Abstract:
A wafer carrier comprises a base and a shielding plate positioned on the top surface of the base in a disassembled manner. The top surface of the base is configured to retain a plurality of wafers, and the shielding plate has a plurality of openings exposing the wafers. In particular, the shielding plate shields one portion of the base other than the other portions occupied by the wafers to prevent the reaction gases from conducting the chemical reaction to generate the reactant directly on the surface of the base. Consequently, the base is isolated from the chemical reaction, and it is not necessary to replace the base before conducting the next fabrication process or to clean the reactants on the surface of the base by thermal baking or etching.

Description:
[0001]    This present application is a divisional application of U.S. patent application Ser. No. 12/194,013, filed on Aug. 19, 2008, which claims foreign priority 097122071 filed on Jun. 13, 2008, and the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    (A) Field of the Invention 
         [0003]    The present invention relates to a wafer carrier and epitaxy machine using the same, and more particularly, to a wafer carrier using a replaceable shielding plate to prevent reaction gases from generating products directly on the surface of a base and an epitaxy machine using the same. 
         [0004]    (B) Description of the Related Art 
         [0005]    III-V compounds have been widely applied to the optical devices such as high luminance light-emitting diode (LED) and laser diode. The light-emitting structure of these optical devices has been improved from the early p/n junction structure, heterojunction structure to the multi-layer quantum well structure, and the luminance increases with improvements in light-emitting structure technology. The light-emitting structures such as the heterojunction structure and the multi-layer quantum well structure are formed on the semiconductor substrate by the molecular beam epitaxy technique or the chemical vapor phase deposition technique. In particular, the metal organic chemical vapor deposition (MOCVD) has become the most widely used technique for preparing the light-emitting structure. 
         [0006]    MOCVD apparatus includes a processing chamber, a graphite base configured to retain wafers in the processing chamber, and gas lines configured to transfer reaction gases to the surface of the wafers in the processing chamber. During the deposition process, the semiconductor substrate is placed on the graphite base and heated to a reaction temperature, and the reaction gases are then transferred to the surface of the wafers in the processing chamber via the gas lines such that the chemical reaction occurs and forms layers on the surface of the wafers in the processing chamber. 
         [0007]    The reaction gases are transferred not only to the surface of the wafers, but also to the graphite base where the reaction occurs to form reaction product on the graphite base. Therefore, before replacing the semiconductor substrate to conduct the next deposition process, the processing chamber is baked at high temperature or an etching process is performed to remove the reaction process formed on the surface of the graphite base. Then, the same graphite base can be used in the next deposition process; however, the processing time is obviously longer. To shorten the fabrication time, the prior art replaces the graphite base after each deposition process; however, the thermal conductivity is inconsistent from one graphite base to another, and replacing the graphite base after each deposition process results in greater difficulty in controlling the semiconductor substrate temperature, and consequently reduced temperature control leads to poor yield. 
       SUMMARY OF THE INVENTION 
       [0008]    One aspect of the present invention provides a wafer carrier using a replaceable shielding plate to prevent reaction gases from generating products directly on the surface of a base and an epitaxy machine using the same. 
         [0009]    A wafer carrier according to this aspect of the present invention comprises a base having a top surface configured to retain a plurality of wafers and a shielding plate positioned on the top surface of the base in a disassembled manner, wherein the shielding plate has a plurality of openings exposing the wafers. 
         [0010]    Another aspect of the present invention provides an epitaxy machine comprising a processing chamber, a plurality of inlets coupled to the processing chamber, a shaft having an upper end in the processing chamber, and a wafer carrier positioned on the upper end. 
         [0011]    Compared to the prior art, the shielding plate of the present application covers the portion of the base not configured to retain the wafers to prevent the reaction gases from generating reaction products on the top surface of the base. Consequently, it is not necessary to replace the base before performing the next deposition process, to bake the processing chamber at high temperature to remove the reaction products on the top surface, or to perform an etching process to remove the reaction products on the top surface. 
