Abstract:
A new and improved lift mechanism which is suitably adapted for raising and lowering a pedestal/heater assembly inside a processing chamber for semiconductor wafer substrates. The pedestal/heater assembly lift mechanism includes a drive motor which is directly coupled through a shaft coupling to a threaded lead screw for rotating the lead screw in the clockwise or counterclockwise direction. The lead screw threadibly engages the pedestal/heater assembly for selectively raising and lowering the pedestal/heater assembly inside the processing chamber.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a lift mechanism for a pedestal/heater assembly in a process chamber for semiconductor substrates. More particularly, the present invention relates to a pedestal/heater assembly lift mechanism which includes a direct lead drive screw for transmitting driving rotation directly from a drive motor to a pedestal/heater assembly.  
         BACKGROUND OF THE INVENTION  
         [0002]    The fabrication of various solid state devices requires the use of planar substrates, or semiconductor wafers, on which integrated circuits are fabricated. The final number, or yield, of functional integrated circuits on a wafer at the end of the IC fabrication process is of utmost importance to semiconductor manufacturers, and increasing the yield of circuits on the wafer is the main goal of semiconductor fabrication. After packaging, the circuits on the wafers are tested, wherein non-functional dies are marked using an inking process and the functional dies on the wafer are separated and sold. IC fabricators increase the yield of dies on a wafer by exploiting economies of scale. Over 1000 dies may be formed on a single wafer which measures from six to twelve inches in diameter.  
           [0003]    In the semiconductor production industry, various processing steps are used to fabricate integrated circuits on a semiconductor wafer. These steps include the deposition of layers of different materials including metallization layers, passivation layers and insulation layers on the wafer substrate, as well as photoresist stripping and sidewall passivation polymer layer removal. In modern memory devices, for example, multiple layers of metal conductors are required for providing a multi-layer metal interconnection structure in defining a circuit on the wafer. A current drive in the semiconductor device industry is to produce semiconductors having an increasingly large density of integrated circuits which are ever-decreasing in size. These goals are achieved by scaling down the size of the circuit features in both the lateral and vertical dimensions. Vertical downscaling requires that the thickness of conductive and insulative films on the wafer be reduced by a degree which corresponds to shrinkage of the circuit features in the lateral dimension. Ultrathin device features will become increasingly essential for the fabrication of semiconductor integrated circuits in the burgeoning small/fast device technology.  
           [0004]    Chemical vapor deposition (CVD) processes are widely used to form layers of materials on a semiconductor wafer. CVD processes include thermal deposition processes, in which a gas is reacted with the heated surface of a semiconductor wafer substrate, as well as plasma-enhanced CVD processes, in which a gas is subjected to electromagnetic energy in order to transform the gas into a more reactive plasma. Forming a plasma can lower the temperature required to deposit a layer on the wafer substrate, to increase the rate of layer deposition, or both. Other CVD processes include APCVD (atmospheric pressure chemical vapor deposition), and LPCVD (low pressure chemical vapor deposition). While APCVD systems have high equipment throughput, good uniformity and the capability to process large-diameter wafers, APCVD systems consume large quantities of process gas and often exhibit poor step coverage. Currently, LPCVD is used more often than APCVD because of its lower cost, higher production throughput and superior film properties. LPCVD is commonly used to deposit nitride, TEOS oxide and polysilicon films on wafer surfaces for front-end-of-line (FEOL) processes.  
           [0005]    A conventional CVD chamber  30 , such as a Centura DxZ CVD chamber available from Applied Materials, Inc., of Santa Clara, Calif., is shown in cross-section in FIG. 1. The CVD chamber  30  includes a pedestal/heater assembly  31  having a pedestal  32  which contains a heater  92  and has a wafer supporting surface  34  on which a wafer  36  to be subjected to the CVD process is supported. Lift pins  38  are slidably mounted in the pedestal  32 , and the lower ends of the lift pins  38  are engaged by a vertically movable lift ring  39  which extends the lift pins  38  from the surface  34  of the pedestal  32 . The pedestal/heater assembly  31  is vertically movable by actuation of a mechanism which will be hereinafter described. After a robot blade (not shown) transfers the wafer  36  into the chamber  30 , the lift pins  38  initially lift the wafer  36  off the robot blade and the pedestal  32  then raises the wafer  36  from the lift pins  38  and onto the supporting surface  34 .  
