Patent Publication Number: US-2022235486-A1

Title: Graphite Plate

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Chinese Patent Application No. 202120203604.1, filed on Jan. 25, 2021, which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present application relates to the technical field of semiconductor material growth, more particular, to a graphite plate. 
     BACKGROUND 
     A Light Emitting Diode (LED) is a solid-state semiconductor diode light-emitting device, which is widely used in lighting fields such as indicator light, display screens, etc. At the present stage, a method of producing LED wafers is mainly realized by metal-organic chemical vapor deposition (MOCVD), and it&#39;s process may be briefly described as follows: a substrate is placed into a recess of a graphite plate, the graphite plate loaded with the substrate is placed into the MOCVD reaction chamber, the reaction chamber temperature is heated to a preset temperature, and an organic metal compound and group V gases are input, so that a chemical bond thereof may be broken on the substrate and re-polymerize to form a LED epitaxial layer. 
     However, an epitaxial wafer obtained according to the above process has poor performance uniformity, such as, uneven LED wavelength, uneven two-dimensional electron gas, etc. 
     SUMMARY 
     In view of this, embodiments of the present application are devoted to providing a graphite plate to solve a problem of poor performance uniformity of an epitaxial wafer obtained by using a graphite plate for epitaxial growth. 
     The application provides a graphite plate, including a graphite plate body, the graphite plate body includes a carrying recess, and at least part of the inner wall of the carrying recess is covered with a heat insulation material. By providing a heat insulation material at a preset position (such as a high temperature position) of the carrying recess, the temperature difference between different positions of the inner wall of the carrying recess is decreased, so that a substrate can be evenly heated. 
     In an embodiment, a central area of a bottom wall of the carrying recess is covered with the heat insulation material. Through research, the inventor found that the temperature of the central area of the carrying recess is higher than that of other areas. Therefore, by providing the heat insulation material at the central area, it may be more targeted to balance the temperatures at various positions of the inner wall of the carrying recess. 
     In an embodiment, the bottom wall includes a recess, and the heat insulation material is filled in the recess, a surface of the heat insulation material is flush with the bottom wall. Thus, compared with directly forming the heat insulation material on the bottom wall surface of the carrying recess, it can ensure that the supporting surface of the carrying recess is a flat surface, so as to achieve a better supporting effect. 
     In an embodiment, the bottom wall of the carrying recess is a flat surface, the central area of the bottom wall includes a plurality of support areas spaced apart from each other, and each of the support areas is covered with the heat insulation material. Thus, due to the thickness of the heat insulation material, a support frame structure may be formed on the bottom wall of the carrying recess and the substrate placed in the carrying recess is arranged overhead by the support frame structure, thus avoiding that the corresponding local area of the substrate caused by the central area of the carrying recess is overheated. 
     In an embodiment, each of the support areas is provided with a protrusion, and the protrusion is covered with the heat insulation material. By providing the protrusions with the heat insulation material, a support frame structure may be formed on the bottom wall of the carrying recess, and the substrate placed in the carrying recess is arranged overhead by the support frame structure, thus avoiding the corresponding local area of the substrate caused by the central area of the carrying recess is overheated. 
     In an embodiment, the plurality of support areas are annularly arranged on the bottom wall. Thus, it is possible to ensure that a plurality of heat insulation materials form a stable support frame structure to provide stable support. 
     In an embodiment, at least part of sidewall of the carrying recess is covered with the heat insulation material. 
     In an embodiment, a part of the sidewall of the carrying recess away from a center of the graphite plate body is covered with the heat insulation material. Since the substrate located in the carrying recess is subjected to centrifugal force during the rotation of the graphite plate, the edge region of the substrate away from the center of the graphite plate body is always in contact with the inner wall of the carrying recess, which tends to cause higher temperature at the contact position than at other position of the sidewall of the substrate. Therefore, by providing the heat insulation material on the sidewall, the heating of the substrate may be further balanced, thereby improving the performance uniformity of the epitaxial wafer. 
     In an embodiment, a thickness of the heat insulation material ranges from 0.1 micron to 100 microns. 
     In an embodiment, a material of the heat insulation material includes any one of following materials: aluminum oxide, silicon oxide and silicon nitride. 
