Abstract:
A wafer carrier comprises a supporting body having an opening therein, wherein said opening in said supporting body has a concave sidewall and a bottom surface in said supporting body which is curved in cross section; a plurality of vertical supporting rods configured to support and contact a wafer received in said opening and to displace said wafer from the bottom surface of the opening in said supporting body; wherein one of said supporting rods has an end for contacting and supporting said wafer; and wherein when viewing from a top view of the wafer carrier, one of said supporting rods has a base lining on the concave sidewall of said opening in said supporting body, a first concave side opposite to the base and two second concave sides connecting the base and the first concave side.

Description:
TECHNICAL FIELD 
     The application relates to a wafer carrier, and more particularly, to a wafer carrier having a supporting body and a plurality of supporting rods formed around a periphery of the supporting body. 
     REFERENCE TO RELATED APPLICATION 
     This application claims the right of priority based on Taiwan application Serial No. 100137510, filed on Oct. 14, 2011, and the content of which is hereby incorporated by reference in its entirety. 
     DESCRIPTION OF BACKGROUND ART 
     In the manufacturing of a light-emitting diode (LED), an epitaxial layer is grown on a substrate. The substrate functions as a seed layer. When the lattice constant of the substrate is similar to the lattice constant of the epitaxial layer, a defect such as dislocation between the epitaxial layer and the substrate can be reduced. When the epitaxial layer is formed on the substrate, a stress is formed between the epitaxial layer and the substrate under different temperature regions of the reactor furnace. The stress affects the epitaxial quality of the epitaxial layer, and the stress may result in warp in the epitaxial layer. Thus, the material of the substrate is preferably similar to the material of the epitaxial layer. Because of the similar physical characteristics, such as the lattice constant, of the substrate and the epitaxial layer, the stress can be reduced. However, for some epitaxial layers, there is no suitable substrate available for use, neither the same material as the epitaxial layer, nor the same lattice constant as the epitaxial layer. Further, in consideration of the cost of the production, there may be no suitable substrate available. 
     Based on the reasons described above, once the material of the substrate and the material of the epitaxial layer are different, one or more materials of the epitaxial layer is different from the material of the substrate when the epitaxial layer is composed of a plurality of materials, or the lattice constant, the thermal expansion coefficient or the hardness of the epitaxial layer is different from that of the substrate, which results in different degrees of stress between the substrate and the epitaxial layer at different temperatures of the reactor furnace when the epitaxial layer is formed on the substrate. The stress may result in different degrees of curvature or warp. Mild stress may result in uneven heating of the epitaxial layer, which further results in poor epitaxial quality. The bending caused by the epitaxial layer warp also impacts the following process. However, if the stress is too large, the epitaxial layer may rupture. 
     The growth method of the epitaxial layer of the light emitting diode comprises vapor phase epitaxy (VPE) or metal organic chemical vapor deposition (MOCVD). The metal organic chemical vapor deposition (MOCVD) method is most commonly used to grow the epitaxial layer, such as GaN or AlGaInP. First, a substrate is disposed on a wafer carrier. After that, an epitaxial layer is formed on the substrate to form a wafer structure in a reactor furnace. The temperature of the reactor furnace changes continually during the formation of the epitaxial layer. Because the lattice constants or the thermal expansion coefficients of the epitaxial layer and the substrate are different from each other, the wafer structure has different degrees of curvature or warp in different temperature regions. 
     When the wafer structure is bowed, the wafer cannot contact with the wafer carrier closely, which results in uneven temperature distribution across the whole wafer surface. If the light-emitting layer is grown on the wafer, the light-emitting wavelength distribution range across the whole wafer is large. 
