Abstract:
A substrate support is provided, is configured to support a substrate in a plasma processing chamber, and includes first, second and third insulative layers, conduits and leads. The first insulative layer includes heater zones arranged in rows and columns. The second insulative layer includes conductive vias. First ends of the conductive vias are connected respectively to the heater zones. Second ends of the conductive vias are connected respectively to power supply lines. The third insulative layer includes power return lines. The conduits extend through the second insulative layer and into the third insulative layer. The leads extend through the conduits and connect to the heater zones. The heater zones are connected to the power return lines by the leads and are configured to heat corresponding portions of the substrate to provide a predetermined temperature profile across the substrate during processing of the substrate in the plasma processing chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. Non-Provisional application Ser. No. 14/056,604, filed on Oct. 17, 2013, which is a divisional of U.S. Non-Provisional application Ser. No. 12/582,991, filed on Oct. 21, 2009. The entire disclosures of the applications referenced above are incorporated herein by reference. 
     
    
     BACKGROUND OF THE DISCLOSURE 
       [0002]    With each successive semiconductor technology generation, substrate diameters tend to increase and transistor sizes decrease, resulting in the need for an ever higher degree of accuracy and repeatability in substrate processing. Semiconductor substrate materials, such as silicon substrates, are processed by techniques which include the use of vacuum chambers. These techniques include non plasma applications such as electron beam deposition, as well as plasma applications, such as sputter deposition, plasma-enhanced chemical vapor deposition (PECVD), resist strip, and plasma etch. 
         [0003]    Plasma processing systems available today are among those semiconductor fabrication tools which are subject to an increasing need for improved accuracy and repeatability. One metric for plasma processing systems is increased uniformity, which includes uniformity of process results on a semiconductor substrate surface as well as uniformity of process results of a succession of substrates processed with nominally the same input parameters. Continuous improvement of on-substrate uniformity is desirable. Among other things, this calls for plasma chambers with improved uniformity, consistency and self diagnostics. 
       SUMMARY OF THE INVENTION 
       [0004]    In accordance with one embodiment, a heating plate for a substrate support assembly used to support a semiconductor substrate in a semiconductor plasma processing apparatus, comprises at least a first electrically insulating layer, planar heater zones comprising at least first, second, third and fourth planar heater zones laterally distributed across the first electrically insulating layer, electrically conductive power supply lines comprising at least a first power supply line electrically connected to the first and second heater zones and a second power supply line electrically connected to the third and fourth heater zones, electrically conductive power return lines comprising at least a first power return line electrically connected to the first and third heater zones, and a second power return line electrically connected to the second and fourth heater zones. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0005]      FIG. 1  is a schematic of the cross-sectional view of a substrate support assembly in which a heating plate with an array of heater zones is incorporated, the substrate support assembly also comprising an electrostatic chuck (ESC). 
           [0006]      FIG. 2  illustrates the topological connection between power supply and power return lines to an array of heater zones in one embodiment of a heating plate which can be incorporated in a substrate support assembly. 
           [0007]      FIG. 3A  shows an embodiment wherein the power supply lines and the heater zones are on the same plane. 
           [0008]      FIG. 3B  shows the power return lines on a plane separated from the plane in  FIG. 3A  by an electrically insulating layer and the power return lines are connected to the heater zones through vias extending through the electrically insulating layer. 
           [0009]      FIG. 3C  is a schematic of the cross-sectional view of a substrate support assembly in which the heating plate of  FIG. 3A and 3B  is incorporated. 
           [0010]      FIG. 4A  shows an embodiment wherein the power supply lines and the heater zones are on the same plane. 
           [0011]      FIG. 4B  shows a plane separated from the plane in  FIG. 4A  by an electrically insulating layer wherein the power supply lines are connected to leads in this plane through vias, and brought to a single hole in the cooling plate (not shown). The power return lines on this plane are connected to the heater zones through vias extending between this plane and the plane in  FIG. 4A . The power return lines are also brought to a single hole in the cooling plate (not shown). 
           [0012]      FIG. 5A  shows an embodiment wherein the heater zones are on a plane without the power supply lines or power return lines on that plane. The heater zones are connected to power supply lines and power return lines on one or more different planes through vias. 
