Patent Publication Number: US-2022238363-A1

Title: Graphite Plate

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Chinese Patent Application No. 202120219432.7, filed on Jan. 26, 2021, which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The application relates to the technical field of semiconductor material growth device, 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 the 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 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 for epitaxial growth of a semiconductor material. A graphite plate includes: a graphite plate body, including a carrying recess and a recess disposed at one side of the carrying recess away from a central point of the graphite plate body; and a stopper, which is embedded in the recess in a matching manner, and the stopper protrudes from a bottom surface of the carrying recess to form a limiting structure. In accordance with the graphite plate provided by embodiments of the application, by providing the stopper, a sidewall of a substrate and a sidewall of the carrying recess are spaced apart, so as to avoid direct contact between the sidewall of the substrate and the sidewall of the carrying recess, and thus the contact point is overheated can be avoided, so that the epitaxial wafer is heated more evenly, thus improving the performance uniformity of epitaxial wafer. 
     In an embodiment, a heat insulation layer is provided between the recess and the stopper. Thus, the heat transfer between the graphite plate body and the stopper may be reduced, thereby avoiding the overheating of the stopper to further balance the heated temperature of the substrate. 
     In an embodiment, the stopper is coated in the heat insulation layer. A heat insulation layer is formed on the outer surface of the stopper, on the one hand, it is easy for industrial production; on the other hand, it ensures all-round heat insulation. 
     In an embodiment, a heat conducting hole is provided on the stopper. That improve heat dissipation of the stopper by using the heat conducting hole, thereby further avoiding the overheating of the stopper, balancing the heated temperature of the substrate. 
     In an embodiment, the stopper includes a stop surface perpendicular to a bottom surface of the carrying recess, and the stop surface is a curved surface. Since the substrate is usually the shape of a disk, by setting the stop surface to be a curved surface, a surface matching the side of the substrate can be formed to avoid stress concentration points at the contact surface between the substrate and the stopper, thereby improving the reliability of the stopper. 
     In an embodiment, the carrying recess and the graphite plate body are both round, and the stopper is symmetrical about an extension line of a connecting line between a central point of the graphite plate body and a central point of the carrying recess. Thus, it may ensure that the centrifugal force on the substrate reacts at the central point of the stopper, so that the force on the stopper is more uniform, and the reliability of the stopper is further improved. 
     In an embodiment, the stopper includes a stop part perpendicular to the bottom surface of the carrying recess, and a predetermined spacing is provided between the stop part and a sidewall of the carrying recess. Thus, the heat conduction between the graphite plate body and the stopper can be reduced, so as to avoid the overheating of the stopper, thereby improving the heating uniformity of substrate. 
     In an embodiment, the stopper is an L-shaped stopper, and the opening of the L-shaped stopper faces away from the central point of the graphite plate body. The L-shaped stopper is simple in structure and easy to be realized in industry. 
     In an embodiment, a part of the stopper protruding from the bottom surface of the carrying recess is provided to be inclined toward the central point of the graphite plate. 
     In an embodiment, the outer edge line at the corner of the L-shaped stopper is arc-shaped. Thus, a chamfer is disposed at the corner of the stopper, so that facilitate the mounting and dismounting of the stopper and the recess. 
     In an embodiment, a material of the stopper comprises any one of silicon carbide and quartz. Thus, on the one hand, sufficient hardness can be ensured; on the other hand, due to the low heat conductivity of silicon carbide and quartz, it may be avoided that the stopper is overheated, thereby further improving the uniformity of substrate heating. 
     In accordance with a graphite plate provided by embodiments of the application, by using a stopper to space a sidewall of a substrate and a sidewall of the carrying recess, so as to avoid direct contact between the sidewall of the substrate and the sidewall of the carrying recess, and thus the contact point is overheated can be avoided, so that the epitaxial wafer is heated more uniformly, thus improving the performance uniformity of the epitaxial wafer. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of a structure of a graphite plate provided by an embodiment of the application. 
         FIG. 2  is a local cross-sectional schematic diagram of the graphite plate along the line A 1 A 2  shown in  FIG. 1  provided by the first embodiment of the application. 
         FIG. 3  is a local cross-sectional schematic diagram of the graphite plate along the line A 1 A 2  shown in  FIG. 1  provided by the second embodiment of the application. 
         FIG. 4  is a local cross-sectional schematic diagram of the graphite plate along the line A 1 A 2  shown in  FIG. 1  provided by the third embodiment of the application. 
         FIG. 5  is a schematic diagram of a structure of a graphite plate provided by another embodiment of the application. 
