Patent Publication Number: US-7718932-B2

Title: Electrostatic chuck having radial temperature control capability

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of prior application Ser. No. 11/245,764, filed on Oct. 6, 2005, now U.S. Pat. No. 7,161,121, which is a continuation-in-part of prior application No. 11/001,218, filed on Nov. 30, 2004, now U.S. Pat. No. 7,274,004, which is a divisional of application Ser. No. 10/062,395, filed on Feb. 1, 2002, now U.S. Pat. No. 6,847,014 B1, which is a continuation-in-part of application Ser. No. 09/846,432, filed on Apr. 30, 2001, now abandoned. This application is also related to application Ser. No. 11/001,219, filed on Nov. 30, 2004, and application Ser. No. 11/004,179, filed on Dec. 2, 2004. The disclosure of each above-identified application is incorporated herein by reference. 

   BACKGROUND 
   Semiconductor wafer (“wafer”) fabrication often includes exposing a wafer to a plasma to allow the reactive constituents of the plasma to modify the surface of the wafer, e.g., remove material from unprotected areas of the wafer surface. The wafer characteristics resulting from the plasma fabrication process are dependent on the process conditions, including the plasma characteristics and wafer temperature. For example, in some plasma processes a critical dimension, i.e., feature width, on the wafer surface can vary by about one nanometer per degree Celsius of wafer temperature. It should be appreciated that differences in wafer temperature between otherwise identical wafer fabrication processes will result in different wafer surface characteristics. Thus, a drift in process results between different wafers can be caused by variations in wafer temperature during plasma processing. Additionally, center-to-edge wafer temperature variations can adversely effect a die yield per wafer. 
   A general objective in wafer fabrication is to optimize a die yield per wafer and fabricate each wafer of a common type in as identical a manner as possible. To meet these objectives, it is necessary to control fabrication parameters that influence the plasma processing characteristics across an individual wafer and among various wafers of a common type. Because plasma constituent reactivity is proportional to temperature, wafer temperature can have an strong influence on plasma processing results across the wafer and among various wafers. Therefore, a continuing need exists for improvements in wafer temperature control during plasma fabrication processes. 
   SUMMARY 
   In one embodiment, an electrostatic chuck is disclosed for controlling a radial temperature profile across a substrate when exposed to a plasma. The electrostatic chuck includes a support member having a bottom surface and a top surface. The top surface of the support member is configured to support the substrate. The electrostatic chuck also includes a base plate positioned beneath the support member and in a spaced apart relationship from the support member. The base plate includes a number of annular grooves that are each defined by an inner wall, an outer wall, and a bottom surface. A number of thermally insulating annular zone partitions are respectively disposed within the number of annular grooves of the base plate. Each of the annular zone partitions has a top surface connected in a sealed manner to the bottom surface of the support member. Also, each of the annular zone partitions has a bottom surface connected in a sealed manner to the bottom surface of the annular groove within which the annular zone partition is disposed. The spaced apart relationship between the base plate and the support member combines with the annular zone partitions to define a number of radially configured independently controllable gas volumes within the electrostatic chuck. 
   In another embodiment, another electrostatic chuck is disclosed for controlling a radial temperature profile across a substrate when exposed to a plasma. The electrostatic chuck includes a support member having a top surface configured to support the substrate. The support member also includes a planar region and a number of annular fin structures. The planar region is defined between the top surface configured to support the substrate and a bottom surface. Each of the annular fin structures extends perpendicularly from the bottom surface of the planar region of the support member. The electrostatic chuck further includes a base plate positioned beneath the support member and in a spaced apart relationship from the support member. The base plate includes a number of annular grooves. Each of the annular grooves is defined by an inner wall, an outer wall, and a bottom surface. A number of the annular grooves are defined to receive the annular fin structures of the support member. The electrostatic chuck also includes a number of thermally insulating annular zone partitions respectively disposed within a number of the annular grooves of the base plate that are not defined to receive the annular fin structures. Each of the annular zone partitions has a top surface connected in a sealed manner to the bottom surface of the planar region of the support member. Also, each of the annular zone partitions has a bottom surface connected in a sealed manner to the bottom surface of the annular groove within which the annular zone partition is disposed. The spaced apart relationship between the base plate and the support member combines with the annular zone partitions to define a number of radially configured independently controllable gas volumes within the electrostatic chuck. 
