Abstract:
A closed-loop, dome thermal control apparatus containing a high-volume fan, a heat exchange chamber, and an enclosure that encloses the fan and the heat exchange chamber. The fan blows air over a dome of a semiconductor wafer processing system and through the heat exchange chamber to uniformly control the temperature of a dome of a plasma chamber to prevent particle contamination of the wafer. The enclosure recirculates the temperature controlled air to the fan to form a closed-loop apparatus.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part application of co-pending U.S. patent application Ser. No. 08/767,071, filed Dec. 16, 1996 now abandoned. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     1. Field of the Invention 
     The present invention relates to semiconductor wafer processing systems, and more particularly, to systems for etching semiconductor wafers in a thermally controlled environment. 
     2. Description of the Background Art 
     A semiconductor wafer processing system that performs dry etching of semiconductor wafers typically accomplishes the etching within a process chamber. The chamber is a vacuum sealed enclosure containing a wafer pedestal for mounting a wafer in a stationary position within the chamber during the etch process. To plasma enhance the etch process, a plasma is generated within the chamber by filling the chamber with a reactant gas, and applying a substantial RF field to the reactant gas to generate a plasma. The RF field is generated by conductive coils that circumscribe the outer circumference of the chamber as well as a cathode positioned within the chamber. These coils form an antenna that is driven by a high powered RF signal to produce a substantial magnetic field within the chamber. The cathode is also driven by an RF signal that produces a substantial electric field within the chamber. The magnetic and electric fields interact with the reactant gas to form a plasma within the chamber. The antenna is positioned at a location on the exterior of the chamber to ensure that the plasma is uniformly generated above the wafer surface that is to be etched. 
     To reduce the temperature change that is experienced by the chamber when the plasma is cycled on and off, the dome is typically heated to approximately 80° C. using a radiant heat lamp source. The radiant source is generally a plurality of high-power lamps mounted outside of the chamber. The lamps are mounted in an array above the dome. Typically, a reflector assembly is positioned proximate the lamps to focus their radiant energy upon the dome surface. To maintain the dome temperature at approximately 80° C. during plasma cycling (i.e., during periods when the plasma is present and not present), a fan is mounted proximate the dome to provide a continuous flow of room temperature air across the dome and thereby maintaining the dome at a constant temperature when the plasma is present. However, such a cooling technique is not very effective and the dome temperature may fluctuate as much as ±40° C. depending upon the ambient room temperature. Large thermal fluctuation of the chamber surfaces cause the chamber to expand and contract such that material deposited on the chamber walls and dome during the etch process flakes and falls upon the wafer being processed. The microcontamination particles makes the wafer unusable. 
     Therefore, a need exists in the art for a dome temperature control apparatus that maintains the temperature of the dome within at least ±5° C. of a preset nominal temperature during cycling of the plasma. 
     SUMMARY OF THE INVENTION 
     The disadvantages heretofore associated with the prior art are overcome by the present invention of a closed-loop dome temperature control apparatus. The apparatus contains a centrally-located, high-volume fan, a heat exchange chamber and an enclosure that encloses both the fan and the heat exchange chamber to form a closed-loop air flow circulation system. The closed loop system circulates air within the enclosure to stabilize the temperature of a dome of a semiconductor wafer processing system. To facilitate optimal air flow over the dome, the apparatus contains an air flow director. 
     In a first embodiment of the invention, the fan blows air from above a lamp assembly downward through a central portal defined by the lamp array assembly. The fan also blows air across the circumference of the lamp array assembly and through a vortex generator (one embodiment of an air flow director) containing a circular array of air directing nozzles. These nozzles direct the air flow toward the dome in a circular fashion generating a vortex or cyclone of air that swirls about the top of the dome. As the air swirls past the dome, it exits the edge of the dome into a heat exchange chamber wherein a plurality of tubes carrying a heat transfer fluid to chill or heat the air. The air passes through the heat exchange chamber over a fan shroud and back to the fan which again pushes the air down across the lamps and the upper portion of the dome. As such, a closed-loop, dome temperature control apparatus is produced. 
     In a second embodiment of the invention, an axial flow fan module blows air from above a lamp assembly through a central portal defined by the lamp assembly. The air flows through an air flow director containing a circular array of stationary air directing blades (i.e., stator blades). 
     These blades direct the air flow along an axial path toward the dome to provide a uniform cascade of air that, upon impact with the dome, flows radially outward over the top of the dome. As the air flows past the dome, it exits the edge of the dome into a heat exchange chamber wherein a plurality of finned tubes carry a heat transfer fluid to chill (or heat) the air. The air passes through the heat exchange chamber as the air flows back to the fan which again pushes the air down toward the center portion of the dome. A series of upper stator blades located above the fan are also utilized to prevent back flow of air from the axial fan. 
