Abstract:
The present application provides a PECVD reaction chamber for processing semiconductor wafers comprising a susceptor for supporting a semiconductor wafer inside the reaction chamber wherein the susceptor comprises a plurality vertical through-bores, a moving means for moving the susceptor vertically between at least a first position and a second position, wafer-lift pins passing through the through-bores wherein the lower end of each wafer pin is attached to a lift member, and a lift member linked with an elevating mechanism for moving the wafer-lift pins vertically. The disclosed apparatus reduces contamination on the underside of the semiconductor wafer.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    The present application relates to a reaction chamber for processing semiconductor wafers, and in particular, to wafer-supporting pins for lifting semiconductor wafers inside a reaction chamber.  
         BACKGROUND OF THE INVENTION  
         [0002]    Currently, most semiconductor processing devices are single-wafer-devices processing type devices which process semiconductor wafers sheet by sheet. These single-wafer-processing type devices generally possess a susceptor inside a reaction chamber on which processing is performed while heating semiconductor wafers at a given temperature on the susceptor.  
           [0003]    A typical susceptor in a single-wafer-processing type device comprises a disc-shaped body made of metal or ceramic having high heat conductivity, and has a built-in heating element such as an electric heater. This type of susceptor has at least three through-bores into which substrate-supporting pins are inserted vertically such that the pins can move freely. When an external transfer device carries a semiconductor wafer into the reaction chamber, the substrate-supporting pins extend upwards from the through-bores to receive the semiconductor wafer. The substrate-supporting pins then retract, setting the semiconductor wafer onto the susceptor.  
           [0004]    When removing a processed semiconductor wafer from the reaction chamber, the substrate-supporting pins reextend from the through-bores, supporting the semiconductor wafer, whereupon the transfer device carries the semiconductor wafer out of the reaction chamber.  
           [0005]    To extend and retract the substrate-supporting pins out of and into the through-bores of the susceptor, a horizontal support engaging the lower end of each substrate-supporting pin is provided immediately beneath the susceptor. This horizontal support is raised and lowered by a driving device such as an air cylinder.  
           [0006]    The through-bores are typically provided on the inward side away from the periphery of a semiconductor wafer, and are blocked off from the processing environment by the semiconductor wafer during the semiconductor wafer processing.  
           [0007]    In ultrafine and high-density semiconductor devices, particle contamination on the back of the semiconductor wafer is a problem. Conventional substrate-supporting pins directly contact the back of the semiconductor wafer. Particles often adhere to the back of the wafer at these points of contact.  
           [0008]    The head of the wafer-supporting pin may be tapered to block-off the through-bore of the susceptor. Because the wafer-supporting pin is seated solely by its own weight, the pin may bind and not properly seat.  
           [0009]    If the wafer-supporting pin is situated at the periphery of the semiconductor wafer, a step in the head of the wafer-supporting pin must be provided to hold the edge of the semiconductor wafer, necessitating a whirl-stop.  
         SUMMARY OF THE INVENTION  
         [0010]    One preferred embodiment of the present invention provides a reaction chamber with substrate-supporting pins that stably raise and lower a semiconductor wafer without the substrate-supporting pin getting caught.  
           [0011]    A second embodiment provides a reaction chamber with substrate-supporting pins having a reduced contact area with the semiconductor wafer to minimize particle contamination.  
           [0012]    A third embodiment provides a reaction chamber with substrate-supporting pins that block off the through-bores from reaction gases during semiconductor wafer processing.  
           [0013]    A reaction chamber for processing semiconductor wafers according to the present invention comprises:  
           [0014]    a susceptor for supporting a semiconductor wafer inside the reaction chamber wherein the susceptor comprises a plurality vertical through-bores,  
           [0015]    a moving means for moving the susceptor vertically between at least a first position and a second position,  
           [0016]    wafer-lift pins passing through the through-bores wherein the lower end of each wafer pin is attached to a lift member, and  
           [0017]    a lift member linked with an elevating mechanism for moving the wafer-lift pins vertically.  
           [0018]    Preferably, a wafer-lift pin comprises a head with a columnar shape and a columnar body with a diameter smaller than that of the head forming a step between the head and the body.  
           [0019]    Preferably, the top of the head of the wafer-lift pin has a step for engaging the edge of a semiconductor wafer.  
           [0020]    Preferably, the disclosed mechanism comprises an elastic member to which the lift member is dynamically connected.  
           [0021]    The elevating mechanism comprises a power source and a power transmission means. The power source is a cylinder driven electrically or pneumatically. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0022]    [0022]FIG. 1( a ) is a cross section of a preferred embodiment of a reaction chamber.  
         [0023]    [0023]FIG. 1( b ) is an detail view of area “B” of FIG. 1( a ).  
         [0024]    [0024]FIG. 1( c ) is a cross section of FIG. 1( b ) across section “C”.  
         [0025]    [0025]FIG. 2 is a cross section of a preferred embodiment of a reaction chamber in which the wafer is raised by the wafer supporting pins.  
         [0026]    [0026]FIG. 3 is a cross section of a preferred embodiment of a reaction chamber during a deposition on a semiconductor wafer. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    The present invention is described in detail by reference to the accompanying figures. FIG. 1( a ) provides a cross section of a preferred embodiment of a reaction chamber according to the present invention. FIG. 1( b ) is a detail view of area “B” of FIG. 1( a ). Inside the reaction chamber  1 , a disk-shaped susceptor  4  for supporting a semiconductor wafer is provided. Above the susceptor  4 , a shower plate  2  for emitting a jet of reaction gas toward the semiconductor wafer is provided facing the susceptor  4 . In plasma-enhanced CVD (PECVD), both the susceptor and the shower plate comprise electrodes of a high-frequency power source. The susceptor  4  is raised and lowered by a susceptor drive motor  7 . During the deposition process, the susceptor  4  is raised to provide a reduced reaction area (see FIG. 3).  
