METHOD FOR ADJUSTING THERMAL FIELD OF SILICON CARBIDE SINGLE CRYSTAL GROWTH

Abstract

Provides a method for adjusting a thermal field of silicon carbide single crystal growth, and steps comprise: (A) screening a silicon carbide source, and filling into a bottom of a graphite crucible; (B) placing a guide inside the graphite crucible; (C) placing a rigid heat conductive material on the guide, so that a gap between the guide and a crucible wall of the graphite crucible is reduced; (D) fixing a seed crystal on a top of the graphite crucible; (E) placing the graphite crucible equipped with the silicon carbide source and the seed crystal in an induction high-temperature furnace used by physical vapor transport method; (F) performing a silicon carbide crystal growth process; and (G) obtaining a silicon carbide single crystal.

Claims

1. A method for adjusting a thermal field of silicon carbide single crystal growth, steps comprising: (A) screening a silicon carbide source, and filling into a bottom of a graphite crucible; (B) placing a guide inside the graphite crucible; (C) placing a rigid heat conductive material on the guide, so that a gap between the guide and a crucible wall of the graphite crucible is reduced; (D) fixing a seed crystal on a top of the graphite crucible; (E) placing the graphite crucible equipped with the silicon carbide source and the seed crystal in an induction high-temperature furnace used by physical vapor transport method; (F) performing a silicon carbide crystal growth process; and (G) obtaining a silicon carbide single crystal.

2. The method for adjusting a thermal field of silicon carbide single crystal growth according to claim 1, wherein the rigid heat conductive material is graphite, tantalum carbide (TaC), niobium carbide (NbC) or tungsten carbide (WC) of a high-temperature and low-pressure resistant material, thermal conductivity >10 W/m.Math.K.

3. The method for adjusting a thermal field of silicon carbide single crystal growth according to claim 1, wherein the number of the rigid heat conductive materials is at least one or more, a geometric shape thereof is an axisymmetric geometric shape of disk or polygon.

4. The method for adjusting a thermal field of silicon carbide single crystal growth according to claim 3, wherein the number of the rigid heat conductive materials is more than two, the rigid heat conductive materials go with each other in different geometric shapes.

5. The method for adjusting a thermal field of silicon carbide single crystal growth according to claim 1, wherein a gap between the rigid heat conductive material and the crucible wall is ≤15 mm.

6. The method for adjusting a thermal field of silicon carbide single crystal growth according to claim 1, wherein a distance between a top of the rigid heat conductive material and a top of the guide is 1 mm to 30 mm.

7. The method for adjusting a thermal field of silicon carbide single crystal growth according to claim 1, wherein the rigid heat conductive material has a thickness ≤15 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 is a schematic view of a graphite crucible of prior art.

[0020] FIG. 2 is a schematic view of a guide of the graphite crucible of prior art.

[0021] FIG. 3 is a schematic view of a graphite crucible of the silicon carbide crystal growth of the present disclosure.

[0022] FIG. 4 shows images of wafer testing of the present disclosure.

[0023] FIG. 5 is a flow chart of a method for adjusting a thermal field of silicon carbide single crystal growth of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The implementation of the disclosure is further described by the specific embodiments as below, and a person having ordinary skill in the art can easily understand other advantages and effects of the present disclosure by the content of the specification.

[0025] Referring to FIGS. 5 and 3, FIG. 5 is a flow chart of a method for adjusting a thermal field of silicon carbide single crystal growth of the present disclosure, FIG. 3 is a schematic view of a graphite crucible of the silicon carbide crystal growth of the present disclosure. The present disclosure is to provide a method for adjusting a thermal field of silicon carbide single crystal growth, steps comprising: step S1, screening a silicon carbide source 2, and filling into a bottom of a graphite crucible 3; step S2, placing a guide 6 inside the graphite crucible 3; step S3, placing a rigid heat conductive material 7 on the guide 6, so that a gap between the guide 6 and a crucible wall of the graphite crucible 3 is reduced; step S4, fixing a seed crystal 1 on a top of the graphite crucible 3; step S5, placing the graphite crucible 3 equipped with the silicon carbide source 2 and the seed crystal 1 in an induction high-temperature furnace used by physical vapor transport method; step S6, performing a silicon carbide crystal growth process; step S7, obtaining a silicon carbide single crystal.

[0026] In the embodiment, the rigid heat conductive material 7 may be graphite, tantalum carbide (TaC), niobium carbide (NbC) or tungsten carbide (WC) of a high-temperature and low-pressure resistant material, thermal conductivity >10 W/m.Math.K. Further, the number of the rigid heat conductive materials 7 placed on the guide 6 may be at least one or more, a geometric shape thereof may be an axisymmetric geometric shape of disk or polygon. Moreover, if the number of the rigid heat conductive materials 7 placed on the guide 6 is more than two, the rigid heat conductive materials 7 may go with each other in different geometric shapes.

[0027] In the present embodiment, a gap A between the rigid heat conductive material 7 and the crucible wall of the graphite crucible 3 is ≤15 mm. Further, a distance between a top of the rigid heat conductive material 7 and a top of the guide 6 may be 1 mm to 30 mm. Moreover, the rigid heat conductive material 7 has a thickness ≤15 mm, the gap between the thin shell guide 6 and the crucible wall of the graphite crucible 3 can be reduced by the rigid heat conductive material 7, so that the thin shell guide 6 maintains a higher temperature, and reduces or avoids the deposition of polycrystal. Not only can it reduce the grain boundary defects extended by the silicon carbide polycrystal to make the usable area increase, but it can also be used in the expansion experiment in the future.