     According to the graphite plate provided by the present application, by providing a heat insulation material at a preset position of the carrying recess, such as a high temperature position, the temperature difference between different positions of the inner wall of the carrying recess is decreased, so that a substrate can be evenly heated. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of a structure of a graphite plate provided by the first embodiment of the present application. 
         FIG. 2  is a cross-section diagram of the graphite plate as shown in  FIG. 1 . 
         FIG. 3  is a cross-section diagram of a graphite plate provided by the second embodiment of the present application. 
         FIG. 4  is a schematic diagram of a structure of a graphite plate provided by the third embodiment of the present application. 
         FIG. 5  is a schematic diagram of the cross-sectional structure of the graphite plate along the line A 1 A 2  as shown in  FIG. 4 . 
         FIG. 6  is a cross-section diagram of a graphite plate provided by the fourth embodiment of the present application. 
         FIG. 7  is a cross-section diagram of a graphite plate provided by the fifth embodiment of the present application. 
         FIG. 8  is a schematic diagram of a structure of a graphite plate provided by the sixth embodiment of the utility model. 
         FIG. 9  is a sectional view of the graphite plate shown in  FIG. 8 . 
         FIG. 10  is a sectional view of a graphite plate provided by the seventh embodiment of the utility model. 
         FIG. 11  is a sectional view of a graphite plate provided by the eighth embodiment of the utility model. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     As described in the background, an epitaxial wafer obtained by using a graphite plate for epitaxial growth has poor performance uniformity. Through research, the inventor found that the reasons for the poor uniformity performance of the epitaxial wafer include at least: in a process of the epitaxial growth, a heating wire directly heats the graphite plate, and the temperature distribution around the graphite plate is uneven, which results in that the substrate in contact with the graphite plate is unevenly heated. An overheated area on the substrate are prone to plastic deformation. It is precisely because of the plastic deformation in the substrate, the performance of the epitaxial wafer obtained by epitaxial growth is not uniform. 
     In view of this, in accordance with a graphite plate of embodiments of the present application, by providing a heat insulation material at a preset position of the carrying recess, such as a high temperature position, the temperature difference between different positions of the inner wall of the carrying recess is decreased, so that a substrate can be evenly heated. 
     The technical schemes in the embodiments of the present application will be clearly and completely described below in combination with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, and all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present application. 
       FIG. 1  is a schematic diagram of a structure of a graphite plate provided by the first embodiment of the present application.  FIG. 2  is a cross-section diagram of the graphite plate as shown in  FIG. 1 . Combined with  FIG. 1  and  FIG. 2 , a graphite plate  10  includes a graphite plate body  11 , and the graphite plate body  11  includes a carrying recess  110 , and at least part of an inner wall of the carrying recess  110  is covered with a heat insulation material  12 . 
     The carrying recess  110  is used for carrying a substrate, and after the substrate is grown with a semiconductor material, a semiconductor epitaxial wafer is obtained. A shape of the carrying recess  110  may be reasonably set according to actual needs. In an embodiment, the carrying recess  110  is a circular recess. Since the substrate is generally in a shape of a disk, the carrying recess  110  is implemented as a circle, so that the shape of the carrying recess  110  may be adapted to the shape of the substrate. And although the graphite plate body  11  shown in  FIG. 1  and  FIG. 2  is provided with only one carrying recess  110 , the number of the carrying recesses  110  on the graphite plate body  11  is not limited thereto, and the number of the carrying recess  110  may be reasonably set according to actual needs. When the graphite plate body  11  is provided with a plurality of carrying recesses  110 , in an embodiment, the plurality of carrying recesses  110  are annularly arranged layer by layer with the circle center of the graphite plate body  11  as the center. 
     A material of the heat insulation material  12  may be selected from any material of which thermal conductivity is lower than that of graphite. In an embodiment, the material of the heat insulation material  12  includes any one of following materials: aluminum oxide, silicon oxide and silicon nitride. A thickness of the heat insulation material  12  may be reasonably set according to actual needs. In an embodiment, the thickness of the heat insulation material ranges from 0.1 micron to 100 microns. In an embodiment, the thickness of the heat insulation material  12  varies in different areas of the inner wall of the carrying recess  110 . Since the thickness of the heat insulation material  12  may control the temperature of the corresponding position, by setting the thickness of the heat insulation material  12  on different areas of the inner wall of the carrying recess  110  to be different, thus the various positions of the inner wall of the carrying recess  110  may be better balanced, so that the substrate can be evenly heated. 
