Abstract:
A workpiece support pedestal includes an insulating puck having a workpiece support surface, a conductive plate underlying the puck, the puck containing electrical utilities and thermal media channels, and an axially translatable coaxial RF path assembly underlying the conductive plate. The coaxial RF path assembly includes a center conductor, a grounded outer conductor and a tubular insulator separating the center and outer conductors, whereby the puck, plate and coaxial RF path assembly comprise a movable assembly whose axial movement is controlled by a lift servo. Plural conduits extend axially through the center conductor and are coupled to the thermal media utilities. Plural electrical conductors extend axially through the tubular insulator and are connected to the electrical utilities.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 61/126,611, filed May 5, 2008. 
     
    
     BACKGROUND 
       [0002]    There is a need for a movable cathode or wafer support pedestal by which the gap or distance between the workpiece or semiconductor wafer and the ceiling can be adjusted by as much as several inches, for a 300 mm wafer diameter. One of the reasons for this need is that certain process parameters may be improved for a given process by changing the wafer-ceiling gap. There is a further need to efficiently couple RF bias power to the cathode. There is another need to transmit AC power to independent inner and outer heater elements within the cathode through pairs of supply and return AC electrical conductors. There is a yet further need to provide supply and return conduits carrying helium gas to backside cooling channels in the wafer support surface of the cathode. There a still further need to provide supply and return conduits carrying coolant for coolant passages within the cathode. There is a need to provide a conductor for carrying high voltage DC power to an electrostatic clamping (chucking) electrode that is in the cathode. The various conduits and electrical conductors must be electrically compatible with the transmission of high levels RF power to the cathode while at the same time allowing for controlled axial movement of the cathode over a large range of several (e.g., four) inches. 
       SUMMARY 
       [0003]    A workpiece support pedestal is provided within a plasma reactor chamber. The pedestal includes an insulating puck having a workpiece support surface, a conductive plate underlying the puck, the puck containing electrical utilities and thermal media channels, and an axially translatable coaxial RF path assembly underlying the conductive plate. The coaxial RF path assembly includes a center conductor, a grounded outer conductor and a tubular insulator separating the center and outer conductors, whereby the puck, plate and coaxial RF path assembly comprise a movable assembly whose axial movement is controlled by a lift servo. Plural conduits extend axially through the center conductor and are coupled to the thermal media utilities. Plural electrical conductors extend axially through the tubular insulator and are connected to the electrical utilities. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    So that the manner in which the exemplary embodiments of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be appreciated that certain well known processes are not discussed herein in order to not obscure the invention. 
           [0005]      FIG. 1  depicts a plasma reactor in accordance with one embodiment. 
           [0006]      FIG. 2  is a cross-sectional elevational view of a wafer support pedestal of the plasma reactor of  FIG. 1 . 
           [0007]      FIG. 3  is an enlarged view of a portion of the top of the wafer support pedestal of  FIG. 2 . 
           [0008]      FIG. 4  is a cross-sectional plan view taken along line  4 - 4  of  FIG. 2 . 
           [0009]      FIG. 5  is a cross-sectional plan view taken along line  5 - 5  of  FIG. 2 . 
       
    
    
       [0010]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
       DETAILED DESCRIPTION 
       [0011]    Referring to  FIG. 1 , a plasma reactor has a chamber  100  defined by a cylindrical sidewall  102 , a ceiling  104  and a floor  106  whose peripheral edge meets the sidewall  102 . The ceiling  104  may be a gas distribution plate that received process gas from a process gas supply  108 . Plasma RF source power may be inductively coupled into the chamber  100  from respective inner and outer coil antennas  110 ,  112  that are connected to respective RF source power generators  114 ,  116  through respective RF impedance match elements  118 ,  120 . The ceiling or gas distribution plate  104  may be formed of a non-conductive material in order to permit inductive coupling of RF power from the coil antennas  110 ,  112  through the ceiling  104  and into the chamber  100 . Alternatively, or in addition, RF plasma source power from another RF generator  122  and impedance match  124  may be capacitively coupled from an overhead electrode  126 . In order to permit inductive coupling into the chamber  100  of RF power from the coil antennas  110 ,  112 , the overhead electrode  126  is provided in the form of a Faraday shield of the type well-known in the art consisting of an outer ring conductor  128  and plural conductive fingers  130  extending radially inwardly from the outer ring conductive  128 . Alternatively, in the absence of the coil antennas  110 ,  112 , the ceiling  104  may be formed of metal and serve as the overhead electrode connected to the RF generator  122  through the impedance match  124 . The sidewall  104  and floor  106  may be formed of metal and connected to ground. A vacuum pump  132  evacuates the chamber  100  through the floor  106 . 
