JPH08143396A - Method for growing silicon carbide single crystal - Google Patents

Abstract

PURPOSE: To obtain a large-sized good-quality single crystal reduced in micropipe defects by newly taking out a wafer from an SiC single crystal with the specified crystal face grown as a seed crystal and again growing a single crystal by sublimation and recrystallization. CONSTITUTION: A seed crystal 8 is mounted on a seed crystal mounting part 7 in a graphite crucible 4, and an SiC material 5 is charged. A crystal inclined to a (0001) face at an angle of 60-120 deg. is used as the first seed crystal 8. The crucible 4 is evacuated, the raw material is heated to 2000 deg.C, and the crucible is kept at about 600Torr while introducing an inert gas. The crucible is then evacuated to 1-50Torr, and the growth of a single crystal is started at the raw material temp. of 2100-2500 deg.C. The seed crystal temp. is 40 to 100 deg.C lower than the raw material temp., and the temp. and pressure are adjusted so that the growth rate of the single crystal is controlled to 0.5-1.5mm/hr. The obtained ingot 2 is cut to form a (0001) wafer 3, and an SiC single crystal is grown on the (0001) face from the same material with the wafer as a second seed crystal 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a SiC single crystal.

More particularly, the present invention relates to a method for growing a large-sized, high-quality SiC single crystal ingot which will be used as a substrate wafer for short-wavelength light emitting diodes, electronic devices, and the like.

[0003]

2. Description of the Related Art Forbidden band widths of SiC semiconductors are Si and GaA.
Since it is a material that is larger than s, etc., is physically and chemically stable, and can withstand high temperatures and radiation, it is expected to be applied as an environment-resistant semiconductor element material. It is also used as a short-wavelength light emitting diode material.

The S required to make such an element
The iC substrate wafer is cut out from a SiC single crystal ingot grown by a sublimation recrystallization method called a modified Rayleigh method. Conventionally, a SiC single crystal {0001} wafer substrate is used as a seed crystal.
The SiC single crystal ingot was grown on the surface. A {0001} wafer was again cut out from this growth ingot, growth was performed using this wafer as a seed crystal, and this was repeated to increase the diameter and increase the production of wafers. However, J. Crystal Growth
h 128 (1993) 358-362, in SiC {0001} wafers taken from ingots grown by such conventional methods, the number of diameters penetrating the wafer is called micropipe defects. It contained 10 ² to 10 ³ micron pinholes / cm ² . IEEE ELECTRON DEVICE
As described in LETTER 15 (1994) 63 to 65, these defects cause electric leakage when a device is manufactured, and have become the most serious problem in application of SiC to electronic devices. In addition to this, Phisica B185 (1993) 211-2
As described in No. 16, hollow black linear defects (Channel) extended from the seed crystal to the grown crystal, which deteriorated the quality of the wafer.

Japanese Unexamined Patent Publication (Kokai) No. 5-262599 discloses a method for growing a single crystal free from micropipe defects. Although the SiC {0001} wafer obtained by this method does not have this kind of defect, it is cut out in the growth direction as shown in FIG. 1, so that there is no unevenness of impurities or nonuniform carrier concentration in the plane of the {0001} wafer. It is easy to occur.
Furthermore, the outer shape of the obtained wafer is unlikely to be circular,
Shape processing is required.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for growing a large-sized SiC single crystal of good quality with very few micropipe defects.

[0007]

DISCLOSURE OF THE INVENTION According to the present invention, a seed crystal SiC, which is slightly lower than the raw material, is obtained by heating and subliming a SiC raw material powder in an inert gas atmosphere in a graphite crucible.
In the sublimation recrystallization method for growing a SiC single crystal on a single crystal substrate, the first seed crystal is about 6 from the {0001} plane.
From the first SiC single crystal grown using the crystal plane of the SiC single crystal inclined from 0 ° to about 120 °, {000 is newly added.
The problem is solved by taking out the 1} wafer and using this as a second seed crystal to grow the second SiC single crystal again by the sublimation recrystallization method.

