Abstract:
In a plasma reactor including a reactor chamber, a workpiece support for holding a workpiece inside the chamber during processing and an inductive antenna, a window electrode proximal a wall of the chamber, the antenna and wall being positioned adjacently, the window electrode being operable as (a) a capacitive electrode accepting RF power to capacitively coupled plasma source power into the chamber, and (b) a window electrode passing RF power therethrough from said antenna into the chamber to inductively couple plasma source power into the chamber.

Description:
RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 09/350,234, filed Jul. 9, 1999 now U.S. Pat. No. 6,365,063, entitled “Plasma Reactor Having A Dual Mode RF Power Application” (currently pending), which is a continuation of application Ser. No. 08/733,555, filed Oct. 21, 1996 (now issued as U.S. Pat. No. 6,063,233), which is a continuation-in-part of application Ser. No. 08/648,254, filed May 13, 1996 (now issued as U.S. Pat. No. 6,165,311), which is a continuation-in-part of application Ser. No. 08/580,026, filed Dec. 20, 1995 (currently pending), which is a continuation application Ser. No. 08/041,796, filed Apr. 1, 1993 (now U.S. Pat. No. 5,556,501), which is a continuation of application Ser. No. 07/722,340, filed Jun. 27, 1991 (now abandoned). This application is furthermore a continuation-in-part of application Ser. No. 08/503,467, filed Jul. 18, 1995 (now issued as U.S. Pat. No. 5,770,099), which is a divisional of application Ser. No. 08/138,060, filed Oct. 15, 1993 (now issued as U.S. Pat. No. 5,477,975). This application is furthermore a continuation-in-part of application Ser. No. 08/597,577, filed Feb. 2, 1996 (now issued as U.S. Pat. No. 6,077,384), which is a continuation-in-part of application Ser. No. 08/521,668, filed Aug. 31, 1995 (now abandoned), which is a continuation-in-part of application Ser. No. 08/289,336, filed Aug. 11, 1994 (now abandoned), which is a continuation of application Ser. No. 07/984,045, filed Dec. 1, 1992 (now abandoned). In addition, U.S. application Ser. No. 08/648,265 filed May 13, 1996 (now issued as U.S. Pat. No. 6,165,311) discloses related subject matter. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention is related to heating and cooling apparatus in an inductively coupled RF plasma reactors of the type having a reactor chamber ceiling overlying a workpiece being processed and an inductive coil antenna adjacent the ceiling. 
     2. Background Art 
     In a plasma processing chamber, and especially in a high density plasma processing chamber, RF (radio frequency) power is used to generate and maintain a plasma within the processing chamber. As disclosed in detail in the above-referenced applications, it is often necessary to control temperatures of surfaces within the process chamber, independent of time varying heat loads imposed by processing conditions, or of other time varying boundary conditions. In some cases where the window/electrode is a semiconducting material, it may be necessary to control the temperature of the window/electrode within a temperature range to obtain the proper electrical properties of the window. Namely, for the window/electrode to function simultaneously as a window and as an electrode, the electrical resistivity is a function of temperature for semiconductors, and the temperature of the window/electrode is best operated within a range of temperatures. The application of RF power to generate and maintain the plasma leads to heating of surfaces within the chamber, including windows (such as used for inductive or electromagnetic coupling of RF or microwave power) or electrodes (such as used for capacitive or electrostatic coupling of RF power, or for terminating or providing a ground or return path for such capacitive or electrostatic coupling of RF power) or for combination window/electrodes. Heating of those surfaces can occur due to 1) ion or electron bombardment, 2) absorption of light emitted from excited species, 3) absorption of power directly from the electromagnetic or electrostatic field, 4) radiation from other surfaces within the chamber, 5) conduction (typically small effect at low neutral gas pressure), 6) convection (typically small effect at low mass flow rates), 7) chemical reaction (i.e. at the surface of the window or electrode due to reaction with active species in plasma). 
     Depending on the process being performed with the plasma process chamber, it may be necessary to heat the window or electrode to a temperature above that temperature which the window or electrode would reach due to internal sources of heat as described above, or it may be necessary to cool the window or electrode to a temperature below that temperature which the window or electrode would reach due to internal sources of heat during some other portion of the operating process or sequence of processes. In such cases, a method for coupling heat into the window or electrode and a method for coupling heat out of the window or electrode is required. 
     Approaches for heating window/electrodes from outside the process chamber include the following: 
     1. heating the window/electrode by an external source of radiation (i.e., a lamp or radiant heater, or an inductive heat source), 
     2. heating the window/electrode by an external source of convection (i.e. forced fluid, heated by radiation, conduction, or convection), 
     3. heating the window/electrode by an external source of conduction (i.e., a resistive heater). 
     The foregoing heating methods, without any means for cooling, limit the temperature range available for window or electrode operation to temperatures greater than the temperature which the window or electrode would reach due to internal sources of heat alone. 
     Approaches for cooling window/electrodes from outside the process chamber include the following: 
     1. cooling the window/electrode by radiation to a colder external surface, 
     2. cooling the window/electrode by an external source of convection (i.e., natural or forced), 
     3. cooling the window/electrode by conduction to an external heat sink. 
     The foregoing cooling methods, without any means for heating other than internal heat sources, limit the temperature range available for window or electrode operation to temperatures less than that temperature which the window or electrode would reach due to internal sources of heat alone. 
     Additionally the foregoing cooling methods have the following problems: 
     1. cooling the window/electrode by radiation is limited to low heat transfer rates (which in many cases are insufficient for the window or electrode temperature range required and the rate of internal heating of window or electrodes) at low temperatures due to the T 4  dependence of radiation power, where T is the absolute (Kelvin) temperature of the surface radiating or absorbing heat; 
     2. cooling the window/electrode by an external source of convection can provide large heat transfer rates by using a liquid with high thermal conductivity, and high product of density &amp; specific heat when high flow rates are used, but liquid convection cooling has the following problems: 
     A) it is limited to maximum temperature of operation by vapor pressure dependence of liquid on temperature (i.e. boiling point) (unless a phase change is allowed, which has its own problems—i.e. fixed temperature of phase change—no control range, as well safety issues), 
     B) incompatibility of liquid cooling with the electrical environment, depending upon liquid electrical properties, 
     C) general integration issues with liquid in contact with reactor structural elements. Cooling the window or electrode by an external source of convection (e.g., a cooling gas) is limited to low heat transfer rates which in many cases are insufficient for the window or electrode temperature range required and the rate of internal heating of window or electrodes; 
     3. cooling the window/electrode by conduction to an external heat sink can provide high rates of heat transfer if the contact resistance between the window or electrode and the heat sink is sufficiently low, but low contact resistance is difficult to attain in practice. 
     Approaches for both heating and cooling window/electrodes from outside the process chamber include heating the window/electrode by an external source of conduction (i.e., a resistive heater) in combination with cooling the window/electrode by conduction to an external heat sink. In one implementation, the structure is as follows: a window or electrode has a heater plate (a plate with an embedded resistive heater) adjacent an outer surface of the window electrode. Additionally, a heat sink (typically liquid cooled) is placed proximate the opposite side of the heater plate from the window or electrode. Contact resistances are present between window or electrode and heater plate, and between the heater plate and the heat sink. In such a system integrated with automatic control of window or electrode temperature, a temperature measurement is made (continuously or periodically) of the window or electrode to be controlled, the temperature measurement is compared with a set point temperature, and based on the difference between the measured and set point temperatures a controller determines through a control algorithm how much power to apply to the resistive heater, or alternatively, how much cooling to apply to the heat sink, and the controller commands output transducers to output the determined heating or cooling levels. The process is repeated (continuously or periodically) until some desired degree of convergence of the window or electrode temperature to the set point temperature has occurs, and the control system remains active ready to respond to changes in requirements of heating or cooling levels due to changes in internal heat or cooling levels or to changes in the set point temperature. Besides contact resistance problems that limit the cooling capability of the system to control the temperature of the window or electrode, the system exhibits a time lag in transferring heat from the window or electrode to the head sink as required when the internal heating or cooling load changes during plasma reactor operation. This is due in part to the contact resistance between the window or electrode and the heater, and contact resistance between the heater and the heat sink, as well as the thermal capacitance of the heater and the window or electrode. For example, as the internal heat load is increased in a process or sequence of processes, the system senses the increase by measuring an increase in window or electrode temperature. As described above, the system reduces the heater power or increases the cooling power in response to the increase in window or electrode temperature, but there is a lag time for the heat to diffuse through the window or electrode, across the contact resistance between window or electrode and heater, through the heater plate, across the contact resistance between the heater and heat sink. In addition, “excess” heat energy “stored” in the heater diffuses across the contact resistance between the heater and heat sink. This lag causes more difficulty in controlling the temperature of the window or electrode as the internal heat or cooling load changes, typically resulting in some oscillation of the window or electrode temperature about the set point. 
     A further problem for a window or window/electrode (of the type that allows electromagnetic or inductive RF or microwave power to be coupled from outside the chamber to inside the chamber via the window or window/electrode) is that the presence of heat transfer apparatus (heater and/or heat sinks) interferes with the coupling of such electromagnetic or inductive RF or microwave power, and/or the presence of RF or microwave power coupling apparatus may interfere with heat transfer between heater and/or heat sink and window or window/electrode. 
     Thus a method is sought for heating and/or cooling a window or electrode or window electrode used in a plasma processing chamber so that the temperature of the window or electrode or window/electrode may be controlled sufficiently close to a set point such that a desired process or sequence of processes may be carried out within the plasma process chamber, independent of the change of internal heating or cooling loads within the chamber or changes in other boundary conditions. 
     Additionally, a method is sought for heating and/or cooling a window or window/electrode used in a plasma processing chamber so that the temperature of the window or electrode or window/electrode may be controlled sufficiently close to a set point temperature, without interference to coupling of electromagnetic or inductive RF or microwave power through the window or window/electrode such that a desired process or sequence of processes may be carried out within the plasma process chamber, independent of the change of internal heating or cooling loads within the chamber or changes in other boundary conditions. 