     Using this invention of a closed-loop apparatus, the dome temperature can be maintained to ±5° C., about a nominal temperature of 80° C. The temperature can further be controlled to raise or lower the nominal temperature by adjusting the power that is delivered to the lamps. The lamp control is facilitated by an infrared sensor that is focused upon the surface of the dome. The sensor signal is processed through a conventional software implementation of a feed-back loop. The feedback loop utilizes a preset temperature value to which the measured temperature is compared. The closed loop system controls the current delivered to the infrared lamp array to cause the measured temperature to equal the preset temperature value. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
     FIG. 1 depicts a partially sectional, perspective view of the present invention; 
     FIG. 2 depicts a cross-sectional view of the present invention; 
     FIG. 3 depicts a perspective view of a nozzle ring; 
     FIG. 4 depicts a perspective view of a nozzle ; 
     FIG. 5 depicts a cross-sectional view of the nozzle depicted in FIG. 4 taken along line  5 — 5 ; 
     FIG. 6 depicts a schematic of the electrical circuitry of the present invention; 
     FIG. 7 depicts a flow diagram of a software implementation of a routine for controlling the dome temperatures; 
     FIG. 8 depicts a schematic diagram of the coolant flow through the apparatus of the present invention; 
     FIG. 9 depicts a partially sectional, exploded view of a second embodiment of the present invention; 
     FIG. 10 depicts a cross-sectional view of a second embodiment of the present invention; 
     FIG. 11 depicts a perspective view of a baffle; 
     FIG. 12 depicts an exploded perspective view of a lamp assembly; 
     FIG. 13 depicts a perspective view of an lower stator; 
     FIG. 14 depicts a perspective view of a lower stator blade; 
     FIG. 15 depicts a perspective view of a fan cowling; 
     FIG. 16 depicts a top plan view of an upper stator; 
     FIG. 17 depicts a side view of the upper stator; 
     FIG. 18 depicts a perspective view of the cooling tubes; and 
     FIG. 19 depicts a cross-sectional view of an end-point detector incorporated into the apparatus of the present invention. 
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
     DETAILED DESCRIPTION 
     FIG. 1 depicts a partially sectional, perspective view of a closed-loop dome temperature control apparatus  100  of the present invention. The apparatus  100  is mounted above a conventional ceramic dome  102  of a plasma etch reaction chamber. The dome  102  is circumscribed by a inductively coupled coil  104 , e.g., an antenna, that is conventionally driven with RF power to generate a magnetic plasma field within the chamber. The present invention maintains the surface of the dome at a relatively constant temperature whether a plasma is present in the reaction chamber or not. 
     Specifically, the apparatus  100  of a first embodiment of the present invention comprises a fan  106 , an infrared sensor  108 , a lamp assembly  110 , a nozzle assembly  112 , a heat exchange chamber  114 , and a fan shroud  116 . More specifically, the apparatus has an outer housing  118  that is substantially cylindrical and is attached to the circumferential edge  120  of the reaction chamber by a fastening assembly  122 . The apparatus also contains a cylindrical shaped inner housing  124  that has a slightly smaller diameter than the outer housing  118 . The inner and outer housings are concentric with respect to a central axis passing through the ceramic dome and reaction chamber. The inner and outer housings are in a spaced-apart relationship to define a space  126  there between. Within the space  126  is mounted a heat exchanger coil  128  such that the outer housing, inner housing and coil form the heat exchange chamber  114  or heat exchanger channel. 
     Upon the top edge of the outer housing is mounted a fan cover  130  that forms a closed loop circulatory system for the entire apparatus i.e., air circulating in the apparatus is not exhausted from the apparatus. To a top edge  132  of the inner housing  124  is mounted a fan shroud  116 . The fan shroud  116  contains a central aperture  136  to which the fan  106  is mounted. As such, the fan  106  pulls air through the heat exchange chamber  114  through a space (air channel  117 ) between the fan cover  130  and the fan shroud  116  and into the central aperture  136  to be pulled through the fan  106 . 
