JP4224195B2 - Seed crystal for growing silicon carbide single crystal and method for producing silicon carbide single crystal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a seed crystal for growing a silicon carbide single crystal, a silicon carbide single crystal ingot, a silicon carbide single crystal wafer, and a method for producing a silicon carbide single crystal.
[0002]
[Prior art]
Silicon carbide (SiC) is also attracting attention as an environmentally resistant semiconductor material because of its excellent heat resistance and mechanical strength and physical and chemical properties such as resistance to radiation. In recent years, the demand for SiC single crystal wafers has increased as a substrate wafer for short wavelength optical devices from blue to ultraviolet, high frequency high voltage electronic devices, and the like. 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.
[0004]
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). In this method, a large-area single crystal can be obtained, but only a SiC single crystal containing many defects (−10 ⁷ cm ⁻² ) can be grown due to a lattice mismatch with the substrate of about 20%. It is not easy to obtain a high-quality SiC single crystal.
[0005]
In order to solve these problems, an improved Rayleigh method in which sublimation recrystallization is performed 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 by controlling the atmospheric pressure from about 100 Pa to about 15 kPa with an inert gas, the growth rate of the crystal can be controlled with good reproducibility. You can
[0006]
The principle of the improved Rayleigh method will be described with reference to FIG. A seed crystal 101 made of a SiC single crystal and a SiC crystal powder 102 as a raw material are stored in a crucible (usually graphite) 103 and in an atmosphere of an inert gas 104 such as argon (133 Pa to 13.3 kPa), 2000 to 2000 Heat to 2400 ° C. At this time, the temperature gradient is set so that the seed crystal 101 is slightly lower in temperature than the raw SiC crystal powder 102. After sublimation, the raw material is diffused and transported in the direction of the seed crystal 101 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 growth crystal 105 can be controlled by adding an impurity gas to the atmosphere of the inert gas 104 or mixing an impurity element or a compound thereof in the SiC crystal powder 102. Typical examples of substitutional impurities in the SiC single crystal include n-type nitrogen, p-type boron, and aluminum. 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.
[0007]
Currently, SiC single crystal wafers having a diameter of 2 inches (about 50 mm) to 3 inches (about 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, pinholes having a diameter of several μm to penetrate the growth direction - Le defects (micropipe defects) there has been a problem that contains the extent of 50 to 200 pieces / cm ^2.
[0008]
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 Japanese Patent No. 596-606, many of the micropipe defects are those that were present in the seed crystal and succeeded to 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. As described in 166-167, most of them occur at the early stage of growth. 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.
[0009]
Japanese Patent No. 2804860 discloses a technique for growing a SiC single crystal in a direction perpendicular to the <0001> c-axis direction by using a plane perpendicular to the {0001} plane as a seed crystal to suppress the micropipe defect. Has been. In this method, when a {0001} plane wafer useful for device fabrication is 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 shorter shape 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 229-240, when a SiC single crystal is grown in a direction perpendicular to the c-axis, a large number of (0001) area layer defects generated during the growth exist in the SiC single crystal. .
[0010]
[Problems to be solved by the invention]
As described above, when the method disclosed in Japanese Patent No. 2804860 is used, although micropipe defects do not occur, it becomes difficult to produce a large {0001} wafer useful for device fabrication. A lot of defects occur.
[0011]
The present invention has been made in view of the above circumstances, a method of manufacturing a SiC single crystal for growing seed crystals Contact good beauty S iC single crystal for good reproducibility supply a large diameter wafer of high quality with few defects It is to provide.
[0012]
[Means for Solving the Problems]
As a result of earnest research and development to solve the above problems of the prior art, the present inventors have found that a high-quality large-diameter single crystal with few defects can be obtained by devising the surface shape of the seed crystal. The title and the present invention have been completed.
[0013]
That is, the gist of the present invention is as follows.
[0014]
(1) A seed crystal composed of a SiC single crystal, which is a seed crystal for growing a SiC single crystal, having a groove having a width of 2 to 10 mm on a single crystal growth surface of the seed crystal.
