JPH11106297A - Growth of silicon carbide single crystal having low resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for growing a SiC single crystal having low resistance in a high yield. SOLUTION: This method for growing a SiC single crystal comprises arranging a seed crystal composed of a SiC single crystal and SiC raw material powder in a crucible made of graphite, heating and sublimating the raw material powder and recrystallizing the seed crystal kept at a temperature lower than the temperature of the raw material. In this case, a nitrogen gas is used as an atmosphere gas and a crystal plane substrate having an angle of inclination a in the [0001] direction from 11-20} plane in the range of -30 deg.<=α<=+30 deg. and an angle of rotation β around [0001] axis in the range of -10 deg.<=β<=+10 deg. is used as the seed crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for growing a low-resistance SiC single crystal.

[0002]

2. Description of the Related Art SiC semiconductors have a larger forbidden band width than Si semiconductors and the like, and have excellent electrical characteristics.
It is expected to be applied as a material for power devices and high-temperature devices. Further, it is used as a substrate material for GaN-based thin film devices because of its lattice mismatch with GaN crystal and small difference in thermal expansion coefficient, high thermal conductivity, and good cleavage matching.

[0003] SiC wafers are described in J. Cryst. Gro
wth 43 (1978) 209-212, 52 (19
81) It can be cut out from a SiC single crystal ingot grown by a sublimation method called “improved Rayleigh method” described in 146-150. The modified Rayleigh method is
In this method, a SiC raw material powder is heated and sublimated in an inert gas atmosphere, and recrystallized on a SiC single crystal seed crystal substrate kept at a lower temperature. Argon gas was mainly used as the inert gas, and was introduced to control the diffusion and transport of the raw material SiC sublimation gas. During growth, nitrogen gas is mixed with a growth atmosphere inert gas to perform nitrogen doping as a donor impurity, thereby controlling the resistivity of the grown single crystal.

[0004] At present, SiC wafers having lower resistivity are required for reasons of device application such as reduction of electrode resistance. Jpn. J. Appl. Phys. 3
4 (1995) 4694-4698, a crystal having a desired resistivity can be grown by changing the nitrogen gas flow rate with respect to the atmosphere inert gas flow rate. Generally, the amount of nitrogen taken into the crystal depends on the nitrogen partial pressure in the atmospheric gas pressure. Therefore, in order to grow a low resistance crystal, it is necessary to introduce a very large amount of nitrogen gas with respect to the inert gas. However, when the partial pressure of nitrogen in the growth atmosphere is increased, crystal grains having different orientations are generated on the surface of the grown crystal during the growth, and single crystal growth is hindered. Due to this polycrystallization, the production yield of the target low-resistance single crystal wafer has been significantly reduced.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for completely preventing generation of polycrystals and growing a low-resistance SiC single crystal.

[0006]

The present invention provides (1) SiC
In a method in which a seed crystal made of a single crystal and a SiC raw material powder are placed in a graphite crucible, the raw material powder is heated and sublimated, and recrystallized on a seed crystal kept at a temperature lower than the raw material temperature. Nitrogen gas is used as the gas, and the inclination angle α from the {11-20} plane to the [0001] direction is in the range of −30 ° ≦ α ≦ + 30 ° and the rotation angle about the [0001] axis as the seed crystal. β is −10 ° ≦ β ≦ + 1
A method of growing a SiC single crystal, characterized by using a crystal plane substrate in the range of 0 °, (2) a seed crystal of {11-
The inclination angle α from the 20 ° plane is in the range of −10 ° ≦ α ≦ + 10 °, and the rotation angle β about the [0001] axis is −5 °
The growing method according to (1) using a crystal plane substrate in the range of ≦ β ≦ + 5 °, (3) the growing method according to (1) using a {11-20} plane substrate as a seed crystal, and (4) atmosphere The growing method according to (1) to (3), wherein the gas pressure is 5 to 40 Torr.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The contents of the present invention will be described in detail.

In the conventional improved Rayleigh method, an inert gas such as an argon gas is introduced into a growth system, and the inert gas atmosphere pressure is changed to control the flux of the SiC raw material gas to control the crystal growth rate. I was Also, since nitrogen atoms act as donors in the SiC crystal,
Nitrogen doping was performed by introducing an appropriate amount of nitrogen gas into the growing system, and the resistivity of the grown crystal was controlled.However, when the nitrogen partial pressure in the atmosphere gas was increased to perform high concentration doping, polycrystalline The occurrence of frequent occurrence has made it impossible to obtain a SiC single crystal having a low resistivity with a high yield.