         [0012]    A wafer support pedestal  200  is provided inside the chamber  100  and has a top wafer support surface  200   a  and a bottom end  200   b  below the floor  106 . RF bias power is coupled through the pedestal bottom  200   b  to a cathode electrode (to be described) below the top surface  200   a  through a coaxial feed functioning as an RF transmission line. The coaxial feed, which is described in detail below, includes an axially movable coaxial assembly  234  consisting of a cylindrical inner conductor  235  surrounded by an annular insulator layer  250  and an outer annular conductor  253  surrounding the annular insulator layer  250 . As will be described in detail below, plural coolant conduits and plural gas conduits (not shown in  FIG. 1 ) within the center conductor provide supply and return paths for coolant and helium gas from the pedestal bottom  200   b  to coolant passages underneath the wafer support surface  200   a  and to backside helium channels in the wafer support surface  200   a,  respectively. Electrical lines (not shown in  FIG. 1 ) extend from the pedestal bottom  200   b  through the above-mentioned annular insulator layer to carry AC power to internal heaters below the pedestal top surface  200   a,  DC power to an internal chucking electrode below the top surface  200   a  and to carry optical temperature probe signals from the sensors at the top surface  200   a  and out through the pedestal bottom  200   b.  The internal structure of the pedestal  200  will now be described in detail. 
         [0013]    Referring to  FIG. 2 , the pedestal  200  includes elements mechanically coupled to the coaxial movable assembly  234  and which therefore elevate and depress with the movable assembly  234 . The elements mechanically coupled to the movable assembly include a disk-shaped insulating puck or top layer  205  forming the top wafer support surface  200   a,  and may be formed of aluminum nitride, for example. The puck  205  contains an internal chucking electrode  210  close to the top surface  200   a.  The puck  205  also contains inner and outer electrically resistive heating elements  215 ,  216 . Underlying the puck  205  is a disk-shaped metal plate  220 , which may be formed of aluminum. The wafer support surface  200   a  is the top surface of the puck  205  and has open channels  207  through which a thermally conductive gas such as helium is pumped to govern thermal conductivity between the backside of a wafer being processed on the support surface  200   a  and the puck  205 . Internal coolant passages  225  are provided in the puck  205  or alternatively in the plate  220 . A disk-shaped quartz insulator or planar insulator layer  230  underlies the metal plate  220 . A conductive support dish  237  underlies the insulator  230  and may support a cylindrical wall  239  surrounding the insulator  230 , the plate  220  and the puck  205 . The puck  205 , the metal plate  220 , the insulator layer  230  and the support dish  237  are elements of the pedestal  200  which elevate and depress with the movable coaxial assembly  234 , and are mechanically coupled to the movable coaxial assembly  234  as follows: the support dish  237  engages the coaxial outer conductor  253 ; the insulator  230  engages the coaxial insulator sleeve  250 ; the metal plate  220  engages the coaxial inner conductor  235 . 
         [0014]    The coaxial inner conductor  235  is configured as an elongate stem or cylindrical rod extending from the pedestal bottom  200   b  through the metal plate  220 . The bottom end of the stem  235  is connected to one or both of two RF bias power generators  240 ,  242 , through respective RF impedance match elements  244 ,  246 . The stem  235  conducts RF bias power to the plate  220 , and the plate  220  functions as an RF-hot cathode electrode. An annular insulator layer or sleeve  250  surrounds the inner conductor or stem  235 . An annular outer conductor  253  surrounds the insulator sleeve  250  and the inner conductor  235 , the coaxial assembly  235 ,  250 ,  253  being a coaxial transmission line for the RF bias power. 
         [0015]    The outer conductor  253  is constrained by a tubular stationary guide sleeve  255  connected to the floor  106 . A movable tubular guide sleeve  260  extending from the support dish  237  surrounds the stationary guide sleeve  255 . An outer stationary guide sleeve  257  extending from the floor  106  constrains the movable guide sleeve  260 . A bellows  262  confined by the movable guide sleeve  260  is compressed between a top surface  255   a  of the stationary guide sleeve  255  and a bottom surface  237   a  of the dish  237 . 