         [0012]    The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter, which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The objectives and advantages of the present invention will become apparent upon reading the following description and upon reference to the accompanying drawings in which: 
           [0014]      FIG. 1  illustrates a cross-sectional view of an epitaxy machine according to the first embodiment of the present invention; 
           [0015]      FIG. 2  illustrates a disassembled view of a wafer carrier according to the first embodiment of the present invention; 
           [0016]      FIG. 3  illustrates a partial cross-sectional view of the wafer carrier according to the first embodiment of the present invention; 
           [0017]      FIG. 4  illustrates a cross-sectional view of a wafer carrier according to the second embodiment of the present invention; 
           [0018]      FIG. 5  illustrates a disassembled view of an epitaxy machine according to the second embodiment of the present invention; 
           [0019]      FIG. 6  illustrates a partial cross-sectional view of the wafer carrier according to the second embodiment of the present invention; 
           [0020]      FIG. 7  illustrates a cross-sectional view of an epitaxy machine according to the third embodiment of the present invention; 
           [0021]      FIG. 8  illustrates a disassembled view of a wafer carrier according to the third embodiment of the present invention; 
           [0022]      FIG. 9  illustrates a partial cross-sectional view of an epitaxy machine according to the third embodiment of the present invention; 
           [0023]      FIG. 10  illustrates a cross-sectional view of an epitaxy machine according to the fourth embodiment of the present invention; 
           [0024]      FIG. 11  illustrates a disassembled view of a wafer carrier according to the fourth embodiment of the present invention; and 
           [0025]      FIG. 12  illustrates a partial cross-sectional view of the wafer carrier according to the fourth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]      FIG. 1  to  FIG. 3  illustrate an epitaxy machine  10 A according to a first embodiment of the present invention. Referring to  FIG. 1 , which is a cross-sectional view of the epitaxy machine  10 A according to the first embodiment of the present invention, the epitaxy machine  10 A comprises a processing chamber  20 , a showerhead  34  positioned on an upper portion of the processing chamber  20 , a first inlet  22  coupled to the processing chamber  20  and configured to transfer a first reactant to the processing chamber  20 , a second inlet  24  coupled to the processing chamber  20  and configured to transfer a second reactant to the processing chamber  20 , an outlet  26  configured to transfer exhaust gases from the processing chamber  20 , a shaft  32  having an upper end  32 A in the processing chamber  20 , a wafer carrier  60 A positioned on the upper end  32 A, and a heater  30  positioned below the wafer carrier  60 A. 
         [0027]      FIG. 2  is a disassembled view of the wafer carrier  60 A according to the first embodiment of the present invention, and  FIG. 3  is a partial cross-sectional view of the wafer carrier  60 A according to the first embodiment of the present invention. The wafer carrier  60 A comprises a base  40 A and a shielding plate  50 A. The base  40 A has a plurality of protrusions (retaining regions)  42  on the top surface for retaining several wafers  12 . The base  40 A can be a graphite base, which is coated with a layer of silicon carbide in advance for protecting the graphite base from the corrosive effect of the reaction gases. 
         [0028]    The shielding plate  50 A is positioned on the top surface of the base  40 A in a disassembled manner, and has a plurality of openings  52  exposing the protrusions  42  of the base  40 A, and the openings  52  are circular and have a diameter substantially equal to the diameter of the wafer  12 . The thickness of the shielding plate  50 A substantially equals the thickness of the protrusion  42  plus the thickness of the wafer  12 . The protrusion  42  of the base  40 A can fix the shielding plate  50 A on the top surface of the base  40 A, and the shielding plate  50 A will not depart from the base  40 A as the shaft  32  rotates the wafer carrier  60 A. 
         [0029]    In particular, the shielding plate  50 A covers a portion of the top surface of the base  40 A other than the protrusions  42 , i.e., the other portion of the top surface not configured to retain the wafers  12 , such that the reaction product is formed on the shielding plate  50 A rather than directly formed on the top surface of the base  40 A. Consequently, it is not necessary for the operators to replace the base  40 A before performing the next deposition process, to bake the processing chamber  20  at high temperature to remove the reaction products on the top surface, or to perform an etching process to remove the reaction products on the top surface. 
         [0030]    Furthermore, since the shielding plate  50 A is positioned on the top surface of the base  40 A in a disassembled manner, the operators need only to replace the old shielding plate  50 A with a new one before performing the next deposition process, instead of replacing the base  40 A after each deposition process. Consequently, the thermal conductivity of the base  40 A is the same, and the temperature of the wafer  12  on the base  40 A can be easily controlled to increase the yield. 