FIG. 1 shows an example of an apparatus used in the method for growing a bulk SiC single crystal of the present invention. The graphite crucible is composed of a bottomed crucible body 1 containing a SiC raw material powder 2 and a crucible lid 3 covering an opening of the crucible body 1 having a mounting portion 4 for a SiC substrate seed crystal 5. It is covered with a heat insulating material 6 made of graphite felt, and is placed in a container that can be evacuated to a high vacuum by an evacuation device and that can control the internal atmospheric pressure. A desired flow rate of nitrogen can be introduced from a nitrogen cylinder placed outside through a flow meter.

According to the present invention, growth is carried out in a nitrogen gas atmosphere without introducing any inert gas and introducing only nitrogen gas.
Nitrogen gas has both a growth rate control and a dopant action. And in the growth in the nitrogen gas atmosphere,
When the {11-20} plane of the SiC single crystal is used as a seed crystal, polycrystal generation can be completely suppressed, a higher carrier concentration (1 × 10 ¹⁹ / cm ³ or more), a lower resistivity (2
× 10 ⁻² Ωcm or less).

FIG. 2 is an explanatory view of a crystal plane of a seed crystal used in the present invention. In the figure, the hatched surface is the hexagonal Si
This corresponds to the (11-20) plane of C. This (11-20)
The angle of inclination from the surface to the [0001] direction is α, and [000]
1] Let β be the rotation angle from the (11-20) plane around the axis. There are six index planes equivalent to this (11-20) plane, which can be generically expressed as {11-20}. In the present invention, it is assumed that all equivalent exponential planes are included. These seed crystal substrates are, for example, Si grown by the improved Rayleigh method.
A single crystal ingot obtained by cutting out a target crystal face from a C single crystal ingot is used. The seed crystal composed of the SiC single crystal used in the present invention includes −30 ° ≦ α ≦ + 30 ° and −30 ° ≦ α ≦ + 30 °.
A crystal plane substrate in a range of 10 ° ≦ β ≦ + 10 ° is used. Preferably, -10 ° ≦ α ≦ + 10 ° and −
A crystal plane substrate in the range of 5 ° ≦ β ≦ + 5 ° is used. More preferably, a (11-20) plane substrate is used.

Crystal growth was performed in a nitrogen atmosphere using substrate surfaces of various crystal orientations of 6H—SiC as seed crystals, and the occurrence rate of polycrystals was statistically examined. FIG. 3a shows (11
FIG. 3B shows the result of using a crystal plane substrate tilted in the [0001] direction from the (-20) plane as a seed crystal, and FIG. 3B shows a crystal plane substrate having a rotation angle around the [0001] axis from the (11-20) plane. The results used as crystals are shown. In this experiment, when at least one crystal grain having a different orientation from the seed crystal was generated in the grown crystal, it was considered that polycrystallization had occurred.

-30 ° ≦ α ≦ + 30 ° and -10 ° ≦ β
Within the range of ≦ + 10 °, the polycrystal generation rate was suppressed to 20% or less. Also, -10 ° ≦ α ≦ + 10 ° and -5 ° ≦
Within the range of β ≦ + 5 °, polycrystal generation was not observed at all.

Many of the polycrystals generally occurred on facets. In particular, the incidence of crystal grains having different orientations on the (0001) Si plane and the {1-100} prism plane was increased. Further, in the growth in a nitrogen atmosphere, polycrystals frequently occurred on other surfaces. The {11-20} plane is 90 each with the {0001} plane and the {1-100} plane.
It has characteristics different from other surfaces, such as being tilted by 30 ° and 30 °, so that it is hardly affected by these surfaces, and having a very large surface energy density. From these facts, it is presumed that they have an effect of suppressing the generation of polycrystals even when grown in a nitrogen gas atmosphere.

In the present invention, the control pressure in the growth vessel, that is, the atmospheric pressure is 1 to 50 Torr.
The r range is preferred. This is because nitrogen gas is used as a growth rate control gas instead of an inert gas, so that optimum temperature conditions and growth rates can be realized in this pressure range, and high-quality single crystals can be grown. If it is less than 1 Torr, it is difficult to control the growth, and 50 Torr.
If the pressure exceeds, it is necessary to raise the growth temperature in order to realize a sufficient growth rate, and the crystal quality is degraded.

Next, the present invention will be exemplified by one of the specific growing methods.

The heating is performed by, for example, a high frequency induction coil.
The temperature of the crucible is measured, for example, by providing an optical path 7 in a heat insulating material below the crucible, extracting light from the optical path 7, and using a two-color thermometer or the like. This temperature is regarded as the raw material temperature. Similarly, the temperature measured by the optical path above the crucible is regarded as the seed crystal temperature.