[0016]
( 2 ) The SiC single crystal growing seed crystal according to (1 ), wherein an aspect ratio of the groove represented by the width / depth of the groove is 0.1 to 1.5.
[0017]
( 3 ) The seed crystal for growing a silicon carbide single crystal according to (1) or (2) , wherein a groove surface occupation ratio in the single crystal growth surface of the seed crystal is 0.2 to 10.
[0020]
( 4 ) A step of growing a silicon carbide single crystal on the seed crystal by a sublimation recrystallization method using the silicon carbide single crystal growth seed crystal according to any one of (1) to ( 3 ). This is a method for producing a silicon carbide single crystal.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
The SiC single crystal growth seed crystal of the present invention has a structure having a groove on the single crystal growth surface, thereby preventing the occurrence of micropipe defects and stacking faults during the growth of the single crystal. Even when a crystal ingot is produced, a good quality single crystal with few defects can be obtained.
[0022]
The defect generation prevention mechanism by the seed crystal for SiC single crystal growth of the present invention will be described with reference to FIG. Fig.2 (a) shows the arrangement | positioning condition of the seed crystal of this invention. The face with the seed crystal groove must be arranged in the crystal growth direction. When a SiC single crystal is grown on this seed crystal by the sublimation recrystallization method, crystal growth starts on the surface having the seed crystal groove, as shown in FIG. At this time, crystal growth proceeds in both the direction parallel to and perpendicular to the c-axis of the seed crystal. By the way, when the growth rate parallel to the c-axis and the growth rate perpendicular to the c-axis are compared, the growth rate perpendicular to the c-axis is larger (Takahashi et al., Journal of Crystal Growth, vol. 181). (1997) pp. 229-240), crystal growth from the groove side wall is given priority, and growth from the groove bottom is blocked. As a result, at the time when the groove portion is filled by crystal growth, a crystal portion grown in a direction parallel to the c-axis on a surface other than the groove portion and a crystal portion grown in the direction perpendicular to the c-axis in the groove portion are mixed ( FIG. 2 (c)). That is, the micropipe defect existing at the bottom of the groove is completely blocked by crystal growth from the side wall of the groove, and the micropipe defect is not inherited by the grown crystal. On the other hand, in the crystal growth in the direction perpendicular to the c-axis (side wall of the groove), stacking faults on the (0001) plane exist (Takahashi et al., Journal of Crystal Growth, vol. 181 (1997) pp. 229-240). This plane defect is not inherited by crystal growth in the direction parallel to the c-axis. Therefore, in the subsequent crystal growth in the direction parallel to the c-axis, an SiC single crystal having no micropipe defects or stacking faults is obtained on the groove portion of the seed crystal (FIG. 2D). Note that micropipe defects existing in portions other than the groove portion exist in the single crystal as in the conventional case with the growth of the SiC single crystal, but depending on the area ratio between the groove portion and the groove portion in the seed crystal, Since the existence ratio of the micropipe defects is remarkably reduced, it is possible to obtain a SiC single crystal ingot with greatly reduced crystal defects. In addition, if the seed crystal has few micropipe defects, it is possible to produce a SiC single crystal ingot in which micropipe defects are completely eliminated by using a seed crystal in which a groove is formed only at a site where the defect exists. It is.
[0023]
As the shape of the groove formed in the seed crystal, a stripe shape, a lattice shape, a mesh shape, or the like is preferable from the viewpoint of easiness of groove processing. The shape is not limited.
[0024]
Width of the formed groove is 2 to 10 mm. When it is less than 2 mm, that a hardly occurs crystal growth in the direction perpendicular to the c-axis in the entire groove wall. In the case of more than 10 mm, micropipe defects and dislocation defects are likely to occur at the meeting portion of crystals grown in the direction perpendicular to the c-axis from the groove side wall (which can be formed at the center of the groove).