     Additionally, a method is sought for heating and/or cooling an electrode or window/electrode used in a plasma processing chamber so that the temperature of the electrode or window/electrode may be controlled sufficiently close to a set point temperature, without interfering with capacitive or electrostatic coupling of RF power, or interfering with terminating or providing a ground or return path for such capacitive or electrostatic coupling of RF power, such that a desired process or sequence of processes may be carried out within the plasma process chamber, independent of the change of internal heating or cooling loads within the chamber or changes in other boundary conditions. 
     Additionally, a method is sought for heating and/or cooling a window or electrode or window/electrode used in a plasma processing chamber so that the temperature of the electrode or window/electrode may be controlled sufficiently close to a set point temperature, without interfering with capacitive or electrostatic coupling of RF power, or interfering with terminating or providing a ground or return path for such capacitive or electrostatic coupling RF power, and without interfering with coupling of electromagnetic or inductive RF or microwave power through the window or window/electrode such that a desired process or sequence of processes may be carried out within the plasma process chamber, independent of the change of internal heating or cooling loads within the chamber or changes in other boundary conditions. 
     SUMMARY OF THE INVENTION 
     In a plasma reactor including a reactor chamber, a workpiece support for holding a workpiece inside the chamber during processing and an inductive antenna, a window electrode proximal a wall of the chamber, the antenna and wall being positioned adjacently, the window electrode being operable as (a) a capacitive electrode accepting RF power to capacitively couple plasma source power into the chamber, and (b) a window electrode passing RF power therethrough from said antenna into the chamber to inductively coupled plasma source power into the chamber. A window electrode according to the present invention includes a semiconductor electrode, including an RF plasma source power supply connected to the window electrode to produce a capacitively coupled plasma. The RF plasma source power supply is connected across the workpiece support and the window electrode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cut-away side view of an inductively coupled plasma reactor of the type employed in a co-pending U.S. patent application referred to above employing generally planar coil antennas. 
     FIG. 2 is a log—log scale graph of induction field skin depth in a plasma in cm (solid line) and of electron-to-neutral elastic collision mean free path length (dashed line) as functions of pressure in torr (horizontal axis). 
     FIG. 3A is a graph of plasma ion density as a function of radial position relative to the workpiece center in the reactor of FIG. 1 for a workpiece-to-ceiling height of 4 inches, the curves labelled A and B corresponding to plasma ion densities produced by outer and inner coil antennas respectively. 
     FIG. 3B is a graph of plasma ion density as a function of radial position relative to the workpiece center in the reactor of FIG. 1 for a workpiece-to-ceiling height of 3 inches, the curves labelled A and B corresponding to plasma ion densities produced by outer and inner coil antennas respectively. 
     FIG. 3C is a graph of plasma ion density as a function of radial position relative to the workpiece center in the reactor of FIG. 1 for a workpiece-to-ceiling height of 2.5 inches, the curves labelled A and B corresponding to plasma ion densities produced by outer and inner coil antennas respectively. 
     FIG. 3D is a graph of plasma ion density as a function of radial position relative to the workpiece center in the reactor of FIG. 1 for a workpiece-to-ceiling height of 1.25 inches, the curves labelled A and B corresponding to plasma ion densities produced by outer and inner coil antennas respectively. 
     FIG. 3E is a graph of plasma ion density as a function of radial position relative to the workpiece center in the reactor of FIG. 1 for a workpiece-to-ceiling height of 0.8 inches, the curves labelled A and B corresponding to plasma ion densities produced by outer and inner coil antennas respectively. 
     FIG. 4A is a cut-away side view of a plasma reactor employing a single three-dimensional center non-planar solenoid winding. 
     FIG. 4B is an enlarged view of a portion of the reactor of FIG. 4A illustrating a preferred way of winding the solenoidal winding. 
     FIG. 4C is a cut-away side view of a plasma reactor corresponding to FIG. 4A but having a dome-shaped ceiling. 
     FIG. 4D is a cut-away side view of a plasma reactor corresponding to FIG. 4A but having a conical ceiling. 
     FIG. 4E is a cut-away side view of a plasma reactor corresponding to FIG. 4D but having a truncated conical ceiling. 
     FIG. 5 is a cut-away side view of a plasma reactor employing inner and outer vertical solenoid windings. 
     FIG. 6 is a cut-away side view of a plasma reactor corresponding to FIG. 5 in which the outer winding is flat. 
     FIG. 7A is a cut-away side view of a plasma reactor corresponding to FIG. 4 in which the center solenoid winding consists of plural upright cylindrical windings. 
     FIG. 7B is a detailed view of a first implementation of the embodiment of FIG.  7 A. 
     FIG. 7C is a detailed view of a second implementation of the embodiment of FIG.  7 A. 
     FIG. 8 is a cut-away side view of a plasma reactor corresponding to FIG. 5 in which both the inner and outer windings consist of plural upright cylindrical windings. 
     FIG. 9 is a cut-away side view of a plasma reactor corresponding to FIG. 5 in which the inner winding consists of plural upright cylindrical windings and the outer winding consists of a single upright cylindrical winding. 
     FIG. 10 is a cut-away side view of a plasma reactor in which a single solenoid winding is placed at an optimum radial position for maximum plasma ion density uniformity. 
     FIG. 11 is a cut-away side view of a plasma reactor corresponding to FIG. 4 in which the solenoid winding is an inverted conical shape. 
     FIG. 12 is a cut-away side view of a plasma reactor corresponding to FIG. 4 in which the solenoid winding is an upright conical shape. 
     FIG. 13 is a cut-away side view of a plasma reactor in which the solenoid winding consists of an inner upright cylindrical portion and an outer flat portion. 
     FIG. 14 is a cut-away side view of a plasma reactor corresponding to FIG. 10 in which the solenoid winding includes both an inverted conical portion and a flat portion. 
     FIG. 15 is a cut-away side view of a plasma reactor corresponding to FIG. 12 in which the solenoid winding includes both an upright conical portion and a flat portion. 
     FIG. 16 illustrates a combination of planar, conical and dome-shaped ceiling elements. 
     FIG. 17A illustrates a separately biased silicon side wall and ceiling and employing electrical heaters. 
     FIG. 17B illustrates separately biased inner and outer silicon ceiling portions and employing electrical heaters. 
     FIG. 18 is a cut-away cross-sectional view illustrating a first embodiment of the present invention having a thermally conductive gas interface at each face of the thermally conductive torus of FIG.  5 . 
     FIG. 19 is a cut-away cross-sectional view illustrating a second embodiment of the present invention having a thermally conductive gas interface at the one face of a thermally conductive torus integrally formed with the semiconductor window electrode. 
     FIG. 20 is a cut-away cross-sectional view illustrating a third embodiment of the present invention having a thermally conductive solid interface material at each face of the thermally conductive torus of FIG.  5 . 
     FIG. 21 is a cut-away cross-sectional view illustrating a fourth embodiment of the present invention having a thermally conductive solid interface material at the one face of a thermally conductive torus integrally formed with the semiconductor window electrode. 
     FIG. 22 is a cut-away cross-sectional view illustrating a fifth embodiment of the present invention in which the disposable silicon-containing ring of FIG. 5 is cooled by a cold plate with a thermally conductive gas interface between the cold plate and the disposable silicon ring. 
     FIG. 23 is a cut-away cross-sectional view illustrating a sixth embodiment of the present invention in which the disposable silicon-containing ring of FIG. 5 is cooled by a cold plate with a thermally conductive solid interface material between the cold plate and the disposable silicon ring. 
     FIG. 24 illustrates a seventh embodiment of the present invention in which the chamber wall and an interior chamber liner are cooled using a thermally conductive gas in the interfaces across the heat conduction paths. 
     FIG. 25 illustrates a modification of the embodiment of FIG. 24 in which the interfaces are each filled with a solid thermally conductive layer instead of the thermally conductive gas. 
     FIG. 26 illustrates the embodiment of FIG. 22 in which the ring is electrostatically clamped to seal the thermally conductive gas. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Disclosure of the Parent Application 
     In a plasma reactor having a small antenna-to-workpiece gap, in order to minimize the decrease in plasma ion density near the center region of the workpiece corresponding to the inductive antenna pattern center null, it is an object of the invention to increase the magnitude of the induced electric field at the center region. The invention accomplishes this by concentrating the turns of an inductive coil overlying the ceiling near the axis of symmetry of the antenna and maximizing the rate of change (at the RF source frequency) of magnetic flux linkage between the antenna and the plasma in that center region. 
     In accordance with the invention, a solenoidal coil around the symmetry axis simultaneously concentrates its inductive coil turns near the axis and maximizes the rate of change of magnetic flux linkage between the antenna and the plasma in the center region adjacent the workpiece. This is because the number of turns is large and the coil radius is small, as required for strong flux linkage and close mutual coupling to the plasma in the center region. (In contrast, a conventional planar coil antenna spreads its inductive field over a wide radial area, pushing the radial power distribution outward toward the periphery.) As understood in this specification, a solenoid-like antenna is one which has plural inductive elements distributed in a non-planar manner relative to a plane of the workpiece or workpiece support surface or overlying chamber ceiling, or spaced at different distances transversely to the workpiece support plane (defined by a workpiece supporting pedestal within the chamber) or spaced at different distances transversely to an overlying chamber ceiling. As understood in this specification, an inductive element is a current-carrying element mutually inductively coupled with the plasma in the chamber and/or with other inductive elements of the antenna. 
     A preferred embodiment of the invention includes dual solenoidal coil antennas with one solenoid near the center and another one at an outer peripheral radius. The two solenoids may be driven at different RF frequencies or at the same frequency, in which case they are preferably phase-locked and more preferably phase-locked in such a manner that their fields constructively interact. The greatest practical displacement between the inner and outer solenoid is preferred because it provides the most versatile control of etch rate at the workpiece center relative to etch rate at the workpiece periphery. The skilled worker may readily vary RF power, chamber pressure and electro-negativity of the process gas mixture (by choosing the appropriate ratio of molecular and inert gases) to obtain a wider range or process window in which to optimize (using the present invention) the radial uniformity of the etch rate across the workpiece. Maximum spacing between the separate inner and outer solenoids of the preferred embodiment provides the following advantages: 
     (1) maximum uniformity control and adjustment; 
     (2) maximum isolation between the inner and outer solenoids, preventing interference of the field from one solenoid with that of the other; and 
     (3) maximum space on the ceiling (between the inner and outer solenoids) for temperature control elements to optimize ceiling temperature control. 