[0028] As stated above, the present disclosure uses the physical vapor transport method (PVT) for silicon carbide single crystal growth, and under the premise of induction heating in a crystal growth furnace, the thin shell guide 6 is used and a rigid heat conductive material 7 is used to connect to the heat source of the crucible wall, so that the heat transfer quickly gets to the guide 6, and the rigid heat conductive material 7 connecting the crucible wall and (graphite) guide 6 is adjusted according to different design needs of thermal field, including adjusting the material, size, geometry and contact area.

[0029] The present disclosure uses a SiC crystal growth furnace having an induction heating furnace body to perform SiC single crystal growth with the rigid heat conductive material 7 connecting to the thin shell guide 6 and graphite crucible wall, the rigid heat conductive material 7 may be metal, carbide, carbon material and other pure elements or compounds of a high-temperature and low-pressure resistant material. By means of quick heat transfer, the heat generated outside the crucible 3 is introduced into the guide 6 to reduce or avoid crystallization on the guide 6 during growth, thereby increasing the usable region of the single crystal.

[0030] The present disclosure uses induction heating technology for consideration to make alternating current of a specific frequency pass through a copper coil to produce an alternating magnetic field around the coil, using electromagnetic induction to make the crucible 3 produce eddy current to achieve the purpose of heating, and because of the influence of the skin effect, the eddy current is concentrated on the surface of the crucible 3. In other words, the heat source is concentrated on the surface of the crucible 3, and the crucible 3 is equipped with a thin shell guide 6 therein, the heat source is not easy to reach the guide 6, so the inventors of the present disclosure use the rigid heat conductive material 7 to connect the thin shell guide 6 and the crucible wall of the graphite crucible 3, so that the thin shell guide 6 maintains a higher temperature to reduce or avoid the deposition of polycrystals.

[0031] The present disclosure uses the rigid heat conductive material 7 to connect the thin shell guide 6, the rigid heat conductive material 7 must be able to withstand a high-temperature and low-pressure environment, such as graphite, tantalum carbide (TaC), niobium carbide (NbC) or tungsten carbide (WC) and the like; the connection method can be full contact, no contact, etc.; the geometric shape can vary according to the needs of use, but based on the principle of axisymmetric relationship. As shown in FIG. 3, gap A, distance B and thickness C are all adjustable dimensions.

[0032] The present embodiment will compare four experiments, as shown in FIG. 4, respectively: (1) the upper left image (a) is a wafer produced by a normal (Normal) guide tube 6. (2) the upper right image (b) is a wafer produced by a heat conductive configuration guide pipe 6, the gap A, distance B and thickness C are all 8 mm, and the rigid heat conductive material 7 is graphite. (3) the lower left image (c) is a wafer produced by a heat conductive configuration guide pipe 6, the gap A=1 mm, the distance B=5 mm, the thickness C=1 mm, and the rigid heat conductive material 7 is TaC. (4) the lower right image (d) is a wafer produced by a heat conductive configuration guide pipe 6, the gap A=1 mm, the distance B=5 mm, the thickness C=5 mm, and the rigid heat conductive material 7 is graphite. These are respectively mounted on top of the graphite crucible 3 containing 3.5 kg of silicon carbide source 2, and an insulation material 4 is wrapped on the mounted graphite crucible 3, which is placed in a heating furnace for growth, growing at a temperature of 2100 to 2200° C., the pressure is 5 Torr, and after 100 hours of growth, each silicon carbide crystal with a thickness about 1.5 cm can be obtained.

[0033] Using the seed crystal of silicon carbide as the datum, a place going upwards 1 cm is cut therefrom, and the cut wafer is tested by X-Ray Topography (XRT) to observe the grain boundaries around the wafer. As shown in FIG. 4, the upper left image (a) is the wafer produced by the normal guide tube, and the gradual decrease of the surrounding defects can be observed from (a) to (d) in FIG. 4. Thus, the present disclosure may effectively improve wafer yield.

[0034] In summary, the present disclosure is a method for adjusting a thermal field of silicon carbide single crystal growth, configuration design is carried out regarding the physical vapor transport method, and induction heating technology and that the crucible 3 is equipped with a thin shell guide 6 therein are considered, so that the heat source concentrated on the surface of the crucible 3 can make the thin shell guide 6 maintain a higher temperature to reduce or avoid the deposition of polycrystal by using the rigid heat conductive material 7 to reduce the gap between the thin shell guide 6 and the crucible wall of the graphite crucible 3. Accordingly, not only can it reduce the grain boundary defects extended by the silicon carbide polycrystal to make the usable area increase, but it can also be used in the expansion experiment in the future.

[0035] The above embodiments of the disclosure made only by way of example to describe the feature and effect of the disclosure, and it should not be considered as the scope of substantial technical content is limited thereby. Various possible modifications and alternations of the embodiments could be carried out by the those of ordinary skill in the art without departing from the spirit and scope of the disclosure. Therefore, the scope of the disclosure is based on the appended claims.