JPH09157092A - Production of silicon carbide single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease micropipe-like defects when a silicon carbide single crystal is grown by sublimation recrystallization method with using a seed crystal, by incorporating impurity elements in the growing atmosphere to supply a large amt. of impurities in the growing crystal. SOLUTION: A substrate 1 comprising silicon carbide is prepared as a seed crystal and attached to the inner face of a lid 4 of a crucible 3. After a source material 2 comprising a silicon carbide powder is supplied in the crucible 3, the crucible 3 is disposed in a double quartz tube 5. After the quartz tube 5 is evacuated, a work coil 8 is energized to heat the source material 2 to about 2000 deg.C. Then an atmosphere gas containing impurity atoms such as nitrogen in an amt. preferably >=10<19> cm<-3> is introduced into the tube 5 to grow a silicon carbide single crystal by sublimation recrystallization method, while a large amt. of impurities is introduced into the growing surface and the growing crystal. Thereby, micropipe-like defects can be decreased and the obtd. silicon carbide single crystal can be used as a light-emitting element for blue colors having excellent optical characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicon carbide single crystal, and more particularly to a method for growing a large-sized single crystal ingot of good quality which is used as a substrate wafer for blue light emitting diodes, electronic devices and the like.

[0002]

2. Description of the Related Art Silicon carbide (SiC) has attracted attention as an environment-resistant semiconductor material due to its physical and chemical properties such as excellent heat resistance and mechanical strength and resistance to radiation. Especially 6H
Type silicon carbide crystal has a forbidden band width of about 3 eV at room temperature,
Used as a blue light emitting diode material.

However, a crystal growth technique capable of stably supplying a high-quality silicon carbide single crystal having a large area on an industrial scale has not yet been established. Therefore, silicon carbide has been hampered in practical use despite the semiconductor material having many advantages and possibilities as described above.

Conventionally, on a laboratory scale, for example, a silicon carbide single crystal is grown by a sublimation recrystallization method (Rayleigh method),
Thus, a silicon carbide single crystal having a size capable of manufacturing a semiconductor element has been obtained. However, in this method, the area of the obtained single crystal is small, and it is difficult to control the size and shape with high precision. Further, it is not easy to control the crystal polymorphism and impurity carrier concentration of silicon carbide.

In addition, a cubic silicon carbide single crystal is also grown by heteroepitaxial growth on a heterogeneous substrate such as silicon (Si) using a chemical vapor deposition method (CVD method). Although a large area single crystal can be obtained by this method, many defects are included due to the lattice mismatch with the substrate of about 20% (-10 ⁷ cm ^-2 ).
Only a silicon carbide single crystal can be grown, and it is not easy to obtain a high quality silicon carbide single crystal.

In order to solve these problems, an improved Rayleigh method of sublimation recrystallization using a seed crystal has been proposed (Yu.M. Tairov and VF Tsvetkov, Journal.
of Crystal Growth vol.52 (1981) pp.146-150). In this method, since the seed crystal is used, it is possible to control the nucleation process of the crystal, and by controlling the atmospheric pressure from several Torr to 100 Torr with an inert gas, the crystal growth rate and the like can be reproduced with good reproducibility. You can control.
Furthermore, the crystal resistivity, that is, the amount of impurities in the crystal is
Add an impurity gas to the atmosphere consisting of an inert gas,
Alternatively, it can be controlled by mixing an impurity element or its compound into the silicon carbide raw material powder. At this time, as disclosed in Kazuyuki Koga, Semiconductor Research Vol. 39, p. 151, the resistivity of the crystal is determined by introducing nitrogen, aluminum, or boron atoms into the crystal at 10 ¹⁶ to 10 ¹⁹ cm ^-3. , Was controlled in the range of 0.04 to 200 Ωcm.

As described above, by using the sublimation recrystallization method using a seed crystal, a large-sized silicon carbide single crystal can be grown with good reproducibility while controlling the crystal polymorphism (polytype), shape and resistivity. You can

[0008]

When a silicon carbide single crystal is grown by the above-mentioned conventional method, a pinhole having a diameter of several microns penetrating the crystal called a micropipe defect in the growth direction is about 10 ² to 10 ³ cm ^-2. It was contained in the grown crystal.
PG Neudeck et al., IEEE Electron Device Letters
As described in vol.15 (1994) pp.63-65, these defects cause leakage currents in the fabrication of devices, and their reduction is the most important issue in device application of silicon carbide single crystals. It is said that.

