Abstract
Provided is a method of enhancing silicon carbide monocrystalline growth yield, including the steps of: (A) filling a bottom of a graphite crucible with a silicon carbide raw material selected; (B) performing configuration modification on a graphite seed crystal platform; (C) fastening a silicon carbide seed crystal to the modified graphite seed crystal platform with a graphite clamping accessory; (D) placing the graphite crucible containing the silicon carbide raw material and the silicon carbide seed crystal in an inductive high-temperature furnace; (E) performing silicon carbide crystal growth process by physical vapor transport; and (F) obtaining silicon carbide monocrystalline crystals. The geometric configuration of the surface of the graphite seed crystal platform is modified to eradicate development of peripheral grain boundary.
Claims
1. A method of enhancing silicon carbide monocrystalline growth yield, comprising the steps of: (A) filling a bottom of a graphite crucible with a silicon carbide raw material selected; (B) performing configuration modification on a graphite seed crystal platform; (C) fastening a silicon carbide seed crystal to the modified graphite seed crystal platform with a graphite clamping accessory; (D) placing the graphite crucible containing the silicon carbide raw material and the silicon carbide seed crystal in an inductive furnace; (E) performing silicon carbide crystal growth process by physical vapor transport; and (F) obtaining silicon carbide monocrystalline crystals, wherein the configuration modification in step (B) formed a space at an edge of the graphite seed crystal platform, corresponds in position to a clamping point of the silicon carbide seed crystal, and is defined with a configuration width, a configuration depth and a configuration angle; wherein the configuration angle is substantially 30°, such that when step (E) taking place, the silicon carbide seed crystal above the space is gradually sublimed, and the resultant atmosphere accumulates in accordance with the geometric configuration of the graphite seed crystal platform, so that the silicon carbide monocrystalline crystals bind with peripherally-located polycrystalline silicon carbide so as to be fixed to the graphite seed crystal platform.
2. (canceled)
3. The method of enhancing silicon carbide monocrystalline growth yield according to claim 1, wherein the graphite seed crystal platform has an alignment depth and an alignment width which correspond to the silicon carbide seed crystal.
4. The method of enhancing silicon carbide monocrystalline growth yield according to claim 3, wherein the alignment width is greater than or equal to 1.5% of a diameter of the silicon carbide seed crystal.
5. The method of enhancing silicon carbide monocrystalline growth yield according to claim 2, wherein the configuration depth is greater than or equal to 3% of a diameter of the silicon carbide seed crystal.
6. The method of enhancing silicon carbide monocrystalline growth yield according to claim 2, wherein the configuration width is greater than or equal to 3% of a diameter of the silicon carbide seed crystal.
7. (canceled)
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 (PRIOR ART) is a schematic view of a conventional graphite seed crystal platform.
[0020] FIG. 2 (PRIOR ART) is a schematic view, depicting the difficulty in applying adhesive to a conventional silicon carbide seed crystal and fixing it in place.
[0021] FIG. 3 (PRIOR ART) is a schematic view, depicting the difficulty in applying adhesive to a conventional silicon carbide seed crystal and physically clamping it.
[0022] FIG. 4 is a schematic view of how to fix seed crystal in place, using sublimed silicon carbide, according to the present disclosure.
[0023] FIG. 5 is a schematic view of a graphite seed crystal platform of the present disclosure.
[0024] FIG. 6A shows picture taken of a conventional XRT wafer.
[0025] FIG. 6B shows picture taken of an XRT wafer of the present disclosure.
[0026] FIG. 7A shows the configuration and the dimension of a normal graphite seed crystal platform.
[0027] FIG. 7B shows the configuration and the dimension of a modification graphite seed crystal platform.
DETAILED DESCRIPTION OF THE INVENTION
[0028] To facilitate understanding of the object, characteristics and effects of this present disclosure, embodiments together with the attached drawings for the detailed description of the present disclosure are provided.