   In another embodiment, a system is disclosed for controlling a radial temperature profile across a substrate when exposed to a plasma. The system includes an electrostatic chuck, a gas supply system, and a computing platform. The electrostatic chuck is defined to include a number of independently controllable gas volumes. The independently controllable gas volumes are defined in a radial configuration relative to a top surface of the electrostatic chuck upon which the substrate is to be supported. The gas supply system is in fluid communication with each of the independently controllable gas volumes. The gas supply system is defined to regulate a gas pressure within each of the independently controllable gas volumes. The gas pressure within a particular independently controllable gas volume influences a thermal conductivity through the particular independently controllable gas volume. The computing platform is defined to monitor a gas pressure within each of the independently controllable gas volumes. In response to the monitored gas pressure within each of the independently controllable gas volumes, the computing platform is defined to control the gas supply system such that a prescribed radial temperature profile is maintained across the substrate to be supported by the electrostatic chuck. 
   In another embodiment, a plasma chamber for substrate processing is disclosed. The plasma chamber includes a chuck disposed within the chamber to hold a substrate in exposure to a plasma to be generated during operation of the chamber. The chuck is configured to have a plurality of independently controllable gas volumes defined between a base plate and a support member. 
   Other aspects and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an illustration showing a generalized representation of a plasma chamber for semiconductor wafer processing, in accordance with one embodiment of the present invention; 
       FIG. 2A  is an illustration showing a vertical cross-section view of an ESC, in accordance with one embodiment of the present invention; 
       FIG. 2B  is an illustration showing a close-up view of Zone 2 as previously described with respect to  FIG. 2A ; 
       FIG. 3A  is an illustration showing a vertical cross-section view of an ESC for controlling a radial temperature profile across the substrate when exposed to a plasma, in accordance with another embodiment of the present invention; 
       FIG. 3B  is an illustration showing a close-up view of the interface between the metal member and the base plate within a radial temperature control zone, in accordance with one embodiment of the present invention; and 
       FIG. 4  is an illustration showing a system for controlling a radial temperature profile across a substrate when exposed to a plasma, in accordance with one embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. 
     FIG. 1  is an illustration showing a generalized representation of a plasma chamber  100  for semiconductor wafer (“substrate” hereafter) processing, in accordance with one embodiment of the present invention. The chamber  100  is defined by surrounding walls  101 , a top  102 , and a bottom  104 . A chuck  103  is disposed within the chamber  100  to hold a substrate  105  in exposure to a plasma  107  to be generated within the chamber  100 . In one embodiment, the chuck  103  is defined as an electrostatic chuck (ESC) capable of being electrically charged to clamp the substrate  105  to the ESC  103 . In one embodiment, a coil  109  is defined above the chamber to provide energy for generating the plasma  107  within the chamber internal volume. 
   During operation, a reactant gas flows through the chamber  100  from a gas lead-in port (not shown) to a gas exhaust port (not shown). High frequency power (i.e., RF power) is then applied from a power supply (not shown) to the coil  109  to cause an RF current to flow through the coil  109 . The RF current flowing through the coil  109  generates an electromagnetic field about the coil  109 . The electromagnetic field generates an inductive current within the etching chamber  100  internal volume. The inductive current acts on the reactant gas to generate the plasma  107 . During the etching process, the coil  109  performs a function analogous to that of a primary coil in a transformer, while the plasma  107  performs a function analogous to that of a secondary coil in the transformer. Although the chamber  100  is described as an inductively coupled plasma chamber, it should be understood that the embodiments of the ESC  103  as presented herein are applicable to any type of plasma processing chamber. 