The inside of the container is evacuated, and the raw material temperature is set to about 1800.
Increase to ° C. After that, nitrogen gas is introduced into the container and about 60
Keep the pressure at 0 Torr and raise the raw material temperature. Then 1
The pressure is reduced over 0 to 90 minutes, and the atmospheric pressure is 1 to 50 T
orr, more preferably 5 to 40 Torr. The raw material temperature is 2100 to 2500 ° C, more preferably 2200 to 2400 ° C, and the seed crystal temperature is 40 ° C or lower than the raw material temperature.
~ 120C, more preferably 50-80C lower, the temperature gradient is 5-25C / cm, more preferably 10-20C / cm.
cm. Further, the relationship between the temperature and the pressure is preferably set so that the crystal growth rate is 0.2 to 1.6 mm / h, more preferably 0.5 to 1.3 mm / h. If the speed is higher than this, the crystal quality is deteriorated, which is not suitable. If the speed is lower than this, productivity is not good. In general, the higher the raw material temperature, the larger the temperature gradient, and the higher the nitrogen gas atmosphere pressure, the higher the crystal growth rate. The growth temperature is an element that determines the Si / C ratio in the source gas that affects the quality of the grown crystal, and the above-mentioned source temperature, seed crystal temperature, temperature gradient, and atmospheric pressure are suitable for efficiently growing a good-quality crystal. It is the range of temperature and pressure. The single crystal is grown by maintaining the temperature and pressure in such a range for a certain period of time.

The electrical characteristics of the grown crystal are evaluated, for example, by measuring the Hall effect. A desired surface is cut out from the grown crystal 8 to obtain a desired SiC wafer. Further, a square sample is cut out from the {0001} wafer, and ohmic electrodes are attached at four corners, and measurement is performed according to the van der Pauw method. Thereby, the resistivity, the carrier concentration, and the mobility of the crystal are obtained.

On the other hand, evaluation of crystal grains having different orientations,
That is, polycrystallization can be easily evaluated by a method of directly observing a grown crystal, a method of observing a cut wafer with a polarizing microscope, a method of observing the surface by performing molten KOH etching, and the like.

[0021]

EXAMPLE 1 A 6H-SiC (11-20) substrate wafer was used as a seed crystal, the raw material temperature was 2340 ° C., and the seed crystal temperature was 228.
Single crystals were grown at 0 ° C. and a nitrogen atmosphere pressure of 10 Torr. Observation of the grown crystal surface revealed no crystal grains having different orientations. Further, when the ingot was cut and the inside thereof was examined by a polarizing microscope or an etching method, no crystal grains having different orientations were observed. From this, it can be concluded that complete single crystal growth was performed without polycrystallization. The grown crystal was a perfect 6H form, and the carrier concentration determined by Hall effect measurement was 1.
Very high 2 × 10 ¹⁹ / cm ³ and resistivity 1.1
It was a very low value of × 10 ^-2 Ωcm. Same growth 1
No polycrystallization was observed at all even after performing 0 times, and similar results were obtained.

Example 2 A 4H-SiC (11-20) substrate wafer was used as a seed crystal, the raw material temperature was 2340 ° C., and the seed crystal temperature was 228.
Single crystals were grown at 0 ° C. and a nitrogen atmosphere pressure of 10 Torr. Observation of the grown crystal surface revealed no crystal grains having different orientations. Further, when the ingot was cut and the inside thereof was examined with a polarizing microscope or an etching method, no crystal grains having different orientations were observed. From this, it can be concluded that complete single crystal growth was performed without polycrystallization. The grown crystal was a perfect 4H form, and the carrier concentration determined by Hall effect measurement was 1.
It is as high as 5 × 10 ¹⁹ / cm ³ and has a resistivity of 8.9.
It showed a very low value of × 10 ⁻³ Ωcm. Same growth 1
No polycrystallization was observed at all even after performing 0 times, and similar results were obtained.

Example 3 A 6H-SiC substrate wafer having a crystal plane having an inclination angle α = 30 ° and a rotation angle β = 10 ° from the (11-20) plane was used as a seed crystal at a raw material temperature of 2340 ° C. A single crystal was grown at a crystal temperature of 2280 ° C. and a nitrogen atmosphere pressure of 10 Torr. Observation of the grown crystal surface revealed no crystal grains having different orientations. Further, when the ingot was cut and the inside thereof was examined by a polarizing microscope or an etching method, no crystal grains having different orientations were observed. From this, it can be concluded that complete single crystal growth was performed without polycrystallization. The grown crystal is complete 6H
The carrier concentration measured by the Hall effect measurement was as high as 1.2 × 10 ¹⁹ / cm ^3, and the resistivity was as low as 1.1 × 10 ^-2 Ωcm. Same growth 1
0 times, the generation of crystal grains with different orientations,
That is, although polycrystallization was observed twice, all the resistivity values were low.