       FIG. 1  illustrates a conventional wafer carrier  10 . The wafer carrier  10  comprises a carrier body  100  having an opening  102 . A bottom surface  103  of the opening  102  is a flat surface. A wafer  104  comprises a growth substrate and an epitaxial layer grown on the growth substrate, and the epitaxial layer comprises a light-emitting layer. When the epitaxial layer is grown on the growth substrate, the furnace temperature is changed continually. Due to the lattice constants and the thermal expansion coefficients of the epitaxial layer and the growth substrate are different from each other, different degrees of curvature and warp are produced on the wafer in different temperature regions. As shown in  FIG. 1 , the wafer  104  is convex warp in a cross-sectional view. When the light-emitting layer is grown on the growth substrate, only partial surface of the wafer  104  is contacted with the bottom surface  103  of the opening  102  of the wafer carrier  10 . When the reactor furnace temperature for the growth of the light emitting layer is set at a value by considering the condition of the center area of the wafer  104 , the growth temperature of the edge of the wafer  104  is different from the growth temperature of the center of the wafer  104 . Because the growth temperature varies with different regions of the wafer  104 , the light-emitting wavelengths of different regions of the wafer  104  are also different. 
       FIG. 2  illustrates a conventional wafer carrier  20 . The wafer carrier  20  comprises a carrier body  200  having an opening  202 . A bottom surface  203  of the opening  202  is a flat surface. A wafer  204  comprises a growth substrate and an epitaxial layer grown on the growth substrate, and the epitaxial layer comprises a light-emitting layer. As illustrated in  FIG. 2 , the wafer  204  is concave warp in a cross-sectional view. When the light-emitting layer is grown on the growth substrate, only partial surface of the wafer  204  is contacted with the bottom surface  203  of the opening  202  of the wafer carrier  20 . The wafer  204  is shaken easily and may fly out when the wafer carrier  20  is rotated at high speed. 
       FIG. 3A  illustrates a conventional wafer carrier  30 . The wafer carrier  30  comprises a carrier body  300  having an opening  302 , wherein a bottom surface  303  of the opening  302  is a flat surface; and a supporting ring  305  provided around a periphery of the carrier body  300 . A wafer  304  comprises a growth substrate and an epitaxial layer grown on the growth substrate, and the epitaxial layer comprises a light-emitting layer. 
       FIG. 3B  illustrates a top view of the conventional wafer carrier  30 . As illustrated in  FIG. 3B , the top view of the supporting ring  305  is approximately a circular shape. The supporting ring  305  supports the wafer  304  around a periphery of the wafer  304  and the wafer  304  is not shaken easily. But the temperature of the wafer periphery contacted directly with the supporting ring  305  and the temperature of the wafer center not directly contacted with the supporting ring  305  are different, which results in different growth temperatures in different regions of the wafer  304  when the light-emitting layer is grown on the growth substrate. 
     SUMMARY OF THE APPLICATION 
     A wafer carrier comprises a supporting body having a height and comprising an opening, wherein a bottom surface of the opening is a curved surface; and a plurality of supporting rods formed around a periphery of the supporting body. Another aspect of the present application provides a manufacturing method of the wafer carrier. The method comprises forming an epitaxial layer on a growth substrate to form a wafer structure; measuring a curvature radius of the wafer structure; and providing the wafer carrier described above in accordance with the curvature radius of the wafer structure. 
     A wafer carrier comprises a supporting body having an opening therein, wherein said supporting body has a concave sidewall and a bottom surface in said supporting body which is curved in cross section: a plurality of supporting rods configured to support and contact a wafer received in said opening and to displace said wafer from the bottom surface of the opening in said supporting body; wherein one of said supporting rods has an end for contacting and supporting said wafer; and wherein when viewing from a top view of the wafer carrier, one of said supporting rods has a base lining on the concave sidewall of said opening in said supporting body, a first concave side opposite to the base and two second concave sides connecting the base and the first concave side. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a cross-sectional view of a conventional wafer carrier; 
         FIG. 2  illustrates a cross-sectional view of a conventional wafer carrier; 
         FIG. 3A  illustrates a cross-sectional view of a conventional wafer carrier; 
         FIG. 3B  illustrates a top view of a conventional wafer carrier; 
         FIG. 4A  illustrates a cross-sectional view of a wafer carrier in accordance with a first embodiment of the present application; 
         FIG. 4B  illustrates a top view of a wafer in accordance with a first embodiment of the present application; 
         FIG. 5A  illustrates a cross-sectional view of a wafer carrier in accordance with a second embodiment of the present application; 
         FIG. 5B  illustrates a top view of a wafer in accordance with a second embodiment of the present application; 
         FIG. 6  illustrates a top view of a wafer carrier in accordance with an embodiment of the present application; 
         FIG. 7  illustrates a top view of each supporting rod of a wafer carrier in accordance with an embodiment of the present application; 
         FIG. 8A  illustrates a top view of a wafer carrier comprising a flat edge in accordance with an embodiment of the present application; and 
         FIG. 8B  illustrates a top view of a wafer and a wafer carrier in accordance with an embodiment of the present application. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The embodiment of the application is illustrated in detail, and is plotted in the drawings. The same or the similar part is illustrated in the drawings and the specification with the same number. 