     The lamp assembly  110  is centrally mounted just below the fan within the apparatus  100 . The lamp assembly  110  is maintained in place by the nozzle assembly  112 . The nozzle assembly  112  is affixed to the inner surface of the inner housing  124  and extends inwardly at an angle toward the center of the apparatus  100 . The nozzle assembly contains a central aperture  138 . Upon an edge  140  that defines the central aperture  138  is mounted the lamp assembly  110 . The lamp assembly  110  includes a lamp reflector  142 , a lamp cooling plate  144 , and a lamp mounting plate  146 . The lamps themselves are not shown in FIG. 1 for simplicity. To provide cooling for the lamp assembly, the coolant, after passing through the heat exchanger coil  128 , is channeled through passages in the lamp cooling plate  144 . The lamp assembly is generally constructed and operates in a manner that is well-known in the art. The lamp reflector  142 , the lamp cooling plate  144 , and the lamp mounting plate  146  define a central aperture  148  that allows air to pass from the fan  106  toward the center of the dome  102 . In other words, air passes along the central axis of the apparatus  100 . Along that central axis is mounted the infrared sensor  108  having a mounting portion  150  attached to the lamp mounting plate  146  and extending into the central aperture  148 . The infrared sensor that is positioned above the dome will sense an area of about 1.8 inches in diameter on the surface. This provides an accurate indication of the surface temperature of the dome. 
     The nozzle assembly  112  contains a plurality of apertures  152  about the circumference of the assembly. In each of those apertures  152  is positioned an air directing nozzle  154 . Each nozzle has an axis that points air passing through the nozzle in a direction that is tangent to a circle that is coaxial with the center axis of the apparatus  100 , where the circle has a diameter of 3 to 4 inches. Consequently, air flowing down from the fan  106  through central apertures  148  and  138  of the apparatus, as well as through each of the nozzles  154 , forms a vortex or cyclone just above the ceramic dome  102 . Consequently, this cyclone moves air across the dome toward the edge  120  thereof and effectively cools the dome. The air, as it passes over the dome  102 , then exits the circumferential edge  120  of the dome through aperture  156  into the heat exchange chamber  114  and is returned to the fan  106  via channel  117 . Consequently, the air is circulated over the dome  102  through the heat exchange chamber  114  and back to the fan  106  in a closed-loop path. 
     Further, temperature control is provided by the infrared sensor  108  being attached to a feedback loop that controls lamp intensity. One example of such a feedback loop is described below with respect to FIGS. 6 and 7. FIG. 2 a depicts a cross-sectional view of the closed-loop, dome temperature control apparatus  100  showing the airflow paths through the apparatus as a plurality of arrows. The fan  106  pulls air through the channel  117  between the fan shroud  116  and the fan cover  130  at approximately 315 cfm. The fan, illustratively, is a backward curved motorized impeller fan produced by EBM Corporation. Without back pressure, such a fan can propel air at 710 cfm. The air is forced downward through central apertures  148  and  138  as well as through the air directing nozzles  154 . As air passes through the nozzles, the angled nozzles produce a centrifugal air flow over the dome  102 . The air then flows to the heat exchange chamber  114 , rises through the chamber  114  due to the negative pressure of the fan  106 . To achieve sufficient cooling of the air, the coolant coils are provided glycol from a coolant supply  199  (e.g., a refrigerator or heat exchanger) that maintains the coolant at approximately 10° C. The coolant is supplied at 40 to 60 psi to achieve a flow rate of approximately 0.4 to 0.6 gal/min. A schematic diagram of the coolant flow through the apparatus is shown in FIG. 8 below. 
     To provide further cooling, the coolant is also channeled through the lamp assembly  110 . Specifically, the coolant flows through the cooling plate  144  of the lamp assembly. The coolant supply for the lamp assembly may be independent from the dome heat exchanger coils coolant supply. Optionally, the coolant may be channeled through the antenna coils. The antenna coils are hollow tubes that can be coupled to the coolant supply. 
     Once chilled, the fan pulls the air up into the air channel  117  between the fan shroud  116  and the fan cover  130  to once again push the cool air down over the lamp assembly  110  and through the nozzles  154  to complete a closed-loop air flow path. Such a centrifugal air flow pattern forms a vortex over the dome which pushes air from the inside, or central portion of the dome, to the outside portion of the dome, creating greater, and more uniform, air flow over the dome surface. Such a vortex of air better cools the dome surface than if the air were merely directed downward from the fan over the surface of the dome. 
     FIG. 3 is a perspective view of the nozzle assembly  112 . The nozzle assembly  112  contains a nozzle ring  300  and a plurality of nozzles  154 . The nozzle ring  300  contains a vertical portion  302  for mounting to the inner surface of the inner housing, a horizontal portion  304  for supporting the lamp assembly and defining the central aperture  138 , and slanted portion  306  for interconnecting the vertical portion  302  with the horizontal portion  304 . The slanted portion is slanted inward at approximately 45° from vertical. The vertical and horizontal portions  302  and  304  contain a plurality of mounting holes  308  and alignment slots  310 . The slanted portion  306  nozzle ring  300  contains a plurality of apertures  152  (e.g., thirty-six apertures) formed in a ring about the circumference of the slated portion  306 . Each aperture maintains a nozzle  154  in a particular orientation that is described in detail with respect to FIGS. 4 and 5 below. 