     FIG. 2A  is an illustration showing a vertical cross-section view of an ESC  103 A, in accordance with one embodiment of the present invention. The ESC  103 A is defined to control a radial temperature profile across the substrate  105  when exposed to a plasma. As will be described in further detail below, the ESC  103 A includes a number of independently controllable gas volumes that are each defined in a radial configuration relative to a top surface of the ESC  103 A upon which the substrate  105  is to be supported. Each of the independently controllable gas volumes includes a respective heat generation source. During exposure of the substrate  105  to the plasma, a gas pressure and heat generation within each independently controllable gas volume is controlled to influence thermal conduction through the ESC  103 A such that a prescribed radial temperature profile is achieved across the substrate  105 . 
   The ESC  103 A includes a support member  201  having a bottom surface  201 A and a top surface  201 B. In one embodiment, the support member  201  has a top-to-bottom surface thickness of about 1 millimeter (mm). However, it should be appreciated that in other embodiments the support member  201  can be defined to have essentially any thickness so long as the thickness is suitable for process requirements such as heat transfer. For example, in another embodiment, the support member  201  can have a thickness of about 1 cm. The term “about” as used herein means within plus or minus ten percent of a given value. The top surface  201 B of the support member  201  is configured to support the substrate  105  during exposure to the plasma. In various embodiments, the support member  201  can be defined as either a ceramic layer, a base material having a plasma sprayed ceramic coated thereon, a polyimide material, or a polyimide/metal stack. In yet another embodiment, the support member  201  is defined to include an upper layer of a first material and a lower layer of a second material. For example, the upper layer may be defined by a ceramic material, and the lower layer may be defined by a metal such as aluminum. Additionally, the upper and lower layers of the support member  201  can be thermally connected to one another through mechanical means or by using a thermally conductive adhesive. It should be appreciated that the support member  201  can be defined by essentially any material or material combination that is compatible with the substrate  105  and is capable of supporting the substrate  105  during exposure to the plasma while providing appropriate heat transfer performance. 
   In the embodiment of  FIG. 2A , the ESC  103 A uses electrical force to attract the substrate  105  to the top surface  201 B of the support member  201  and hold the substrate  105  during the plasma process. It should be appreciated, however, that the radial temperature control capability described herein with respect to the ESC  103 A can also be implemented within other types of chucks that do not necessarily use electrical force to clamp the substrate  105 . For example, the radial temperature control capability as described with respect to the ESC  103 A can also be implemented in a chuck that uses mechanical force to hold the substrate  105  during the plasma process. 
   The ESC  103 A also includes a base plate  205  positioned beneath the support member  201  and in a spaced apart relationship from the support member  201  in a region underlying the substrate  105 . In one embodiment, the base plate is defined to have a diameter of about 15 inches and a top-to-bottom thickness of about 2 inches. However, it should be appreciated that in other embodiments the base plate  205  can be defined to have a different size. In one embodiment, the base plate  205  is formed from a high thermal conductivity material, e.g., aluminum, and includes a number of cooling channels  213  such that the base plate  205  functions as a heat sink. In one embodiment, a liquid coolant such as water is flowed through the cooling channels  213  to remove heat from the ESC  103 A. It should be appreciated, however, that in other embodiments, other types of coolants can be used so long as the particular type of coolant is chemically compatible with the ESC  103 A materials. 
   The base plate  205  includes a number of annular grooves. Each of the annular grooves is defined by an inner wall, an outer wall, and a bottom surface. Also, each of the annular grooves is defined to be substantially centered about a vertical centerline of the ESC  103 A. For example, the exemplary ESC  103 A of  FIG. 2A  shows four annular grooves. The inner walls of the annular grooves are defined by surfaces  209 A,  209 D,  209 G, and  209 J. The outer walls of the annular grooves are defined by surfaces  209 B,  209 E,  209 H, and  209 K. The bottom surfaces of the annular grooves are defined by surfaces  209 C,  209 F,  209 I, and  209 L. 