     FIG. 4A illustrates a single solenoid embodiment (not the preferred embodiment) of an inductively coupled RF plasma reactor having a short workpiece-to-ceiling gap, meaning that the skin depth of the induction field is on the order of the gap length. As understood in this specification, a skin depth which is on the order of the gap length is that which is within a factor of ten of (i.e., between about one tenth and about ten times) the gap length. 
     FIG. 5 illustrates a dual solenoid embodiment of an inductively coupled RF plasma reactor, and is the preferred embodiment of the invention. Except for the dual solenoid feature, the reactor structure of the embodiments of FIGS. 4A and 5 is nearly the same, and will now be described with reference to FIG.  4 A. The reactor includes a cylindrical chamber  40  similar to that of FIG. 1, except that the reactor of FIG. 4A has a non-planar coil antenna  42  whose windings  44  are closely concentrated in non-planar fashion near the antenna symmetry axis  46 . While in the illustrated embodiment the windings  44  are symmetrical and their symmetry axis  46  coincides with the center axis of the chamber, the invention may be carried out differently. For example, the windings may not be symmetrical and/or their axis of symmetry may not coincide. However, in the case of a symmetrical antenna, the antenna has a radiation pattern null near its symmetry axis  46  coinciding with the center of the chamber or the workpiece center. Close concentration of the windings  44  about the center axis  46  compensates for this null and is accomplished by vertically stacking the windings  44  in the manner of a solenoid so that they are each a minimum distance from the chamber center axis  46 . This increases the product of current (I) and coil turns (N) near the chamber center axis  46  where the plasma ion density has been the weakest for short workpiece-to-ceiling heights, as discussed above with reference to FIGS. 3D and 3E. As a result, the RF power applied to the non-planar coil antenna  42  produces greater induction [d/dt][N•I] at the wafer center—at the antenna symmetry axis  46 —(relative to the peripheral regions) and therefore produces greater plasma ion density in that region, so that the resulting plasma ion density is more nearly uniform despite the small workpiece-to-ceiling height. Thus, the invention provides a way for reducing the ceiling height for enhanced plasma process performance without sacrificing process uniformity. 
     The drawing of FIG. 4B best shows a preferred implementation of the windings employed in the embodiments of FIGS. 4A and 5. In order that the windings  44  be at least nearly parallel to the plane of the workpiece  56 , they preferably are not wound in the usual manner of a helix but, instead, are preferably wound so that each individual turn is parallel to the (horizontal) plane of the workpiece  56  except at a step or transition  44   a  between turns (from one horizontal plane to the next). 
     The cylindrical chamber  40  consists of a cylindrical side wall  50  and a circular ceiling  52  integrally formed with the side wall  50  so that the side wall  50  and ceiling  52  constitute a single piece of material, such as silicon. However, the invention may be carried out with the side wall  50  and ceiling  52  formed as separate pieces, as will be described later in this specification. The circular ceiling  52  may be of any suitable cross-sectional shape such as planar (FIG.  4 A), dome (FIG.  4 C), conical (FIG.  4 D), truncated conical (FIG.  4 E), cylindrical or any combination of such shapes or curve of rotation. Such a combination will be discussed later in this specification. Generally, the vertical pitch of the solenoid  42  (i.e., its vertical height divided by its horizontal width) exceeds the vertical pitch of the ceiling  52 , even for ceilings defining 3-dimensional surfaces such as dome, conical, truncated conical and so forth. The purpose for this, at least in the preferred embodiment, is to concentrate the induction of the antenna near the antenna symmetry axis, as discussed previously in this specification. A solenoid having a pitch exceeding that of the ceiling is referred to herein as a non-conformal solenoid, meaning that, in general, its shape does not conform with the shape of the ceiling, and more specifically that its vertical pitch exceeds the vertical pitch of the ceiling. A 2-dimensional or flat ceiling has a vertical pitch of zero, while a 3-dimensional ceiling has a non-zero vertical pitch. 
     A pedestal  54  at the bottom of the chamber  40  supports a planar workpiece  56  in a workpiece support plane during processing. The workpiece  56  is typically a semiconductor wafer and the workpiece support plane is generally the plane of the wafer or workpiece  56 . The chamber  40  is evacuated by a pump (not shown in the drawing) through an annular passage  58  to a pumping annulus  60  surrounding the lower portion of the chamber  40 . The interior of the pumping annulus may be lined with a replaceable metal liner  60   a . The annular passage  58  is defined by the bottom edge  50   a  of the cylindrical side wall  50  and a planar ring  62  surrounding the pedestal  54 . Process gas is furnished into the chamber  40  through any one or all of a variety of gas feeds. In order to control process gas flow near the workpiece center, a center gas feed  64   a  can extend downwardly through the center of the ceiling  52  toward the center of the workpiece  56  (or the center of the workpiece support plane). In order to control gas flow near the workpiece periphery (or near the periphery of the workpiece support plane), plural radial gas feeds  64   b , which can be controlled independently of the center gas feed  64   a , extend radially inwardly from the side wall  50  toward the workpiece periphery (or toward the workpiece support plane periphery), or base axial gas feeds  64 c extend upwardly from near the pedestal  54  toward the workpiece periphery, or ceiling axial gas feeds  64 d can extend downwardly from the ceiling  52  toward the workpiece periphery. Etch rates at the workpiece center and periphery can be adjusted independently relative to one another to achieve a more radially uniform etch rate distribution across the workpiece by controlling the process gas flow rates toward the workpiece center and periphery through, respectively, the center gas feed  64   a  and any one of the outer gas feeds  64   b-d . This feature of the invention can be carried out with the center gas feed  64   a  and only one of the peripheral gas feeds  64   b-d.    
     The solenoidal coil antenna  42  is wound around a housing  66  surrounding the center gas feed  64 . A plasma source RF power supply  68  is connected across the coil antenna  42  and a bias RF power supply  70  is connected to the pedestal  54 . 
     Confinement of the overhead coil antenna  42  to the center region of the ceiling  52  leaves a large portion of the top surface of the ceiling  52  unoccupied and therefore available for direct contact with temperature control apparatus including, for example, plural radiant heaters  72  such as tungsten halogen lamps and a water-cooled cold plate  74  which may be formed of copper or aluminum for example, with coolant passages  74   a  extending therethrough. Preferably the coolant passages  74   a  contain a coolant of a known variety having a high thermal conductivity but a low electrical conductivity, to avoid electrically loading down the antenna or solenoid  42 . The cold plate  74  provides constant cooling of the ceiling  52  while the maximum power of the radiant heaters  72  is selected so as to be able to overwhelm, if necessary, the cooling by the cold plate  74 , facilitating responsive and stable temperature control of the ceiling  52 . The large ceiling area irradiated by the heaters  72  provides greater uniformity and efficiency of temperature control. (It should be noted that radiant heating is not necessarily required in carrying out the invention, and the skilled worker may choose to employ an electric heating element instead, as will be described later in this specification.) If the ceiling  52  is silicon, as disclosed in co-pending U.S. application Ser. No. 08/597,577 filed Feb. 2, 1996 by Kenneth S. Collins et al., then there is a significant advantage to be gained by thus increasing the uniformity and efficiency of the temperature control across the ceiling. Specifically, where a polymer precursor and etchant precursor process gas (e.g., a fluorocarbon gas) is employed and where it is desirable to scavenge the etchant (e.g., fluorine), the rate of polymer deposition across the entire ceiling  52  and/or the rate at which the ceiling  52  furnishes a fluorine etchant scavenger material (silicon) into the plasma is better controlled by increasing the contact area of the ceiling  52  with the temperature control heater  72 . The solenoid antenna  42  increases the available contact area on the ceiling  52  because the solenoid windings  44  are concentrated at the center axis of the ceiling  52 . 
     The increase in available area on the ceiling  52  for thermal contact is exploited in a preferred implementation by a highly thermally conductive torus  75  (formed of a ceramic such as aluminum nitride, aluminum oxide or silicon nitride or of a non-ceramic like silicon or silicon carbide either lightly doped or undoped) whose bottom surface rests on the ceiling  52  and whose top surface supports the cold plate  74 . One feature of the torus  75  is that it displaces the cold plate  74  well-above the top of the solenoid  42 . This feature substantially mitigates or nearly eliminates the reduction in inductive coupling between the solenoid  42  and the plasma which would otherwise result from a close proximity of the conductive plane of the cold plate  74  to the solenoid  42 . In order to prevent such a reduction in inductive coupling, it is preferable that the distance between the cold plate  74  and the top winding of the solenoid  42  be at least a substantial fraction (e.g., one half) of the total height of the solenoid  42 . Plural axial holes  75   a  extending through the torus  75  are spaced along two concentric circles and hold the plural radiant heaters or lamps  72  and permit them to directly irradiate the ceiling  52 . For greatest lamp efficiency, the hole interior surface may be lined with a reflective (e.g., aluminum) layer. The center gas feed  64   a  of FIG. 4 may be replaced by a radiant heater  72  (as shown in FIG.  5 ), depending upon the particular reactor design and process conditions. The ceiling temperature is sensed by a sensor such as a thermocouple  76  extending through one of the holes  75   a  not occupied by a lamp heater  72 . For good thermal contact, a highly thermally conductive elastomer  73  such as silicone rubber impregnated with boron nitride is placed between the ceramic torus  75  and the copper cold plate  74  and between the ceramic torus  75  and the silicon ceiling  52 . 
     As disclosed in the above-referenced co-pending application, the chamber  40  may be an all-semiconductor chamber, in which case the ceiling  52  and the side wall  50  are both a semiconductor material such as silicon or silicon carbide. As described in the above-referenced co-pending application, controlling the temperature of, and RF bias power applied to, either the ceiling  52  or the wall  50  regulates the extent to which it furnishes fluorine scavenger precursor material (silicon) into the plasma or, alternatively, the extent to which it is coated with polymer. The material of the ceiling  52  is not limited to silicon but may be, in the alternative, silicon carbide, silicon dioxide (quartz), silicon nitride, aluminum nitride or a ceramic such as aluminum oxide. 
     As described in the above-referenced co-pending application, the chamber wall or ceiling  50 ,  52  need not be used as the source of a fluorine scavenger material. Instead, a disposable semiconductor (e.g., silicon or silicon carbide) member can be placed inside the chamber  40  and maintained at a sufficiently high temperature to prevent polymer condensation thereon and permit silicon material to be removed therefrom into the plasma as fluorine scavenging material. In this case, the wall  50  and ceiling  52  need not necessarily be silicon, or if they are silicon they may be maintained at a temperature (and/or RF bias) near or below the polymer condensation temperature (and/or a polymer condensation RF bias threshold) so that they are coated with polymer from the plasma so as to be protected from being consumed. While the disposable silicon member may take any appropriate form, in the embodiment of FIG. 4 the disposable silicon member is an annular ring  62  surrounding the pedestal  54 . Preferably, the annular ring  62  is high purity silicon and may be doped to alter its electrical or optical properties. In order to maintain the silicon ring  62  at a sufficient temperature to ensure its favorable participation in the plasma process (e.g., its contribution of silicon material into the plasma for fluorine scavenging), plural radiant (e.g., tungsten halogen lamp) heaters  77  arranged in a circle under the annular ring  62  heat the silicon ring  62  through a quartz window  78 . As described in the above-referenced co-pending application, the heaters  77  are controlled in accordance with the measured temperature of the silicon ring  62  sensed by a temperature sensor  79  which may be a remote sensor such as an optical pyrometer or a fluoro-optical probe. The sensor  79  may extend partially into a very deep hole  62   a  in the ring  62 , the deepness and narrowness of the hole tending at least partially to mask temperature-dependent variations in thermal emissivity of the silicon ring  62 , so that it behaves more like a gray-body radiator for more reliable temperature measurement. 