           [0006]    The pedestal  32  further raises the wafer  36  into close proximity to a gas distribution plate (GDP) or “showerhead”  40  which includes passageways  42  that dispense a process gas into a processing space  56  towards the wafer  36 . The process gas is initially injected into the chamber  30  through a central gas inlet  44  in a gas-feed cover plate  46 , into a disk-shaped manifold  48 , through passageways  50  in a baffle plate  52 , through a second disk-shaped manifold  54  in the rear portion of the showerhead  40 , and finally, through the passageways  42  in the showerhead  40 . The process gas reacts with the surface of the wafer  36  to deposit the material in a layer on the wafer  36 . Unreacted process gas and reaction byproducts flow radially outwardly to an annular pumping channel  60  that surrounds the upper periphery of the pedestal  32 . The pumping channel  60  is connected through a constricted exhaust aperture  74  to a pumping plenum  76 , and a valve gate  78  gates the exhaust through an exhaust vent  80  to a vacuum pump  82 . Accordingly, the process gas and its reaction byproducts flow from the center of the showerhead  40  across the surface of the wafer  36  and toward the periphery of the pedestal  32  along radial paths, and then to the pumping channel  60  through a choke aperture  62 . The gas then flows circumferentially in the pumping channel  60 , to the exhaust aperture  74  and then through the exhaust plenum  76  and the exhaust vent  80 , respectively, to the vacuum pump  82 . Because of restrictions  62 ,  74 , in the gas flow path, the radial flow of the gas across the wafer  36  is nearly uniform in the horizontal direction.  
           [0007]    The CVD chamber  30  is capable of operation in either of two modes, a thermal mode and plasma-enhanced mode. In the thermal mode, an electrical power source  90  supplies power to the heater  92  in the top portion of the pedestal  32  to heat the pedestal  32 , and thus, the wafer  36  to a temperature sufficient to thermally activate the CVD reaction. In the plasma-enhanced mode, an RF electrical source  94  is passed by a switch  96  to the metallic showerhead  40 , which thus acts as an electrode. The showerhead  40  is electrically insulated from the lid rim  66  and the main chamber body  72  by an annular isolator ring  64 , which is typically formed of an electrically non-conductive ceramic. The pedestal  32  is connected to a biasing element  98  associated with the RF source  94  such that RF power is split between the showerhead  40  and the pedestal  32 . Sufficient voltage and power is applied by the RF source  94  to cause the process gas in the processing space  56  between the showerhead  40  and the pedestal  32  to discharge and form a plasma.  
           [0008]    A schematic view of a conventional lift mechanism  84  for the pedestal/heater assembly  31  is shown in FIG. 2 and includes a drive motor  85  that directly engages a drive pulley  86 . A driven pulley  88  is provided on the bottom end portion of a threaded lead screw  89  that threadibly engages the pedestal/heater assembly  31 . A drive belt  87  trained around the drive pulley  86  and the driven pulley  88  connects the drive motor  85  to the lead screw  89  in parallel. Thus, the drive belt  87  transmits rotation from the drive motor  85  to the lead screw  89  to facilitate raising and lowering along the Y-axis of the pedestal/heater assembly  31  in the CVD chamber  30 .  
           [0009]    The conventional belt-driven lift mechanism  31  has several drawbacks, one being inordinate failure of the drive belt  87  to precisely transfer rotation from the drive pulley  86  to the driven pulley  88  and achieve the intended vertical or Y-axis translation of the pedestal/heater assembly  31  within the chamber  30 . This problem, usually caused by a gradual loss of elasticity in the drive belt  87 , results in non-uniform coating of the CVD material on the wafer  34 , as well as potential damage to the wafer transfer robot and scratching of and/or damage to the wafer  34 . This additionally causes activation of the re-homing alarm for the lift mechanism, requiring re-working and sometimes scrapping of the wafer  34  as well as downtime and maintenance or repair of the CVD process tool. Another drawback of the conventional belt-driven lift mechanism  31  is that the horizontal force exerted against the driven pulley  88  by the drive belt  87  causes excessive and premature wearing of a lead screw bearing (not shown) through which the lead screw  89  extends. Accordingly, a new and improved lift mechanism is needed for accurately, reliably and efficiently transmitting rotational force from a drive motor to a lead screw for a pedestal/heater assembly in a process chamber.  
           [0010]    An object of the present invention is to provide a new and improved lift mechanism for a pedestal/heater assembly in a processing chamber for semiconductor wafers.  
           [0011]    Another object of the present invention is to provide a new and improved pedestal/heater assembly lift mechanism for a process chamber, which pedestal/heater assembly is characterized by reliable and essentially trouble-free operation.  
           [0012]    Another object of the present invention is to provide a new and improved pedestal/heater assembly lift mechanism which is compatible with pedestal/heater assemblies of a variety of process chambers for substrates.  