[0008]

When a SiC single crystal is grown on the {0001} plane, if the seed crystal substrate surface contains micropipe defects, the grown crystals will inherit the micropipe defects. Even if such a micropipe defect does not exist in the seed crystal substrate due to the growth on the {0001} plane, the micropipe defect or dislocation occurs at the initial stage of the growth. Therefore, once the single crystal ingot is grown, {00
When a 01} wafer is taken out and grown using this as a seed crystal, the number of micropipe defects generally increases more than that seed crystal.

In the conventional growth on the {0001} plane, in order to grow a single crystal having less micropipe defects, a {0001} wafer having no or very few micropipe defects as seed crystals is used. Is required. However, the currently available SiC single crystal, the Acheson crystal, has few micropipe defects and can grow a good quality crystal with few defects. However, since the crystal size is as small as 1 cm, a large-diameter ingot is You can't get it with the degree of growth.

Therefore, the method disclosed in JP-A-5-262599, that is, about 60 ° to about 12 from the {0001} plane is used.
A crystal plane tilted by 0 ° was used as a first seed crystal, and a single crystal ingot grown was cut out as shown in FIG.
The 01} wafer may be used as the seed crystal. This wafer has no micropipe defects penetrating the wafer, and the micropipe defects transmitted from the seed crystal can be prevented.
In addition, since the {0001} wafer has almost no penetrating dislocations, the generation of black defects extending from the seed crystal can be suppressed. In addition, it can be used as a seed crystal {000
Since a 1} wafer having a size sufficiently larger than that of an Acheson crystal can be obtained, a large crystal can be easily grown by using this wafer.

Generally, in single crystal ingot growth, the axis of the growth direction is preferably an axis having better crystal symmetry. This affects the quality of the grown crystal and the ease of further processing. In that sense, the more preferable first seed crystal is a crystal plane perpendicular to the {0001} plane.

[0012]

[Outside 2]

This is because it is difficult to receive a sound and it is easy to grow a good quality crystal. At this time, the crystal plane perpendicular to {0001} does not mean strictly perpendicular, but the same effect can be expected if the inclination is within 10 °.

The contents of the present invention will be described in detail below with reference to the drawings. FIG. 2 shows an example of a single crystal growth apparatus used in the method for growing a SiC single crystal of the present invention. As shown in the figure, the graphite crucible used in the single crystal growth apparatus comprises a bottomed crucible 4 and a SiC substrate seed crystal 8.
And a crucible lid 6 made of graphite for covering the opening of the crucible 4 having a mounting part 7 of the crucible 4. The container is placed in a container that can be evacuated by a vacuum exhaust device and whose internal atmosphere can be pressure-controlled by an inert gas such as Ar. The heating is performed by, for example, a high frequency induction coil wound outside the container. Measuring the crucible temperature,
For example, in the center of the felt that covers the lower part of the crucible, a diameter of 2-4 m
The optical path 10 of m is provided and the light in the lower part of the crucible is extracted, and the light is constantly measured using a two-color thermometer. This temperature is regarded as the raw material temperature.
A similar optical path is provided in advance on the upper felt, the temperature of the crucible lid is measured, and this is regarded as the temperature of the seed crystal.

FIG. 3 is a diagram for explaining a crystal plane used as the first seed crystal. The crystal plane used as the first seed crystal of the present invention is about 60 ° to 120 ° from the {0001} plane.
It is an inclined surface, and this inclination angle is indicated by θ in the figure. The SiC single crystal substrate wafer having the desired surface is attached as a seed crystal to the crucible lid, and crystal growth is performed as follows, for example.