         FIG. 6  is a schematic diagram of a structure of a graphite plate provided by another embodiment of the application. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     As described in the background, an epitaxial wafer obtained by using the graphite plate for epitaxial growth has poor performance uniformity. Through research, the inventor found that the reasons for the poor uniformity performance of epitaxial wafer include at least: in a process of the epitaxial growth, a substrate rotates together with the graphite plate, and due to a centrifugal force, the edge of the substrate away from the central point of the graphite plate is directly contact with the sidewall of the carrying recess of the graphite plate, which results in that a temperature of the contact position is higher than that of other positions at the sidewall of the substrate, and uneven heating of the substrate, furthermore, leading to plastic deformation of the substrate. It is precisely because of the plastic deformation of the substrate that the performance of the epitaxial wafer obtained by epitaxial growth is not uniform. 
     In view of this, an embodiment of the present application provides a graphite plate, including: a graphite plate body and a stopper. The graphite plate body includes a carrying recess and a recess located at one side of the carrying recess away from a central point of the graphite plate body. A stopper is embedded in the recess in a matching manner, and the stopper protrudes from the bottom surface of the carrying recess to form a limiting structure. In accordance with the graphite plate provided by the embodiments of the present application, by disposing a stopper at a position where a sidewall of the substrate and a sidewall of the carrying recess are in contact, the sidewall of the substrate and the sidewall of the carrying recess are spaced apart, so as to avoid direct contact between the sidewall of the substrate and the sidewall of the carrying recess causing the contact point to have a higher temperature than the non-contact position, thereby ensuring that the epitaxial wafer is heated more evenly, to improve the performance uniformity of the epitaxial wafer. 
     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 application, rather than all the embodiments. Based on the embodiments of the application, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the application. 
       FIG. 1  is a schematic diagram of a structure of a graphite plate provided by an embodiment of the application.  FIG. 2  is a local cross-sectional schematic diagram of the graphite plate along the line A 1 A 2  as shown in  FIG. 1  provided by the first embodiment of the application. Combined with  FIG. 1  and  FIG. 2 , a graphite plate  10  includes a graphite plate body  11 , the graphite plate body  11  includes a carrying recess  110 , and a recess  111  is disposed at the bottom surface of the carrying recess  110 , the recess  111  is located at the edge area of the bottom surface of the carrying recess  110 . The graphite plate  10  also includes a stopper  12 , a stopper  12  is embedded in the recess  111  in a matching manner, and the stopper  12  protrudes from the bottom surface of the carrying recess  110  to form a limiting structure. 
     The graphite plate body  11  is provided with a plurality of carrying recesses  110 , each of the carrying recesses  110  is used to carry a substrate, and an epitaxial wafer is obtained after a substrate has been epitaxial grown with a semiconductor material. The shape of the carrying recess  110  may be set according to the shape of the substrate to be grown. In an embodiment, the carrying recess  110  is a circular recess. A stopper  12  is disposed at the edge region of the carrying recess  110  away from the central point O 1  of the graphite plate  12 . Specifically, a recess  111  is provided at the bottom surface of the carrying recess  110 , and one end of the stopper  12  is embedded in the recess  111  to realize the fixing of the stopper  12 ; the other end of the stopper  12  protrudes from the bottom surface of the carrying recess  110 , which is in contact with the sidewall of the substrate to make sure that a part of the sidewall of the substrate subsequently placed in the carrying recess  110  and the sidewall of the carrying recess  110  are spaced apart, thereby avoiding direct contact between the sidewall of the substrate and the sidewall of the carrying recess  110  causing the contact point to have a higher temperature of than other positions on the sidewall of the substrate, thereby ensuring that the substrate is heated more uniformly, and thus an epitaxial wafer with better performance uniformity is obtained. 
     A shape of the stopper  12  and a shape of the recess  111  restrict each other, so that a chimeric relationship can be realized. In an embodiment, the stopper  12  is fixed to the recess  111  by means of a detachable connection. That is, the chimeric relationship between the recess  111  and the stopper  12  is reversible, that is, the stopper  12  may be connected to the recess  111  in an embedded manner, or the recess  111  and the stopper  12  may also be released from chimera to separate from each other. The recess  111  and the stopper  12  are implemented in a detachable connection relationship, which facilitates the replacement of the stopper  12  and improves the utilization rate of the graphite plate body  11 . 