[0025]
Moreover, it is preferable that the aspect ratio of the groove | channel represented by the width / depth of a groove | channel is 0.1-1.5. If the aspect ratio is less than 0.1, uniform crystal growth on the groove wall surface may be difficult to occur. In other words, crystal growth is likely to occur only in the vicinity of the groove opening, and crystal growth is unlikely to occur at the bottom of the groove. Therefore, the groove is closed at the groove opening, and the bottom of the groove remains as a cavity, from which void defects are formed. Etc. are likely to occur. On the other hand, if the aspect ratio is more than 1.5, crystal growth in the direction parallel to the c-axis from the bottom of the groove cannot be ignored, and the inside of the groove is occupied by the crystal grown in the direction parallel to the c-axis. There is a greater risk that the effect of reducing defects cannot be obtained.
[0026]
Furthermore, the groove surface occupation ratio (groove area / area other than the groove) represented by the ratio of the groove area to the area other than the groove on the crystal growth surface of the seed crystal is 0.2 to 10 Preferably there is. When the groove surface occupancy ratio is less than 0.2, the area having the effect of reducing the micropipe defects described above becomes small, and there is a possibility that a sufficient effect of reducing the micropipe defects cannot be obtained. In addition, when the groove surface occupancy ratio exceeds 10, the portion other than the groove becomes too small, and crystal growth may be difficult, or the seed crystal must be thickened to ensure crystal strength in the groove. Therefore, there is a risk of increasing the manufacturing cost.
[0027]
Next, a method for producing an SiC single crystal using the above-described sublimation recrystallization method using the seed crystal will be described. FIG. 3 shows an example of the configuration of an SiC single crystal growth apparatus by the modified Rayleigh method using the seed crystal of the present invention. A seed crystal 1 made of a SiC single crystal having a groove on the crystal growth surface is attached to the inner surface of a lid 4 of a graphite crucible 3. At this time, the crystal growth surface having the groove must be arranged in the crystal growth direction (downward in the drawing). The graphite crucible 3 is filled with SiC powder 2 as a raw material. When the graphite crucible 3 is induction-heated to 2300 to 2400 ° C. by the high-frequency coil 8, sublimation gas is generated from the raw material powder 2. The generated sublimation gas diffuses in the crucible space whose atmosphere is controlled by an inert gas (for example, Ar gas), moves in the direction of the seed crystal, and is recrystallized on the seed crystal 1. By continuing this process for several hours to several tens of hours, a SiC single crystal is produced. Usually, in order to obtain a SiC single crystal having a large diameter and a good quality, a high-quality seed crystal having a diameter almost equal to that is required, but it is extremely difficult to obtain such a seed crystal. However, if the seed crystal of the present invention is used, a high-quality SiC single crystal ingot can be easily obtained over the entire desired diameter even if the seed crystal contains a large amount of defects such as micropipe defects as long as the diameter is large. Can be produced.
[0028]
The SiC single crystal ingot manufactured by the manufacturing method of the present invention can have a large diameter of 50 mm or more, and if the SiC single crystal wafer is obtained by processing and polishing the ingot, the wafer diameter is The number of micropipe defects can be further reduced to 30 pieces / cm ² or less. With such a SiC single crystal wafer, for example, when producing a blue light emitting element, the production yield can be 90% or more.
[0029]
【Example】
Examples of the present invention will be described below. The SiC single crystal growth apparatus shown in FIG. 3 was used. First, this single crystal growth apparatus will be briefly described. As described above, crystal growth was performed by using SiC single crystal 1 having a groove on the surface as a seed crystal and subliming and recrystallizing SiC powder 2 as a raw material on SiC single crystal 1. The seed crystal SiC single crystal 1 was attached to the inner surface of the lid 4 of the graphite crucible 3. The raw material SiC powder 2 was filled in a graphite crucible 3. Such a graphite crucible 3 was 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 shield was installed. As the double quartz tube 5, a tube that can be evacuated at high vacuum (10 ⁻³ Pa or less) by the vacuum evacuation device 11 and that can control the pressure of the internal atmosphere with Ar gas. Further, a work coil (high frequency coil) 8 is installed on the outer periphery of the double quartz tube 5, and the graphite crucible 3 is heated by flowing a high frequency current to heat the raw material and the seed crystal to a desired temperature. can do. The temperature of the crucible was measured using a two-color thermometer by providing an optical path with 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 was the raw material temperature, and the temperature at the top of the crucible was the seed temperature.