           [0013]      FIG. 5B  shows the power supply lines on a second plane separated from the plane in  FIG. 5A  by an electrically insulating layer. The power supply lines are connected to the heater zones through vias extending between the two planes in  FIG. 5A and 5B . 
           [0014]      FIG. 5C  shows the power return lines on a third plane separated from the planes in  FIG. 5A and 5B  by another electrically insulating layer. The power return lines are connected to the heater zones through vias extending between all three planes in  FIG. 5A-C . The leads connected to the power supply lines in  FIG. 5B  are also routed through feedthroughs in this plane. 
           [0015]      FIG. 5D  is a schematic of the cross-sectional view of a substrate support assembly in which the heating plate in  FIG. 5A-C  is incorporated. 
           [0016]      FIG. 5E  is a schematic of the cross-sectional view of a substrate support assembly in which an alternative heating plate in  FIG. 5A-C  is incorporated. 
           [0017]      FIG. 6  is a schematic of the cross-sectional view of a substrate support assembly in which a heating plate is incorporated, the substrate support assembly further including a primary heater layer above the array of heater zones, the primary heater located on an additional plane separated from all the planes in the heating plate by an electrically insulating layer. 
           [0018]      FIG. 7A  is a schematic of an exemplary plasma processing chamber, which can include a substrate support assembly with the heating plate described herein. 
           [0019]      FIG. 7B  is a schematic of an RF isolation approach. 
           [0020]      FIG. 8  shows a block diagram of signal flow in one embodiment of the control electronics for the substrate support assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Radial and azimuthal substrate temperature control in a semiconductor processing apparatus to achieve desired critical dimension (CD) uniformity on the substrate is becoming more demanding. Even a small variation of temperature may affect CD to an unacceptable degree, especially as CD approaches sub-100 nm in semiconductor fabrication processes. 
         [0022]    A substrate support assembly may be configured for a variety of functions during processing, such as supporting the substrate, tuning the substrate temperature, and power supplying radio frequency power. The substrate support assembly can comprise an electrostatic chuck (ESC) useful for electrostatically clamping a substrate onto the substrate support assembly during processing. The ESC may be a tunable ESC (T-ESC). A T-ESC is described in commonly assigned U.S. Pat. Nos. 6,847,014 and 6,921,724, which are hereby incorporated by reference. The substrate support assembly may comprise a ceramic substrate holder, a fluid-cooled heat sink (hereafter referred to as cooling plate) and a plurality of concentric heater zones to realize step by step and radial temperature control. Typically, the cooling plate is maintained between 0° C. and 30° C. The heaters are located on the cooling plate with a layer of thermal insulator in between. The heaters can maintain the support surface of the substrate support assembly at temperatures about  0  ° C. to 80° C. above the cooling plate temperature. By changing the heater power within the plurality of heater zones, the substrate support temperature profile can be changed between center hot, center cold, and uniform. Further, the mean substrate support temperature can be changed step by step within the operating range of 0 to 80° C. above the cooling plate temperature. A small azimuthal temperature variation poses increasingly greater challenges as CD decreases with the advance of semiconductor technology. 
         [0023]    Controlling temperature is not an easy task for several reasons. First, many factors can affect heat transfer, such as the locations of heat sources and heat sinks, the movement, materials and shapes of the media. Second, heat transfer is a dynamic process. Unless the system in question is in heat equilibrium, heat transfer will occur and the temperature profile and heat transfer will change with time. Third, non-equilibrium phenomena, such as plasma, which of course is always present in plasma processing, make theoretical prediction of the heat transfer behavior of any practical plasma processing apparatus very difficult if not impossible. 
         [0024]    The substrate temperature profile in a plasma processing apparatus is affected by many factors, such as the plasma density profile, the RF power profile and the detailed structure of the various heating the cooling elements in the chuck, hence the substrate temperature profile is often not uniform and difficult to control with a small number of heating or cooling elements. This deficiency translates to non-uniformity in the processing rate across the whole substrate and non-uniformity in the critical dimension of the device dies on the substrate. 
         [0025]    In light of the complex nature of temperature control, it would be advantageous to incorporate multiple independently controllable heater zones in the substrate support assembly to enable the apparatus to actively create and maintain the desired spatial and temporal temperature profile, and to compensate for other adverse factors that affect CD uniformity. 
