JP4256567B2 - Manufacturing method of silicon carbide single crystal ingot and mask for growing silicon carbide single crystal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a manufacturing method and silicon carbide single crystal growth mask for silicon carbide single crystal Ingo' DOO, particularly, it relates to a method of manufacturing a blue light emitting diode and large single crystal Ingo' preparative high quality as the substrate wafer such as an electronic device Is.
[0002]
[Prior art]
Silicon carbide (SiC) has excellent heat resistance and mechanical strength, and has attracted attention as an environmentally resistant semiconductor material because of its physical and chemical properties such as resistance to radiation. In recent years, the demand for SiC single crystal wafers as substrate wafers for short-wavelength optical devices from blue to ultraviolet and high-frequency high-voltage electronic devices has been increasing. However, a crystal growth technique that can stably supply a high-quality SiC single crystal having a large area on an industrial scale has not yet been established. Therefore, practical use of SiC has been hindered despite the semiconductor material having many advantages and possibilities as described above.
[0003]
Conventionally, on a laboratory scale scale, for example, a SiC single crystal was grown by a sublimation recrystallization method (Rayleigh method) to obtain a SiC single crystal of a size capable of producing a semiconductor element. However, with this method, the area of the obtained single crystal is small, and it is difficult to control its size and shape with high accuracy. Moreover, it is not easy to control the crystal polymorphism and impurity carrier concentration of SiC. Also, a cubic silicon carbide single crystal is grown by heteroepitaxial growth on a heterogeneous substrate such as silicon (Si) using chemical vapor deposition (CVD). In this method, a single crystal having a large area can be obtained, but only a SiC single crystal containing many defects (about 10 ⁷ / cm ² ) can be grown due to a lattice mismatch of about 20% with the substrate. It is not easy to obtain a high-quality SiC single crystal. In order to solve these problems, an improved Rayleigh method for performing sublimation recrystallization using a SiC single crystal (0001) wafer as a seed crystal has been proposed (Yu. M. Tailov and VF Tsvetkov) , Journal of Crystal Growth, vol. 52 (1981) pp. 146-150). In this method, since the seed crystal is used, the nucleation process of the crystal can be controlled, and the growth rate of the crystal can be controlled with good reproducibility by controlling the atmospheric pressure from about 100 Pa to about 15 kPa with an inert gas. The principle of the improved Rayleigh method will be described with reference to FIG. The SiC single crystal as a seed crystal and the SiC crystal powder as a raw material are stored in a crucible (usually graphite) and heated to 2000 to 2400 ° C. in an inert gas atmosphere such as argon (133 Pa to 13.3 kPa). . At this time, the temperature gradient is set so that the seed crystal has a slightly lower temperature than the raw material powder. After sublimation, the raw material is diffused and transported in the direction of the seed crystal by a concentration gradient (formed by a temperature gradient). Single crystal growth is realized by recrystallization of the source gas that has arrived at the seed crystal on the seed crystal. At this time, the resistivity of the crystal can be controlled by adding an impurity gas in an atmosphere made of an inert gas or mixing an impurity element or a compound thereof in the SiC raw material powder. Typical substitutional impurities in the SiC single crystal include nitrogen (n-type), boron, and aluminum (p-type). By using the modified Rayleigh method, it is possible to grow a SiC single crystal while controlling the crystal polymorphism (6H type, 4H type, 15R type, etc.) and the shape, carrier type and concentration of the SiC single crystal.
[0004]
Currently, SiC single crystal wafers having a diameter of 2 inches (50 mm) to 3 inches (75 mm) are cut out from the SiC single crystal produced by the above-described improved Rayleigh method, and are used for epitaxial thin film growth and device production. However, these SiC single crystal wafer, pinhole defects with a diameter of several microns through the growth direction (micropipe defects) were included degree 50 to 200 / cm ^2.