     It should be noted that an expression of an element or a material layer being formed or connected to another element or another material layer comprises the element or the material layer being directly or indirectly formed or connected to another element or another material layer, that is to say other elements or material layers can be formed there between. If the present application describes an element or a material layer being directly formed or connected to another element or material layer, that is to say no other elements or material layers are formed there between. 
       FIG. 4A  illustrates a cross-sectional view of a wafer carrier  40  in accordance with a first embodiment of the present application. As shown in  FIG. 4A , the wafer carrier  40  comprises a supporting body  400  having a height  401 ; and a plurality of supporting rods  405  formed around a periphery of the supporting body  400 . The supporting body  400  comprises an opening  402 , wherein a bottom surface  403  of the opening  402  is a curved surface. 
     A top view of the opening  402  of the wafer carrier  40  is approximately a circle shape. The opening  402  can accommodate a commercial wafer having a diameter between 2 in and 8 in. The top view of the wafer carrier  40  can be referred to  FIG. 8A .  FIG. 8A  illustrates a top view of a wafer carrier  80  in accordance with an embodiment of the present application. If the wafer carrier  80  is used to support a wafer having a diameter of 4 in or above, the top view of the opening (not shown) of the wafer carrier  80  further comprises a flat edge  803 . As shown in  FIG. 4A , a wafer  404  comprises a growth substrate and an epitaxial layer formed on the growth substrate, and the epitaxial layer comprises a light-emitting layer. The material of the epitaxial layer comprises an element selected from a group consisting of Gallium (Ga), aluminum (Al), indium (In), phosphorus (P), nitrogen (N), zinc (Zn), cadmium (Cd) and selenium (Se). 
     The material of the supporting body  400  comprises composite material, such as ceramic material; semiconductor material, such as boron nitride (BN) or silicon carbide (SiC); conductive material, such as graphite or metal, wherein the metal comprises molybdenum (Mo), tungsten (W), titanium (Ti), zirconium (Zr) or the combination thereof; or non-conductive material, such as quartz. 
     In accordance with the first embodiment of the present application, the top view of the opening  402  is approximately a circle shape, wherein the top view of the opening  402  comprises a side and a center. The bottom surface  403  of the opening  402  is a curved surface and the curved surface is a convex surface, wherein the center of the opening  402  has a height  403   a  protruding from the side of the opening  402 . The height  403   a  of the convex surface can be between 15 μm and 1000 μm. The height  403   a  of the convex surface is proportional to the diameter of the wafer  404  supported by the wafer carrier  40 , and a ratio between the diameter of the wafer  404  and the height  403   a  of the convex surface is between 7 and 125. When the epitaxial layer is formed on the growth substrate to form the wafer  404  at high temperature, the wafer  404  is bowed easily. The larger the diameter of the wafer  404  is, the more easily bowed the wafer  404  is. Thus, the height  403   a  of the convex surface is increased accompanied with the increase of the diameter of the wafer  404 . In an embodiment, the diameter of the wafer  404  is 2 in, and the height  403   a  of the convex surface of the supporting body  400  can be between 15 μm and 65 μm. In another embodiment, the diameter of the wafer  404  is 4 in, and the height  403   a  of the convex surface of the supporting body  400  can be between 15 μm and 160 μm. In another embodiment, the diameter of the wafer  404  is 6 in, the height  403   a  of the convex surface of the supporting body  400  can be between 15 μm and 400 μm. In another embodiment, the diameter of the wafer  404  is 8 in, the height  403   a  of the convex surface of the supporting body  400  can be between 15 μm and 1000 μm. 
