is inserted movably in the axial direction with a gap from the lower hot wall 1b. The lower portion of the crucible 3 for accommodating Si is fixed on the upper surface of a disk-shaped crucible support 4 slidable on the inner peripheral surface of the lower hot wall 1b. A cylindrical support shaft 5 connected to a drive source (not shown) is fixedly provided. That is, as the support shaft 5 moves up and down, the crucible 3 for accommodating Si can move in the axial direction. Further, since the support shaft 5 has a hollow cylindrical shape, the temperature of the bottom surface of the crucible 3 can be measured with a two-temperature pyrometer.

Further, an Ar gas supply pipe 6 for supplying Ar gas as a carrier gas is provided at the center of the support shaft 5, the crucible support 4 and the crucible 3.
A plurality of hydrocarbon supply holes 7 for supplying hydrocarbons as a gas containing carbon are formed in the outer periphery of the crucible support 4 so as to penetrate in the axial direction.

The crucible 3 contains a solid Si source 8. On the upper surface of the Si source 8, a disk-shaped shield 9 for controlling the Si vapor pressure made of carbon, quartz or SiC is mounted. The shield 9 for controlling the Si vapor pressure is made so that the Si vapor can pass through.
A plurality of passage holes 9a penetrating in the axial direction are formed.
The shield 9 controls the area of the interface between molten liquid phase Si and gas phase Si in order to control the vapor pressure from the Si source 8.

A disk-shaped control plate 10 for uniformly supplying the vapor of Si is fixed on the upper part of the crucible 3. The control plate 10 is made of the same material as the shield 9 and is formed by providing a disk at the upper end of a cylinder erected in the crucible 3 and providing the disk with a plurality of through holes 10a penetrating in the axial direction. .

On the other hand, inside the hot wall 1, a cylindrical substrate holder support rod 1 penetrating through the center of the lid 2
1 is inserted movably in the axial direction. At the lower end of the substrate holder support rod 11, a disk-shaped substrate holder 12 is fixed so as to close the lower end opening. On the lower surface of the substrate holder 12, SiC
Is fixed by a paste obtained by melting glucose at a high temperature. Since the substrate holder supporting rod 11 has a hollow cylindrical shape, the temperature of the substrate 13 can be measured with a two-temperature pyrometer. Also, the substrate holder support rod 11
Is provided so as to be able to rotate up to 1500 rpm around the axis. Further, a plurality of gas exhaust holes 14 for exhausting gas are provided in the outer periphery of the lid 2 so as to penetrate in the axial direction.

Outside the hot wall 1, three heat shields 15 are arranged concentrically in the radial direction of the hot wall 1. Each of the heat shields 15 has a plurality of strip-shaped graphite plates disposed adjacent to each other with a gap therebetween to form a substantially cylindrical shape.
5 is provided so that the gap does not overlap in the radial direction. Further, since the heat shield 15 is not formed of carbon fiber or porous graphite, which is a commonly used cause of impurity contamination, there is no concern about impurity contamination.

Outside the outermost heat shield 15, a cylindrical quartz tube 16 made of quartz is disposed concentrically with the heat shield 15. Cooling water such as water flows inside the quartz tube 16, so that the quartz tube 16 is protected. Further, an RF work coil 17 is provided outside the quartz tube 16 so that the hot wall 1 and the like can be heated at a high frequency.

Incidentally, the whole of the hot wall 1 and the heat shield 15 and the like are configured to be able to be in a vacuum state within a range surrounded by the inner wall of the quartz tube 16.

In the synthesizing apparatus having such a configuration, R
The temperature of the Si source 8 is set to 1300 by the F work coil 17.
To 1600 ° C., and the temperature of the substrate 13 is 1500 to 22 ° C.
Heating can be controlled to 00 ° C. respectively. In other words, the synthesis apparatus includes a low-temperature region T ₁ of the Si source 8 and a high-temperature region T _{2 of the} substrate 13 in the hot wall 1.
Are formed so that the two regions described above can be formed.

A method for synthesizing a SiC single crystal using the synthesizing apparatus having the above configuration will be described below.

First, after setting the Si source 8 and the SiC single crystal substrate 13 at predetermined positions, the substrate holder support rod 11 is moved upward to raise the substrate 13, and the Si source 8 together with the crucible 3 is moved downward. After that, vacuum evacuation was performed for 1 hour in a space formed inside the inner wall of the quartz tube 16. Next, Ar gas is flowed into the apparatus to normal pressure (760 Torr), the hot wall 1 is set to 2800 ° C. while cooling water is flown into the quartz tube 16, and air baking is performed for 1 hour to discharge gas. Was.

Next, the Si source 8 is moved upward together with the crucible 3 to the state shown in FIG. 1, the substrate holder supporting rod 11 and the substrate 13 are lowered to predetermined positions, and then the substrate holder supporting rod 11 is moved at 1000 rpm. While rotating, the RF work coil 17 for high frequency heating was adjusted to
3 was 2300 ° C., and the Si source 8 was 1450 ° C. By setting the temperature at such normal pressure, it is possible to prevent the growth of crystals having poor crystallinity.