[0005]
[Problems to be solved by the invention]
As described above, the SiC single crystal produced by the conventional technique contained about 50 to 200 micropipe defects / cm ² . Takahashi et al. , Journal of Crystal Growth, vol. 167 (1996) pp. As described in 596-606, most of the micropipe defects are those that were present in the seed crystal but inherited by the grown crystal. In addition, micropipe defects newly introduced into the grown crystal are described in Koga et al. , Technical Digest of International Conference of Silicon Carbide and Related Materials 1995, pp. Most of them occur at the early stage of growth, as described in 166-167. Furthermore, P.I. G. Neudec et al. , IEEE Electron Device Letters, vol. 15 (1994) p. As described in 63-65, these defects cause a leakage current or the like when an element is manufactured, and the reduction thereof is regarded as the most important issue in SiC single crystal device application.
[0006]
This micropipe defect can be completely prevented by growing a SiC single crystal in a direction perpendicular to the [0001] direction using a plane perpendicular to the (0001) plane as a seed crystal. It is disclosed in the publication. In this method, when a (0001) plane wafer useful for device fabrication is to be taken out from the grown ingot, it is necessary to cut the ingot in the growth direction. However, Koga et al., Vacuum vol. 30 (1987) pp. 30. As shown in 886-892, it is usually not easy to increase the size of the ingot in the growth direction, and the growth ingot has a shape shorter in the growth direction than in the radial direction. For this reason, cutting the ingot in the growth direction is extremely disadvantageous from the viewpoint of increasing the diameter. Furthermore, Takahashi et al. , Journal of Crystal Growth, vol. 181 (1997) pp. As described in H.229-240, when a SiC single crystal is grown in a direction perpendicular to the [0001] direction, a large amount of (0001) area layer defects generated during the growth are present in the SiC single crystal. Exists. As a result, when the method disclosed in JP-A-5-262599 is used, micropipe defects do not occur, but it becomes difficult to produce a large (0001) wafer useful for device fabrication. A large number of stacking faults occur.
[0007]
The present invention has been made in view of the above circumstances, and provides an SiC single crystal manufacturing method capable of manufacturing a high-quality large-diameter (0001) wafer with few defects with good reproducibility.
[0008]
[Means for Solving the Problems]
A method for producing a SiC single crystal of the present invention is a method for heating and sublimating a raw material made of SiC, supplying the raw material on a seed crystal made of SiC single crystal, and growing the SiC single crystal on the seed crystal,
(1) A mask having a width of 1 to 5 mm between the openings on the seed crystal and a mask opening ratio represented by an area ratio of the openings / mask portions of 0.2 to 2 was applied. A method for producing a SiC single crystal ingot, in which a SiC single crystal is grown over the mask afterwards (2) The mask is made of one or more materials selected from graphite, tungsten, molybdenum or tantalum. SiC production method (3) of the single crystal ingot thickness of the mask is a is (1) producing how the SiC single crystal ingot according 0.1 to 3 mm.
[0009]
The present invention is also (6) a SiC single crystal ingot obtained by the production method according to any one of (1) to (5) above, wherein the diameter of the ingot is 50 mm or more. It is an ingot.
[0010]
Furthermore, the present invention provides
( 4 ) A mask made of one or more materials selected from graphite, tungsten, molybdenum or tantalum, wherein the width of the mask portion sandwiched between the openings is 1 to 5 mm, This is a mask for growing an SiC single crystal by a sublimation recrystallization method having a mask aperture ratio represented by an area ratio of 0.2 to 2 and a thickness of 0.1 to 3 mm.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the manufacturing method of the present invention, a mask is formed on the seed crystal, and a SiC single crystal is grown over the mask, thereby preventing the occurrence of micropipe defects and stacking faults. Further, a (0001) plane wafer having a large diameter is formed. Obtainable.