     Because the lattice constants or the thermal expansion coefficients of the epitaxial layer and the growth substrate are different from each other, the warp degree and the warp shape of the wafer are different in different temperature regions. When the warp shape of the wafer is a convex surface, the wafer carrier  40  having the convex surface is preferably provided, which results in more even temperature distribution across the wafer surface, and more even distribution of the light-emitting wavelength of the light-emitting layer across the whole wafer. 
     In accordance with the first embodiment of the present application, the wafer carrier  40  further comprises the plurality of supporting rods  405  formed around the periphery of the supporting body  400 . In the embodiment, there are at least three supporting rods  405 . The top view of the plurality of supporting rods  405  formed around the periphery of the supporting body  400  can be referred to  FIG. 6 .  FIG. 6  illustrates a top view of a wafer carrier  60  in accordance with an embodiment of the present application. As illustrated in  FIG. 6 , there are at least three supporting rods  605 , and the plurality of supporting rods  605  is formed around the periphery of the supporting body  600 . 
     A top view of each supporting rod  405  can be referred to  FIG. 7 .  FIG. 7  illustrates a top view of each supporting rod  704  of a wafer carrier  701  in accordance with an embodiment of the present application. Each supporting rod  704  comprises a first side  702  and a plurality of second sides  703 , wherein the first side  702  comprises a first arc surface having a first curvature radius, and each of the plurality of second sides  703  comprises a second arc surface having a second curvature radius, wherein the second curvature radius is not equal to the first curvature radius. 
     As illustrated in  FIG. 4A , each of the plurality of supporting rods  405  comprises a height  405   a  smaller than the height  401  of the supporting body  400 . The height  405   a  of each of the plurality of supporting rods  405  is larger than the height  403   a  of the convex surface of the supporting body  400 . The height  405   a  of the supporting rod  405  can be between 15 μm and 1000 μm. The material of the plurality of supporting rods  405  comprises composite material, such as ceramic material; semiconductor material, such as boron nitride (BN) or silicon carbide (SiC); conductive material, such as graphite or metal, wherein the metal comprises molybdenum (Mo), tungsten (W), titanium (Ti), zirconium (Zr) or the combination thereof; or non-conductive material, such as quartz. 
       FIG. 4B  illustrates a top view of the wafer  404  in accordance with an embodiment of the present application. The wafer  404  comprises a flat edge  4041 . As illustrated in  FIG. 4A , after the wafer  404  is supported by the plurality of supporting rods  405 , the wafer  404  cannot directly contact with the bottom surface  403  of the wafer carrier  40 . Thus, it is not easy to heat the wafer  404 , especially the flat edge  4041 , and that impacts the light-emitting wavelength emitted from the light-emitting layer of the wafer  404 . This phenomenon is more pronounced accompanied with increasing the diameter of the wafer  404 .  FIG. 8A  illustrates the top view of the wafer carrier  80  comprising the flat edge  803 .  FIG. 8B  illustrates the top view of the wafer carrier  80  comprising the flat edge  803  and the wafer  804  comprising a flat edge  8041 . As illustrated in  FIG. 8A  and  FIG. 8B , when the wafer carrier  80  comprises the flat edge  803 , a gap  803   a  between a flat edge  8041  of a wafer  804  and the flat edge  803  of the wafer carrier  80  is reduced, and that improves the heating uniformity. In accordance with the embodiment illustrated in  FIG. 8B , when the wafer carrier  40  is used to support the wafer  404  having a diameter of 4 in or above and the flat edge  4041 , the wafer carrier  40  preferably comprises a flat edge. 