Thereafter, the pressure inside the inner wall of the quartz cylinder 16 is increased to A
By lowering the pressure to 5 Torr in an r gas atmosphere and maintaining this state, Ar gas as a carrier gas flows from the Ar gas supply pipe 6 so that Si vapor passes through the passage hole 9 a of the shield 9 and the control plate 10. Passing hole 10
a, and reacted with the hydrocarbon supplied from the hydrocarbon supply hole 7 near the substrate 13. Then, the SiC forming gas is allowed to reach the substrate 13 so that 100 μm
An SiC single crystal was grown at a speed of m / h, and finally an epitaxial film of a 2 inch φ and 0.5 mm thick SiC single crystal was formed.

When the photoluminescence characteristics of the epitaxial film thus obtained were examined, it was found that the peak wavelength was about 490 nm, and it was a 6H type SiC epitaxial film. In addition, when the Hall measurement was performed, the electrical characteristics were as follows.
m, the carrier density was about 3 × 10 ¹⁴ cm ⁻³ , and it was found that an epitaxial film having n-type conductivity and high resistance and low carrier density could be synthesized. When the substrate on the back side was scraped off and the light transmittance of this epitaxial film was examined,
It was good for the wavelength of m, and it was found that this epitaxial film was a good crystal with little incorporation of impurities.

As described above, according to this embodiment, since the solid Si source 8 is used as a raw material, the partial pressure of hydrogen in the atmosphere is reduced, and the problem of film etching is eliminated. In addition, since an unstable gas is not used as the Si source 8,
Sufficient Si can be supplied without the problem of particles due to gas decomposition in the gas phase, and high-speed growth can be achieved.

The raw materials Si and hydrocarbons are
High-purity materials can be obtained at low cost, and the impurity concentration of the epitaxially grown film can be significantly reduced.

Further, since the substrate holder support rod 11 and the substrate 13 are rotated at 100 rpm or more, the film thickness distribution can be made uniform, and the in-plane uniformity can be improved.
Diffusion can be promoted to increase the growth rate.

Since the inner peripheral surface of the hot wall 1 is made of diamond-like carbon or glassy carbon, natural nucleation can be suppressed and high quality SiC
A single crystal can be obtained.

The heat shield 15 suppresses heat radiation due to heat radiation and suppresses induced current due to high-frequency heating.

[0043]

As described above, according to the method for synthesizing a SiC single crystal of the present invention, carbon, which is a constituent element of SiC, and Si
Is separately supplied as a gas containing carbon atoms and solid Si, whereby a large-sized, high-quality SiC epitaxial film can be synthesized at a high speed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a synthesizing apparatus used in an embodiment of the present invention.

FIG. 2 is a graph showing temperature dependence of Si partial pressure of a main reaction for growing SiC in SiC thermal CVD.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Hot wall, 3 ... Crucible, 6 ... Ar gas supply pipe, 7 ... Hydrocarbon supply hole, 8 ... Si source, 9 ... Shield,
10: control plate, 11: substrate holder support rod, 13: substrate,
15: heat shield, 17: RF work coil

Claims (7)

[Claims] 1. Two temperature regions T ₁ and T ₂ are formed in a gas containing carbon, and the temperature of each region is set to T ₁ <T _2.
Solid Si in the low temperature region T ₁ and SiC in the high temperature region T ₂
The seed crystal or SiC single crystal substrate is installed, respectively,
The low temperature region to evaporate the Si from T _1, its evaporated Si was reacted with carbon component in said gas to form a SiC-forming gas, said SiC-forming gas in the high temperature region T ₂ seed crystal or the SiC single A method for synthesizing a SiC single crystal, wherein the method reaches a crystal substrate and synthesizes a SiC single crystal. Wherein the interface between the Si of the Si and the gas phase of the liquid phase in the low temperature region T _1, SiC, characterized by controlling the vapor pressure of the Si is provided a shield made of carbon, quartz, or SiC A method for synthesizing a single crystal. 3. The method for synthesizing a SiC single crystal according to claim 1, wherein an argon gas is used as a carrier gas of Si evaporated from the low-temperature region T ₁ . Wherein the species of the high temperature region T ₂ crystal or SiC
The method for synthesizing a SiC single crystal according to any one of claims 1 to 3, wherein the single crystal substrate is synthesized while rotating at a high speed of 100 rpm or more. 5. The SiC unit according to claim 1, wherein an inner surface of the container forming the low temperature region T ₁ and the high temperature region T ₂ is made of diamond-like carbon or glassy carbon. Crystal synthesis method. 6. The SiC unit according to claim 1, wherein a heat shield made of graphite is arranged outside a container forming the low temperature region T ₁ and the high temperature region T _2. Crystal synthesis method. 7. The heat shield, wherein a plurality of strip-shaped graphite plates are arranged adjacent to each other with a gap provided therebetween so as to form a substantially cylindrical shape, and a plurality of the heat shields are arranged in a radial direction of the container. The method for synthesizing a SiC single crystal according to claim 6.