[0029] Refer to FIG. 4 and FIG. 5. FIG. 4 is a schematic view of how to fix seed crystal in place, using sublimed silicon carbide, according to the present disclosure. FIG. 5 is a schematic view of a graphite seed crystal platform of the present disclosure. The present disclosure provides a method of enhancing silicon carbide monocrystalline growth yield, comprising the steps of filling the bottom of the graphite crucible with a silicon carbide raw material and then performing configuration modification on a graphite seed crystal platform 1′, such that a space 10 is formed at the edge of the graphite seed crystal platform 1′ and corresponding in position to a clamping point of a silicon carbide seed crystal 2. The space 10 is defined by a configuration width 14, configuration depth 15 and configuration angle 16. The graphite seed crystal platform 1′ has an alignment depth 12 and alignment width 13 required for alignment of the silicon carbide seed crystal 2. The silicon carbide seed crystal 2 is fastened to the modified graphite seed crystal platform 1′ with a graphite clamping accessory 4. After that, a graphite crucible which contains a silicon carbide raw material and the silicon carbide seed crystal 2 is placed in an inductive high-temperature furnace. Next, a silicon carbide crystal growth process is carried out by physical vapor transport (PVT) to obtain silicon carbide monocrystalline crystals.
[0030] According to the present disclosure, the physical vapor transport (PVT) carried out to achieve silicon carbide monocrystalline growth is described below. The physically clamped silicon carbide seed crystal 2 is placed on the graphite seed crystal platform 1′ and then on the top of the graphite crucible; meanwhile, the silicon carbide raw material is placed in its bottom. The graphite crucible is depressurized, in the presence of inert gas, to less than 0.1˜50 Torr and heated up to 2000˜2400° C. to cause sublimation of the silicon carbide raw material and control the heat field to transfer the gas source to the surface of the silicon carbide seed crystal 2 for the sake of crystal growth. The present disclosure begins with physical clamping and entails modifying the geometric configuration of the surface of the graphite seed crystal platform 1′ to eradicate the development of peripheral grain boundary 9, thereby enhancing crystal growth yield.
[0031] In this embodiment, physical vapor transport (PVT) essentially attains the sublimation point of silicon carbide at high temperature and low pressure, such that the resultant gaseous silicon carbide moves toward a cooling zone of the graphite crucible and accumulates there. Then, given heat field control, a sublimed silicon carbide atmosphere 11 is guided to the silicon carbide seed crystal 2 and accumulates there, allowing silicon carbide monocrystalline growth to begin. Since the atmosphere 11 always moves toward the upper half of the graphite crucible, the silicon carbide eventually accumulates on the top of the graphite crucible. Thus, the silicon carbide seed crystal 2 has to lie at the uppermost end of the graphite crucible in order not to turn into the atmosphere 11 by sublimation and thereby accumulate at the top end.
[0032] According to the present disclosure, fixation of silicon carbide seed crystal 2 is initially achieved by physical clamping but subsequently by binding. In this regard, the binding process is carried out with polycrystalline silicon carbide 8 instead of graphite adhesive 3, as shown in FIG. 4, from left to right. First, the geometric configuration of the graphite seed crystal platform 1′ is modified to form the space 10, and then the silicon carbide seed crystal 2 is physically clamped thereto. Next, high-temperature, low-pressure silicon carbide growth takes place; meanwhile, the silicon carbide seed crystal 2 above the space 10 is gradually sublimed, and thus the resultant atmosphere 11 accumulates in accordance with the geometric configuration of the graphite seed crystal platform 1′. In this regard, peripheral sublimation of the polycrystalline silicon carbide 8 is accompanied by central growth of the monocrystalline silicon carbide 6 synchronously. At last, the monocrystalline silicon carbide 6 binds with the peripherally-located polycrystalline silicon carbide 8 so as to be fixed to the graphite seed crystal platform 1′.