     As described in U.S. application Ser. No. 08/597,577 referred to above, an advantage of an all-semiconductor chamber is that the plasma is free of contact with contaminant producing materials such as metal, for example. For this purpose, plasma confinement magnets  80 ,  82  adjacent the annular opening  58  prevent or reduce plasma flow into the pumping annulus  60 . To the extent any polymer precursor and/or active species succeeds in entering the pumping annulus  60 , any resulting polymer or contaminant deposits on the replaceable interior liner  60   a  may be prevented from re-entering the plasma chamber  40  by maintaining the liner  60   a  at a temperature significantly below the polymer condensation temperature, for example, as disclosed in the referenced co-pending application. 
     A wafer slit valve  84  through the exterior wall of the pumping annulus  60  accommodates wafer ingress and egress. The annular opening  58  between the chamber  40  and pumping annulus  60  is larger adjacent the wafer slit valve  84  and smallest on the opposite side by virtue of a slant of the bottom edge of the cylindrical side wall  50  so as to make the chamber pressure distribution more symmetrical with a non-symmetrical pump port location. 
     Maximum mutual inductance near the chamber center axis  46  is achieved by the vertically stacked solenoidal windings  44 . In the embodiment of FIG. 4, another winding  45  outside of the vertical stack of windings  44  but in the horizontal plane of the bottom solenoidal winding  44   a  may be added, provided the additional winding  45  is close to the bottom solenoidal winding  44   a.    
     Referring specifically now to the preferred dual solenoid embodiment of FIG. 5, a second outer vertical stack or solenoid  120  of windings  122  at an outer location (i.e, against the outer circumferential surface of the thermally conductive torus  75 ) is displaced by a radial distance  6 R from the inner vertical stack of solenoidal windings  44 . Note that in FIG. 5 confinement of the inner solenoidal antenna  42  to the center and the outer solenoidal antenna  120  to the periphery leaves a large portion of the top surface of the ceiling  52  available for direct contact with the temperature control apparatus  72 ,  74 ,  75 , as in FIG.  4 A. An advantage is that the larger surface area contact between the ceiling  52  and the temperature control apparatus provides a more efficient and more uniform temperature control of the ceiling  52 . 
     For a reactor in which the side wall and ceiling are formed of a single piece of silicon for example with an inside diameter of 12.6 in (32 cm), the wafer-to-ceiling gap is 3 in (7.5 cm), and the mean diameter of the inner solenoid was 3.75 in (9.3 cm) while the mean diameter of the outer solenoid was 11.75 in (29.3 cm) using {fraction (3/16)}″ in diameter hollow copper tubing covered with a 0.03 thick teflon insulation layer, each solenoid consisting of four turns and being 1 in (2.54 cm) high. The outer stack or solenoid  120  is energized by a second independently controllable plasma source RF power supply  96 . The purpose is to permit different user-selectable plasma source power levels to be applied at different radial locations relative to the workpiece or wafer  56  to permit compensation for known processing non-uniformities across the wafer surface, a significant advantage. In combination with the independently controllable center gas feed  64   a  and peripheral gas feeds  64   b-d , etch performance at the workpiece center may be adjusted relative to etch performance at the edge by adjusting the RF power applied to the inner solenoid  42  relative to that applied to the outer solenoid  90  and adjusting the gas flow rate through the center gas feed  64   a  relative to the flow rate through the outer gas feeds  64   b-d . While the present invention solves or at least ameliorates the problem of a center null or dip in the inductance field as described above, there may be other plasma processing non-uniformity problems, and these can be compensated in the versatile embodiment of FIG. 5 by adjusting the relative RF power levels applied to the inner and outer antennas. For effecting this purpose with greater convenience, the respective RF power supplies  68 ,  96  for the inner and outer solenoids  42 ,  90  may be replaced by a common power supply  97   a  and a power splitter  97   b  which permits the user to change the relative apportionment of power between the inner and outer solenoids  42 ,  90  while preserving a fixed phase relationship between the fields of the inner and outer solenoids  42 ,  90 . This is particularly important where the two solenoids  42 ,  90  receive RF power at the same frequency. Otherwise, if the two independent power supplies  68 ,  96  are employed, then they may be powered at different RF frequencies, in which case it is preferable to install RF filters at the output of each RF power supply  68 ,  96  to avoid off-frequency feedback from coupling between the two solenoids. In this case, the frequency difference should be sufficient to time-average out coupling between the two solenoids and, furthermore, should exceed the rejection bandwidth of the RF filters. A preferred mode is to make each frequency independently resonantly matched to the respective solenoid, and each frequency may be varied to follow changes in the plasma impedance (thereby maintaining resonance) in lieu of conventional impedance matching techniques. In other words, the RF frequency applied to the antenna is made to follow the resonant frequency of the antenna as loaded by the impedance of the plasma in the chamber. In such implementations, the frequency ranges of the two solenoids should be mutually exclusive. In an alternative mode, the two solenoids are driven at the same RF frequency and in this case it is preferable that the phase relationship between the two be such as to cause constructive interaction or superposition of the fields of the two solenoids. Generally, this requirement will be met by a zero phase angle between the signals applied to the two solenoids if they are both wound in the same sense. Otherwise, if they are oppositely wound, the phase angle is preferably 180°. In any case, coupling between the inner and outer solenoids can be minimized or eliminated by having a relatively large space between the inner and outer solenoids  42 ,  90 , as will be discussed below in this specification. 
     The range attainable by such adjustments is increased by increasing the radius of the outer solenoid  90  to increase the spacing between the inner and outer solenoids  42 ,  90 , so that the effects of the two solenoids  42 ,  90  are more confined to the workpiece center and edge, respectively. This permits a greater range of control in superimposing the effects of the two solenoids  42 ,  90 . For example, the radius of the inner solenoid  42  should be no greater than about half the workpiece radius and preferably no more than about a third thereof. (The minimum radius of the inner solenoid  42  is affected in part by the diameter of the conductor forming the solenoid  42  and in part by the need to provide a finite non-zero circumference for an arcuate—e.g., circular—current path to produce inductance.) The radius of the outer coil  90  should be at least equal to the workpiece radius and preferably 1.5 or more times the workpiece radius. With such a configuration, the respective center and edge effects of the inner and outer solenoids  42 ,  90  are so pronounced that by increasing power to the inner solenoid the chamber pressure can be raised into the hundreds of mT while providing a uniform plasma, and by increasing power to the outer solenoid  90  the chamber pressure can be reduced to on the order of 0.01 mT while providing a uniform plasma. Another advantage of such a large radius of the outer solenoid  90  is that it minimizes coupling between the inner and outer solenoids  42 ,  90 . 
     FIG. 5 indicates in dashed line that a third solenoid may be added as an option, which is desirable for a very large chamber diameter. 
     FIG. 6 illustrates a variation of the embodiment of FIG. 5 in which the outer solenoid  90  is replaced by a planar winding  100 . 
     FIG. 7A illustrates a variation of the embodiment of FIG. 4 in which the center solenoidal winding includes not only the vertical stack  42  of windings  44  but in addition a second vertical stack  102  of windings  104  closely adjacent to the first stack  42  so that the two stacks constitute a double-wound solenoid  106 . Referring to FIG. 7B, the doubly wound solenoid  106  may consist of two independently wound single solenoids  42 ,  102 , the inner solenoid  42  consisting of the windings  44   a ,  44   b , and so forth and the outer solenoid  102  consisting of the winding  104   a ,  104   b  and so forth. Alternatively, referring to FIG. 7C, the doubly wound solenoid  106  may consist of vertically stacked pairs of at least nearly co-planar windings. In the alternative of FIG. 7C, each pair of nearly co-planar windings (e.g., the pair  44   a ,  104   a  or the pair  44   b ,  104   b ) may be formed by helically winding a single conductor. The term “doubly wound” used herein refers to winding of the type shown in either FIG. 7B or  7 C. In addition, the solenoid winding may not be merely doubly wound but may be triply wound or more and in general it can consists of plural windings at each plane along the axis of symmetry. Such multiple-wound solenoids may be employed in either one or both the inner and outer solenoids  42 ,  90  of the dual-solenoid embodiment of FIG.  5 . 
     FIG. 8 illustrates a variation of the embodiment of FIG. 7A in which an outer doubly wound solenoid  110  concentric with the inner doubly wound solenoid  106  is placed at a radial distance  6 R from the inner solenoid  106 . 
     FIG. 9 illustrates a variation of the embodiment of FIG. 8 in which the outer doubly wound solenoid  110  is replaced by an ordinary outer solenoid  112  corresponding to the outer solenoid employed in the embodiment of FIG.  5 . 
     FIG. 10 illustrates another preferred embodiment in which the solenoid  42  of FIG. 5 is placed at a location displaced by a radial distance or from the center gas feed housing  66 . In the embodiment of FIG. 4, δr is zero while in the embodiment of FIG. 10 δr is a significant fraction of the radius of the cylindrical side wall  50 . Increasing δ to the extent illustrated in FIG. 10 may be helpful as an alternative to the embodiments of FIGS. 4,  5 ,  7  and  8  for compensating for non-uniformities in addition to the usual center dip in plasma ion density described with reference to FIGS. 3D and 3E. Similarly, the embodiment of FIG. 10 may be helpful where placing the solenoid  42  at the minimum distance from the chamber center axis  46  (as in FIG. 4) would so increase the plasma ion density near the center of the wafer  56  as to over-correct for the usual dip in plasma ion density near the center and create yet another non-uniformity in the plasma process behavior. In such a case, the embodiment of FIG. 10 is preferred where δr is selected to be an optimum value which provides the greatest uniformity in plasma ion density. Ideally in this case, δr is selected to avoid both under-correction and over-correction for the usual center dip in plasma ion density. The determination of the optimum value for δr can be carried out by the skilled worker by trial and error steps of placing the solenoid  42  at different radial locations and employing conventional techniques to determine the radial profile of the plasma ion density at each step. 
     FIG. 11 illustrates an embodiment in which the solenoid  42  has an inverted conical shape while FIG. 12 illustrates an embodiment in which the solenoid  42  has an upright conical shape. 