       FIG. 5A  illustrates a cross-sectional view of a wafer carrier  50  in accordance with a second embodiment of the present application. As shown in  FIG. 5A , the wafer carrier  50  comprises a supporting body  500  having a height  501 ; and a plurality of supporting rods  505  formed around a periphery of the supporting body  500 . The supporting body  500  comprises an opening  502 , wherein a bottom surface  503  of the opening  502  is a curved surface. 
     A top view of the opening  502  of the wafer carrier  50  is approximately a circle shape. The opening  502  can accommodate a commercial wafer having a diameter between 2 in and 8 in. The top view of the wafer carrier  50  can be referred to  FIG. 8A .  FIG. 8A  illustrates a top view of a wafer carrier  80  in accordance with an embodiment of the present application. If the wafer carrier  80  is used to support a wafer having a diameter of 4 in or above, the top view of the opening (not shown) of the wafer carrier  80  further comprises a flat edge  803 . As shown in  FIG. 5A , a wafer  504  comprises a growth substrate and an epitaxial layer formed on the growth substrate, wherein the epitaxial layer comprises a light-emitting layer. The material of the epitaxial layer comprises an element selected from a group consisting of Gallium (Ga), aluminum (Al), indium (In), phosphorus (P), nitrogen (N), zinc (Zn), cadmium (Cd) and selenium (Se). 
     The material of the supporting body  500  comprises composite material, such as ceramic material; semiconductor material, such as boron nitride (BN) or silicon carbide (SiC); conductive material, such as graphite or metal, wherein the metal comprises molybdenum (Mo), tungsten (W), titanium (Ti), zirconium (Zr) or the combination thereof; or non-conductive material, such as quartz. 
     In accordance with the second embodiment of the present application, the top view of the opening  502  is approximately a circle shape, wherein the top view of the opening  502  comprises a side and a center. The bottom surface  503  of the opening  502  is a curved surface and the curved surface is a concave surface, wherein the center of the opening  502  has a depth  503   a  sinking from the side of the opening  502 . The depth  503   a  of the concave surface can be between 15 μm and 1000 μm. The depth  503   a  of the concave surface is proportional to the diameter of the wafer  504  supported by the wafer carrier  50 , and a ratio between the diameter of the wafer  504  and the depth  503   a  of the concave surface is between 7 and 125. When the epitaxial layer is formed on the growth substrate to form the wafer  504  at high temperature, the wafer  504  is bowed easily. The larger the diameter of the wafer  504  is, the more easily bowed the wafer  504  is. Thus, the depth  503   a  of the concave surface is increased accompanied with the increase of the diameter of the wafer  504 . In the embodiment, the diameter of the wafer  504  is 2 in, and the depth  503   a  of the concave surface of the supporting body  500  can be between 15 μm and 65 μm. In another embodiment, the diameter of the wafer  504  is 4 in, and the depth  503   a  of the concave surface of the supporting body  500  can be between 15 μm and 160 μm. In another embodiment, the diameter of the wafer  504  is 6 in, and the depth  503   a  of the concave surface of the supporting body  500  can be between 15 μm and 400 μm. If the diameter of the wafer  504  is 8 in, the depth  503   a  of the concave surface of the supporting body  500  can be between 15 μm and 1000 μm. 
     Because the lattice constants or the thermal expansion coefficients of the epitaxial layer and the growth substrate are different from each other, the warp degree and the warp shape of the wafer are different in different temperature regions. When the bow shape of the wafer is a concave surface, the wafer carrier  50  having the concave surface is preferably provided, which results in more even temperature distribution across the wafer surface, and more even distribution of the light-emitting wavelength of the light-emitting layer across the whole wafer. 
     In accordance with the second embodiment of the present application, the wafer carrier  50  further comprises the plurality of supporting rods  505  formed around the periphery of the supporting body  500 . In the embodiment, there are at least three supporting rods  505 . The top view of the plurality of supporting rods  505  formed around the periphery of the supporting body  500  can be referred to  FIG. 6 .  FIG. 6  illustrates a top view of a wafer carrier  60  in accordance with an embodiment of the present application. As illustrated in  FIG. 6 , there are at least three supporting rods  605 , and the plurality of supporting rods  605  is formed around the periphery of the supporting body  600 . 