     In an embodiment, as shown in  FIG. 2 , the stopper  12  includes a stop part  122  perpendicular to the bottom surface of the carrying recess  110 , there is a predetermined spacing D between the stop part  122  and the sidewall of the carrying recess  110 . Specifically, the stopper  12  includes an integrated fixing part  121  and the stop part  122 , and the fixing part  121  is embedded in the recess  111  for connecting the stopper  12  to the graphite plate body  11 ; the stop part  122  protrudes from the bottom surface of the carrying recess  110 , which is in contact with the sidewall of the substrate, to make sure that a part of the sidewall of the substrate and the sidewall of the carrying recess  110  are spaced apart, a dividing line between the fixing part  121  and the stop part  122  as shown as the dotted line in  FIG. 2 . By setting the spacing between the stopper  122  and the sidewall of the carrying recess  110 , the heat conduction between the graphite plate body  11  and the stopper  12  can be weakened, so as to increase the temperature difference between the graphite plate body  11  and the stopper  12 , so that even if the stopper  12  is in direct contact with the substrate sidewall, it will not cause that the temperature of the contact point is too high compared to other positions on the sidewall of the substrate, thereby further improving the heating uniformity of substrate. 
     Specifically, in an embodiment, the stopper  12  is an L-shaped stopper, and an opening of the L-shaped stopper faces away from the central point O 1  of the graphite plate body  11 . In this case, in order to achieve that the recess  111  is embedded in the stopper  12  in a matching manner, in an embodiment, the cross section of the recess  111  in the thickness direction of the graphite plate body  11  is a rectangle, the recess  111  includes an opening, and the width of the opening is smaller than the width of the bottom surface of the rectangular recess  111 . In this case, when the fixing part  121  of the L-shaped stopper is embedded in the recess  111 , the upper wall of the recess  111  may form a stopping structure, so as to restrict the stopper  12  in the recess  111 , thereby releasing the chimeric relationship between the stopper  12  and the recess  111 . 
     In an embodiment, as shown in  FIG. 2 , the stopper  12  includes a stop surface S which is perpendicular to the bottom surface of the carrying recess  110 , and the stop surface S is a curved surface. That the stop surface S is perpendicular to the bottom surface of the carrying recess  110  means that the normal plane of the stop surface S is perpendicular to the bottom surface of the carrying recess  110 . The stop surface S is subsequently in contact with the sidewall of the substrate to limit the position of the substrate. 
     Specifically, the stop part  122  includes the stopper surface S. For example, the stop part  122  is in the shape of an arc-shaped plate. Thus, the stop surface S may be adapted to the shape of the sidewall of the substrate, so as to avoid a stress concentration point when the substrate and the stop surface S are in contact. For example, the surface of the stop part  122  on the side close to the central point O 1  of the carrying recess  110  is arc-shaped. The recess  111  is implemented as a strip-shaped recess, the strip-shaped recess is arc-shaped, and the strip-shaped recess, the stop part  122  and the carrying recess  110  are arranged concentrically. Thus, it can be ensured that the distance between the part of the sidewall of the substrate in contact with the stop surface S and the sidewall of the carrying recess  110  is equal everywhere, which further ensures that the substrate is evenly heated. For another example, the stop part  122  is divided into upper and lower regions, a second region Q 2  located in the recess  111  and a first region Q 1  protruding from the bottom surface of the carrying recess  110 , the interface of the first region Q 1  and the second region Q 2  is coplanar with the bottom surface of the carrying recess  110 , and the interface is shown as the dotted line in  FIG. 2 . The first region Q 1  located above includes a first surface facing the central point of the carrying recess  110 , and the first surface is an arc-shaped surface to form a stop surface for contacting the sidewall of the substrate; the second region Q 2  located below includes a second surface facing the central point of the carrying recess  110 , and the second surface is a flat surface for contacting with the sidewall of the recess  111 . The first surface and the second surface may be connected by a third surface, and the third surface is coplanar with the bottom wall of the carrying recess  110 , for example, the third surface is a crescent shape. In this case, the recess  111  may be implemented as strip-shaped recess, and the strip-shaped recess is in the shape of straight line. The linear strip-shaped recess is convenient for production and industrial implementation. 
     In an embodiment, a heat insulation layer (not shown in the figure) is further provided between the recess  111  and the stopper  12 . The heat insulation layer may be a filler disposed in the recess  111 , such as foam; the heat insulation layer may also be a coating, and the coating may be formed on at least part of the inner wall of the recess  111 , and may also be formed on at least part of the outer wall of the stopper  12 . By providing the heat insulation layer, the heat conduction between the graphite plate body  11  and the stopper  12  can be weakened, so as to increase the temperature difference between the graphite plate body  11  and the stopper  12 , so that even if the stopper  12  is in direct contact with the substrate, the temperature of the contact point will not be too high compared to the temperature of other positions on the sidewall of the substrate, thereby further improving the heating uniformity of substrate. In an embodiment, the stopper  12  is coated in the heat insulation layer. The heat insulation layer is formed on the outer surface of the stopper  12 , on the one hand, which is easy for industrial production, on the other hand, which may ensure all-round heat insulation, thereby improving heat insulation effect. 