   A number of thermally insulating annular zone partitions  207 A- 207 D are respectively disposed within the annular grooves of the base plate  205 . Each of the annular zone partitions  207 A- 207 D has a top surface connected in a sealed manner to the bottom surface  203 A of the support member  201 . Also, each of the annular zone partitions  207 A- 207 D has a bottom surface connected in a sealed manner to the bottom surface ( 209 C,  209 F,  209 I,  209 L) of the annular groove within which the annular zone partition  207 A- 207 D is disposed. It should be appreciated that each of the annular zone partitions  207 A- 207 D is positioned within its respective annular groove without contacting either the inner wall ( 209 A,  209 D,  209 G,  209 J) of the annular groove or the outer wall ( 209 B,  209 E,  209 H,  209 K) of the annular groove. Therefore, the thermally insulating annular zone partitions  207 A- 207 D function to limit an amount of solid-to-solid thermal conduction between the support member  201  and the base plate  205 . In one embodiment, the annular zone partitions  207 A- 207 D are defined from a plastic material that can be glued to both the support member  201  and the base plate  205 . 
   In one exemplary embodiment, the depth of the annular grooves within the base plate  205  is within a range extending from about 0.5 inch to about 0.75 inch. In this embodiment, it should be appreciated that the annular grooves are relatively deep, such that the thermally insulating annular zone partitions span a relatively large vertical distance from the support member  201  to the base plate  205 . Therefore, in this embodiment, it is less likely that an appreciable amount of heat transfer will occur between the support member  201  and the base plate  205  through the low thermal conductivity annular zone partitions  207 A- 207 D. 
   The base plate  205  also includes a peripheral support structure  206  upon which the support member  201  is disposed in a sealed manner. The support structure  206  not only provides structural support for the support member  201  and the substrate  105 , but also enables the RF power to flow from the base plate  205  through the support member  201  to the substrate  105 . In the embodiment of  FIG. 2A , the support structure  206  is depicted as an extension of the base plate  205 . However, in other embodiments, the support structure  206  can be defined by a separate low thermal conductivity material. For example, in one embodiment, the support structure  206  can be defined by an insulating material that is coated with a sufficiently thick RF conductive layer. 
   The spaced apart relationship between the base plate  205  and the support member  201  combined with the annular zone partitions  207 A- 207 D connected between the base plate  205  and the support member  201  serve to define a number of independently controllable gas volumes  225 A- 225 E within the ESC  103 A. More specifically, each of the independently controllable gas volumes  225 A- 225 E is defined between the base plate  205  and the support member  201 , with separation provided by the annular zone partitions  207 A- 207 D serving as insulating dividers. The ESC  103 A also includes a number of heat generation sources  211 A- 211 E, such as thin film heaters, respectively disposed within the number of independently controllable gas volumes  225 A- 225 E. Each of the heat generation sources  211 A- 211 E is defined to be in contact with the bottom surface  203 A of the support member  201  and to avoid contact with the base plate  205 . It should be appreciated that each of the independently controllable gas volumes corresponds to a radial temperature control zone (Zone 1-Zone 5) within the ESC  103 A. 
     FIG. 2B  is an illustration showing a close-up view of Zone 2 as previously described with respect to  FIG. 2A . It should be appreciated that the exemplary description provided for Zone 2 with respect to  FIG. 2B  is equally applicable to other radial temperature control zones within the ESC  103 A as depicted in  FIG. 2A . The gas volume  225 B of Zone 2 is shown to be bounded by the annular zone partitions  207 A and  207 B, the support member  201 , and the base plate  205 . A gas conduit  215  is provided within the base plate  205  to be in fluid communication with the gas volume  225 B. During the plasma process, a gas can be supplied or exhausted via the gas conduit  215 , as indicated by arrow  217 , to achieve a specified gas pressure within the gas volume  225 B. 