     According to the graphite plate  10  provided by the embodiment, by providing the heat insulation material  12  on at least part of the inner wall of the carrying recess  110 , such as the high temperature area of the inner wall of the carrying recess  110 , the temperature difference between different positions of the graphite plate may be reduced to balance the temperatures at various positions of the inner wall of the carrying recess  110 , so that the substrate can be evenly heated. 
     In an embodiment, as shown in  FIG. 2 , a central area of the bottom wall of the carrying recess  110  is covered with the heat insulation material  12 . The central area refers to a circular area co-centered with the carrying recess  110 , and the area of the central area is not limited in this embodiment. In an embodiment, the thickness of the heat insulation material  12  decreases in the direction along the circle center of the central area to the edge. In an embodiment, the thickness of the heat insulation material  12  increases in the direction along the circle center of the central area to the edge. 
     Through research, the inventor found that the temperature of the central area of the carrying recess  110  is higher than that of other areas, and the temperature decreases in the direction along the circle center of the central area to the edge. Therefore, by providing the heat insulation material  12  at the central area, and setting the thickness of the heat insulation material  12  to decrease in the direction along the circle center to the edge, it may be more targeted to balance the temperatures at various positions of the inner wall of the carrying recess  110 . 
       FIG. 3  is a cross-section diagram of a graphite plate provided by the second embodiment of the present application. As shown in  FIG. 3 , the bottom wall of a carrying recess  210  of a graphite plate  20  includes a recess  211 , and the heat insulation material  22  is filled in the recess  211 , a surface of the heat insulation material  22  is flush with the bottom wall. Thus, compared with the graphite plate  10  shown in  FIG. 1  and  FIG. 2 , in which the heat insulation material  12  is formed directly on the bottom wall surface, thus the supporting surface of the carrying recess  210  may be ensured to be flat in this embodiment, so as to provide a better support effect. 
     The recess  211  may be formed at any position of the bottom wall of the carrying recess  210 . For example, the recess  211  is located in the central area of the bottom wall of the carrying recess  210 . In this case, in an embodiment, the depth of the recess  211  decreases in a direction along the circle center of the central area to the edge, and accordingly, the thickness of the heat insulation material  22  decreases in a direction along the center of the central area to the edge. 
       FIG. 4  is a schematic diagram of a structure of a graphite plate provided by the third embodiment of the present application.  FIG. 5  is a schematic diagram of the cross-sectional structure of the graphite plate along the line A 1 A 2  as shown in  FIG. 4 . Combined with  FIG. 4  and  FIG. 5 , a bottom wall of a carrying recess  310  is flat, and the central area of the bottom wall includes a plurality of support areas spaced apart from each other, and each of the support areas is covered with a heat insulation material  32 . 
     Specifically, a plurality of areas of the bottom wall of the carrying recess  310  are selected, the plurality of areas spaced apart from each other, and the heat insulation material  32  is formed on each of the areas. Thus, due to the thickness of the heat insulation material  32 , a support frame structure is formed on the bottom wall of the carrying recess  310 , and the substrate placed in the carrying recess  310  is arranged overhead by the support frame structure, thus avoiding that the corresponding local area of the substrate caused by the central area of the carrying recess  310  is overheated. 
     The shapes of the plurality of support areas are the same or different. The shape of each of the support areas is selected from any one of circle, triangle, rectangle and polygon. Accordingly, the shapes of the plurality of heat insulation materials  32  are the same or different. The shape of each heat insulation material  32  is selected from any one of cylinder, frustum, cone, cube, and polyhedron. In an embodiment, as shown in  FIG. 4 , the plurality of support areas are annularly arranged on the bottom wall. Thus, it is possible to ensure that the plurality of heat insulation materials  32  form a stable support frame structure to provide stable support. 
       FIG. 6  is a cross-section diagram of a graphite plate provided by the fourth embodiment of the present application. As shown in  FIG. 6 , the surface of the bottom wall of a carrying recess  410  is flat, and the central area of the bottom wall includes a plurality of support areas spaced apart from each other, and each of the support areas is provided with a protrusion  43 , and the protrusion  43  is covered with a heat insulation material  42 . 