         [0028]    On the surface of the susceptor  4 , a top plate  3  having about the same diameter as the susceptor is installed. The top plate  3  is preferably made of ceramic or aluminum. In an alternative embodiment, a top plate is unnecessary.  
         [0029]    Near the periphery of the susceptor  4  and the top plate  3 , at least three through-bores  16  are formed vertically at roughly even intervals. Preferably, the through-bores  16  each have a diameter of from about 10 mm to about 15 mm in the top plate  3 , and a diameter of about 6 mm to about 10 mm in the susceptor  4 . The diameter of the through-bore  16  is preferably larger in the top plate  3  than in the susceptor  4 . A shoulder portion  17  is formed at the boundary between the top plate  3  and the susceptor  4 .  
         [0030]    Inside the through-bore  16 , a wafer-lift pin  5  is inserted. The wafer-lift pin  5  comprises a head  18  with a columnar shape and a columnar body  19  with a diameter smaller than the diameter of the head  18 . The diameter of the head  18  preferably is slightly smaller than the diameter of the through-bore in the top plate. The diameter of the body  19  is preferably slightly smaller than the diameter of through-bore in the susceptor. The wafer-lift pin  5  is preferably ceramic, for example Al 2 O 3  or AlN. Preferably, a bushing  13  is installed in the gap between the body  19  of the wafer-lift pin  5  and the through-bore  16 . Bushing  13  is preferably ceramic, for example Al 2 O 3  or AlN. The bushing prevents binding of the wafer-lift pin  5  in the susceptor  4  at high temperatures if the susceptor  4  is aluminum. A step  15  is formed between the head  18  and the body  19  of the wafer-lift pin  5 . The step  15  engages with the shoulder portion  17  of the through-bore  16 . On the top surface of the head  18  of the wafer-lift pin  5 , a step  14  is provided to engage the edge a semiconductor wafer. Preferably, the surface shape of the head  18  conforms with or is similar to the surface shape of the top plate  3 . Accordingly, the head  18  is minimally affected by deposition.  
         [0031]    [0031]FIG. 1( c ) is a cross section of FIG. 1( b ) along section “C”. In one preferred embodiment, the lower end  23  of the body  19  of the wafer-lift pin has flattened profile. The lower end  23  is slidably engaged in a corresponding hole  22  provided in a toric wafer-lift bar  6 , preventing rotation of the wafer-lift pin  5 . The hole  22  of the wafer-lift bar  6  is elongated  24  to accommodate movement of the wafer-lift pin  5  from thermal expansion of the susceptor  4 .  
         [0032]    Accordingly, binding of the wafer-lift pin  5  inside the through-bore  16  is eliminated. Furthermore, because the wafer-lift pin  5  does not rotate, the orientation of step  14  on the head  18  does not vary, thus maintaining engagement with the edge of the semiconductor wafer.  
         [0033]    The wafer-lift bar  6  is raised and lowered by an elevating mechanism. The elevating mechanism preferably comprises a power source  8 , driven electrically or pneumatically, and a power transmission portion that transmits the vertical motion from power source  8  to the wafer-lift bar  6 . The transmission portion comprises a vertically extending cylinder  12  joined with the wafer-lift bar  6 , a piston  11  inserted into the cylinder  12 , and an elevating plate  20 , joined to the lower end of the piston  11 , which transmits the vertical motion from the power source  8  to the piston  11 . The transmission portion is preferably isolated by bellows  10 . As described below, between the cylinder  12  and the elevating plate  20 , is provided a spring  9 .  
         [0034]    [0034]FIG. 2 depicts the wafer-lift pins  5  in their extended positions supporting the semiconductor wafer  21 . A shaft  22  extending from the power source  8  raises the elevating plate  20 . As the piston  11  is raised, the elevating plate  20  at the lower end of the piston  11  and the lower end surface of the cylinder  12  contact, raising the cylinder  12 . As the cylinder  12  rises, the wafer-lift bar  6  rises, and the wafer-lift pin  5  extends from the surface of the susceptor  4 . Simultaneously, the bellows  10  and the spring  9  are compressed. The semiconductor wafer edge-contacting the step  14  of the head  18  of the wafer-lift pin  5  minimizes contamination.  
         [0035]    [0035]FIG. 3 depicts a reaction chamber during deposition on a semiconductor wafer  21 . From the position shown in FIG. 2, the susceptor  4  is raised by the susceptor drive motor  7 . The distance  30  between the shower plate  2  and the susceptor  4  is preferably adjusted to about 10 mm to about 20 mm. As the susceptor  4  rises, the step  15  of the wafer-lift pin  5  engages the shoulder portion  17  of the through-bore  16  raising the wafer-lift pin  5 . The wafer-lift bar  6  also rises with the wafer-lift pin  5 , pulling up the cylinder  12 . The engagement between the cylinder  12  with the piston  11  is broken, allowing the cylinder  12  to rise. Because the position of the elevating plate  20  does not change, the spring  9  provided between the cylinder  12  and the elevating plate  20  stretches. The tension of the spring  9  is transmitted through the cylinder  12  and the wafer-lift bar  6  to the wafer-lift pin  5  engaging the step  15  of the wafer-lift pin  5  to the shoulder portion  17  of the throughhole  16 , and preventing reaction gases from entering the through-bore  16  of the susceptor  4 .  
         [0036]    The embodiments illustrated and described above are provided as example of certain preferred embodiments of the present invention. Various changes and modifications can be made to the embodiments presented herein by those skilled in the art without departure from the spirit and scope of this invention, the scope of which is limited only the claims appended hereto.