The container is evacuated and the raw material temperature is about 2000.
Raise to ℃. After that, while keeping the inert gas at about 600 Torr, the raw material temperature is raised to the target temperature. The depressurization is performed for 10 to 90 minutes, and the atmospheric pressure is 1 to 50 Torr, more preferably 5 to 20 Torr.
The raw material temperature is 2100 to 2500 ° C., more preferably 22.
It is desirable to set the temperature to 00 to 2400 ° C. and start the growth. If the temperature is lower than this, the raw material is less likely to be vaporized, and if the temperature is higher than this, it becomes difficult to grow a good quality single crystal due to thermal etching or the like. Further, the seed crystal temperature is 40 to
100 ° C, more preferably 50 to 70 ° C lower, temperature gradient 5 to 25 ° C / cm, more preferably 10 to 20 ° C / h.
It is desirable to set so that Furthermore, the relationship between temperature and pressure is that the growth rate of a single crystal is 0.5 to 1.5 mm /
h, more preferably 0.8 to 1.3 mm / h. If the speed is higher than this, the crystal quality is deteriorated, which is not suitable, and if the speed is lower than this, the productivity is not good.

The ingot thus obtained is shown in FIG.
Then, the wafer is cut as described above and polished to produce a {0001} wafer. Using this wafer as a seed crystal for the second growth, the {0001} plane is grown, for example, under the same growth conditions as described above. The {0001} wafer may be tilted by about 20 ° from the {0001} plane as long as the growth is not adversely affected.

The evaluation of the single crystal obtained by the twice growth was carried out by the following procedure. The produced single crystal ingot is cut and polished into a {0001} wafer. At this time, be careful not to leave processing distortion on the wafer. The etching was performed with a KOH melt at about 530 degrees for about 10 minutes.
After etching, the number of etch pits generated by a Nomarski differential interference microscope was measured. At this time, a large regular hexagonal etch pit corresponds to the micropipe defect. Also, the observation of a cut-out {0001} wafer with a transmission polarization microscope in which polarizing plates are attached to the front and the back can measure micropipe defects by the contrast corresponding to the crystal strain accompanied. The hole measurement of the crystal was performed by the van der Pauw method.

[0019]

【Example】

 Example 1

[0020]

[Outside 3]

Single crystal growth was carried out at 2280 ° C. and an atmospheric pressure of 10 Torr. A {0001} wafer was taken out from the obtained single crystal ingot, and this wafer was used as a seed crystal to grow again under the same growth conditions. When the {0001} wafer was taken out from the growth ingot and observed by etching or a polarization microscope, micropipe defects showed a very small value of 100 defects / cm ² or less on average. Also, there were many areas in the wafer where this defect did not exist at all. Furthermore, the black line defects that are usually found near the seed crystal were hardly found in this crystal. When the in-plane distribution of the wafer was examined by hole measurement, the carrier concentration was almost uniform in the plane.

Example 2 Using a crystal plane inclined by 90 ° from the {0001} plane as a seed crystal, the raw material temperature was 2370 ° C. and the seed crystal temperature was 231.
Single crystal growth was performed at 0 ° C. and an atmospheric pressure of 20 Torr. A {0001} wafer was taken out from the obtained single crystal ingot, and this wafer was used as a seed crystal to grow again under the same growth conditions. From growth ingot {000
1} The wafer was taken out and observed by etching and a polarization microscope. Micropipe defects were 100 / c on average.
The value was as small as m ² or less. Furthermore, the black line defects that are usually found near the seed crystal were hardly found in this crystal. When the in-plane distribution of the wafer was examined by hole measurement, the carrier concentration was almost uniform in the plane.

Example 3 Using a crystal plane inclined by 60 ° from the {0001} plane as a seed crystal, the raw material temperature was 2370 ° C. and the seed crystal temperature was 231.
Single crystal growth was performed at 0 ° C. and an atmospheric pressure of 20 Torr. A {0001} wafer was taken out from the obtained single crystal ingot, and this wafer was used as a seed crystal to grow again under the same growth conditions. From growth ingot {000
1} The wafer was taken out and observed by etching and a polarization microscope. Micropipe defects were 200 / c on average.
The value was as small as m ² or less. Furthermore, the black line defects that are usually found near the seed crystal were hardly found in this crystal. When the in-plane distribution of the wafer was examined by hole measurement, the carrier concentration was almost uniform in the plane.