         [0026]    Described herein is a heating plate for a substrate support assembly in a semiconductor processing apparatus with multiple independently controllable heater zones. This heating plate comprises a scalable multiplexing layout scheme of the heater zones and the power supply and power return lines. By tuning the power of the heater zones, the temperature profile during processing can be shaped both radially and azimuthally. Although this heating plate is primarily described for a plasma processing apparatus, this heating plate can also be used in other semiconductor processing apparatuses that do not use plasma. 
         [0027]    Also described are methods for manufacturing this heating plate, a substrate support assembly comprising such a heating plate, and methods for powering and controlling a substrate support assembly comprising such a heating plate. 
         [0028]    The heater zones in this heating plate are preferably arranged in a defined pattern, for example, a rectangular grid, a hexagonal grid, a polar array, concentric rings or any desired pattern. Each heater zone may be of any suitable size and may have one or more heater elements. All heater elements in a heater zone are turned on or off together. To minimize the number of electrical connections, power supply and power return lines are arranged such that each power supply line is connected to a different group of heater zones and each power return line is connected to a different group of heater zones with each heater zone being in one of the groups connected to a particular power supply line and one of the groups connected to a particular power return line. No two heater zones are connected to the same pair of power supply and power return lines. Thus, a heater zone can be activated by directing electrical current through a pair of power supply and power return lines to which this particular heater zone is connected. The power of the heater elements is preferably smaller than 20 W, more preferably 5 to 10 W. The heater elements may be resistive heaters, such as polyimide heaters, silicone rubber heaters, mica heaters, metal heaters (e.g. W, Ni/Cr alloy, Mo or Ta), ceramic heaters (e.g. WC), semiconductor heaters or carbon heaters. The heater elements may be screen printed, wire wound or etched foil heaters. In one embodiment, each heater zone is not larger than four device dies being manufactured on a semiconductor substrate, or not larger than two device dies being manufactured on a semiconductor substrate, or not larger than one device die being manufactured on a semiconductor substrate, or between 2 and 3 cm 2  in area to correspond to the device dies on the substrate. The thickness of the heater elements may range from 2 micrometers to 1 millimeter, preferably 5-80 micrometers. To allow space between heater zones and/or power supply and power return lines, the total area of the heater zones may be up to 90% of the area of the upper surface of the substrate support assembly, e.g. 50-90% of the area. The power supply lines or the power return lines (power lines, collectively) may be arranged in gaps ranging from 1 to 10 mm between the heater zones, or in separate planes separated from the heater zones plane by electrically insulating layers. The power supply lines and the power return lines are preferably made as wide as the space allows, in order to carry large current and reduce Joule heating. In one embodiment, in which the power lines are in the same plane as the heater zones, the width of the power lines is preferably between 0.3 mm and 2 mm. In another embodiment, in which the power lines are on different planes than the heater zones, the width of the power lines can be as large as the heater zones, e.g. for a 300 mm chuck, the width can be 1 to 2 inches. The materials of the power supply and power return lines may be the same as or different from the materials of the heater elements. Preferably, the materials of the power supply and power return lines are materials with low resistivity, such as Cu, Al, W, Inconel® or Mo. 
         [0029]      FIGS. 1-2  show a substrate support assembly comprising one embodiment of the heating plate having an array of heater zones  101  incorporated in two electrically insulating layers  104 A and  104 B. The electrically insulating layers may be a polymer material, an inorganic material, a ceramic such as silicon oxide, alumina, yttria, aluminum nitride or other suitable material. The substrate support assembly further comprises (a) an ESC having a ceramic layer  103  (electrostatic clamping layer) in which an electrode  102  (e.g. monopolar or bipolar) is embedded to electrostatically clamp a substrate to the surface of the ceramic layer  103  with a DC voltage, (b) a thermal barrier layer  107 , (c) a cooling plate  105  containing channels  106  for coolant flow. 