     FIG. 4 depicts a perspective view of the nozzle  154  and FIG. 5 depicts a cross-sectional view of a nozzle  154  taken along line  5 — 5  in FIG.  4 . To best understand the invention, the reader should simultaneously refer to FIGS. 4 and 5. The nozzle  154  has a flange  400  for mounting against a nozzle ring aperture. A cylindrical nozzle portion  402  extends from the flange  400 . The nozzle is formed at angle  500  with respect to a central axis  502  of the nozzle. As such, the orientation of the nozzle about the central axis  502  determines the angle of the air flow through the nozzle. The arcuate exhaust portion of the nozzle  404  defines an exhaust aperture  406 . 
     The nozzles  154  are generally oriented within the ring such that they are offset from alignment with the center of the apparatus by 1 to 5 degrees. This alignment is achieved by an alignment flat  408 . Each alignment flat abuts a neighboring flat assuring, once assembled, that all the nozzles are properly aligned. As such, the axis  500  extending through the center of the nozzle exhaust aperture  406  is tangent to a circle located just above the dome and having a 3 to 4 inch diameter. As such, simultaneous air flow through all thirty-six nozzles forms the air vortex over the dome. 
     The apparatus features a number of safety interlocks that are implemented to avoid injury or damage to the hardware. For example, in FIG. 2, an airflow sensor  200  is provided to trigger a shut-down of the RF power and the heating lamps in the event of a fan failure. The sensor is mounted to the housing assembly and contains an electronic air flow switch that opens the circuit should air flow subside. In addition, there are two over temperature sensors  202  and  204 , located on the lamp assembly  110 , which trigger the shut-down of the RF power and the lamp power in the event of overheating of the dome. Furthermore, there is an interlock switch  206  that senses the fan cover, the RF cable and the control cables such that removal of the cover or either of these cables will trigger a shut-down of the RF power, lamp power and the high voltage supply to the electrostatic chuck that retains a wafer within the etch chamber during electrochemical processing. 
     FIG. 6 depicts a schematic diagram of the electrical circuitry incorporated within the closed-loop dome temperature control apparatus of the present invention. The electronics include a lamp driver  600  for lamp array  110 , the fan  106 , the infrared temperature sensor  108 , and a plurality of relays  604  for controlling power to the fan and to the lamp driver. A number of interlocks  606 , which are controlled by sensors  612  that sense air flow, over-temperature and various interlocking switches, are used to control the relays  604 . The interlocks  606  drive the relays  604  into a closed position such that power is supplied to the fan  106  and the lamp driver  600 . More specifically,  31 ,  208  VAC is supplied to the lamp driver  600  which distributes the power to the six lamps L 1 -L 6 . Two lamps in series are connected to each phase, e.g., a delta arrangement. The array produce approximately 1,600 watts of power when driven with  208  VAC across each lamp pair. The voltage applied to the lamps is controlled by the lamp driver such that the lamp intensity is controllable. If a sensor  12  indicates an air flow problem, an over-temperature situation or an interlock being broken, the interlock  606  disconnects power from the relays  604 . In response, the relays switch to a normally open position, disconnecting power from the lamp driver  600  and fan  106 . Consequently, the dome thermal control apparatus is deactivated. 
     To control the dome temperature, an analog-to-digital converter  608  is used to convert the analog signal from the infrared temperature sensor  108  into a digital signal which is supplied to a computer  610 . The computer  610  analyzes the temperature sensor signal to generate a lamp driver control voltage (path  614 ). This voltage is generated by the computer as a digital signal and is converted from digital to analog form in a digital-to-analog converter  616  and then sent to the lamp driver  600 . This voltage forms the lamp driver set point such that the lamp driver, in response to this voltage, will alter the intensity of the lamp array to achieve a particular temperature as measured the temperature sensor. 
     The computer  610  is a general purpose computer containing a central processing unit  618  and a memory  620 . The general purpose computer when executing a software program becomes a special purpose apparatus that implements the steps of the software program. One program executed by the computer is a routine for producing the lamp driver set point voltage, i.e., a temperature control routine. 