         [0031]      FIG. 4  to  FIG. 6  illustrate an epitaxy machine  10 B according to a second embodiment of the present invention.  FIG. 4  is a cross-sectional view of the epitaxy machine  10 B according to the second embodiment of the present invention. The epitaxy machine  10 B comprises a processing chamber  20 , a showerhead  34  positioned on an upper portion of the processing chamber  20 , a first inlet  22  coupled to the processing chamber  20  and configured to transfer a first reactant to the processing chamber  20 , a second inlet  24  coupled to the processing chamber  20  and configured to transfer a second reactant to the processing chamber  20 , an outlet  26  configured to transfer exhaust gases from the processing chamber  20 , a shaft  32  having an upper end  32 A in the processing chamber  20 , a wafer carrier  60 B positioned on the upper end  32 A, and a heater  30  positioned below the wafer carrier  60 B. 
         [0032]      FIG. 5  is a disassembled view of the wafer carrier  60 B according to the second embodiment of the present invention, and  FIG. 6  is a partial cross-sectional view of the wafer carrier  60 B according to the second embodiment of the present invention. The wafer carrier  60 B comprises a base  40 B and a shielding plate  50 B positioned on the top surface of the base  40 B in a disassembled manner. The base  40 B can be a graphite base, which is coated with a layer of silicon carbide in advance for protecting the graphite base from the corrosive effect of the reaction gases. 
         [0033]    The top surface of the base  40 B is a planar surface, which can retain several wafers  12 . The shielding plate  50 A has a plurality of openings  53  exposing the wafers  12 . The thickness of the shielding plate  50 B substantially equals the thickness of the wafer  12 . The wafer carrier  60 B further comprises a fixing member  44  such as bolts configured to fix the shielding plate  50 B on the base  40 B by the interference with the holes  54  of the shielding plate  50 B such that the shielding plate  50 B will not depart from the base  40 B as the shaft  32  rotates the wafer carrier  60 B. 
         [0034]    In particular, the shielding plate  50 B covers a portion of the top surface not configured to retain the wafers  12 , such that the reaction product is formed on the shielding plate  50 B rather than directly on the top surface of the base  40 B. Consequently, it is not necessary for the operators to replace the base  40 B before performing the next deposition process, to bake the processing chamber  20  at high temperature to remove the reaction products on the top surface, or to perform an etching process to remove the reaction products on the top surface. 
         [0035]    Furthermore, since the shielding plate  50 B is positioned on the top surface of the base  40 B in a disassembled manner, the operators need only to replace the used shielding plate  50 B with a new one before performing the next deposition process, instead of replacing the base  40 B after each deposition process. Consequently, the thermal conductivity of the base  40 B can be kept consistent, and the temperature of the wafer  12  on the base  40 B can be easily controlled to increase the yield. 
         [0036]      FIG. 7  to  FIG. 9  illustrate an epitaxy machine  10 C according to a third embodiment of the present invention.  FIG. 7  is a cross-sectional view of the epitaxy machine  10 C according to the third embodiment of the present invention. The epitaxy machine  10 C comprises a processing chamber  20 , a showerhead  34  positioned on an upper portion of the processing chamber  20 , a first inlet  22  coupled to the processing chamber  20  and configured to transfer a first reactant to the processing chamber  20 , a second inlet  24  coupled to the processing chamber  20  and configured to transfer a second reactant to the processing chamber  20 , an outlet  26  configured to transfer exhaust gases from the processing chamber  20 , a shaft  32  having an upper end  32 A in the processing chamber  20 , a wafer carrier  60 C positioned on the upper end  32 A, and a heater  30  positioned below the wafer carrier  60 C. 
         [0037]      FIG. 8  is a disassembled view of the wafer carrier  60 C according to the third embodiment of the present invention, and  FIG. 9  is a partial cross-sectional view of the wafer carrier  60 C according to the third embodiment of the present invention. The wafer carrier  60 C comprises a base  40 C and a shielding plate  50 C. The base  40 C includes a plurality of depressions (retaining regions)  46  on the top surface, and the depressions  46  are configured to retain several wafers  12 . The depth of the depression  46  substantially equals the thickness of the wafer  12 . Generally, the base  40 C can be a graphite base, which has been coated with a layer of silicon carbide in advance for protecting the graphite base from the corrosive effect of the reaction gases. 
         [0038]    The shielding plate  50 C is positioned on the top surface of the base  40 C in a disassembled manner, and has a plurality of openings  56  exposing the depressions  46  of the base  40 C. The openings  56  are circular and have a diameter substantially smaller than the diameter of the wafer  12 , i.e., the shielding plate  50 C covers an edge portion of the wafers  12 . The diameter of the openings  56  can be optionally designed to substantially equal the diameter of the wafers  12 . The wafer carrier  60 C further comprises a fixing member  44  such as bolts configured to fix the shielding plate  50 C on the base  40 C by the interference with the holes  54  of the shielding plate  50 C such that the shielding plate  50 C will not depart from the base  40 C as the shaft  32  rotates the wafer carrier  60 B. 