[0033] Referring to FIG. 5, there is shown a schematic view of a graphite seed crystal platform of the present disclosure. As shown in the diagram, the silicon carbide seed crystal 2 is physically clamped to the modified graphite seed crystal platform 1′ with a graphite accessory. The modified graphite seed crystal platform 1′ has an alignment depth 12 and an alignment width 13 which correspond to the silicon carbide seed crystal 2. The alignment depth 12 is slightly less than the thickness of the silicon carbide seed crystal 2 and is intended to ensure the precise attachment of the graphite clamping accessory 4. The alignment width 13 depends on the diameter of the silicon carbide seed crystal 2. In this embodiment, the alignment width 13 is greater than or equal to 1.5% of the diameter of the silicon carbide seed crystal 2 and is intended to prevent the silicon carbide seed crystal 2 from bending because of the graphite clamping accessory 4. In case of excessive bending, the silicon carbide crystal growth will experience excessive stress and thus cause the development of defects or even cracks. The geometric configuration includes a configuration width 14, configuration depth 15 and configuration angle 16. The modification of configuration must be performed according to a principle: upon completion of the sublimation of the silicon carbide seed crystal 2, the polycrystalline silicon carbide 8 is precisely bound to the monocrystalline silicon carbide 6. Thus, in case of excessive configuration depth 15 and excessive configuration angle 16, the polycrystalline silicon carbide 8 has not yet bound with the edges of the monocrystalline silicon carbide 6 at the end of the sublimation of the silicon carbide seed crystal 2, thereby causing the silicon carbide seed crystal 2 to fall onto the surface of the silicon carbide raw material and fail. Conversely, insufficient configuration depth 15 and insufficient configuration angle 16 enable the polycrystalline silicon carbide 8 to bind with the edges of the monocrystalline silicon carbide 6 at the end of the sublimation of the silicon carbide seed crystal 2, but the polycrystalline silicon carbide 8 comes into contact with the monocrystalline silicon carbide 6 so soon to increase the chance of the grain boundary affecting the silicon carbide monocrystalline and decrease the available area of the silicon carbide crystal. Likewise, the configuration width 14, configuration depth 15 and configuration angle 16 depend on the diameter of the silicon carbide seed crystal 2. In this embodiment, the configuration depth 15 is greater than or equal to 3% of the diameter of the silicon carbide seed crystal 2, the configuration width 14 is greater than or equal to 3% of the diameter of the silicon carbide seed crystal 2, and the configuration angle 16 is 1°˜90°. The size of the graphite crucible depends on the target size of the silicon carbide crystal to grow. The weight and cross-sectional area of the silicon carbide raw material vary with the target size of the silicon carbide crystal to grow. Thus, the growth of larger silicon carbide crystal requires more silicon carbide atmosphere 11 and larger space 10 to prevent the overflow of the polycrystalline silicon carbide 8. Therefore, the present disclosure has advantages as follows: the polycrystalline silicon carbide 8 binds with the monocrystalline silicon carbide 6; the monocrystalline silicon carbide 6 has grown to acquire a certain thickness; the monocrystalline silicon carbide 6 is always higher than the polycrystalline silicon carbide 8 throughout the course of growth to thereby prevent the polycrystalline silicon carbide 8 from generating the grain boundary 9 which will otherwise affect the monocrystalline silicon carbide 6.
[0034] Referring to FIGS. 6A and 6B, FIG. 6A shows picture taken of a conventional XRT wafer; and FIG. 6B shows picture taken of an XRT wafer of the present disclosure. The present disclosure is based on two experiments: A: normal graphite seed crystal platform, as shown in FIG. 7A; B: modification graphite seed crystal platform, as shown in FIG. 7B. The modification graphite seed crystal platform has parameters as follows: an alignment width 13 of 2 mm, configuration width 14 of 5 mm, configuration depth 15 of around 8.7 mm, and configuration angle 16 of 30°. The silicon carbide seed crystal 2 with a diameter of 6 inches and a thickness of 1 mm is fastened to both the normal and modification graphite seed crystal platforms with the graphite clamping accessory 4. They are mounted on the graphite crucibles which contain 3 kg of silicon carbide raw material, respectively. The graphite crucibles, which are fully mounted in place, are encapsulated with a heat insulating material and placed in a heating furnace to undergo growth at temperature of around 2100˜2200° C. and pressure of 5 Torr. After the growth process has taken place for 70 hours, silicon carbide crystals of a thickness of 1.5 cm each are obtained.
[0035] The two silicon carbide crystals are cut at 1 cm above the seed crystal functioning as a standard surface. The resultant wafers undergo XRT inspection to observe the wafers' peripheral grain boundary and available area. Referring to FIGS. 6A and 6B, the wafer on the left is produced by the normal graphite seed crystal platform, whereas the wafer on the right is produced by the modification graphite seed crystal platform, showing conspicuously that in FIG. 6A the peripheral defects are much more serious than B, with the longest defect being nearly 3 cm long, causing a great reduction in the available area. In FIG. 6B, only the top shows some defects. Thus, the present disclosure is effective in enhancing the wafer yield.
[0036] In conclusion, the present disclosure provides a method of enhancing silicon carbide monocrystalline growth yield to physically clamp the silicon carbide seed crystal 2, reduce the chance of a fall of the silicon carbide seed crystal 2, and use the geometric configuration of the surface of the modification graphite seed crystal platform 1′ to prevent the development of the peripheral grain boundary 9 and effectively enhance the crystal growth yield.
[0037] While the present disclosure has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the present disclosure set forth in the claims.