Example 4 Using a crystal plane inclined by 120 ° from the {0001} plane as a seed crystal, the raw material temperature was 2370 ° C. and the seed crystal temperature was 23.
Single crystal growth was performed at 10 ° C. and an atmospheric pressure of 20 Torr. From the obtained single crystal ingot {0001}
The wafer was taken out, and this wafer was used as a seed crystal to grow again under the same growth conditions. From growth ingot {00
When the {01} wafer was taken out and observed by etching or a polarization microscope, micropipe defects were 200 / average on average.
The value was as small as cm ² or less. Furthermore, the black line defects that are usually found near the seed crystal were hardly found in this crystal. When the in-plane distribution of the wafer was examined by hole measurement, the carrier concentration was almost uniform in the plane.

Comparative Example 1 A {0001} plane was used as a seed crystal and the raw material temperature was set to 23.
40 ° C, seed crystal temperature 2280 ° C, atmospheric pressure 10T
Single crystal growth was performed as orr. A {0001} wafer was taken out from the obtained single crystal ingot. The wafer contained numerous micropipe defects.
This wafer was used as a seed crystal and grown again under the same growth conditions. When the {0001} wafer was taken out from the growth ingot and observed by etching or a polarization microscope, micropipe defects were on average 10 ² to 10 ³ / cm ^2.
And showed a very large value. Further, the wafer cut out near the seed crystal contained black line defects.

Comparative Example 2 Using a crystal plane inclined by 40 ° from the {0001} plane as a seed crystal, the raw material temperature was 2370 ° C. and the seed crystal temperature was 221.
Single crystal growth was performed at 0 ° C. and an atmospheric pressure of 20 Torr. A {0001} wafer was taken out from the obtained single crystal ingot. The wafer contained many micropipe defects and black line defects. This wafer was used as a seed crystal to grow again under the same growth conditions. When {0001} wafer was taken out from the growth ingot and observed by etching or a polarization microscope, micropipe defects were very large on average of 10 ² to 10 ³ / cm ² , and many black line defects were also observed. .

[0027]

By using the present invention, it is possible to supply a large-diameter single crystal wafer with few micropipe defects, which is useful for various applications of electronic devices using a high-quality large-sized SiC single crystal.

[Brief description of drawings]

[Outside 4] FIG.

FIG. 2 is a cross-sectional view schematically showing the structure of an example of a single crystal growth apparatus used for SiC single crystal growth of the present invention.

FIG. 3 is a diagram illustrating a crystal plane used as a first seed crystal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Seed crystal, 2 ... Growth single crystal, 3 ... {0001} wafer, 4 ... Crucible, 5 ... SiC raw material, 6 ... Crucible lid, 7 ... Seed crystal attachment part, 8 ... Seed crystal, 9 ... Insulating felt, 10 ... Optical path, 11 ... SiC single crystal.

Claims (2)

[Claims] 1. A sublimation recrystallization in which a SiC raw material powder is heated and sublimated in a graphite crucible in an inert gas atmosphere to grow a SiC single crystal on a seed crystal SiC single crystal substrate which is slightly lower than the raw material. In the method, a first SiC grown by using a crystal plane of a SiC single crystal tilted by about 60 ° to about 120 ° from a {0001} plane as a first seed crystal.
A method in which a {0001} wafer is newly taken out from a single crystal, and this is used as a second seed crystal, and a second SiC single crystal is grown again by the sublimation recrystallization method. 2. The method according to claim 1, wherein a crystal plane perpendicular to the {0001} plane is used as the first seed crystal. [Outside 1] the method of.