         [0016]    A lift servo  265  anchored to the frame of the reactor (e.g., to which the sidewall  102  and floor  106  are anchored) is mechanically linked to the movable coaxial assembly  234  and elevates and depresses the axial position of the movable coaxial assembly  234 . The floor  106 , the sidewall  102 , the servo  265  and the stationary tube  255  form a stationary assembly. 
         [0017]    A grate  226  extends from the pedestal side wall  239  toward the chamber side wall  102  ( FIG. 1 ). Referring still to  FIG. 2 , a process ring  218  overlies the edge of the puck  205 . An insulation ring  222  provides electrical insulation between the plate  220  and the pedestal side wall  239 . A skirt  224  extends from the floor and surrounds the pedestal side wall  239 . Lift pins  228  extend through the floor  106 , the dish  237 , the insulator plate  230 , the metal plate  220  and the puck  205 . 
         [0018]    Referring now to  FIG. 3 , in one embodiment the outer conductor  253  has its top end  253   a  spaced sufficiently below the aluminum plate  220  to avoid electrical contact between them. As shown in  FIG. 3 , the coaxial insulator  250  has its top end  250   a  spaced sufficiently below the puck  205  to permit electrical contact between the coaxial center conductor  235  and the aluminum plate  220 . 
         [0019]    Referring again to  FIG. 2 , the outer conductor  253  of the coaxial assembly is grounded through the stationary guide sleeve  255  contacting the grounded floor  106 . The movable guide sleeve  260  and the pedestal skirt  224  and support dish  237  are also grounded by contact between the movable sleeve  260  with the stationary guide sleeve  255 . 
         [0020]    Referring now to  FIG. 2  and the cross-sectional views of  FIGS. 4 and 5 , a pair of helium conduits  270 ,  272  extend axially through the stem or inner conductor  235  from the bottom  200   b  to the top surface of the stem  235  where it interfaces with the facilities plate  220 . The helium conduits  270 ,  272  communicate with the backside helium channels  207  in the wafer support surface  200   a  of the puck  205 . Flex hoses  278  provide connection at the movable stem bottom  200   b  between the gas conduits  270 ,  272  and a stationary helium gas supply  279 . 
         [0021]    A pair of coolant conduits  280 ,  282  extend axially through the stem or inner conductor  235  through the stem  235  to communicate with the internal coolant passages  225 . Flex hoses  288  provide connection at the movable stem bottom  200   b  between the coolant conduits  280 ,  282  and a stationary coolant supply  289 . 
         [0022]    Connection between a D.C. wafer clamping voltage source  290  and the chucking electrode  210  is provided by a conductor  292  extending axially within the annular insulator  250 , and extending through the puck  205  to the chucking electrode  210 . A flexible conductor  296  provides electrical connection at the movable at the stem bottom  200   b  between the conductor  292  and the stationary D.C. voltage supply  290 . 
         [0023]    Connection between the inner heater element  215  and a first stationary AC power supply  300  is provided by a first pair of AC power conductor lines  304 ,  306  extending axially from the stem bottom  200   b  and through the insulation sleeve  250 . 
         [0024]    Connection between the outer heater element  216  and a second stationary AC power supply  302  is provided by a first pair of AC power conductor lines  307 ,  308  extending axially from the stem bottom  200   b  and through the insulation sleeve  250 . The AC lines  307 ,  308  further extend radially through the puck  205  to the outer heater element  216 . 
         [0025]    In one embodiment, an inner zone temperature sensor  330  extends through an opening in the wafer support surface  200   a  and an outer zone temperature sensor  332  extends through another opening in the wafer support surface  200   a.  Electrical (or optical) connection from the temperature sensors  330 ,  332  to sensor electronics  333  is provided at the stem bottom  200   b  by respective electrical (or optical) conductors  334 ,  336  extending from the stem bottom  200   b  through the insulator sleeve  250  and through the puck  205 . The conductor  336  extends radially through the puck  205  to the outer temperature sensor  332 . 
         [0026]    Referring to  FIGS. 3 and 5 , those portions of the electrical conductors  292 ,  304 ,  306 ,  307 ,  308 ,  334 ,  336  lying within the aluminum plate  220  are surrounded by individual electrically insulating cylindrical sleeves  370 . These arrangements are optional and other implementations may be constructed to enable electrical connection between the center conductor  235  and the plate  220  while providing insulation of the electrical conductors  292 ,  304 ,  306 ,  307 ,  308 ,  334 ,  336 . 
         [0027]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.