           [0013]    Still another object of the present invention is to provide a new and improved pedestal/heater assembly lift mechanism for transmitting drive rotation directly from a drive motor to a lead screw for Y-axis movement of a pedestal/heater assembly.  
           [0014]    A still further object of the present invention is to provide a new and improved pedestal/heater assembly lift mechanism which is economical and efficient in operation.  
           [0015]    Yet another object of the present invention is to provide a new and improved pedestal/heater assembly lift mechanism which significantly improves product yield in the fabrication if integrated circuits on semiconductor wafer substrates.  
           [0016]    A still further object of the present invention is to provide a new and improved pedestal/heater assembly lift mechanism which utilizes a lead screw directly coupled to a drive motor to facilitate the selective raising and lowering of a pedestal/heater assembly in a process chamber.  
           [0017]    Yet another object of the present invention is to provide a new and improved lift mechanism for a pedestal/heater assembly in a process chamber, which lift mechanism may be retrofitted to existing pedestal/heater assemblies.  
         SUMMARY OF THE INVENTION  
         [0018]    In accordance with these and other objects and advantages, the present invention is generally directed to a new and improved lift mechanism which is suitably adapted for raising and lowering a pedestal/heater assembly along a Y-axis inside a processing chamber for semiconductor wafer substrates. The pedestal/heater assembly lift mechanism includes a drive motor which is directly coupled through a shaft coupling to a threaded lead screw for rotating the lead screw in the clockwise or counterclockwise direction. The lead screw threadibly engages the pedestal/heater assembly for selectively raising and lowering the pedestal/heater assembly inside the processing chamber. Accordingly, the shaft coupling directly transmits rotation from the drive motor to the lead screw to facilitate raising or lowering of the pedestal/heat assembly without the possibility of slippage between the drive motor and the lead screw.  
           [0019]    The lift mechanism may further include a coupling support block having a coupling cradle for supporting the shaft coupling. The shaft coupling may include a motor shaft collar provided on a motor shaft engaged by the motor, a lead screw collar provided on the lead screw, and bottom coupling splines provided on the motor shaft collar and meshing with companion top coupling splines on the lead screw collar. A shaft bearing block, within which is mounted a shaft bearing through which the lead screw extends, may be provided on the coupling support block. An assembly mount block or flange may be provided on the shaft bearing block or other element of the lift assembly to facilitate retrofitting the lift assembly to a structural mounting element on the CVD or other process tool.  
         BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS  
         [0020]    The invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
           [0021]    [0021]FIG. 1 is a cross-sectional view of a typical conventional CVD (chemical vapor deposition) chamber suitable for implementation of the present invention;  
           [0022]    [0022]FIG. 2 is a schematic view of a conventional lift mechanism for a pedestal/heater assembly of the CVD chamber shown in FIG. 1;  
           [0023]    [0023]FIG. 3 is an exploded, perspective view of a pedestal/heater assembly lift mechanism of the present invention;  
           [0024]    [0024]FIG. 4 is a perspective view of the assembled lift mechanism of the present invention;  
           [0025]    [0025]FIG. 5 is a top view of the lift mechanism;  
           [0026]    [0026]FIG. 6 is a side view of the assembled lift mechanism, mounted on a process tool in implementation of the present invention; and  
           [0027]    [0027]FIG. 7 is a schematic view of the lift mechanism in implementation of the invention.  
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    The present invention has particularly beneficial utility in the selective raising and lowering of a pedestal/heater assembly inside a CVD chamber used in the deposition of material layers on a semiconductor wafer substrate, and is particularly suitable for raising and lowering a pedestal/heater assembly inside a Centura DxZ chamber available from Applied Materials, Inc., of Santa Clara, Calif. However, the invention is not so limited in application, and while references may be made to such CVD chamber, the invention is more generally applicable to raising and lowering pedestal assemblies or substrate supports in chambers used for carrying out other semiconductor fabrication processes or other industrial applications.  
         [0029]    Referring to FIGS. 3-7, an illustrative embodiment of the lift assembly of the present invention is generally indicated by reference numeral  1  and includes a drive motor  13  that drivingly engages a motor shaft  14 , as shown in FIG. 6. A typically aluminum coupling support block  2 , which may have a base portion  3  which engages the upper surface of the drive motor  13 , includes a vertical intermediate portion  5  which extends from the base portion  3  and a top portion  4  which extends horizontally from the intermediate portion  5 , in generally parallel relationship to the base portion  3 . A coupling cradle  6  is provided in the base portion  3  and intermediate portion  5 , and communicates with a top opening  7  that extends through the top portion  4 . The coupling cradle  6  further communicates with a bottom opening (not shown) which extends downwardly through the base portion  3  and receives the motor shaft  14 . A coupling access gap  12 , the purpose of which will be hereinafter described, is defined between the base portion  3  and the top portion  4 .  