     FIG. 13 illustrates an embodiment in which the solenoid  42  is combined with a planar helical winding  120 . The planar helical winding has the effect of reducing the severity with which the solenoid winding  42  concentrates the induction field near the center of the workpiece by distributing some of the RF power somewhat away from the center. This feature may be useful in cases where it is necessary to avoid over-correcting for the usual center null. The extent of such diversion of the induction field away from the center corresponds to the radius of the planar helical winding  120 . FIG. 14 illustrates a variation of the embodiment of FIG. 13 in which the solenoid  42  has an inverted conical shape as in FIG.  11 . FIG. 15 illustrates another variation of the embodiment of FIG. 13 in which the solenoid  42  has an upright conical shape as in the embodiment of FIG.  12 . 
     The RF potential on the ceiling  52  may be increased, for example to prevent polymer deposition thereon, by reducing its effective capacitive electrode area relative to other electrodes of the chamber (e.g., the workpiece and the sidewalls). FIG. 16 illustrates how this can be accomplished by supporting a smaller-area version of the ceiling  52 ′ on an outer annulus  200 , from which the smaller-area ceiling  52 ′ is insulated. The annulus  200  may be formed of the same material (e.g., silicon) as the ceiling  52 ′ and may be of a truncated conical shape (indicated in solid line) or a truncated dome shape (indicated in dashed line). A separate RF power supply  205  may be connected to the annulus  200  to permit more workpiece center versus edge process adjustments. 
     FIG. 17A illustrates a variation of the embodiment of FIG. 5 in which the ceiling  52  and side wall  50  are separate semiconductor (e.g., silicon) pieces insulated from one another having separately controlled RF bias power levels applied to them from respective RF sources  210 ,  212  to enhance control over the center etch rate and selectivity relative to the edge. As set forth in greater detail in above-referenced U.S. application Ser. No. 08/597,577 filed Feb. 2, 1996 by Kenneth S. Collins et al., the ceiling  52  may be a semiconductor (e.g., silicon) material doped so that it will act as an electrode capacitively coupling the RF bias power applied to it into the chamber and simultaneously as a window through which RF power applied to the solenoid  42  may be inductively coupled into the chamber. The advantage of such a window-electrode is that an RF potential may be established directly over the wafer (e.g., for controlling ion energy) while at the same time inductively coupling RF power directly over the wafer. This latter feature, in combination with the separately controlled inner and outer solenoids  42 ,  90  and center and peripheral gas feeds  64   a ,  64   b  greatly enhances the ability to adjust various plasma process parameters such as ion density, ion energy, etch rate and etch selectivity at the workpiece center relative to the workpiece edge to achieve an optimum uniformity. In this combination, gas flow through individual gas feeds is individually and separately controlled to achieve such optimum uniformity of plasma process parameters. 
     FIG. 17A illustrates how the lamp heaters  72  may be replaced by electric heating elements  72 ′. As in the embodiment of FIG. 4, the disposable silicon member is an annular ring  62  surrounding the pedestal  54 . Preferably, the annular ring  62  is high purity silicon and may be doped to alter its electrical or optical properties. In order to maintain the silicon ring  62  at a sufficient temperature to ensure its favorable participation in the plasma process (e.g., its contribution of silicon material into the plasma for fluorine scavenging), plural radiant (e.g., tungsten halogen lamp) heaters  77  arranged in a circle under the annular ring  62  heat the silicon ring  62  through a quartz window  78 . As described in the above-referenced co-pending application, the heaters  77  are controlled in accordance with the measured temperature of the silicon ring  62  sensed by a temperature sensor  79  which may be a remote sensor such as an optical pyrometer or a fluoro-optical probe. The sensor  79  may extend partially into a very deep hole  62   a  in the ring  62 , the deepness and narrowness of the hole tending at least partially to mask temperature-dependent variations in thermal emissivity of the silicon ring  62 , so that it behaves more like a gray-body radiator for more reliable temperature measurement. 
     FIG. 17B illustrates another variation in which the ceiling  52  itself may be divided into an inner disk  52   a  and an outer annulus  52   b  electrically insulated from one another and separately biased by independent RF power sources  214 ,  216  which may be separate outputs of a single differentially controlled RF power source. 
     In accordance with an alternative embodiment, a user-accessible central controller  300  shown in FIGS. 17A and 17B, such as a programmable electronic controller including, for example, a conventional microprocessor and memory, is connected to simultaneously control gas flow rates through the central and peripheral gas feeds  64   a ,  64 , RF plasma source power levels applied to the inner and outer antennas  42 ,  90  and RF bias power levels applied to the ceiling  52  and side wall  50  respectively (in FIG. 17A) and the RF bias power levels applied to the inner and outer ceiling portions  52   a ,  52   b  (in FIG.  17 B), temperature of the ceiling  52  and the temperature of the silicon ring  62 . A ceiling temperature controller  218  governs the power applied by a lamp power source  220  to the heater lamps  72 ′ by comparing the temperature measured by the ceiling temperature sensor  76  with a desired temperature known to the controller  300 . A ring temperature controller  222  controls the power applied by a heater power source  224  to the heater lamps  77  facing the silicon ring  62  by comparing the ring temperature measured by the ring sensor  79  with a desired ring temperature stored known to the controller  222 . The master controller  300  governs the desired temperatures of the temperature controllers  218  and  222 , the RF power levels of the solenoid power sources  68 ,  96 , the RF power levels of the bias power sources  210 ,  212  (FIG. 17A) or  214 ,  216  (FIG.  17 B), the wafer bias level applied by the RF power source  70  and the gas flow rates supplied by the various gas supplies (or separate valves) to the gas inlets  64   a-d . The key to controlling the wafer bias level is the RF potential difference between the wafer pedestal  54  and the ceiling  52 . Thus, either the pedestal RF power source  70  or the ceiling RF power source  212  may be simply a short to RF ground. With such a programmable integrated controller, the user can easily optimize apportionment of RF source power, RF bias power and gas flow rate between the workpiece center and periphery to achieve the greatest center-to-edge process uniformity across the surface of the workpiece (e.g., uniform radial distribution of etch rate and etch selectivity). Also, by adjusting (through the controller  300 ) the RF power applied to the solenoids  42 ,  90  relative to the RF power difference between the pedestal  54  and ceiling  52 , the user can operate the reactor in a predominantly inductively coupled mode or in a predominantly capacitively coupled mode. 
     While the various power sources connected in FIG. 17A to the solenoids  42 ,  90 , the ceiling  52 , side wall  50  (or the inner and outer ceiling portions  52   a ,  52   b  as in FIG. 17B) have been described as operating at RF frequencies, the invention is not restricted to any particular range of frequencies, and frequencies other than RF may be selected by the skilled worker in carrying out the invention. 
     In a preferred embodiment of the invention, the high thermal conductivity spacer  75 , the ceiling  52  and the side wall  50  are integrally formed together from a single piece of crystalline silicon. 
     DETAILED DESCRIPTION RELATING TO THE PRESENT INVENTION 
     Referring again to FIG. 5, a preferred plasma processing chamber includes a window/electrode  52 . The window/electrode  52  is fabricated from semiconducting material as described in detail in the above-referenced applications so that it may function as both a window to RF electromagnetic or inductive power coupling from one or more external (outside chamber) antennas or coils to the plasma within the chamber and as an electrode for electrostatically or capacitively coupling RF power to the plasma within the chamber (or for terminating or providing a ground or return path for such capacitive or electrostatic coupling of RF power) or for biasing the workpiece or wafer. 
     The window/electrode  52  may be any shape as described in the above-referenced applications, but in this example is approximately a flat disc which may optionally include a cylindrical wall or skirt extending outward from the disk, such as for plasma confinement as described in the above-referenced applications. 
     The window/electrode  52  is interfaced to the heat sink  74  through the heat transfer material  75 . Typically the heat sink  74  is a water cooled metal plate, preferably a good thermal conductor such as aluminum or copper, but may optionally be a non-metal. The heat sink  74  typically a cooling apparatus preferably of the type which uses a liquid coolant such as water or ethylene-glycol that is forced through cooling passages of sufficient surface area within the heat sink  74  by a closed-loop heat exchanger or chiller. The liquid flow rate or temperature may be maintained approximately constant. Alternatively, the liquid flow rate or temperature may be an output variable of the temperature control system. 
     Preferably, radiant heating is used to apply heat to the window/electrode. The radiant heaters  72  are a plurality of tungsten filament lamps utilizing a quartz envelope filled with a mixture of halogen and inert gases. Radiant heaters are preferred to other heater types because thermal lag is minimized: The thermal capacitance of a tungsten filament lamp is very low, such that the time response of filament temperature (and thus of power output) to a change in power setting is short (&lt;1 second), and since the heat transfer mechanism between lamp filament and load is by radiation, the total thermal lag for heating is minimized. In addition, since the heat transfer mechanism between lamp filament and load is by radiation, the total thermal lag for heating is minimized. In addition, since the thermal capacitance of a tungsten filament lamp is very low, the amount of stored thermal energy in the lamp is very low, and when a reduction in heating power is called for by the control system, the filament temperature may be quickly dropped and the lamp output power thus also quickly drops. As shown in FIG. 5, the lamps  72  directly radiate the load (the window/electrode  52 ) for the fastest possible response. However, alternatively, the lamps  72  may radiate the heat transfer material  75 . Lamp heating may be provided in more than one zone, i. e. lamps at two or more radii from the axis of the window/electrode to improve thermal uniformity of window/electrode. For maximum thermal uniformity, lamps in the two or more zones may be provided with separate control, each zone utilizing its own temperature measurement, control system, and output transducer. This is especially useful when the heat flux spatial distribution from inside the chamber varies depending on process parameters, processes, process sequences, or other boundary conditions. 
     The heat transfer material  75  may be formed integrally with the window/electrode  52  that is formed of the same material into a single piece structure for elimination of a thermal contact resistance that would be present if heat transfer material  75  and window/electrode  52  were two separate parts. Alternatively, the heat transfer material  75  and the window/electrode  52  may be two parts of same or different materials that are bonded together, (preferably with a high electrical resistivity material since the window/electrode  52  is used for inductive or electromagnetic coupling of RF or microwave power using inductive antennas  90 ,  92  and/or  42 ,  44 ), minimizing the thermal contact resistance between the heat transfer material  75  and the window/electrode  52 . 
     Alternatively, the heat transfer material  75  and the window/electrode  52  may be two parts of same or different materials that are interfaced together through a contact resistance. In this case, the heat transfer material  75  is preferably made of a highly thermally conductive material of high electrical resistivity. Additionally, a low product of density and specific heat are preferred. SiC, Si, AIN, and AI 2 O 3  are examples. 
     Properties of SiC are indicated below: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Thermal conductivity: 
                 130 watt/meter * Kelvin 
               