     In an embodiment, as shown in  FIG. 1 , the carrying recess  110  and the graphite plate body  11  are both round, and the stopper  12  is symmetrical about an extension line of a connecting line between a central point O 1  of the graphite plate body  11  and a central point O 2  of the carrying recess  110 . Thus, it may ensure that the centrifugal force on the substrate reacts at the central point of the stopper  12 , so that the force on the stopper  12  is more uniform, and the reliability of the stopper is improved. 
     In an embodiment, a material of the stopper  12  includes any one of silicon carbide and quartz. Thus, on the one hand, sufficient hardness can be ensured; on the other hand, due to low heat conductivity coefficient of silicon carbide and quartz, the heat conduction between the graphite plate body  11  and the stopper  12  is further weakened, thereby further improving the uniformity of substrate heating. 
       FIG. 3  is a local cross-sectional schematic diagram of the graphite plate along the line A 1 A 2  as shown in  FIG. 1  provided by the second embodiment of the application. As shown in  FIG. 3 , the difference between the graphite plate  20  and the graphite plate  10  shown in  FIGS. 1 and 2  is only that the outer edge line at the corner Q of a L-shaped stopper  22  is arc-shaped, that is, a chamfer is disposed at the corner of the L-shaped stopper  22 , so as to facilitate the dismounting of the L-shaped stopper  22  and the recess  111 . 
       FIG. 4  is a local cross-sectional schematic diagram of the graphite plate along the line A 1 A 2  as shown in  FIG. 1  provided by the third embodiment of the application. As shown in  FIG. 4 , the difference between the graphite plate  30  and the graphite plate  10  shown in  FIGS. 1 and 2 , and the graphite plate  20  shown in  FIG. 3  is only that a heat conducting hole  320  is provided on a stopper  32 . A shape and an arrangement of the heat conducting hole  320  may be reasonably set in accordance with actual needs. In an embodiment, the stopper  32  is provided with a plurality of heat conducting holes  320  arranged in parallel, and each of heat conducting holes  320  penetrates the stopper  32  in the thickness direction. The thickness direction of the stopper  32  refers to the direction from the central point O 1  of the graphite plate body  11  to the central point O 2  of the carrying recess  110 . 
     In accordance with the graphite plate  30  provided in the embodiment, the heat dissipation of the stopper  32  is improved by using the heat conducting hole  320 , and it is further avoided that the stopper  32  is overheated, thereby balancing the heating of substrate. 
       FIG. 5  is a schematic diagram of a structure of a graphite plate provided by another embodiment of the application. As shown in  FIG. 5 , the difference between a graphite plate  40  and the graphite plate  10  shown in  FIG. 1  is only that the position of the recess is different. Specifically, in the graphite plate  40 , a recess  411  is disposed at the sidewall of the carrying recess  410  away from the central point O 1  of the graphite plate body  41 , and the opening of the recess  411  faces the central point O 1  of the graphite plate body  41 . Thus, the production process is simpler, the upper wall thickness of the recess  411  is larger, and the structure is more reliable. 
     The recess  411  may be disposed at any position of the sidewall of the carrying recess  410 , for example, as shown in  FIG. 5 , the recess  411  is disposed at the bottom of the sidewall of the carrying recess  410 , a part of sidewall of the recess  411  is flush with bottom wall of the carrying recess  410 . 
     In this embodiment, a stopper  42  may adopt the structural form provided in any of the above embodiments, such as an L-shaped stopper. 
       FIG. 6  is a schematic diagram of a structure of a graphite plate provided by another embodiment of the application. As shown in  FIG. 6 , in the graphite plate  50 , a part of a stopper  52  protruding from the bottom surface of a carrying recess  510  is inclined toward the central point O 1  of the graphite plate. Thus, the stopper  52  can further limit the position of the substrate in the vertical direction to prevent the substrate from flying out of the carrying recess  510  during the rotation of graphite plate, thereby further improving reliability. 
     In an embodiment, the section of a recess  511  in the direction perpendicular to the thickness of the graphite plate body is triangular, and the opening of the recess  511  faces the central point O 1  of the graphite plate body. Thus, the stopper  52  may be implemented as a stop plate, which has a simpler structure and more convenient disassembly. 
     The above descriptions are only preferred embodiments of the application, and are not intended to limit the application. Any modifications, equivalent replacements, or the like, made within the spirit and principles of the application shall fall within the protection scope of the application.