   A close-spaced gap  223  exists between the heat generation source  211 B and the portion of base plate  205  that is bounded by the annular grooves. More specifically, the gap  223  is defined a horizontal gap between the underside of the heat generation source  211 B and the opposing horizontal surface of the base plate  205 . In one embodiment, a vertical thickness of the gap is within a range extending from about 0.001 inch to about 0.003 inch. The majority of heat transfer between the metal layer  203  and the base plate  205  occurs through the heat generation source  211 B and across the horizontal gap  223 . It should be appreciated that by varying the gas pressure within the gas volume  225 B, thermal conductivity across the gap  223  can be varied. Thus, the gas pressure within the gas volume  225 B can be used to control the heat transfer through the ESC  103 A in the vicinity of the radial temperature control zone (Zone 2) corresponding to the gas volume  225 B. Therefore, by defining the ESC  103 A to include the multiple independently controlled gas volumes  225 A- 225 E, the ESC  103 A is defined to have multiple independently controllable radial temperature control zones (Zone 1-Zone 5). Although the embodiment of  FIG. 2A  depicts five radial temperature control zones, it should be appreciated that a different number of radial temperature control zones can be implemented in other embodiments. Implementation of more radial temperature control zones provides more capability with respect to controlling a radial temperature gradient across the substrate  105 . 
   By controlling the gas pressure, and hence thermal conductivity, within the various radial temperature control zones (Zone 1-Zone 5), a prescribed radial temperature gradient can be established from the center of the substrate  105  to the edge of the substrate  105 . In one embodiment, the gas pressure within a particular gas volume  225 A- 225 E can be controlled within a range extending from about 10 torr to about 1 atm. In one embodiment, helium gas is supplied to the various gas volumes  225 A- 225 E. However, in other embodiments, other types of gas or gas mixtures, e.g., nitrogen, can be supplied the various gas volumes  225 A- 225 E. In yet another embodiment, a liquid rather than a gas can be supplied to the various gas volumes  225 A- 225 E. Additionally, although the present invention is described as having radially-shaped temperature control zones, it should be appreciated that in other embodiments the various independently controllable gas volumes within the ESC  103 A can be defined to correspond to non-radial geometric configurations. For example, in other embodiments, the various gas volumes within the ESC  103 A can be defined in a hexagonally divided configuration or in a quadrant divided configuration. 
   The heat transfer through a particular radial temperature control zone (Zone 1-Zone 5) of the ESC  103 A is not only influenced by the pressure-dependent thermal conductivity of the gas within the particular zone, but is also influenced by the thermal output of the heat generation source  211 A- 211 E disposed within the particular zone. More specifically, each heat generation source  211 A- 211 E can be controlled independently to enhance the plasma heat flux to enable creation of stronger temperature gradient through the ESC  103 A from the substrate  105  to the base plate  205 . It should be appreciated that the thermal output of each heat generation sources  211 A- 211 E can be increased or decreased in a common manner to adjust a dynamic temperature range of a process window without changing the radial temperature profile as defined by the various gas pressures within the various radial temperature control zones. Additionally, the heat generation sources  211 A- 211 E can be under computer control based on temperature monitoring feedback or a prescribed process recipe to ensure that the appropriate temperature within each zone is maintained. For example, in one embodiment, closed-loop feedback control is used to control the heat generation sources in two zones, while the heat generation sources in the other three zones are statically set based on calculation. Rather than requiring temperature monitors in all five radial zones, this particular example embodiment only requires temperature monitors in the two zones that have closed-loop feedback control. Thus, this example embodiment saves the cost and space associated with temperature monitors in the three zones that do not have closed-loop feedback control. In addition to the above-described example embodiment, it should be appreciated that many different schemes regarding heat generation source control can be implemented to satisfy varying process and system requirements. 
   In one embodiment, the heat generation source  211 A- 211 E present in each radial temperature control zone (Zone 1-Zone 5) can be part of a common heat generation source. In another embodiment, the heat generation source  211 A- 211 E present in each radial temperature control zone (Zone 1-Zone 5) can be independent. In one variation of this embodiment, each of the heat generation sources  211 A- 211 E is defined to provide a common thermal output and be commonly controlled. In another variation of this embodiment, each of the heat generation sources  211 A- 211 E is defined to be independently controlled. Additionally, in the embodiment of  FIGS. 2A-2B , the heat generation sources  211 A- 211 E are disposed within the gas volumes  225 A- 225 E and in contact with the bottom surface  203 A of the support member  201 . However, in another embodiment, each heat generation source  211 A- 211 E can be embedded within the support member  201  at a location overlying its respective radial temperature control zone (Zone 1-Zone 5). It should be appreciated that the flexibility in heat generation source configuration provides an extensive capability to compensate for non-uniform plasmas, particularly plasmas that are non-uniform in the radial direction. 