               
                   
                 Electrical resistivity: 
                 &gt;10 5  ohm * cm 
               
               
                   
                 Specific Heat: 
                 0.66 joule/gram * Kelvin 
               
               
                   
                 Density: 
                 3.2 gram/cm 3   
               
               
                   
                   
               
             
          
         
       
     
     Silicon may also be used, if lightly (not heavily) doped (i.e. 10 14 /cm 3 ) and has the following properties: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Thermal conductivity: 
                 80 watt/meter * Kelvin 
               
               
                   
                 Electrical resistivity: 
                 20-100 ohm * cm 
               
               
                   
                 Specific Heat: 
                 0.7 joule/gram * Kelvin 
               
               
                   
                 Density: 
                 2.3 gram/cm 3   
               
               
                   
                   
               
             
          
         
       
     
     Aluminum nitride or aluminum oxide are other alternatives. 
     The heat transfer material  75  may be bonded to the heat sink  74  by techniques well known in the art (e.g., using bonding materials such as thermoplastics, epoxies, or other organic or inorganic bonding materials), without the restriction of requiring high electrical resistivity bonding material in the area proximate the heat sink  74 . This provides a very low thermal contact resistance between heat transfer material  75  and heat sink  74 . 
     The heat transfer material  75  also serves to separate the inductive antennas  90 ,  92  and/or  42 ,  44  from the heat sink  74  which if it is metal, forms a ground plane or reflector to the induction field generated in the vicinity of each inductive antenna  90 ,  92  and/or  42 ,  44 . If the heat sink  74  is metal and is too close to the inductive antenna  90 ,  92  and/or  42 ,  44 , then eddy currents are induced in the ground plane, causing power loss. In addition, the RF currents through the antenna  90 ,  92  and/or  42 ,  44  become very large to drive a given RF power, increasing I 2 R losses in the circuit. The antennas  90 ,  92  and/or  42 ,  44  are each four turns comprised of {fraction (3/16)}″ diameter water cooled copper tubing insulated with ¼″ outside diameter teflon tubing yielding coils 1″ in height. An acceptable distance between the window/electrode  52  and the metal heat sink  74  is about 2″, yielding about a 1″ distance between the top of the antenna  90 ,  92  and/or  42 ,  44  and the heat sink  74 . 
     As described above, thermal contact resistances between the heat transfer material  75  and the window, electrode  52 , and between the heat transfer material  75  and the heat sink  74  can be minimized by bonding the materials together. Also described above was an example of forming the window/electrode  52  and the heat transfer material  75  from a single piece of material, eliminating one thermal contact resistance. However, in some cases, one or both thermal contact resistances cannot be avoided. However, the thermal contact resistance(s) can be minimized in accordance with a feature of the present invention, which will now be introduced. 
     Thermal contact resistance between two parts is comprised of two parallel elements: 1) mechanical point contact between the parts, and 2) conduction through air (or other medium) between the parts. In the absence of air or other medium, the thermal contact resistance between the two parts is very high and typically unacceptable for heating and/or cooling of the window/electrode  52  due to the high heat loads imposed on it during typical plasma reactor operation. The presence of air yields a lower thermal contact resistance than mechanical point contact alone, but is typically marginal depending on the effective gap between parts, which is a function of the surface roughness and flatness of both parts. For air in the high pressure continuum regime wherein the mean-free-path in the gas is small relative to the effective gap between parts, the thermal conductivity of the air is invariant with gas pressure, and the thermal conductance per unit area is simply the ratio of the thermal conductivity of air to the effective gap. For air at atmospheric pressure and 100 degrees C, the thermal conductivity is about 0.03 watt/meter*Kelvin. Heat transfer across the gap is limited by the low chamber pressure and by the fact that the mechanical contact between the two parts is only point contact. 
     In order to improve heat transfer, a thermally conductive gas such as (preferably) helium or another one of the inert gases such as argon, xenon and so forth, can be placed in the gap between the between the heat transfer material  75  and the heat sink  74  and/or in the gap between the heat transfer material  75  and the window/electrode  52 , in accordance with a first embodiment of the present invention. The thermally conductive gas in the gap is best pressurized above the chamber pressure to as high as atmospheric pressure, although preferably the pressure of the thermal transfer gas in the gap is between the chamber pressure and atmospheric pressure. Helium is a preferred choice for the thermally conductive gas because helium has a thermal conductivity of about 0.18 watt/meter*Kelvin at atmospheric pressure and 100 degree C. To minimize thermal contact resistance between the heat transfer material  75  and the heat sink  74 , helium can be provided to each interface therebetween through a helium distribution manifold within the heat sink  74 , as will be described in detail below in this specification. As will also be described below in detail, an O-ring of small cross-section and low durometer can be used to reduce helium leakage and between heat transfer material  75  and heat sink  74 . Through-holes from the top surface of the heat transfer material or rings  75  can connect a helium passage from an upper interface between the heat sink  74  and the heat transfer material ring  75 , to interface between the heat transfer material ring  75  and the window/electrode  52 . Helium can be supplied to the aforementioned helium distribution manifold located within heat sink  74  at a pressure somewhat above atmospheric to minimize dilution of helium by air which could otherwise increase the thermal contact resistance. 
     Other materials may be used in between the heat transfer material  75  and the window/electrode  52 , and between the heat transfer material  75  and the heat sink  74  to minimize thermal contact resistances. Examples are thermally conductive, compliant elastomeric pads such as boron nitride or silicon carbide or silicon or aluminum nitride or aluminum oxide, and similar materials. Metal-impregnated elastomeric pads may be used at the interface adjacent the heat sink  74 , but not adjacent the window/electrode  52  for the same reasons explained above that in general a conductor may not be placed adjacent the window electrode  52 . Soft metals such as  1100  series aluminum, indium, copper or nickel may be used at the interface adjacent the heat sink  74 , but not adjacent the window/electrode  52  for the reasons explained above. 
     The cooling capability and heating power requirements are best selected or sized depending on 1) temperature control range required of the window/electrode, 2) the minimum and maximum heat internal loads, 3) the material properties and physical dimensions of the window/electrode, the heat transfer materials, the heat sink plate and the interfaces between heat sink plate, heat transfer materials, and window/electrode, and 4) the temperature of the heat sink. Generally, the cooling capability is sized first for the lowest required temperature of operation of the window/electrode with the highest internal heat load, and the heating power is then sized to overwhelm the cooling for the highest required temperature of operation of the window/electrode with the lowest internal heat load (typically zero internal heat load). 
     FIG. 18 corresponds to an enlarged view of a portion of FIG.  5  and illustrates one implementation of the foregoing concept of a thermally conductive gas interface at both faces (top and bottom) of the thermally conductive spacer  75  which is not integrally formed with the semiconductor window electrode  52 . In FIG. 18, the overlying cold plate  74  sandwiches plural cylindrical spacer rings  75  with the underlying semiconductor window electrode  52  as illustrated in FIG.  5 . Each spacer or torus  75  can be a material different from the semiconductor window electrode  52 , as discussed above. A manifold  1000  is formed in the cold plate  74  into which a thermally conductive gas such as helium may be supplied from a source  1010  under positive pressure. Preferably, but not necessarily, the positive pressure of the source  1010  is selected so as to maintain the pressure within the thin gap between the two parts significantly above the reactor chamber pressure but below atmospheric pressure. Gas orifices  1020  connect the manifold  1000  to the top interface  1030  between the cold plate  74  and the spacer  75 , permitting the thermally conductive gas (e.g., Helium) to fill the voids in the interface  1030 . An axial passage  1040  is provided through the spacer  75  between its top and bottom faces. The axial passage  1040  connects the top interface  1030  with a bottom interface  1050  between the bottom face of the spacer  75  and the underlying semiconductor window electrode  52 . The axial passage  1040  permits the thermally conductive gas to flow from the top interface  1030  to the bottom interface  1050  to fill voids in the bottom interface  1050 , so that the thermally conductive gas fills voids in both the top and bottom interfaces  1030 ,  1050 . By the source  1010  maintaining the thermally conductive gas manifold  1000  under positive pressure (e.g., 5 psi higher than the chamber pressure), the gas flows to both interfaces  1030 ,  1050 . In order to reduce or prevent leaking of the thermally conductive gas from the interfaces  1030 ,  1050 , small cross-section O-rings  1070 ,  1080  are sandwiched in the top and bottom interfaces, respectively, at the time of assembly. The O-rings  1070 ,  1080  define nearly infinitesimally thin gas-containing volumes in the respective interfaces  1030 ,  1050  in communication with the respective gas manifold  1000 ,  1040 . 
     FIG. 19 illustrates how the embodiment of FIG. 18 is modified to accommodate an array of conductive torus spacers  75  integrally formed with the semiconductor window electrode  52 . In this case, the only interface to be filled by the thermally conductive gas is the top interface  1030 . 