[0012]
The effect of the present invention will be described with reference to FIG. When a mask is formed on the seed crystal and a SiC single crystal is grown through the mask, the growth occurs almost parallel to the c-axis in the first stage of growth (FIG. 2A). Thereafter, as the growth proceeds, the crystal grows in a direction perpendicular to the c-axis so as to occupy the space on the mask (FIG. 2B). At this time, the occurrence of micropipe defects is suppressed as disclosed in JP-A-5-262599. In addition, the micropipe defect existing in the portion where the seed crystal is covered with the mask is completely shielded by the mask and is not inherited by the grown crystal. As described above, the area where the micropipe defects are suppressed (the area on the mask) includes Takahashi et al. , Journal of Crystal Growth, vol. 181 (1997) pp. As shown in 229-240, (0001) area layer defects exist, but in the latter half of the growth, the growth proceeds again in parallel with the c-axis (FIG. 2 (c)), so that it grows on the mask. The stacking faults, which are (0001) plane defects, are not carried over to the crystal parts grown in the latter half of the above. That is, in the present invention, in the SiC single crystal grown on the mask, there are no micropipe defects and stacking faults except in the very vicinity of the mask. Although the micropipe defect is present in the crystal portion grown in the portion where the seed crystal is not covered with the mask, if the method of the present invention is executed several times while changing the masked region, the entire crystal region is obtained. A good quality SiC single crystal can be obtained over a wide range.
[0013]
As the shape of the mask, a mesh shape or a lattice shape is preferable from the viewpoint of ease of mask processing, but other shapes may be used as long as the above growth mode can be realized. The mask material is preferably graphite, tungsten, molybdenum, or tantalum, but any material can be used as long as it does not dissolve or decompose at the growth temperature and does not cause impurity contamination of the grown crystal.
[0014]
The thickness of the mask is 0.1 to 3.0 mm, the aperture ratio of the mask (the area of the opening ÷ the area of the mask) is 0.2 to 2.0, and the width of the mask between the openings Is preferably 1.0 to 5.0 mm. When the thickness of the mask is 0.1 mm or less, the mask may be deformed or damaged during the growth preparation process or during growth, which is not preferable. On the other hand, when the thickness is 3.0 mm or more, the portion of the grown crystal from which a large-area wafer can be taken out is unnecessarily shortened, which is not preferable. If the aperture ratio is 0.2 or less, it is difficult to take over the growth orientation from the seed crystal, and polycrystals and the like are likely to be generated. On the other hand, if it is 2.0 or more, the portion covered by the mask portion becomes small, and the effect of shielding micropipe defects by the mask becomes small, which is not preferable.
[0015]
Finally, when the width of the mask portion sandwiched between the openings is 1.0 mm or less, the growth in the direction perpendicular to the c-axis is not performed sufficiently long (thus, micropipe defects cannot be completely suppressed). It becomes difficult to obtain the effect. If the width of the mask portion sandwiched between the openings is 5.0 mm or more, it is difficult to cover the entire mask area due to growth in a direction perpendicular to the c-axis (such as a void directly above the mask central portion). This is also not preferable.
[0016]
The SiC single crystal ingot produced by the production method of the present invention has a feature that it has a large diameter of 50 mm or more and extremely few micropipe defects that adversely affect the device.
[0017]
【Example】
Examples of the present invention will be described below. FIG. 3 shows an example of an apparatus for growing a SiC single crystal by the improved Rayleigh method using a seed crystal, which is the production apparatus of the present invention. First, this single crystal growth apparatus will be briefly described. Crystal growth is performed by sublimation recrystallization of SiC powder 2 as a raw material on SiC single crystal 1 used as a seed crystal through mask 12. Seed crystal SiC single crystal 1 and mask 12 are attached to the inner surface of lid 4 of graphite crucible 3. The raw material SiC powder 2 is filled in a graphite crucible 3. Such a graphite crucible 3 is installed inside a double quartz tube 5 by a support rod 6 made of graphite. Around the graphite crucible 3, a graphite felt 7 for heat shielding is installed. The double quartz tube 5 can be high vacuum evacuated (10 ⁻³ Pa or less) by a vacuum evacuation device, and the internal atmosphere can be pressure controlled by Ar gas. In addition, a work coil 8 is provided on the outer periphery of the double quartz tube 5, and the graphite crucible 3 can be heated by flowing a high-frequency current to heat the raw material and the seed crystal to a desired temperature. The temperature of the crucible is measured using a two-color thermometer by providing an optical path having a diameter of 2 to 4 mm at the center of the felt covering the upper and lower parts of the crucible and extracting light from the upper and lower parts of the crucible. The temperature at the bottom of the crucible is the raw material temperature, and the temperature at the top of the crucible is the seed temperature.