This micropipe defect is caused by J. Takahashi.
et al., Journal of Crystal Growth vol. 135 (1994)
As shown in pp.61-70, it occurs along with spiral growth which is a typical growth mode in a silicon carbide single crystal.

The present invention has been made in view of the above circumstances, and provides a method for producing a silicon carbide single crystal capable of cutting a large-sized wafer and producing a good quality single crystal ingot with few defects with good reproducibility. Is.

[0011]

The present invention for achieving the above object has the following construction.

According to a first aspect of the present invention, in a method of growing a silicon carbide single crystal by a sublimation recrystallization method using a seed crystal, an impurity element is contained in a growth atmosphere, and a large amount is contained in a growth surface and a growth crystal. Is a method for growing a silicon carbide single crystal with few micropipe defects.

According to a second aspect of the present invention, nitrogen, aluminum or boron atoms are contained at high concentration as impurities in the growth atmosphere, and as a result, nitrogen, aluminum or boron atoms are contained in the silicon carbide single crystal. 10 ¹⁹ cm ^-3
A silicon carbide single crystal having few micropipe defects is grown by containing the above elements.
The method for producing a single crystal silicon carbide described above.

In the method for producing single crystal silicon carbide according to the present invention, a raw material made of silicon carbide is heated and sublimated, and the raw material is supplied onto a seed crystal made of a silicon carbide single crystal, and the silicon carbide single crystal is grown on the seed crystal. In the method, a high concentration of impurities is contained in the growth atmosphere to supply a large amount of impurities to the growth surface to grow a silicon carbide single crystal having an impurity concentration in the crystal of 10 ¹⁹ cm ^-3 or more.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the manufacturing method of the present invention, a high-concentration impurity is contained in a growth atmosphere, and a large amount of impurities are supplied to the growth surface to form a spiral mode which is a typical growth mode of a silicon carbide single crystal. It is intended to suppress the growth and prevent the generation of micropipes. Spiral growth occurs when molecular species that contribute to growth sufficiently diffuse on the surface and then reach a step formed on the surface by a screw dislocation and are taken into a crystal lattice. This corresponds to a crystal growth mode usually called a step flow mode.
The inventors have found that when a large amount of impurities are present on the surface,
We found that the step flow mode is difficult to occur and the generation of micropipes is suppressed because surface diffusion of molecular species that contribute to growth is hindered and impurities become effective seeds for two-dimensional nucleation. . This is because when the molecular species that contribute to growth do not reach the step and two-dimensional nucleation occurs on the surface, the step formed on the surface by the screw dislocation does not swirl and is succeeded in its original shape. This is because the spiral growth is suppressed as a result.

Further, as a result of supplying a large amount of impurities to the surface during the growth of silicon carbide by the modified Rayleigh method, the silicon carbide contains a high concentration of impurities (10 ¹⁹ cm ⁻³ or more), and the surface energy thereof is increased. Will increase. Frank (FC Fr
According to ank, Acta Cryst. vol. 4 (1951) pp. 497-501), the micropipe diameter becomes smaller for substances with high surface energy. Therefore, according to the present invention, not only the generation of micropipes can be suppressed, but also the diameter of the generated micropipes can be reduced and the influence on the device can be reduced.

As a method for containing a high concentration of impurities in the growth atmosphere, two methods are considered: a method of introducing it as a gas together with an inert gas into a reaction tank, and a method of preliminarily containing it in a silicon carbide powder raw material. Conventionally, the introduction of impurities into such a silicon carbide single crystal is usually 10 ¹⁶ cm ^-3 for the purpose of changing the electrical characteristics (conductivity type, resistivity) of the crystal.
From was done in the range of 10 ¹⁹ cm ^-3 or less, but not be used in 10 ¹⁹ cm ^-3 or more ranges for the purpose of controlling the crystal defects as in the present invention.

[0018]

Example 1 FIG. 1 shows an example of a production apparatus used in the present invention for growing single crystal silicon carbide by an improved Rayleigh method using a seed crystal.