     FIG. 20 corresponds to an enlarged view of a portion of FIG.  5  and illustrates one implementation of the foregoing concept of a thermally conductive solid interface material at both faces (top and bottom) of the thermally conductive spacer  75  which is not integrally formed with the semiconductor window electrode  52 . In FIG. 18, the overlying cold plate  74  sandwiches plural cylindrical spacer rings  75  with the underlying semiconductor window electrode  52  as illustrated in FIG.  5 . Each spacer or torus  75  can be a material different from the semiconductor window electrode  52 , as discussed above. A thermally conductive solid interface material layer  1085 ,  1090  is placed in either or both the top and bottom interfaces  1030 ,  1050 , respectively. If a solid material layer is placed in only one of the top and bottom interfaces  1030 ,  1050 , then the remaining interface may be filled with a thermally conductive gas in the manner of FIG.  18 . However, FIG. 20 illustrates the case in which a thermally conductive solid interface material layer is in both interfaces  1030 ,  1050 . As discussed above, the solid interface material layer  1085  in the top interface  1030  may be a soft metal, but the solid interface material layer  1090  in the bottom interface  1050  cannot be highly electrically conductive because it is next to the electrode  52 . The top layer  1085  may be soft aluminum, indium, copper or nickel or an elastomer impregnated with powders or particles of such metals. Either one of the top and bottom layers  1085 ,  1090  may be an elastomer impregnated with powder or particles of a thermally conductive electrically insulating material such as boron nitride, high electrical resistivity (e.g., bulk) silicon carbide or silicon, aluminum nitride, aluminum oxide and like materials. Alternatively, either one or both of the material layers  1085 ,  1090  may be a bonding material, such as thermoplastic, epoxy or an organic or inorganic bonding material. 
     FIG. 21 illustrates how the embodiment of FIG. 20 is modified to accommodate an array of conductive torus spacers  75  integrally formed with the semiconductor window electrode  52 . In this case, the only interface to be filled is the top interface  1030 . 
     The invention also solves a severe cooling problem with heated parts inside the reactor chamber which are difficult to cool, such as the heated disposable ring  62  of polymer-hardening precursor material described above with reference to FIG.  5 . (The ring  62  may be heated only by plasma heating if no heater is provided, and still require cooling.) It also solves a problem of heating parts inside the reactor chamber which are difficult to heat directly. 
     Referring to FIGS. 22 and 23, a cold plate  1100  directly beneath the ring  62  and in thermal contact has internal coolant jackets  1110  which receive coolant from a coolant circulation pump  1120 . The interface  1130  between the cold plate  1110  and the ring  62  is filled with a thermal conductivity enhancing substance such as a thermally conductive gas (as in FIG. 22) or a thermally conductive solid material layer  1140  (as in FIG.  23 ). The thermally conductive gas may be any gas capable of conducting heat, such as an inert gas or even a gas similar to the process gas employed in the reactor chamber, although an inert gas such as helium is preferred. In the case of the embodiment of FIG. 22 employing the thermally conductive gas, a manifold  1150  through the cold plate  1100  is connected to a thermally conductive gas source  1160  which supplies thermally conductive gas through the manifold  1160  into the interface  1130 . Leakage of the gas from the interface  1130  is preferably controlled to reduce or prevent loss by sandwiching an elastomeric low-cross-section O-ring  1070 ′ between the cold plate  1100  and silicon ring  62  at the time the ring is put into its place. 
     While helium is preferred as the thermally conductive gas in the gap, in the case of application to heated or cooled parts inside the sub-atmospheric reactor chamber, any gas, including a processing gas, could suffice at a pressure greater than the chamber pressure but below atmospheric. In such a case, the gas may be allowed to leak into the chamber so that the use of a peripheral seal such as an O-ring or elastomer may not be necessary. Since the thermally conductive gas (or “thermal transfer gas”) is pressurized above the chamber pressure, some clamping force must be applied. Such a clamping force can be mechanical or may be electrostatically induced between the plate  1100  and the ring  62 . Such an electrostatic clamping feature would require a material which is at least partially electrically insulating to be placed between the plate  1100  and the ring  62 . Such a feature can eliminate the need for a peripheral seal to control leakage of the thermally conductive gas. Such an electrostatic clamping feature is described below in this specification with reference to FIG.  26 . 
     The thermally conductive gas can be derived from any suitable source. For example, if the wafer pedestal employs helium cooling underneath the wafer, then a common helium source may be employed for cooling the wafer as well as other items (such as the ring  62 ) inside the chamber. 
     In the embodiment of FIG. 23, the layer of solid thermally conductive material  1140  may be soft aluminum, indium, copper or nickel or an elastomer impregnated with powders or particles of such metals or it may be an elastomer impregnated with powder or particles of a thermally conductive electrically insulating material such as boron nitride, high resistivity (e.g., bulk) silicon carbide or silicon, aluminum nitride, aluminum oxide and like materials. 
     The present invention also concerns cooling chamber walls and chamber liners in a similar manner. Referring to FIG. 24, the chamber side wall  50  in any of the reactors discussed above may be cooled by an exterior cold plate  1210  adjacent a portion of the exterior of the wall  50 . The cold plate includes internal coolant jackets  1220  through which coolant is recirculated by a coolant pump  1230 . The interface  1240  between the cold plate  1210  and the side wall  50  is filled with a thermally conductive gas (such as helium) fed through a manifold  1245  through the cold plate  1210  into the interface  1240  from a gas source  1250  which maintains the gas at a positive pressure. Leakage of the thermally conductive gas from the interface  1240  is reduced or prevented by an O-ring  1260  sandwiched between the cold plate  1210  and the side wall  50  at the time of assembly. The O-ring  1260  defines a gas-containing volume of the interface  1240  which is nearly infinitesimally thin and in communication with the manifold  1245 . 
     An interior chamber liner  1300  may be cooled by heat conduction to a cooled body, such as the side wall  50 . In accordance with the present invention, such cooling is enhanced by filling the interface  1310  between the liner  1300  and the interior surface of the side wall  50  with a thermally conductive gas such as helium. For this purpose, a radial narrow gas channel  1320  is provided through the side wall  50  to provide gas flow between the interface  1240  on the external side wall surface and the interface  1310  on the internal side wall surface. The thermally conductive gas supplied through the manifold  1245  fills the external surface interface  1240  and, through the channel  1320 , fills the internal surface interface  1310  between the liner  1300  and the side wall  50 . To prevent or reduce gas leakage, an O-ring  1370  is sandwiched between the side wall  50  and the liner  1300  at the time of assembly. The O-ring  1370  defines a nearly infinitesimally thin gas-containing volume within the interface  1310  in communication with the gas channel  1245  in the side wall  50 . 
     FIG. 25 illustrates how the embodiment of FIG. 24 is modified by substituting a solid material layer  1370 ,  1380  in each of the interfaces  1240  and  1310 , respectively, instead of the thermally conductive gas. In the embodiment of FIG. 25, each layer  1370 ,  1380  of solid thermally conductive material may be soft aluminum, indium, copper or nickel or an elastomer impregnated with powders or particles of such metals or it may be an elastomer impregnated with powder or particles of a thermally conductive electrically insulating material such as boron nitride, high resistivity (e.g., bulk) silicon carbide or silicon, aluminum nitride, aluminum oxide and like materials. 
     FIG. 26 illustrates how the embodiment of FIG. 22 may be modified to include the feature of electrostatic clamping of the ring  62  to the cold plate  1100 . In FIG. 26, a dielectric layer  1410  is inserted between the polymer-hardening precursor ring  62  and the cold plate  1100 , and an electrostatic clamping voltage is applied to the cold plate  1100  from a D.C. voltage source  1420  through a clamping switch  1430 . Introduction of the insulating or dielectric layer  1410  creates a gap  1130   a  between the cold plate  1100  and the insulating layer  1410  and a gap  1130   b  between the ring  62  and the insulating layer  1410 . The insulating layer  1410  has passageways  1412  therethrough so that gas supplied from the passageway  1150  into the gap  1130   a  can flow into the other gap  1130   b . While FIG. 26 shows O-rings  1070 ′ sealing both gaps  1130   a  and  1130   b , such O-rings may not be necessary, depending upon the electrostatic clamping force induced. 
     The present invention provides a great improvement (by a factor of about 6 in the case of the introduction of helium) in thermal conductivity across the interface between heat-receiving elements of the reactor either inside the chamber (such as chamber liners, disposable silicon rings) and outside the chamber (such as window electrodes, side walls) and a cooling plate or cold sink. As a result, the automated control of temperature of many critical parts of the plasma reactor is improved to a new capability exceeding that of the prior art. The invention accomplishes this in one or a combination of two characteristic modes at the various interfaces: (a) the introduction of a thermally conductive gas into the interface and (b) the introduction of a thermally conductive solid layer in the interface. This, in combination with efficiently controlled heating of the same elements, permits accurate feedback control of the temperature of each such element thus heated and cooled. 
     In selecting the heat transfer materials and/or physical dimensions of the reactor, the cooling conductance required (G) is determined as follows: 
     G=total maximum internal heat load (watts)/Delta-T1(degree C) 
     where Delta-T1=Difference between heat sink temperature and minimum window/electrode temperature. 
     Alternatively, if the heat transfer materials and physical dimensions have already been chosen, then the required heat sink temperature may be trivially calculated by rearranging the above equation for Delta-T1 as function of G. 
     Heating power is then determined as follows: 
     P=total external heating power required (watts) delivered to control surface, 
     P=(G*Delta-T2)-Pmin 
     where: 
     G is the cooling conductance from above (in watts/degree C), 
     Delta-T2=Difference between heat sink temperature and maximum window/electrode temperature Pmin is the minimum internal heat load on the window/electrode. 
     EXAMPLE 1 
     The window/electrode  52  and the heat transfer rings  75  are integrally formed as a monolithic piece, and the window/electrode  52  is a flat circular disk 12.81 inches in diameter and 0.85 in thick. Formed integrally with the window/electrode  52  is an array of four concentric cylindrical heat transfer rings ( 75 ) 2″ high of the following inside and outside diameters: 
     1. outer heat transfer ring—12.80″ outside dia., 10.79″ inside dia., 
     2. middle heat transfer ring—9.010″ outside dia., 7.595″ inside dia., 
     3. inner heat transfer ring—5.715″ outside dia., 3.940″ inside dia., 
     4. center heat transfer ring—2.260″ outside dia., 0.940″ inside dia. 
     The window/electrode  52  and integral array of concentric cylindrical heat transfer rings  75  are fabricated together from a single ingot of polycrystalline silicon with the following thermal and electrical properties: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Doping level: 
                 10 14 /cm 3 , boron or phosphorous 
               