         [0030]    As shown in FIG. 6, a shaft coupling  9 , contained in the coupling cradle  6  of the coupling support block  2 , couples the motor shaft  14  with the bottom unthreaded portion  16  of a lead screw  15  having a threaded portion  17  with lead screw threads  17   a  above the unthreaded portion  16 . The motor shaft  14  engages a bottom motor shaft collar  10  of the shaft coupling  9 , whereas the unthreaded lower end portion  16  of the lead screw  15  engages a top lead screw collar  11  of the shaft coupling  9 . The motor shaft collar  10  includes multiple drive splines  10   a  which mesh with multiple companion driven splines  11   a  on the lead screw collar  11  of the shaft coupling  9 . It is understood that the shaft coupling  9  may have alternative configurations known by those skilled in the art for coupling the drive collar  14  to the lead screw  15 . As shown in FIG. 7 and hereinafter further described, the threaded portion  17  of the lead screw  15  threadibly engages a pedestal/heater assembly  28  of a CVD or other processing chamber (not shown), in conventional fashion.  
         [0031]    A typically rectangular shaft bearing block  19 , which may be aluminum, is typically mounted on the upper surface of the top portion  4  of the coupling support block  2 , typically using multiple block mount bolts (not shown) which extend downwardly through respective mount bolt openings  21  in the shaft bearing block  19  and are threaded into respective bolt openings  8  in the top portion  4 . A central bearing opening  20  extends vertically through the shaft bearing block  19 . A cylindrical shaft bearing  18 , through which extends the unthreaded portion  16  of the lead screw  15 , is seated in the bearing opening  20 . A typically rectangular bearing retainer plate  24  is mounted on the upper surface of the shaft bearing block  19 , typically by extending multiple plate mount bolts (not shown) through respective mount bolt openings  25  provided in the bearing retainer plate  24  and threading the plate mount bolts into respective mount bolt openings  25   a  in the shaft bearing block  19 , to retain the shaft bearing  18  in the bearing opening  20 . The lead screw  15  extends upwardly through a central plate opening  24   a  provided in the bearing retainer plate  24 , as shown in FIG. 4.  
         [0032]    An assembly mount block  22  which may be aluminum may be welded or otherwise attached to the shaft bearing block  19  to facilitate mounting the lift assembly  1  to the CVD or other process tool (not shown). The assembly mount block  22  may include multiple mount bolt openings  23  in opposite ends thereof which receive respective mount bolts (not shown) that are threaded into a structural mounting element  27  (FIG. 6) of the process tool.  
         [0033]    Referring next to FIG. 7, in operation the lift assembly  1  is used to raise and lower a pedestal/heater assembly  28  along the Y-axis inside a processing chamber such as a CVD chamber (not shown), for such purposes as lifting a wafer (not shown) from wafer lift pins (not shown) onto the pedestal/heater assembly  28  and positioning the wafer into proximity with a plasma or gas in the processing chamber, as heretofore described with respect to FIGS. 1 and 2 in the background section. Accordingly, raising of the pedestal/heater assembly  28  is facilitated by clockwise or counterclockwise rotation of the lead screw  15 , depending on whether the lead screw  15  has right-handed or left-handed threads  17   a , by operation of the drive motor  13  as the lead screw threads  17   a  threadibly engage the interior assembly threads (not shown) inside the pedestal/heater assembly  28 . In similar fashion, lowering of the pedestal/heater assembly  28  is facilitated by rotation of the lead screw  15  by operation of the drive motor  13  in the opposite direction. It will be appreciated by those skilled in the art that because the shaft coupling  9  directly couples the motor shaft  14  to the lead screw  15 , rotation is reliably transmitted to the lead screw  15  without the possibility of slippage occurring between the motor shaft  14  and the lead screw  15  at the coupling  9 . Therefore, precise vertical or Y-axis translation of the pedestal/heater assembly  28  within the process chamber can be accomplished throughout the CVD or other process, substantially enhancing process uniformity and quality. The shaft bearing  18  stabilizes the lead screw  15  in the vertical driving orientation during raising and lowering of the pedestal/heater assembly  28 . The shaft coupling  9  may be accessed for replacement or maintenance, as needed, through the coupling access gap  12  of the coupling support block  2 .  
         [0034]    While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.