First, the single crystal growth apparatus will be briefly described. Crystal growth is performed by sublimating and recrystallizing silicon carbide powder 2 as a raw material on silicon carbide single crystal substrate 1 used as a seed crystal. Seed silicon carbide crystal substrate 1 is attached to the inner surface of lid 4 of crucible 3 made of graphite. Silicon carbide powder 2 as a raw material is filled in a crucible 3 made of graphite. Such a graphite crucible 3 is installed inside a double quartz tube 5 by a graphite support rod 6. Around the graphite crucible 3, a graphite felt 7 for heat shielding is provided. The double quartz tube 5 can be evacuated to a high vacuum (10 ^-5 Torr or less) by a vacuum exhaust device, and the internal atmosphere can be pressure-controlled by a mixed gas of Ar and a dopant gas. In addition, on the outer circumference of the double quartz tube 5,
The work coil 8 is installed, and the graphite crucible 3 can be heated by passing a high frequency current to heat the raw material and the seed crystal to a desired temperature. The crucible temperature is measured at the center of the felt that covers the upper and lower parts of the crucible with a diameter of 2 to 4 m.
An optical path of m is provided to take out light from the upper and lower parts of the crucible,
Perform using a two-color thermometer. The temperature of the lower part of the crucible is the raw material temperature,
The temperature at the top of the crucible is the seed temperature.

Next, an embodiment of the production of a silicon carbide single crystal using this crystal growth apparatus will be described.

First, as a seed crystal, the growth plane orientation is <00.
A substrate 1 made of hexagonal silicon carbide having a 01> direction was prepared. Then, the substrate 1 was attached to the inner surface of the lid 4 of the graphite crucible 3. The raw material 2 was filled in the graphite crucible 3. Next, graphite crucible 3 filled with raw material
Is closed with a lid 4 fitted with a seed crystal, and a graphite felt 7 is attached.
After being coated with, it was placed on a graphite support rod 6 and placed inside the double quartz tube 5. Then, after evacuating the inside of the quartz tube, an electric current is applied to the work coil to adjust the raw material temperature to 20 degrees Celsius.
I raised it to 00 degrees. After that, a mixed gas containing 75% of nitrogen gas in Ar gas was introduced as an atmospheric gas, and the raw material temperature was raised to a target temperature of 2400 degrees Celsius while maintaining the internal pressure of the quartz tube at about 600 Torr. The pressure was reduced to 20 Torr, which is the growth pressure, over about 30 minutes, and then the growth was continued for about 20 hours. The growth rate at this time is about 1 mm
It was every hour. The proportion of nitrogen gas during growth needs to be set within a range of 10 to 100% with respect to an inert gas such as Ar gas. If the concentration is lower than this, the supply of the dopant to the surface is insufficient, the effect of preventing the diffusion of molecular species that contributes to growth cannot be expected, and the nitrogen concentration in the single crystal does not exceed 10 ¹⁹ cm ^-3 . Also, the partial pressure of nitrogen in the reaction tank is 40T.
Above orr, nitrogen on the growth surface adversely affects the crystallinity. That is, polycrystallization or the like occurs.

The silicon carbide single crystal thus obtained was analyzed by X-ray diffraction and Raman scattering, and it was confirmed that a hexagonal system silicon carbide single crystal had grown. The grown crystal was a high-quality silicon carbide single crystal in which the seed crystal was more uniform than the growth outermost surface and there were very few abnormalities related to carbon. Furthermore, when the nitrogen concentration in the crystal was examined by secondary ion mass spectrometry, it was 2 × 10 ²⁰ cm ⁻³ .

For the purpose of evaluating micropipe defects, the grown single crystal ingot was cut and polished to obtain a {0001} plane wafer. Then about 53 degrees Celsius
When the number of large regular hexagonal etch pits corresponding to micropipe defects was examined with a microscope after etching the wafer surface with 0 degree molten KOH, micropipe defects were halved compared to when Ar alone was used as the atmospheric gas. I found out that It was also confirmed by microscopic observation of the surface before etching that the diameter of the generated micropipe was reduced.