               
                   
                 Thermal conductivity: 
                 80 watt/meter * Kelvin 
               
               
                   
                 Electrical resistivity: 
                 from 20 to 100 ohm * cm 
               
               
                   
                 Specific Heat: 
                 0.7 joule/gram * Kelvin 
               
               
                   
                 Density: 
                 2.3 gram/cm 3   
               
               
                   
                   
               
             
          
         
       
     
     A plurality of 750 watt @ 120 volt rms tungsten filament lamps  76  are employed. The number of lamps is selected based on measured 73% efficiency (output power/ac input power) and on 400 watt @ 80 volt rms maximum operating level (for long lamp life). Two heat zones are employed, those on the outer circle comprise one zone (outer), and those on the inner circle and at the center comprise the second (inner) zone. Each zone has its own temperature measurement (a type-K thermocouple spring loaded against the window/electrode surface) and its own output transducer (a phase-angle controller). The lamps, manufactured by Sylvania, are deployed as follows: 
     15 lamps on a 13.55″ diameter circle, equal angular spacing (24 degrees); 
     15 lamps on a 6.655″ diameter circle, equal angular spacing (24 degrees); 
     1 lamp on central axis. 
     The outer lamp circle is surrounded on the outside by a cylindrical polished aluminum reflector that is integral with the heat sink  74 . 
     The outer solenoid antenna  90  is 4 turns comprised of {fraction (3/16)}″ diameter water cooled copper tubing insulated with ¼″ outside diameter teflon tubing yielding coil 1″ in height and 10″ mean diameter, wound as described in the above-referenced parent application. 
     The inner solenoid antenna  42  is 4 turns comprised of {fraction (3/16)}″ diameter water cooled copper tubing insulated with ¼″ outside diameter teflon tubing yielding coil 1″ in height and 3.25 mean diameter, wound as described in the above-referenced parent application. 
     The heat sink plate  74  is a water cooled aluminum plate maintained at 75 degree C. by a closed loop heat exchanger using a 50/50% water/ethylene-glycol mixture at a flow rate of 2 gallons per minute. The heat sink  74  houses lamp sockets and provides cooling for the lamps  76  required due to inherent lamp losses to socket (approximately 27%). The heat sink plate  74  includes feed-through for the inner and outer solenoidal antennas  42 ,  90 . The heat sink  74  also functions as a ground plane for the antennas  42 ,  90 . The heat sink plate  74  includes O-ring grooves to accommodate 0.139 inch diameter, 30 durometer soft O-rings deployed just inside the outer diameter of each heat transfer ring  75  and just outside the inner diameter of each heat transfer ring  75 . The heat sink  74  is mounted on top of the integral array of concentric cylindrical heat transfer rings  75 . Surface roughness of both surfaces (the bottom of the heat sink  74  and the top of heat transfer rings  75 ) is less than a micro-inch. Flatness of each surfaces is less than 0.0005 inch. The effective gap between the bottom of the heat sink and the top of the heat transfer rings is less than 0.001 inch. 
     EXAMPLE 2 
     The window/electrode  52  and the heat transfer rings  75  are separate pieces formed of different materials. The window/electrode  52  is a flat circular disk  14 . 52 inches in diameter and 0.85 inches thick. A separate array of 4 concentric cylindrical heat transfer rings  75  2″ high of the following inside and outside diameters is placed in between the heat sink plate and the window electrode: 
     1. outer heat transfer ring—12.70″ outside dia., 10.67″ inside dia., 
     2. middle heat transfer ring—8.883″ outside dia., 7.676″ inside dia., 
     3. inner heat transfer ring—5.576″ outside dia., 3.920″ inside dia., 
     4. center heat transfer ring—2.080″ outside dia., 1.050″ inside dia. 
     The window/electrode  52  is fabricated from a single ingot of polycrystalline silicon with the following thermal and electrical properties: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Doping level: 
                 10 14 /cm 3 , boron or phosphorous 
               
               
                   
                 Thermal conductivity: 
                 80 watt/meter * Kelvin 
               
               
                   
                 Electrical resistivity: 
                 20-100 ohm * cm 
               
               
                   
                 Specific Heat: 
                 0.7 joule/gram * Kelvin 
               
               
                   
                 Density: 
                 2.3 gram/cm 3   
               
               
                   
                   
               
             
          
         
       
     
     The array of concentric cylindrical heat transfer rings  75  are fabricated from SiC (silicon carbide) with the following thermal and electrical properties: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Thermal conductivity: 
                 130 watt/meter * Kelvin 
               
               
                   
                 Electrical resistivity: 
                 10 5  ohm * cm 
               
               
                   
                 Specific Heat: 
                 0.655 joule/gram * Kelvin 
               
               
                   
                 Density: 
                 3.2 gram/cm 3   
               
               
                   
                   
               
             
          
         
       
     
     A plurality of 750 watt @ 120 volt rms tungsten filament lamps are employed. The number of lamps is selected based on measured 73% efficiency (output power/ac input power) and 400 watt @ 80 volt rms maximum operating level (for long lamp life). Two heat zones are employed, those on the outer circle comprise one zone (outer), and those on the inner circle and at the center comprise the second (inner) zone. Each zone has its own temperature measurement (a type-K thermocouple spring loaded against the window/electrode surface) and its own output transducer (a phase-angle controller). The lamps  76 , manufactured by Sylvania, are deployed as follows: 
     15 lamps on 13.55″ diameter circle, equal angular spacing (24 degree); 
     15 lamps on 6.626″ diameter circle, equal angular spacing (24 degree); 
     1 lamp on central axis. 
     The outer lamp circle is surrounded on the outside by a cylindrical polished aluminum reflector that is integral with the heat sink. 
     The outer solenoid antenna  90  is four turns comprised of {fraction (3/16)}″ diameter water cooled copper tubing insulated with ¼″ outside diameter teflon tubing yielding coil 1″ in height and 10″ mean diameter, wound as described in the above-referenced parent application. 
     The inner solenoid antenna  42  is four turns comprised of {fraction (3/16)}″ diameter water cooled copper tubing insulated with ¼″ outside diameter teflon tubing yielding coil 1″ in height and 3.25 mean diameter, wound as described in the above-reference parent application. 
     The heat sink plate  74  is a water cooled aluminum plate maintained at 75 degrees C. by a closed loop heat exchanger using a 50/50% water/ethylene-glycol mixture at a flow rate of 2 gallons per minute. Heat sink houses lamp sockets and provides cooling for the lamps, required due to inherent lamp losses to socket (approximately 27%). The heat sink plate  74  includes feed-through for the aforementioned inner and outer solenoidal antennas  42 ,  90 . The heat sink  74  also functions as a ground plane for the antennas. The heat sink plate  74  and the window/electrode  52  include O-ring grooves to accommodate 0.139 inch diameter, 30 durometer soft O-rings deployed just inside the outer diameter of each heat transfer ring  75  and just outside the inner diameter of each heat transfer ring  75 . The heat sink  74  is mounted on top of the array of concentric cylindrical heat transfer rings  75 . Surface roughness of all surfaces (bottom of the heat sink and top of the heat transfer rings, bottom of the heat transfer rings and top of the window/electrode) is less than a micro-inch. Flatness of each surface is less than 0.0005 inch. The effective gap between the bottom of the heat sink and the top of the heat transfer rings is less than 0.001 inch. The effective gap between the bottom of the heat transfer rings and the top of the window/electrode is less than 0.001 inch. 
     While the invention has been described in detail by specific reference to preferred embodiments, it is understood that variations and modifications thereof may be made without departing from the true spirit and scope of the invention.