     FIG. 7 depicts a flow diagram of the temperature control routine  700  as implemented in software and executed by the computer. Routine  700  begins at step  702  and proceeds to step  704 . At step  704 , the routine establishes a temperature set point. This value is typically entered by a user through a keyboard. At step  706 , the routine measures the dome temperature, e.g., reads the digitized temperature measurement produced by the A/D converter. At step  708 , the measured temperature is compared to the set point temperature to produce an error value. The error value is used at step  710  to produce a lamp driver control voltage that will bring the measured temperature nearer the set point temperature. At step  712 , the routine queries whether the routine should continue. If the query is affirmatively answered, the routine returns to step  706  to continue the temperature control process. However, if the query is negatively answered, the routine stops at step  714 . 
     FIG. 8 depicts a schematic diagram of the coolant flow through the inventive apparatus. The coolant supply  199  is coupled to an inlet distribution manifold  800  and an outlet distribution manifold  802 . The inlet distribution manifold  800  distributes the coolant flow to the heat exchanger coil  128 , the antenna coils  104  (optional) and the lamp cooling plate  144 . The coolant flow from these cooling elements is coupled to manifold  802  and, ultimately, back to the coolant supply  199 . 
     Although the foregoing description disclosed a coolant flow, the invention may utilize a heated heat transfer fluid that would raise the temperature of the air and the dome. As such, the invention should be broadly interpreted to encompass both heating and cooling of the air within the closed loop system. 
     In a second embodiment of the invention, the inventive apparatus confines the air flow to an axial path or downward laminar flow of air from the fan to the dome and the air flows evenly over the exterior surface dome toward the heat exchange chamber. This configuration maximizes the convective cooling of the dome material. 
     FIG. 9 depicts a partial section, exploded view of an alternative embodiment of the closed-loop dome temperature control apparatus  900  of the second embodiment of the present invention. FIG. 10 depicts an assembled, cross-sectional view of the closed-loop, dome temperature control apparatus  900  showing the airflow paths through the apparatus as a plurality of arrows. To best understand the invention, the reader should simultaneously refer to both FIGS. 9 and 10. 
     The apparatus  900  is mounted above a conventional ceramic dome  938  of a plasma etch reaction chamber. As with the previous embodiment, the dome  938  is circumscribed by a inductive coil  940 , e.g., an antenna, that is dimensionally controlled by insulative coil mounts  902 . The coil is conventionally driven with RF power to generate a magnetic plasma field within the reaction chamber to perform the etching process. The present invention maintains the surface of the dome at a relatively constant temperature whether the plasma is present or not. 
     More specifically, the apparatus  900  comprises an axial fan module  904 , an infrared sensor  906 , a lamp assembly  908 , a heat exchange chamber  910 , and a baffle  912 . The apparatus has an outer housing  914  that is substantially cylindrical and is attached to the circumferential edge of the etch reaction chamber (not shown) by a fastener assembly  939 . To assist lifting and alignment of the invention with respect to the dome, a pair of hand-holds  924  are attached to the outer surface of the outer housing by a plurality of brackets  926 . The apparatus also contains a cylindrical shaped inner housing  916  that has a slightly smaller diameter than the outer housing  914 . The inner and outer housings are coaxial with respect to a central axis passing through the apparatus. The inner and outer housings are in a spaced-apart relationship to define a space  918  therebetween. Within the space  918  is mounted a plurality of finned heat exchanger tubes  920  such that the outer housing, inner housing and tubes form the heat exchange chamber  910 . The finned tube assembly provides greater surface area to permit more substantial convective cooling or heating of the air within the chamber. 