         [0030]    As shown in  FIG. 2 , each of the heater zones  101  is connected to one of the power supply lines  201  and one of the power return lines  202 . No two heater zones  101  share the same pair of power supply  201  and power return  202  lines. By suitable electrical switching arrangements, it is possible to connect a pair of power supply  201  and power return  202  lines to a power supply (not shown), whereby only the heater zone connected to this pair of lines is turned on. The time-averaged heating power of each heater zone can be individually tuned by time-domain multiplexing. In order to prevent crosstalk between different heater zones, a rectifier  250  (e.g. a diode) may be serially connected between each heater zone and the power supply lines connected thereto (as shown in  FIG. 2 ), or between each heater zone and the power return lines connected thereto (not shown). The rectifier can be physically located in the heating plate or any suitable location. Alternatively, any current blocking arrangement such as solid state switches can be used to prevent crosstalk. 
         [0031]      FIGS. 3A, 3B and 3C  show a substrate support assembly comprising an ESC, a cooling plate, and one embodiment of the heating plate wherein the heater zones  101  and power supply lines  201  are arranged in a first plane  302 , and the power return lines  202  are arranged in a second plane  303  separated from the first plane  302  by an electrically insulating layer  304 . The power return lines  202  are connected to the heater zones  101  by conductive vias  301  in the electrically insulating layer  304 , extending between the first plane  302  and the second plane  303 . 
         [0032]    In use, the power supply lines  201  and power return lines  202  are connected to circuitry external to the heating plate through holes or conduits in the cooling plate. It should be appreciated that the presence of holes or conduits in the cooling plate can affect the temperature uniformity of substrate support assembly adversely, therefore reducing the number of holes or conduits in the cooling plate can enhance temperature uniformity. In addition, a small number of holes makes placing them around the edge of the substrate support assembly possible. For example, a single power supply conduit in the cooling plate can be used to feed electrical leads to the power supply lines  201 . In one embodiment ( FIG. 4A and 4B ), the heater zones  101  and power supply lines  201  are arranged in a first plane  402 . The power supply lines  201  are connected to leads  404  in a second plane  403  through conductive vias  301  extending between the first plane  402  and the second plane  403 . The second plane  403  is separated from the first plane  402  by an electrically insulating layer (not shown). The power return lines  202  are arranged in the second plane  403  and are connected to the heater zones  101  through conductive vias  301  extending between the first plane  402  and the second plane  403 . In the second plane  403 , the leads  404  are brought through a hole or conduit  401  in the cooling plate while maintaining electrical insulation between the leads. Similarly, the power return lines  202  are connected to leads  405  brought through a hole or conduit  406  in the cooling plate while maintaining electrical insulation between the leads  405 . 
         [0033]      FIGS. 5A, 5B, 5C and 5D  show a substrate support assembly comprising yet another embodiment of the heating plate, the heater zones  101  are arranged in a first plane  501 ; the power supply lines  201  are arranged in a second plane  502 ; and the power return lines  202  are arranged in a third plane  503 . The first plane  501 , second plane  502  and third plane  503  are separated from each other by electrically insulating layers  504  and  304 . The power supply lines  201  and power return lines  202  are connected to the heater zones  101  through conductive vias  301  in the electrically insulating layers  304  and  504 , extending between the planes  501 ,  502  and  503 . Leads (not shown) connected to the power supply lines  201  are routed through holes or conduits  505  in the layer  504 . It should be appreciated that the planes  501 ,  502  and  503  may be arranged in any order in the vertical direction, provided that the vias and conduits are suitably arranged. Preferably, the heaters are arranged closest to the substrate support assembly upper surface.  FIG. 5E  shows an embodiment wherein each heater zone  101  is connected to the power return line  202  through a rectifier  506  (e.g. a diode). The rectifier  506  only allows electric current flowing from the power supply line  201  through the heater zone  101  to the power return line  202 , and thus prevents crosstalk between heater zones. 
         [0034]    The substrate support assembly can comprise an additional electrically insulating layer  604  in which one or more additional heaters (hereafter referred to as primary heaters  601 ) are incorporated ( FIG. 6 ). Preferably, the primary heaters  601  are individually controlled high-power heaters. The power of the primary heaters is between 100 and 10000 W, preferably, between 1000 and 5000 W. The primary heaters may be arranged as a rectangular grid, concentric annular zones, radial zone or combination of annular zones and radial zones. The primary heaters may be used for changing the mean temperature, tuning the radial temperature profile, or step-by-step temperature control on the substrate. The primary heaters may be located above or below the heater zones of the heating plate. 