[0018]
Next, an example of manufacturing a SiC single crystal using this crystal growth apparatus will be described. First, a hexagonal SiC single crystal wafer having a (0001) face with a diameter of 50 mm was prepared as a seed crystal. Next, the seed crystal 1 was attached to the inner surface of the lid 4 of the graphite crucible 3. Further, a graphite slit-shaped mask 12 was attached thereon so as to cover the seed crystal. The thickness of the mask was 0.5 mm, and the width of the graphite mask portion and the slit-like opening was 1 mm (mask opening ratio 1.0). The raw material 2 was filled in the graphite crucible 3. Next, the graphite crucible 3 filled with the raw material is closed with a lid 4 fitted with a seed crystal and a graphite mask, covered with a graphite felt 7, and then placed on a graphite support rod 6. Installed inside. Then, after evacuating the inside of the quartz tube, a current was passed through the work coil to raise the raw material temperature to 2000 ° C. Thereafter, Ar gas was introduced as an atmospheric gas, and the raw material temperature was raised to the target temperature of 2400 ° C. while maintaining the pressure in the quartz tube at about 80 kPa. The growth pressure was reduced to 1.3 kPa over about 30 minutes, and then the growth was continued for about 20 hours. At this time, the temperature gradient in the crucible was 15 ° C./cm, and the growth rate was about 1 mm / h. The diameter of the obtained crystal was 51 mm, and the height was about 16 mm.
[0019]
When the silicon carbide single crystal thus obtained was analyzed by X-ray diffraction and Raman scattering, it was confirmed that a hexagonal silicon carbide single crystal was grown. For the purpose of evaluating micropipe defects, the (0001) plane wafer was taken out by cutting and polishing the latter half of the grown single crystal ingot. Thereafter, the surface of the wafer was etched with molten KOH at about 530 ° C., and the number of large hexagonal etch pits corresponding to micropipe defects was examined with a microscope, and the portion grown on the mask grew without the mask. It was found that micropipe defects were reduced to about ½ compared to the case.
[0020]
【The invention's effect】
As described above, according to the present invention, a high-quality silicon carbide single crystal with few crystal defects such as micropipe defects can be grown with good reproducibility and homogeneity by an improved Rayleigh method using a seed crystal. it can. By using such a silicon carbide single crystal wafer, it is possible to manufacture a blue light-emitting element having excellent optical characteristics and a high voltage / environment resistant electronic device having excellent electrical characteristics.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining the principle of an improved Rayleigh method.
FIG. 2 is a diagram illustrating the effect of the present invention.
FIG. 3 is a configuration diagram showing an example of a single crystal growth apparatus used in the manufacturing method of the present invention.
[Explanation of number]
1 Seed crystal (SiC single crystal)
2 SiC powder raw material 3 Graphite crucible 4 Graphite crucible lid 5 Double quartz tube 6 Graphite support rod 7 Graphite felt 8 Work coil 9 Ar gas pipe 10 Ar gas mass flow controller 11 Vacuum exhaust device 12 Mask

Claims (4)

A method for producing a silicon carbide single crystal comprising a step of growing a silicon carbide single crystal on a seed crystal by a sublimation recrystallization method, wherein the width of the mask portion sandwiched between the openings on the seed crystal is 1 to 5 mm A silicon carbide single crystal characterized by growing a silicon carbide single crystal over the mask after applying a mask having a mask opening ratio represented by an area ratio of the opening / mask portion of 0.2-2 Ingot manufacturing method.   The method for producing a silicon carbide single crystal ingot according to claim 1, wherein the mask is made of one or more materials selected from graphite, tungsten, molybdenum, and tantalum.   The method for producing a silicon carbide single crystal ingot according to claim 1, wherein the mask has a thickness of 0.1 to 3 mm. A mask made of one or more materials selected from graphite, tungsten, molybdenum, or tantalum, wherein the width of the mask portion sandwiched between the openings is 1 to 5 mm, and the area ratio of the opening / mask portion A mask for growing a silicon carbide single crystal by a sublimation recrystallization method having a mask aperture ratio of 0.2 to 2 and a thickness of 0.1 to 3 mm.

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