     Upon the top edge of the outer housing is mounted a fan cover  942  that forms a closed enclosure for the entire apparatus i.e., air circulating in the apparatus is not exhausted from the apparatus. Within the enclosure, the other components of the invention are mounted to a mounting ring  922  that is affixed to the inner surface of the outer housing  914 . The components are stacked upon the mounting ring  922  in the following order: the baffle  912  rests upon the mounting ring  922 , a lamp module  908  is affixed to the baffle  912 , and the fan module  904  is affixed to the lamp assembly  904 . In this arrangement, the fan module  904  pulls air through the heat exchange chamber  910  and into fan module  904  to cause air to flow axially through the lamp assembly  908  and baffle  912   
     The fan module  904  pulls air from the chamber  910  at approximately 350 cfm. The fan module  904  contains a fan  934  (motor  934 A, mounting bracket  934 B and impeller  934 C), an upper stator  930 , a fan cowling  931  and a lower stator  932 . The fan, illustratively, is an axial flow fan produced by Kooltronics Inc. Without back pressure, such a fan can propel air at 800 cfm at zero inches of mercury. The fan forces air downward through a central aperture  928  defined by the lower stator  932  and the lamp assembly  908 . The lower stator contains a plurality of air directing stator blades  936  that direct the fan&#39;s air flow from both a linear and radial velocity into an axial downward direction. The lower stator  932  is disclosed in detail with respect to FIGS. 13 and 14 below. The air, upon impact with the center of the dome  938 , then evenly flows radially outward over the top surface of the dome  938  and into the heat exchange chamber  910 . The airflow directional system evenly distribute the air flow thereby maximizing the dome cooling efficiency. The air rises through the chamber  910  due to the negative pressure established by the fan  934 . To achieve sufficient cooling (or heating), the finned tubes (discussed below in detail with respect to FIG. 18) are provided heat transfer fluid (e.g., water) from a fluid supply  944 . Generally, to cool the air and dome, the fluid is simply a steady flow of facilities water having a temperature of approximately 22° C. Importantly, this invention has the ability to maintain a continuous dome temperature with heat transfer fluid temperature as high as 35° C. The coolant is supplied at a flow rate of approximately 0.4 to 0.6 gal/min. Generally, in the first embodiment of the invention an independent heat exchanger supplies temperature regulated heat transfer fluid to the dome temperature control unit where the second embodiment of the invention omits this requirement. 
     To provide further cooling of the system, the heat transfer fluid is also channeled through the lamp assembly  908  as shall be discussed in detail with respect to FIG.  12 . In general, the coolant flows through a cooling jacket  952  within the lamp assembly  908 . As such, the base of the lamps  946  are maintained at a relatively low temperature. For easy assembly and disassembly of the apparatus, the heat transfer fluid is provided to the lamp assembly via “quick disconnect” fittings and power is supplied to the lamps through easy disconnect connections on the wire harness. 
     Once chilled, the fan  934  draws the air from the heat exchange chamber  910  and forces the air through the lower stator  932  and the center of the lamp assembly  908  to complete a closed-loop air flow path. The upper stator prevents reverse air flow from the axial fan blade from interfering with the efficient circulatory air flow pattern. The air flow system delivers a uniform channel of air to the center of the dome and then radial laminar flow to the outside portion of the dome, creating greater, and more uniform, air flow over the dome surface. 
     An additional component that is shown but does not form a portion of the present invention is the RF conductor  948  (i.e., an RF feedthrough) that couples RF power from a matching network, located within the cover  942 , to the coil  940 . The feedthrough  948  is completely shielded along portion  949 , i.e., the portion that is outside of the baffle  912  to prevent electrical noise on adjacent electrical components. The portion  951  of the feedthrough within the baffle  912  is generally an unshielded conductor. Importantly, wire harnesses, electronic circuits and sensors are totally shielded from RF energy field to prevent electronic interference on system control circuitry. The fan-lamp-baffle assembly functions as an RF shield that confines the RF radiation from the antenna coil to the space within the fan-lamp-baffle assembly. Consequently, RF interference with the electronic circuitry is substantially reduced. 
     FIG. 11 depicts a perspective view of the baffle  912 . The baffle  912  has a lower mounting flange  1100 , an upper mounting flange  1102  and a sloped wall portion  1104  connecting the upper mounting flange  1102  to the lower mounting flange  1100 . The baffle  912  defines a central aperture  1112  through which air flows toward the dome. The lower mounting flange  1100  contains a plurality of mounting extensions  1106  for affixing the baffle  912  to the mounting ring ( 922  of FIG.  9 ), generally by using bolts. Similarly, the upper mounting flange  1102  contains a plurality of extensions  1118  for affixing the baffle  912  to the lamp assembly ( 908  of FIG.  9 ), generally by using bolts. The sloped portion  1104  of the baffle  912  extends inwardly from the lower mounting flange  1102  to the upper mounting flange  1104  at an angle of approximately 55 degrees relative to horizontal. Approximately half way along the sloped portion  1104  is a sensor mount  1108 . The sensor mount contains a mounting bore  1110  that is angle at approximately 58 degrees relative to horizontal. With the sensor mounted through the baffle  912 , the infrared sensor senses an area of about 1.8 inches in diameter on the surface of the dome. This provides an accurate indication of the surface temperature of the dome for use by the temperature control electronics. The baffle  912  also contains a notch  1114  and an aperture  1116  that facilitate routing the RF conductor through the baffle  912  to the coil. 