[0030]
Next, an example of manufacturing using this crystal growth apparatus will be described.
[0031]
First, a hexagonal SiC single crystal wafer having a (0001) face with a diameter of 50 mm was prepared as a seed crystal. The seed pipe had a micropipe defect density of 50 / cm ² . Next, a slit-like groove having a width of 3.0 mm, an aspect ratio of 1, and a surface occupation ratio of 1.5 was formed on the surface of the seed crystal by machining. The processing damaged layer formed on the seed crystal surface by this machining was removed by etching with a chemical solution. As a comparative example, a seed crystal (micropipe defect density of 50 / cm ² ) that was not machined was also prepared. Each SiC single crystal seed crystal thus produced was attached to the inner surface of the lid 4 of the graphite crucible 3. The graphite crucible 3 was filled with SiC powder 2. Next, the graphite crucible 3 filled with the raw material is closed with a lid 4 fitted with a seed crystal, covered with a graphite felt 7, placed on a graphite support rod 6, and installed inside the double quartz tube 5. did. Then, after evacuating the inside of the quartz tube, a current was passed through the work coil (high frequency coil) 8 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 0.7 mm / h. The crystal obtained from any seed crystal also had a diameter of 51.5 mm and a height of about 14 mm.
[0032]
The SiC single crystal thus obtained was analyzed by X-ray diffraction and Raman scattering. As a result, it was confirmed that a hexagonal SiC single crystal grew. For the purpose of evaluating micropipe defects, {0001} plane wafers were taken out by cutting and polishing the latter half of each grown single crystal ingot. Thereafter, the wafer surface 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 was obtained from the grooved SiC single crystal seed crystal of the present invention. In the wafer, the micropipe defect density was 25 / cm ^2, which was significantly reduced from the defect density of the original seed crystal, whereas in the wafer obtained from the seed crystal without grooves, the defect density was 50 / cm ² . It was the same as the defect density of the seed crystal.
[0033]
【The invention's effect】
As described above, when the seed crystal of the present invention is used, in the SiC single crystal growth by the improved Rayleigh method, a high-quality SiC single crystal with few crystal defects such as micropipe defects can be grown with good reproducibility and homogeneity. Can do. If SiC single crystal wafers obtained from SiC ingots grown in this way are used, blue light-emitting elements with excellent optical characteristics and high-voltage / environment-resistant electronic devices with excellent electrical characteristics can be manufactured with high yield. can do.
[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 a crystal growth process using a seed crystal of the present invention.
FIG. 3 is a schematic configuration diagram of a single crystal growth apparatus used in an example of the present invention.
[Explanation of symbols]
1 Seed crystal (SiC single crystal)
2 SiC powder 3 Graphite crucible 4 Graphite crucible lid 5 Double quartz tube 6 Support rod 7 Graphite felt 8 High-frequency coil 9 Ar gas piping 10 Ar gas mass flow controller 11 Vacuum exhaust device 101 Seed crystal 102 SiC crystal Powder 103 crucible 104 inert gas 105 growth crystal

Claims (4)

A seed crystal for growing a silicon carbide single crystal, which is a seed crystal composed of a silicon carbide single crystal, and has a groove having a width of 2 to 10 mm on a single crystal growth surface of the seed crystal. 2. The seed crystal for growing a silicon carbide single crystal according to claim 1, wherein an aspect ratio of the groove represented by the width / depth of the groove is 0.1 to 1.5. In the single crystal growth surface of the seed crystal, the surface occupation ratio of the grooves, the silicon carbide single crystal growth for seed crystal according to claim 1 or 2 is 0.2 to 10. A silicon carbide single crystal comprising a step of growing a silicon carbide single crystal on the seed crystal by a sublimation recrystallization method using the silicon carbide single crystal growing seed crystal according to any one of claims 1 to 3. Manufacturing method.

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