[0024]

EXAMPLE 2 As in Example 1, a substrate 1 made of hexagonal silicon carbide having a <0001> direction as a seed crystal was prepared as a seed crystal, and the seed crystal was covered with a lid 4 of a graphite crucible 3. It was attached to the inside. Next, the raw material 2 is placed inside the graphite crucible 3.
At this time, 0.25 wt% of boron carbide (B ₄ C), which is a P-type impurity, was mixed in the silicon carbide raw material. Generally, as a method of mixing dopant atoms into a silicon carbide raw material, (1) a dopant element itself is mixed with a silicon carbide raw material, (2) a mixture obtained by further sintering the mixture of (1) is used as a raw material. (3) mixing a compound containing a dopant element (corresponding to this example), (4) using a silicon carbide raw material previously doped with a dopant element,
There are four possible methods.

Vacuum evacuation, temperature control, pressure control, etc., after filling the raw materials were carried out in substantially the same manner as in Example 1. However, the atmosphere gas was 100% Ar. The amount of B ₄ C charged in the silicon carbide raw material needs to be set in the range of 0.1 to 1%. If the concentration is lower than this, the supply of the dopant to the surface is insufficient and the effect of preventing diffusion of molecular species that contributes to growth cannot be expected, and if the concentration is higher than this, good quality single crystal growth cannot be realized.

The silicon carbide single crystal thus obtained was analyzed by X-ray diffraction and Raman scattering, and it was confirmed that a hexagonal system silicon carbide single crystal had grown. The grown crystal was a high-quality silicon carbide single crystal in which the seed crystal was more uniform than the growth outermost surface and there were very few abnormalities related to carbon. Furthermore, when the boron concentration in the crystal was examined by secondary ion mass spectrometry, it was 3 × 10 ¹⁹ cm ⁻³ .

For the purpose of evaluating micropipe defects, the grown single crystal ingot was cut and polished to obtain a {0001} plane wafer. Then about 53 degrees Celsius
When the wafer surface was etched with 0 degree molten KOH and the number of large regular hexagonal etch pits corresponding to the micropipe defects was examined with a microscope, it was found that the micropipe defects were 30 compared with the case where only Ar was used as the atmosphere gas. ~
It was found to have decreased by 40%. Further, it was confirmed by microscopic observation of the surface before etching that the diameter of the generated micropipe was reduced.

[0028]

As described above, according to the first and second aspects of the present invention, in the improved Rayleigh method using a seed crystal, the spiral growth is suppressed, and these are caused. It is possible to grow a high-quality silicon carbide single crystal with a small amount of micropipes, which has good reproducibility and homogeneity.

When such a silicon carbide single crystal is used as a growth substrate and a silicon carbide single crystal thin film is grown on this substrate by a vapor phase epitaxial growth method, a blue light emitting element having excellent optical characteristics and an electrical property can be obtained. It is possible to manufacture high voltage and environment resistant electronic devices with excellent characteristics.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an example of a single crystal growth apparatus used in a manufacturing method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Silicon carbide single crystal substrate (seed crystal), 2 ... Silicon carbide powder raw material, 3 ... Graphite crucible, 4 ... Graphite crucible lid, 5 ... Double quartz tube, 6 ... Support rod, 7 ... Graphite felt, 8 ... Work coil, 9 ... Ar gas pipe, 10 ... Ar gas mass flow controller, 11 ... Impurity gas pipe, 12 ... Impurity gas mass flow controller, 13 ... Vacuum exhaust device.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Masakazu Katsuno Masakazu Katsuno 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Nippon Steel Co., Ltd. Technology Development Division (72) Hirokatsu Yashiro 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Address Nippon Steel Co., Ltd. Technology Development Headquarters (72) Inventor Masatoshi Kanaya 1618 Ida, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Nippon Steel Co., Ltd. Technology Development Headquarters

Claims (2)

[Claims] 1. A method for growing a silicon carbide single crystal by a sublimation recrystallization method using a seed crystal, wherein an impurity element is contained in a growth atmosphere, and a large amount of impurities are supplied to a growth surface and a growth crystal to form a micro crystal. A method for growing a silicon carbide single crystal with few pipe defects. 2. Nitrogen as an impurity in the growth atmosphere,
By containing a high concentration of aluminum or boron atoms, and as a result, by containing nitrogen, aluminum, or boron atoms of 10 ¹⁹ cm ^-3 or more in the silicon carbide single crystal, a silicon carbide single crystal with few micropipe defects can be obtained. The method for producing single crystal silicon carbide according to claim 1, wherein the single crystal silicon carbide is grown.