         [0039]    In particular, the shielding plate  50 C covers a portion of the top surface other than the depressions  56 , i.e., the other portion not configured to retain the wafers  12  is covered by the shielding plate  50 C, such that the reaction product is formed on the shielding plate  50 C rather than directly on the top surface of the base  40 B. Consequently, it is not necessary for the operators to replace the base  40 C before performing the next deposition process, to bake the processing chamber  20  at high temperature to remove the reaction products on the top surface, or to perform an etching process to remove the reaction products on the top surface. 
         [0040]    Furthermore, since the shielding plate  50 C is positioned on the top surface of the base  40 C in a disassembled manner, the operators need only to replace the used shielding plate  50 C with a new one before performing the next deposition process, instead of replacing the base  40 C after each deposition process. Consequently, the thermal conductivity of the base  40 C can be kept consistent, and the temperature of the wafer  12  on the base  40 C can be easily controlled to increase yield. 
         [0041]      FIG. 10  to  FIG. 12  illustrate an epitaxy machine  10 D according to a fourth embodiment of the present invention.  FIG. 10  is a cross-sectional view of the epitaxy machine  10 D according to the fourth embodiment of the present invention. The epitaxy machine  10 D comprises a processing chamber  20 , a shower head  34  positioned on an upper portion of the processing chamber  20 , a first inlet  22  coupled to the processing chamber  20  and configured to transfer a first reactant to the processing chamber  20 , a second inlet  24  coupled to the processing chamber  20  and configured to transfer a second reactant to the processing chamber  20 , an outlet  26  configured to transfer exhaust gases from the processing chamber  20 , a shaft  32  having an upper end  32 A in the processing chamber  20 , a wafer carrier  60 D positioned on the upper end  32 A, and a heater  30  positioned below the wafer carrier  60 D. 
         [0042]      FIG. 11  is a disassembled view of the wafer carrier  60 D according to the fourth embodiment of the present invention, and  FIG. 12  is a partial cross-sectional view of the wafer carrier  60 D according to the fourth embodiment of the present invention. The wafer carrier  60 D comprises a base  40 D and a shielding plate  50 C. The base  40 D includes a plurality of depressions (retaining regions)  48  on the top surface, and the depressions  48  are configured to retain several wafers  12 . The thickness of the wafer  12  substantially equals the thickness of the shielding plate  50   d  plus the depth of the depression  48 . Generally, the base  40 D can be a graphite base, which is coated with a layer of silicon carbide in advance for protecting the graphite base from the corrosive effect of the reaction gases. 
         [0043]    The shielding plate  50 D is positioned on the top surface of the base  40 D in a disassembled manner, and has a plurality of openings  58  exposing the depressions  48  of the base  40 C. The openings  58  are circular and have a diameter substantially equal to the diameter of the wafer  12 . The wafer carrier  60 D further comprises a fixing member  44  such as bolts configured to fix the shielding plate  50 D on the base  40 D by the interference with the holes  54  of the shielding plate  50 D such that the shielding plate  50 D will not depart from the base  40 D as the shaft  32  rotates the wafer carrier  60 B. 
         [0044]    In particular, the shielding plate  50 D covers a portion of the top surface other than the depressions  58 , i.e., the other portion not configured to retain the wafers  12  is covered by the shielding plate  50 D, such that the reaction product is formed on the shielding plate  50 D rather than directly on the top surface of the base  40 B. Consequently, it is not necessary for the operators to replace the base  40 D before performing the next deposition process, to bake the processing chamber  20  at high temperature to remove the reaction products on the top surface, or to perform an etching process to remove the reaction products on the top surface. 
         [0045]    Furthermore, since the shielding plate  50 D is positioned on the top surface of the base  40 D in a disassemble manner, the operators need only to replace the used shielding plate  50 D with a new one before performing the next deposition process, instead of replacing the base  40 D after each deposition process. Consequently, the thermal conductivity of the base  40 D can be kept consistent, and the temperature of the wafer  12  on the base  40 D can be easily controlled to increase the yield. 
         [0046]    Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, many of the processes discussed above can be implemented in different methodologies and replaced by other processes, or a combination thereof. 
         [0047]    Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.