     A top view of each supporting rod  505  can be referred to  FIG. 7 .  FIG. 7  illustrates a top view of each supporting rod  704  of a wafer carrier  701  in accordance with an embodiment of the present application. Each supporting rod  704  comprises a first side  702  and a plurality of second sides  703 , wherein the first side  702  comprises a first arc surface having a first curvature radius, and each of the plurality of second sides  703  comprises a second arc surface having a second curvature radius, wherein the second curvature radius is not equal to the first curvature radius. 
     As illustrated in  FIG. 5A , each of the plurality of supporting rods  505  comprises a height  505   a  smaller than the height  501  of the supporting body  500 . The height  505   a  of each of the plurality of supporting rods  505  is larger than the depth  503   a  of the concave surface of the supporting body  500 . The height  505   a  of the supporting rod  505  can be between 15 μm and 1000 μm. The material of the plurality of supporting rods  505  comprises composite material, such as ceramic material; semiconductor material, such as boron nitride (BN) or silicon carbide (SiC); conductive material, such as graphite or metal, wherein the metal comprises molybdenum (Mo), tungsten (W), titanium (Ti), zirconium (Zr) or the combination thereof; or non-conductive material, such as quartz. 
       FIG. 5B  illustrates a top view of the wafer  504  in accordance with an embodiment of the present application. The wafer  504  comprises a flat edge  5041 . As illustrated in  FIG. 5A , after the wafer  504  is supported by the plurality of supporting rods  505 , the wafer  504  cannot directly contact with the bottom surface  503  of the wafer carrier  50 . Thus, it is not easy to heat the wafer  504 , especially the flat edge  5041 , and that impacts the light-emitting wavelength emitted from the light-emitting layer of the wafer  504 . This phenomenon is more pronounced accompanied with an increase of the diameter of the wafer  504 .  FIG. 8A  illustrates the top view of the wafer carrier  80  comprising the flat edge  803 .  FIG. 8B  illustrates the top view of the wafer carrier  80  comprising the flat edge  803  and the wafer  804  comprising a flat edge  8041 . As illustrated in  FIG. 8A  and  FIG. 8B , when the wafer carrier  80  comprises the flat edge  803 , a gap  803   a  between a flat edge  8041  of a wafer  804  and the flat edge  803  of the wafer carrier  80  is reduced, and the heating uniformity is improved. In the embodiment illustrated in  FIG. 8B , when the wafer carrier  50  is used to support the wafer  504  having a diameter of 4 in or above and the flat edge  5041 , the wafer carrier  50  preferably comprises a flat edge. 
     A manufacturing method of a wafer carrier is provided in accordance with an embodiment of the present application. The method comprises forming an epitaxial layer on a growth substrate to form a wafer structure; measuring a curvature radius of the wafer structure; and providing the wafer carrier as illustrated in the first embodiment or the second embodiment in accordance with the curvature radius of the wafer structure. When the warp shape of the wafer structure is a convex shape, a wafer carrier comprising a convex surface and a plurality of supporting rods is preferably provided, wherein the convex surface comprises a height and the range of the height can be referred to the first embodiment of the present application. When the warp shape of the wafer structure is a concave shape, a wafer carrier comprising a concave surface and a plurality of supporting rods is preferably provided, wherein the concave surface comprises a depth and the range of the depth can be referred to the second embodiment of the present application. The height of the convex surface and/or the depth of the concave surface are proportional to the diameter of the wafer. There are at least three supporting rods. The material of the epitaxial layer comprises an element selected from a group consisting of Gallium (Ga), aluminum (Al), indium (In), phosphorus (P), nitrogen (N), zinc (Zn), cadmium (Cd) and selenium (Se). 
     The principle and the efficiency of the present application illustrated by the embodiments above are not the limitation of the application. Any person having ordinary skill in the art can modify or change the aforementioned embodiments. Therefore, the protection range of the rights in the application will be listed as the following claims.