     Specifically, a plurality of areas spaced apart from each other are selected on the bottom wall of the carrying recess  410 , each of the areas is provided with the protrusion  43 , and the heat insulation material  42  is formed on each of the protrusions  43 , and the heat insulation material  42  may be provided only on the surface of the protrusion  43 , or may cover the entire protrusion  43 . By providing the protrusions  43  with the heat insulation material  42 , a support frame structure may be formed on the bottom wall of the carrying recess  410 , and the substrate placed in the carrying recess  410  is arranged overhead by the support frame structure, thus avoiding overheated of the corresponding local area of the substrate caused by the central area of the carrying recess  410 . 
     In an embodiment, the heights of the plurality of protrusions  43  on the plurality of support areas are not equal, and correspondingly, and the thicknesses of the heat insulation materials  42  on the plurality of protrusions  43  are not equal. The sum of the height of the protrusion  43  and the thickness of the heat insulation material  42  on each of the support areas is equal to that of others 
       FIG. 7  is a cross-section diagram of a graphite plate provided by the fifth embodiment of the present application. As shown in  FIG. 7 , the difference between a graphite plate  50  and the graphite plate provided by any of the above embodiments is that at least part of the sidewall of the carrying recess  510  is also covered with the heat insulation material  52 . 
     In an embodiment, a part of the sidewall of the carrying recess  510  away from a center of the graphite plate body  51  is covered with the heat insulation material  52 . During the rotation of the graphite plate  50 , the substrate located in the carrying recess  510  is subjected to centrifugal force, so that the edge region of the substrate away from the center of the graphite plate body  51  is always in contact with the inner wall of the carrying recess  510 , which tends to cause higher temperature at the contact position than at other positions of the sidewall of the substrate. Therefore, by providing the heat insulation material  52  on the sidewall, the heating of the substrate may be further balanced, thereby improving the performance uniformity of the epitaxial wafer. 
     The thickness of the heat insulation material  52  on the sidewall of the carrying recess  510  may be equal or different at various positions. In an embodiment, the thickness of the heat insulation material  52  on the sidewall of the carrying recess  510  increases first and then decreases along the circumferential direction. Thus, by reasonably setting the position of the heat insulation material  52  on the sidewall of the carrying recess  510 , for example, the heat insulation material  52  can be disposed on the extension line of the connection between the center point O 1  of the graphite plate body  51  and the center point O 2  of the carrying recess  510 , so that the substrate is in contact with the area where the thickness of the heat insulation material  52  is the greatest. 
       FIG. 8  is a schematic diagram of a structure of a graphite plate provided by the sixth embodiment of the utility model.  FIG. 9  is a sectional view of the graphite plate as shown in  FIG. 8 . As shown in  FIG. 8  and  FIG. 9 , a graphite plate  60  includes a graphite plate body  61  and a heat insulation material  62 . A bottom wall of a carrying recess  610  of a graphite plate  60  includes a recess  611 , a bottom surface of the recess  611  is covered with the heat insulation material  62 , and a surface of the heat insulation material  62  is not higher than a surface of the bottom wall. At least part of the surface of the heat insulation material  62  is lower than the surface of the bottom wall. A height of the surface of the heat insulation material  62  increases in a direction along the center of the central area to an edge. 
     In an embodiment, a part of the surface of the heat insulation material  62  is lower than the bottom wall of the carrying recess  610 , and the other part of the surface is flush with the bottom wall of the carrying recess  610 . That is, the surface of the heat insulation material  62  includes a recessed area, the recessed area may be circular in shape, and the center of the recessed area coincides with the center of the carrying recess  610 . A height of the surface of the recessed area increases in the direction along the center of the central area to an edge, correspondingly, a thickness of the heat insulation material  62  increases. More specifically, the height of the surface of the recessed area first increases and then remains unchanged in the direction along the circle center of the central area to an edge. Correspondingly, the thickness of the heat insulation material  62  increases first and then remains unchanged. 
     In another embodiment, the height of the surface of the recessed area gradually increases, and correspondingly, the thickness of the heat insulation material  62  gradually increases in the direction along the circle center of the central area to the edge. 