         [0035]    In one embodiment, at least one of the insulating layers in the heating plate is a sheet of polymer material. 
         [0036]    In another embodiment, at least one of the insulating layers in the heating plate is a sheet of inorganic material such as ceramic or silicon oxide. Examples of suitable insulating and conductive material for use in manufacture of ceramic chucks are disclosed in commonly assigned U.S. Pat. No. 6,483,690, the disclosure of which is hereby incorporated by reference. 
         [0037]    A substrate support assembly can comprise an embodiment of the heating plate, wherein each heater zone of the heating plate is of similar size to or smaller than a single device die or group of device dies on the substrate so that the substrate temperature, and consequently the plasma etching process, can be controlled for each device die position to maximize the yield of devices from the substrate. The scalable architecture of the heating plate can readily accommodate the number of heater zones required for die-by-die substrate temperature control (typically more than 100 dies on a substrate of 300-mm diameter) with minimal number of power supply lines, power return lines, and feedthroughs in the cooling plate, thus reduces disturbance to the substrate temperature, the cost of manufacturing and complexity of the substrate support assembly. Although not shown, the substrate support assembly can comprise features such as lift pins for lifting the substrate, helium back cooling, temperature sensors for providing temperature feedback signals, voltage and current sensors for providing heating power feedback signals, power feed for heaters and/or clamp electrode, and/or RF filters. 
         [0038]    In one embodiment of the method for manufacturing the heating plate, where the insulating layers are ceramic, the insulating layers may be formed by depositing the ceramic on a suitable substrate using techniques such as plasma spraying, chemical vapor deposition or sputtering. This layer can be an initial starting layer or one of the insulating layers of the heating plate. 
         [0039]    In one embodiment of the method for manufacturing the heating plate, where the insulating layers are ceramic, the insulating layers may be formed by pressing a mixture of ceramic powder, binder and liquid into sheets and drying the sheets (hereafter referred as green sheets). The green sheets can be about 0.3 mm in thickness. The vias may be formed in the green sheets by punching holes in the green sheets. The holes are filled with a slurry of conducting powder. The heater elements, power supply and power return lines may be formed by: screen printing a slurry of conducting powder (e.g. W, WC, doped SiC or MoSi 2 ), pressing a precut metal foil, spraying a slurry of conducting powder, or any other suitable technique. Recesses for accommodating any rectifiers such as diodes may be pressed during the forming process of the green sheets or cut in the green sheets after the forming process. Discrete component rectifiers may be mounted into these recesses. Multiple green sheets with a variety of components (power lines, vias, rectifiers and heater elements) are then aligned, pressed and sintered to form an entire heating plate. 
         [0040]    In another embodiment of the method for manufacturing the heating plate, where the insulating layers are ceramic, the insulating layers may be formed by pressing a mixture of ceramic powder, binder and liquid into green sheets and drying the green sheets. The green sheets can be about 0.3 mm in thickness. Holes are punched in the green sheets for accommodating vias. Recesses for accommodating any rectifiers such as diodes may be pressed during the forming process of the green sheets or cut in the green sheets after the forming process. Then, individual green sheets are sintered. The holes in the sintered sheets for accommodating vias are filled with a slurry of conducting power. The heater elements, power supply and power return lines may be screen printed with a slurry of conducting powder (e.g. W, WC, doped SiC or MoSi 2 ), or be formed using any other suitable technique, on the sintered sheets. Discrete component rectifiers may be mounted into the recesses in the sintered sheets. Multiple sintered sheets with a variety of components (lines, vias, rectifiers and heater elements) are then aligned and bonded with an adhesive to form an entire heating plate. 
         [0041]    In one embodiment where the insulating layers are silicon oxide sheets, the insulating layers may be formed by depositing a thin film silicon oxide onto a suitable substrate using techniques such as evaporation, sputtering, PVD, CVD, PECVD. 