     FIG. 12 depicts an exploded, perspective view of the lamp assembly  908 . The lamp assembly  908  is affixed to the baffle by a plurality of extensions  1202  protrude from the mounting flange  1206 . The lamp assembly has two principal components (other than the electrical wiring and the bulbs which are not shown). The first component is the base  1208  and the second component is the cover  1210 . The base  1208  is milled from a solid block of aluminum to form a reflector for the plurality of bulbs (shown as  950  in the cross section of FIG.  10 ), the central air flow aperture  1212 , a coolant channel  1214 , and a plurality of bulb sockets  1216 . The sides of the reflector are sloped at approximately 60 degrees and these surface are gold plated to enhance reflectivity. The cover  1210  contains sockets  1218  that match the sockets  1216  in the base  1208 . To assemble the lamp assembly, the cover  1210  is positioned over the base  1208 , the sockets are aligned and the cover and base are braised to one another. As such, the cover  1210  and channel  1214  form a conduit (i.e., coolant jacket  951  in FIG. 10) for carrying coolant through the lamp assembly  908 . Preferably there are six bulb sockets evenly distributed about a 7.5 inch radius relative to the center of the assembly. The reflector shape as well as bulb placements provides efficient delivery of the IR energy to uniformly heat the dome. 
     FIGS. 13 through 17 depict detailed perspective views of the various components of the fan assembly  904 . For best understanding of the invention, the reader should simultaneously refer to FIGS. 13-18. 
     As mentioned above with respect to FIGS. 9 and 10, the fan assembly  904  contains a fan  934  (motor, impeller and mounting bracket), an upper stator  930  and a lower stator  932 . The upper and lower stators are separated from one another by a fan cowling  931 . 
     The lower stator  932  (shown in FIG. 13) defines a central aperture  1300  that, when the lower stator  932  is affixed atop the lamp assembly, the aperture  1300  is aligned with the central air flow aperture of the lamp assembly. The stator  932  contains a plurality of stator blades  936  (one of which is shown) positioned about the inner circumference of the stator  932 . Each of those blades  936  is curved to perform the air flow control that maintains an axial air flow through the central aperture  1300  and uniformly distributes the air to the dome surface. In essence, the lower stator  932  focuses the air flow from the fan onto the center of the dome. Consequently, this axial flow of air moves radially across the dome toward the dome&#39;s edge and convectively cools the entire dome. 
     More specifically, the stator  932  contains a blade mounting ring  1302  and a plurality of blades  936 . The blade mounting ring  1302  is milled from a block of aluminum to contain a vertical portion  1304  for mounting to the upper surface of the lamp assembly, a mounting flange  1306  for supporting the fan cowling  931  and defining the central aperture  1300 , and a slanted portion  1308  for interconnecting the vertical portion  1304  with the flange  1304 . The slanted portion  1308  is slanted inward at approximately 45 degrees from vertical. The fan cowling, stator ring and lamp housing are sized appropriately to deliver the maximum airflow to the dome surface. The vertical portion  1304  and the flange  1306  contain a plurality of mounting holes for respectively attaching the stator  932  to the fan cowling and the lamp assembly. The slanted portion  1308  contains a plurality of blade mounting holes  1310  (e.g., nine holes) formed and evenly distributed about the inner edge circumference of the slated portion  1308 . Each hole maintains a blade  936  in a particular orientation that is described in detail below. 
     As shown in FIG. 14, each blade  936  has a pin  1400  extending from edge  1404  for locating the blade onto the mounting ring  1302 . The pin  1400  is press fit into the mounting holes  1310 . Each blade is formed with a radius curvature  1402  that is 10% of the radius of the lamp assembly aperture  936 . The curvature is important to redirect the air flow velocity from a radial direction to a conically linear flow to uniformly blanket the dome surface. When affixed to the mounting ring  1302 , an edge  1404  abuts slanted surface  1308 . As such, the orientation and curvature of the blades about the center aperture  1300  of the stator  936  maintains the axial air flow toward the dome. 
     The lower stator  932  is affixed to the fan cowling  931  shown in FIG.  15 . The cowling  931  is a cylinder  1500  that defines a central aperture  1502 . The upper and lower edges of the cylinder  1500  are terminated with peripheral mounting flanges  1504  and  1506 . These flanges have mounting holes to facilitate affixing the upper and lower stators to the cowling. Additionally, the fan mounting bracket (not shown) is affixed to the upper flange  1506  to maintain the fan in a centrally located position within the cowling. 