     FIG. 3A  is an illustration showing a vertical cross-section view of an ESC  103 B for controlling a radial temperature profile across the substrate  105  when exposed to a plasma, in accordance with another embodiment of the present invention. The ESC  103 B includes a support member  301  having a top surface  301 B configured to support the substrate  105 . It should be appreciated that in terms of material composition and flexibility of configuration, the support member  301  of  FIG. 3A  is equivalent to the support member  201  previously described with respect to  FIGS. 2A-2B . 
   The support member  301  includes a planar region  303 A and a number of annular fin structures  303 B. The planar region  303 A of the support member  301  is defined between the top surface  301 B and a bottom surface  301 A. Each of the number of annular fin structures  303 B extends perpendicularly from the bottom surface  301 A of the planar region  303 A. In one embodiment, a top-to-bottom surface thickness of the planar region  303 A is about 1 mm. However, it should be appreciated that in other embodiments the top-to-bottom surface thickness of the planar region  303 A can be defined to have essentially any thickness so long as the thickness is suitable for process requirements such as heat transfer. 
   The ESC  103 B also includes a base plate  305  positioned beneath the support member  301  and in a spaced apart relationship from the support member  301  in a region underlying the substrate  105 . As with the base plate  205 , the base plate  305  is formed from a high thermal conductivity material and includes a number of cooling channels  213  such that the base plate  305  functions as a heat sink. In a manner similar to the base plate  205  previously described with respect to  FIGS. 2A-2B , the base plate  305  includes a number of annular grooves. Each interior annular groove is defined by an inner wall, an outer wall, and a bottom surface. The exterior annular groove is defined by an inner wall and a bottom surface. A number of the annular grooves are defined to receive the annular fin structures  303 B of the metal member  303 . Also, a number of annular grooves are defined to receive thermally insulating zone partitions. 
     FIG. 3B  is an illustration showing a close-up view of the interface between the support member  301  and the base plate  305  within a radial temperature control zone (Zone 1-Zone 5), in accordance with one embodiment of the present invention. The annular grooves for receiving the annular fin structures  303 B are defined by a respective inner wall ( 309 D,  309 G,  309 J), a respective outer wall ( 309 E,  309 H,  309 K), and a respective bottom surface ( 309 F,  309 I,  309 L). In a similar manner, each of the annular fin structures  303 B is defined by a respective inner surface, a respective outer surface, and a respective bottom surface. The spaced apart relationship between the base plate  305  and the support member  301  forms a first gap  323 A between the inner wall of the annular groove and the inner surface of the annular fin structure received by the annular groove. The spaced apart relationship between the base plate  305  and the support member  301  also forms a second gap  323 B between the outer wall of the annular groove and the outer surface of the annular fin structure received by the annular groove. In one embodiment, each of the first and second gaps  323 A and  323 B have a thickness within a range extending from about 0.001 inch to about 0.003 inch. 
   In one embodiment, the support member  301  and the base plate  305  can be accurately machined. In this embodiment, use of index points can enable accurate positioning of the annular fin structures  303 B within their respective annular grooves in the base plate  305 . Additionally, it should be appreciated that a compensating variation in gap thickness  323 A and  323 B on opposing sides of a particular annular fin structure  303 B will cause the net thermal conductivity from the particular annular fin structure  303 B to the base plate  305  to be substantially unaffected by variations in the thickness of the gaps  323 A and  323 B. 