         [0042]    In one preferred embodiment of the method for manufacturing the heating plate, a thin metal sheet (component layer) such as Al, Inconel® or Cu foil, is bonded (e.g. heat pressed, adhered with adhesive) to a first polymer film such as polyimide. A patterned resist film is applied to the surface of the component layer wherein the patterns define the shapes and positions of the electrical components such as heater elements, power supply lines or power return lines. The exposed metal is chemically etched and the resist pattern is retained in the remaining metal sheet. The resist is then removed by dissolution in a suitable solvent or dry stripping. A second polymer film with holes for accommodating vias (via layer) is aligned and bonded to the first polymer film. The sidewalls of the holes may be coated by plating metal therein. Any suitable number of component layers and via layers may be incorporated serially. Finally, exposed metal components are covered by a continuous polymer film for electrical insulation. 
         [0043]    In another embodiment, the heater elements, power supply and power return lines are made of metal films deposited (e.g. plasma sprayed, electroplated, chemical vapor deposition, or sputtered) on an insulating layer or substrate (e.g. a green sheet). 
         [0044]    In another embodiment, the heater elements, power supply and power return lines are made of a thin layer of amorphous conductive inorganic film such as indium tin oxide deposited (e.g. electroplated, chemical vapor deposition, or sputtered) on an insulating layer or substrate (e.g. a green sheet). 
         [0045]    In yet another embodiment, the heater elements, power supply and power return lines are made of a thin layer of conductive ceramic film deposited (e.g. chemical vapor deposition, or sputtered) on an insulating layer or substrate (e.g. a green sheet). 
         [0046]    In one embodiment, the power supply and power return lines in the heating plate may be connected to the external circuitry by terminal connectors such as spring tipped passthroughs embedded in but electrically insulated from the cooling plate. 
         [0047]    In another embodiment, the power supply and power return lines in the heating plate may be connected to the external circuitry by attaching (soldered, bonded with conductive adhesive or spot welded) lead wires to the power supply and power return lines and threading these lead wires through holes or conduits in the cooling plate. 
         [0048]    In a plasma processing system, the RF power applied in the plasma processing chamber is usually above 100 W, sometimes above 1000 W. The amplitude of RF voltages can exceed a kilovolt. Such strong RF power can easily affect the operation of the control and power circuit of the heater zones without proper filtration or isolation. An RF filter can be used to shunt the RF power away from the control and power circuit. An RF filter may be a simple broad-band filter or a tuned-filter for the specific RF frequencies used in the plasma processing system. An RF isolator, in contrast, eliminates direct electrical connection between any RF-coupled components and the control and power circuit. An RF isolator may be an optical coupler or a transformer. 
         [0049]    As an overview of how a plasma processing chamber operates,  FIG. 7A  shows a schematic of a plasma processing chamber comprising a chamber  713  in which an upper showerhead electrode  703  and a substrate support assembly  704  are disposed. A substrate  712  is loaded through a loading port  711  onto the substrate support assembly  704 . A gas line  709  supplies process gas to the upper showerhead electrode  703  which delivers the process gas into the chamber. A gas source  708  (e.g. a mass flow controller power supplying a suitable gas mixture) is connected to the gas line  709 . A RF power source  702  is connected to the upper showerhead electrode  703 . In operation, the chamber is evacuated by a vacuum pump  710  and the RF power is capacitively coupled between the upper showerhead electrode  703  and a lower electrode in the substrate support assembly  704  to energize the process gas into a plasma in the space between the substrate  712  and the upper showerhead electrode  703 . The plasma can be used to etch device die features into layers on the substrate  712 . The substrate support assembly  704  may have heaters incorporated therein. It should be appreciated that while the detailed design of the plasma processing chamber may vary, RF power is coupled through the substrate support assembly  704 . 
         [0050]      FIG. 7B  shows a schematic of an embodiment of RF filtration or isolation, wherein no filters or isolators are connected on the heater zone power supply and power return lines and the control and power circuit  705  is connected to a filter or isolator  706 B, which is connected to the electric ground  701 . The primary heaters (not shown), if present in the substrate support assembly, preferably have separate filters or isolators due to their high power. In this approach, the control and power circuit  705  floats at the RF potential or “high side”. This approach allows multiple heater zones to share only one filter or isolator. 
         [0051]    All the high side circuitry can be housed inside a local floating Faraday cage immediately under the substrate support assembly base structure. 