COMPARATIVE EXAMPLE 1 A (0001) substrate wafer of 6H-SiC was used as a seed crystal, the raw material temperature was 2340 ° C., and the seed crystal temperature was 2280.
A single crystal was grown at a temperature of 10 ° C. and a nitrogen atmosphere pressure of 10 Torr. The grown crystal surface was covered with crystal grains having different orientations. Observation of the cut wafer with a polarizing microscope showed that crystal grains having different directions appeared in different interference colors and were polycrystallized. In addition, molten KOH
It was also shown that the interface of each grain clearly appeared by etching and contained polycrystal. This polycrystal was composed of various types of polytypes. When the same growth was performed 10 times, generation of crystal grains having different orientations, that is, polycrystallization was observed in all cases.

Comparative Example 2 In accordance with the conventional modified Rayleigh method, the growth atmosphere was argon gas, and nitrogen gas was introduced at a rate of 1/20 of the argon flow rate. Using a (0001) substrate wafer of 6H—SiC as a seed crystal, the raw material temperature is 2340 ° C., and the seed crystal temperature is 2
Single crystals were grown at 280 ° C. and an atmospheric pressure of 10 Torr. Clear (0001) facets appeared on the grown crystal surface, and no crystal grains having different orientations were observed. Also, no crystal grains having different orientations were generated inside the crystal, indicating that complete single crystal growth was performed. However, the carrier concentration measured by the Hall effect measurement was as low as 6.5 × 10 ¹⁷ / cm ^3, and the resistivity was 8.0.
The value was as high as × 10 ^-2 Ωcm.

Comparative Example 3 According to the conventional modified Rayleigh method, the growth atmosphere was argon gas, and nitrogen gas was introduced at a rate of 1/20 of the argon flow rate. A 6H-SiC (11-20) substrate wafer was used as a seed crystal, and a single crystal was grown at a raw material temperature of 2340 ° C, a seed crystal temperature of 2280 ° C, and an atmospheric pressure of 10 Torr. No crystal grains with different directions were observed on the grown crystal surface, and no crystal grains with different directions were generated inside the crystal, indicating that complete single crystal growth was performed. However, the carrier concentration measured by the Hall effect measurement was as low as 2.0 × 10 ¹⁸ / cm ^3, and the resistivity was as high as 3.2 × 10 ^-2 Ωcm.

[0027]

According to the present invention, the generation of polycrystals is completely suppressed, a low-resistance SiC single crystal is grown at a high yield, and a low-resistance SiC wafer can be supplied.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing one example of a growth apparatus used for growing a SiC single crystal of the present invention.

FIG. 2 is an explanatory diagram of a plane orientation of a seed crystal.

FIG. 3 is a diagram showing the dependence of the polycrystal generation rate on the seed crystal substrate plane orientation during growth in a nitrogen atmosphere.

[Description of Signs] 1 ... Crucible body 2 ... SiC raw material powder 3 ... Crucible lid 4 ... Seed crystal mounting part 5 ... Seed crystal substrate 6 ... Heat insulation 7 ... Optical path 8 ... SiC single crystal

Claims (4)

[Claims] 1. A seed crystal made of a SiC single crystal and a SiC raw material powder are placed in a graphite crucible, and the raw material powder is heated and sublimated, and recrystallized on a seed crystal kept at a temperature lower than the raw material temperature. Nitrogen gas is used as an atmosphere gas, and the inclination angle α from the {11-20} plane to the [0001] direction is −30 ° ≦ α ≦ + 3 as the seed crystal.
Rotation angle β in the range of 0 ° and about the [0001] axis
Characterized by using a crystal plane substrate having a range of −10 ° ≦ β ≦ + 10 °. 2. As a seed crystal, an inclination angle α from a {11-20} plane to a [0001] direction is −10 ° ≦ α ≦ + 10
The growth method according to claim 1, wherein a crystal plane substrate having a rotation angle β around the [0001] axis in a range of -5 ° ≦ β ≦ + 5 ° is used. 3. The method according to claim 1, wherein a {11-20} plane substrate is used as the seed crystal. 4. The method according to claim 1, wherein the pressure of the atmosphere gas is 1 to 50 Torr.