   The spaced apart relationship between the base plate  305  and the support member  301  forms a third gap  327  between the base plate  305  and the bottom surface  301 A of the planar region  303 A of the support member  301 . The spaced apart relationship between the base plate  305  and the support member  301  also forms a fourth gap  329  between the bottom surface of the annular fin structures  303 B and the base plate  305 . Because heat transfer occurs primarily between the inner and outer surfaces of the annular fin structures  303 B and the inner and outer walls of the annular grooves, respectively, the thickness of gaps  327  and  329  are not critical. Therefore, the thickness of gaps  327  and  329  can be made relatively large to ensure that the support member  301  does not contact the base plate  305  during assembly of the ESC  103 B. 
   The ESC  103 B also includes a number of thermally insulating annular zone partitions  207 A- 207 D respectively disposed within a number of the annular grooves in the base plate  305  that are not defined to receive the annular fin structures  303 B. Each of the annular zone partitions  207 A- 207 D has a top surface connected in a sealed manner to the bottom surface  301 A of the planar region  303 A of the support member  301 . Also, each of the annular zone partitions  207 A- 207 D has a bottom surface connected in a sealed manner to the bottom surface of the annular groove within which the annular zone partition  207 A- 207 D is disposed. Additionally, each of the annular zone partitions  207 A- 207 D is positioned within its respective annular groove without contacting either the inner wall or the outer wall of the annular groove. 
   The spaced apart relationship between the base plate  305  and the support member  301  combines with the annular zone partitions  207 A- 207 D connected between the base plate  305  and the support member  301  to define a number of independently controllable gas volumes within the ESC  103 B. For example,  FIG. 3B  shows an independently controllable gas volume  325  defined between the base plate  305  and the support member  301 , with separation provided by the annular zone partitions  207  serving as insulating dividers. It should be appreciated that each of the independently controllable gas volumes corresponds to a radial temperature control zone (Zone 1-Zone 5) within the ESC  103 B. By controlling the gas pressure, and hence thermal conductivity, within the various radial temperature control zones (Zone 1-Zone 5), a prescribed radial temperature gradient can be established from the center of the substrate  105  to the edge of the substrate  105 . As with the ESC  103 A of  FIGS. 2A-2B , various embodiments of the ESC  103 B can implement a different number of radial temperature control zones or a different geometric configuration of temperature control zones. Also, as with the ESC  103 A, various embodiments of the ESC  103 B can supply helium gas, nitrogen gas, or other types of gas/gas mixtures to the gas volumes within each radial temperature control zone. 
   The ESC  103 B also includes a number of heat generation sources  311 , such as thin film heaters, respectively disposed within the number of independently controllable gas volumes. In one embodiment, each of the heat generation sources  311  is in contact with the bottom surface  301 A of the planar region  303 A of the support member  301  between adjacent annular fin structures  303 B. Each of the heat generation sources  311  is defined to avoid contact with the base plate  305 . In one embodiment, the heat generation source  311  present in each radial temperature control zone (Zone 1-Zone 5) can be part of a common heat generation source. In another embodiment, the heat generation source  311  present in each radial temperature control zone (Zone 1-Zone 5) can be independent. In one variation of this embodiment, each of the heat generation sources  311  is defined to provide a common thermal output and be commonly controlled. In another variation of this embodiment, each of the heat generation sources  311  is defined to be independently controlled. Additionally, in another embodiment, each heat generation source  311  can be embedded within the support member  301  at a location overlying its respective radial temperature control zone (Zone 1-Zone 5). 
   As with the ESC  103 A of  FIGS. 2A-2B , the heat transfer through a particular radial temperature control zone (Zone 1-Zone 5) of the ESC  103 B is not only influenced by the pressure-dependent thermal conductivity of the gas within the particular zone, but is also influenced by the thermal output of the heat generation source  311  disposed within the particular zone. By controlling the gas pressure, and hence thermal conductivity, within the various radial temperature control zones (Zone 1-Zone 5) of the ESC  103 B, a prescribed radial temperature gradient can be established from the center of the substrate  105  to the edge of the substrate  105 . In one embodiment, the gas pressure within a particular gas volume of the ESC  103 B can be controlled within a range extending from about 10 torr to about 1 atm. Also, the thermal output of each heat generation source  311  can be increased or decreased in a common manner to adjust a dynamic temperature range of a process window without changing the radial temperature profile as defined by the various gas pressures within the various radial temperature control zones. 