         [0052]    Alternatively, an isolation transformer is used as the single filter or isolator  706 B to isolate the power and control circuitry  705  from the RF. The control and power circuitry  705  of the heater zones should be capable of operating at relatively high frequency (25 to 250 KHz) because the transformer strongly attenuates DC and low frequency transmission. The control and power circuitry is referenced to a single floating potential (floating ground). This requires that the control and power circuitry connected to this isolation transformer must be subject to very similar RF exposure. If the RF potentials differ substantially between two groups of control and power circuits, significant RF current flows between these groups. In this scenario, each group must have its own filter or isolator, or there must be a filter or isolator between these groups. 
         [0053]    The filter or isolator  706 B may be physically located in the plasma processing chamber or any other suitable location. 
         [0054]    One embodiment of the heater control electronics is depicted in  FIG. 8 . A low side controller  809  may be a microcontroller unit (MCU) or a higher level device such as a computer (PC). Through an optical coupler  807 , the low side controller communicates digitally to the high side MCU  805  which interacts with the heater zones  801 , sensors  803 , and any auxiliary circuits  802 . If the high side MCU  805  has sufficient capability and local memory, any set-point and program may be preloaded into the high side MCU  805  before each run, thus eliminating the need of a real-time link to the low side controller  809 .  804  represents one-way communication links between modules.  806  represents two-way communication links between modules. 
         [0055]    In one embodiment of time-domain multiplexing schemes, the high side MCU supplies power to each heater zone power supply line sequentially. Only one power supply line is connected to a power supply at the same time. During the time when one power supply line is powered, the high side MCU may keep any or all power return lines connected to the floating reference for a portion of this duration. A heater zone is turned on when at least one of the power supply lines connected to this heater zone is connected to the power supply, and at least one of the power return lines connected to this heater zone is connected to the floating reference. The average power of a heater zone is directly proportional to the average duration it is turned on. Alternatively, during the time when one power supply line is powered, the high side MCU may keep any or all power return lines connected to the floating reference for this entire duration and regulate the power transmitted to each heater zone that is turned on. 
         [0056]    For example, with a 10-by-10 grid of heater zones, heater zones in row number N are connected to a power supply line number N; heater zones in column number M are connected to a power return line number M. The high side MCU may control heating such that each of the power supply lines is connected to the power supply for 100 ms, sequentially. For example, during the 100 ms of time when power supply line number 3 is connected to the power supply, the MCU is operable to connect power return lines number 7, 8, and 9 to the floating reference for 10, 50 and 100 ms, respectively, as directed by the particular heating requirement during this 100 ms. Thus, the heater zone in row number 3 and column number 7 has a duty cycle of 1%; the heater zone in row number 3 and column number 8 has a duty cycle of 5%; the heater zone in row number 3 and column number 9 has a duty cycle of 10%. In this particular example, the maximum peak power for each heater zone would be set to ten times the average maximum power desired. 
         [0057]    In order to prevent detectable temperature modulation, the switching frequencies and the entire multiplexing scheme are preferably sufficiently rapid that each heater zone gets addressed frequently (at least 1 Hz). Additional loop control may be implemented using feedback data from one of more temperature sensors. Voltage and current sensors can also be implemented if desired. These sensors can be configured to measure parameters such as temperatures on different locations on the substrate and power of heater zones. These measured parameters are sent to the control and power circuit to be compared with set targets of these parameters so that the control and power circuit can adjust the power delivered to the heater zones accordingly in order to minimize the difference between the measured parameters and their set targets. 
         [0058]    While a heating plate, methods of manufacturing the heating plate, a substrate support assembly comprising the heating plate, and a method of using a plasma processing chamber containing the substrate support assembly have been described in detail with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made, and equivalents employed, without departing from the scope of the appended claims. For instance, the substrate support assembly can include temperature sensors for monitoring substrate temperature, a power feed arrangement to power the ESC with desired clamping voltage, a lifting pin arrangement for raising and lowering a substrate, a heat transfer gas feed arrangement for supplying gas such as helium to the underside of the substrate, a temperature controlled liquid feed arrangement to supply heat transfer liquid to the cooling plate, a power feed arrangement to individually power primary heaters above or below the planar heater zones, a power feed arrangement to supply RF power at one or more frequencies to a lower electrode incorporated in the substrate support assembly, and the like.