     FIG. 16 depicts a top plan view of the upper stator  930  and FIG. 17 depicts a side plan view of the upper stator  930 . The upper stator  930  is a die-cut sheet of metal containing a plurality of stator blades  1600  that circumscribe a central aperture  1602 . Specifically, the stator  930  contains a mounting ring  1604  having a plurality of blades  1600  (e.g., eight) extending inwardly therefrom. The mounting ring contains a pattern of mounting holes  1606  for affixing the upper stator  930  to the cowling  931 . The stator blades extend tangential to the inner circumference of the mounting ring  1604 . Each blade  1600  is approximately 1.75 inches wide and is bent downward toward the fan at an angle of 25 degrees ±15% of the angle. The blades extend in a direction that is opposite the direction of rotation of the fan. The upper stator  930  reduces the back flow that would otherwise occur within the closed loop cooling system. As such, the upper stator, by reducing the back flow, significantly enhances the air flow toward the dome. 
     FIG. 18 depicts a perspective view of the coiling tubes  920  that chill the air flowing through the cooling chamber. The tubes  920  have a 0.375 inch inner diameter and are arranged as a plurality of circular loops  1800   n  (where n is an integer greater than or equal to one) that begin at an inlet manifold  1802  and terminate into an outlet manifold  1804 . The tubes are generally brazed to the manifolds. Each tube contains a thermally conductive conduit with a plurality of thermally conductive radial fins extending from the surface of the conduit. As such, the finned tubing provides a substantial surface area such that a substantial amount of heat can be removed form the air flowing across the tubes. 
     As with the first embodiment of the invention, the second embodiment of the invention also features a number of safety interlocks that are implemented to avoid injury or damage to the hardware. For example, in FIG. 10, an airflow photoelectric sensor  962  is provided to trigger a shut-down of the RF power and the heating lamps in the event of a fan failure. In addition, there are two over temperature sensors  964  and  966 , located on the lamp assembly  908 , which trigger the shut-down of the RF power and the lamp power in the event of overheating of the dome temperature control system. Furthermore, there is at least one interlock switch  960  (and, generally, there are three) that senses removal or improper seating of the fan cover  942 . As such, removal or improper seating of the cover triggers a shut-down of the RF power, lamp power and the high voltage supply to the electrostatic chuck that retains a wafer within the etch chamber. All of the interlock switches are positioned at a distance from the RF antenna and are located outside of the fan-lamp-baffle assembly such that the RF field does not interfere with the operation of the interlock switches or the circuitry related with the switches. The electrical circuitry of the second embodiment of the invention is substantially similar to the schematic diagram of FIG.  6 . 
     Using the apparatus of either the first or second embodiments of the present invention, the dome is designed to be maintained at a temperature of ±10° C. about a nominal temperature of 65-80° C. However, experimentally using the apparatus of the present invention, dome temperatures have been maintained within ±5° C. with energy removal of approximately 1200 watts. 
     FIG. 19 depicts a cross-sectional view of an end-point detector  1900  incorporated into the apparatus of the present invention. Generally, end-point detectors are used to monitor the progress of a process being performed within the reaction chamber  1914 . The depicted end-point detector  1900  is uniquely coupled to a transparent window  1902  located near the apex of the dome  938 . The window is, for example, transparent to visible and/or ultraviolet light. The detector  1902  is connected to the exterior of the temperature control apparatus  900  through a fiber optic conductor  1904 . The conductor  1904  passes through an aperture in the baffle  912 , the inner housing  916  and the outer housing  914 . a conductor support  1906  is mounted to the exterior of the housing  914  to provide a seal surrounding the conductor  1904 . 
     In operation, a laser beam  1908  (or other source of measuring signal) is coupled to the optical fiber conductor, the light passes through the detector  1900 . The detector collimates the light and directs t;he beam toward a wafer  1910  supported by a wafer pedestal  1912  within the reaction chamber  1914 . The beam reflects from the wafer surface and propagates back through the detector  1900  to the conductor  1904 . Ultimately, the reflected beam is compared to the transmitted beam to determine process status. This form of end-point detector is disclosed in commonly assigned U.S. patent application Ser. No. 08/944,240, filed Oct. 6, 1997 and herein incorporated by reference. 
     To incorporate this form of end-point detector into the present invention, the baffle must support the lamp assembly at a distance from the dome to enable the detector to be mounted centrally upon the dome. Such a central mounting location provides an optimal field of view for the detector. 
     Additionally, the lamps must be spaced about the detector such that the detector does not interfere with the uniform heating of the chamber environment. The optical feedthrough, e.g. conductor  1904  and support  1906 , are generally fabricated from dielectric materials to prevent interference with the RF fields produced by the antenna coil  940 . In addition, the use of dielectric materials provides a safety feature to prevent hazardous RF shock or burns due to charging of the optical system. 
     Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.