     In this embodiment, when a substrate is placed in the carrying recess  610 , the substrate is supported by the bottom wall and an area where the heat insulation material  62  is flush with the bottom wall, and the recessed area of the heat insulation material  62  is not in direct contact with the substrate, so that an empty space is formed between the substrate and the heat insulation material  62 . Because the heat conductivity coefficient of air is small, this structure may further reduce heat-conducting capabilities of the central area, thereby reducing a temperature of the central area. And, the thicknesses of the heat insulation materials  62  of different areas are different by adjusting the thickness of the heat insulation material  62 , so that the temperature of the central area everywhere can be adjusted differently, so as to better ensure that the substrate can be evenly heated. In addition, the volume of the heat insulation material  62  in this embodiment is relatively small, which can reduce the production cost of the graphite plate  60 . 
       FIG. 10  is a sectional view of a graphite plate provided by the seventh embodiment of the utility model. As shown in  FIG. 10 , a graphite plate  70  includes a graphite plate body  71  and a heat insulation material  72 . A bottom wall of a carrying recess  710  of the graphite plate  70  includes a recess  711 , a heat insulation material  72  is filled in the recess  711 , and a depth of the recess  711  decreases in a direction along the circle center of the central area to an edge, correspondingly, a thickness of the heat insulation material  72  decreases in the direction along the center of the central area to an edge. More specifically, a depth of the recess  711  first decreases and then remains unchanged in the direction along the center of the central area to an edge, and correspondingly, a thickness of the heat insulation material  72  first decreases and then remains unchanged. 
     In this embodiment, the thickness of the heat insulation material  72  decreases in the direction along the center of the central area to an edge, the structure may further reduce heat-conducting capabilities of the central area, thereby reducing the temperature of the central area. In this embodiment, a downward recessed area is provided in the recess  711 , so that the depths of different positions in the recess  711  are different. More specifically, the depth of the recess  711  gradually decreases in the direction along the center of the central area to an edge. Correspondingly, the thickness of the heat insulation material  72  filled in the recess  711  gradually decreases in the direction along the center of the central area to an edge. At the center of the central area, the thickness of the heat insulation material  72  is the thickest and thermal conductivity is the worst, the thickness of the heat insulation material  72  decreases and thermal conductivity increases gradually in the direction along the center of the central area to an edge, this structure may make different adjustments to the temperature in the central area everywhere, so as to better ensure that the substrate can be evenly heated. 
       FIG. 11  is a sectional view of a graphite plate provided by the eighth embodiment of the utility model. As shown in  FIG. 11 , a graphite plate  80  includes a graphite plate body  81  and a heat insulation material  82 . A bottom wall of a carrying recess  810  of the graphite plate  80  includes a recess  811 , a depth of the recess  811  decreases in a direction along the center of the central area to an edge, and the heat insulation material  82  is filled in a part of the recess  811 . Specifically, the bottom of the recess  811  is recessed downward, and there is a dielectric material  812  between the bottom of the recess  811  and the heat insulation material  82 . The dielectric material  812  may be a filler or a coating. When the dielectric material  812  is a filler, the dielectric material  812  may be an insulation board or foam, or the like. When the dielectric material  812  is a coating, it may be a different material from that of the heat insulation material  82 , and specifically, a material of the dielectric material  812  may be a material with a heat conductivity coefficient smaller than that of the heat insulation material  82 . The distance from the bottom of the recess  811  to the heat insulation material  82  gradually decreases in the direction along the center of the central area to an edge, and correspondingly, a thickness of the dielectric material  812  gradually decreases. 
     In this embodiment, because the heat conductivity coefficient of the dielectric material is small, this structure can further reduce heat-conducting capabilities of the central area, thereby reducing the temperature of the central area. In this embodiment, the dielectric material and the heat insulation material are provided in the recess, and the thickness of the dielectric material gradually decreases in the direction along the center of the central region to an edge. This structure may make different adjustments to the temperature in the central area everywhere, the heat conduction performance is the worst at the center of the central area, and the heat conduction performance gradually is improved in the direction along the center of the central region to an edge, so as to better ensure that the substrate can be evenly heated. 
     The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application. Any modifications, equivalent replacements, or the like, made within the spirit and principles of the present application shall fall within the protection scope of the present application.