   For a number of reasons, such as plasma reactant depletion, there tend to be fewer plasma reactants near the edge of the substrate during the plasma process. As a consequence, lateral etch rates change between the center of the substrate and the edge of the substrate. The lateral etch rates have a direct effect on the resulting critical dimension across the wafer. The multiple radial temperature control zone capability provided by the ESCs of the present invention enables compensation for lateral etch rate variation across the wafer by controlling the radial temperature profile across the wafer. For example, the ESCs of the present invention can create a wafer radial temperature profile as a process tuning vehicle primarily targeting critical, i.e., lateral, dimension control. Thus, the multiple radial temperature zone profiling capability provided by the ESCs of the present invention enable a better fit to critical dimension bias compensation data, particularly at the edge of the substrate. 
   Because the gas pressure within a particular radial temperature zone of the ESC can be adjusted quickly, the thermal conductivity through the particular radial temperature zone can also be adjusted quickly. As a result, the ESC enables real-time control of the radial temperature profile across the substrate. For example, by varying the gas pressures in the different radial zones, the substrate temperature can be changed by up to 4° C./sec. This rapid rate of temperature change can reduce temperature settling time between process steps in cases where the temperature profile must change between steps, which can lead to improved substrate throughput. The ESCs of the present invention also enable a center-to-edge substrate temperature gradient to exceed 30° C. Additionally, the heat generation sources present within the ESCs enable a global temperature profile to be varied by more than 40° C. 
     FIG. 4  is an illustration showing a system for controlling a radial temperature profile across a substrate when exposed to a plasma, in accordance with one embodiment of the present invention. The system includes the plasma processing chamber  100  having either the ESC  103 A or the ESC  103 B present therein. For ease of discussion, the term “ESC” as used in the remainder of this description will refer equally to either the ESC  103 A or the ESC  103 B. The ESC is defined to include a number of independently controllable gas volumes. In one embodiment, these gas volumes are defined in a radial configuration relative to a top surface of the ESC upon which the substrate  105  is to be supported. 
   The system also includes a gas supply system  401  in fluid communication with each of the plurality of independently controllable gas volumes, as indicated by arrow  413 . The gas supply system  401  is defined to regulate a gas pressure within each of the independently controllable gas volumes within the ESC. As previously discussed, the gas pressure within a particular independently controllable gas volume of the ESC influences a thermal conductivity through the particular independently controllable gas volume. Also, as previously discussed, the ESC includes a number of heat generation sources respectively disposed within each of the independently controllable gas volumes. Additionally, one or more of the independently controllable gas volumes of the ESC can include a temperature sensor and/or a pressure sensor. 
   The system further includes a computing platform  403  defined to monitor a temperature and a gas pressure within one or more of the independently controllable gas volumes of the ESC, as indicated by arrows  405  and  407 , respectively. In response to the monitored temperature and gas pressure within the independently controllable gas volumes of the ESC, the computing platform is defined to compute heat generation source and gas pressure adjustments for the independently controllable gas volumes as necessary to maintain a prescribed radial temperature profile across the substrate  105 . Then the computing platform  403  sends appropriate heat generation source control signals to the ESC, as indicated by arrow  409 . Also, the computing platform  403  sends appropriate gas pressure control signals to the gas supply system  401 , as indicated by arrow  411 . In response, the gas supply system  401  ensures that the gas pressure in the independently controllable gas volumes of the ESC is properly adjusted. 
   While this invention has been described in terms of several embodiments, it will be appreciated that those skilled in the art upon reading the preceding specifications and studying the drawings will realize various alterations, additions, permutations and equivalents thereof. Therefore, it is intended that the present invention includes all such alterations, additions, permutations, and equivalents as fall within the true spirit and scope of the invention.