Patent Publication Number: US-2007102118-A1

Title: Method and apparatus for controlling temperature of a substrate

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application is a divisional of U.S. patent application Ser. No. 10/960,874, filed Oct. 7, 2004, which is incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      Embodiments of the present invention generally relate to semiconductor substrate processing systems. More specifically, the invention relates to a method and apparatus for controlling temperature of a substrate in a semiconductor substrate processing system.  
      2. Description of the Related Art  
      In manufacture of integrated circuits, precise control of various process parameters is required for achieving consistent results within a substrate, as well as the results that are reproducible from substrate to substrate. During processing, changes in the temperature and temperature gradients across the substrate may be detrimental to material deposition, etch rate, step coverage, feature taper angles, and other parameters of semiconductor devices. As such, generation of the pre-determined pattern of temperature distribution across the substrate is one of critical requirements for achieving high yield.  
      In some processing applications, a substrate is retained to a substrate pedestal by an electrostatic chuck during processing. The electrostatic chuck is coupled to a base of the pedestal by clamps, adhesive or fasteners. The chuck may be provided with an embedded electric heater, as well as be fluidly coupled to a source of backside heat transfer gas for controlling substrate temperature during processing. However, conventional substrate pedestals have insufficient means for controlling substrate temperature distribution across the diameter of the substrate. The inability to control substrate temperature uniformity has an adverse effect on process uniformity both within a single substrate and between substrates, device yield and overall quality of processed substrates.  
      Therefore, there is a need in the art for an improved method and apparatus for controlling temperature of a substrate during processing the substrate in a semiconductor substrate processing apparatus.  
     SUMMARY OF THE INVENTION  
      The present invention generally is a method and apparatus for controlling temperature of a substrate during processing the substrate in a semiconductor substrate processing apparatus. The method and apparatus enhances temperature control across the diameter of a substrate, and may be utilized in etch, deposition, implant, and thermal processing systems, among other applications where the control of the temperature profile of a workpiece is desirable.  
      In one embodiment of the invention, a substrate pedestal assembly is provided. The pedestal assembly includes a support member that is coupled to a base using a material layer. The material layer has at least two regions having different coefficients of thermal conductivity. In another embodiment, the support member is an electrostatic chuck. In further embodiments, a pedestal assembly has channels formed between the base and support member for providing cooling gas in proximity to the material layer to further control heat transfer between the support member and the base, thereby facilitating control of the temperature profile of a substrate disposed on the support member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
       FIG. 1A  is a schematic diagram of an exemplary semiconductor substrate processing apparatus comprising a substrate pedestal in accordance with one embodiment of the invention;  
       FIGS. 1B-1C  are partial cross-sectional views of embodiments of a substrate pedestal having gaps formed in different locations in a material layer of the substrate pedestal.  
       FIG. 2  is a schematic cross-sectional view of the substrate pedestal taken along a line  2 - 2  of  FIG. 1A ;  
       FIG. 3  is a schematic partial cross-sectional view of another embodiment of the invention;  
       FIG. 4  is a schematic partial cross-sectional view of another embodiment of the invention; and  
       FIG. 5  is a schematic partial cross-sectional view of yet another embodiment of the invention; and  
       FIG. 6  is a flow diagram of one embodiment of a method for controlling temperature of a substrate disposed on a substrate pedestal. 
    
    
      To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.  
     DETAILED DESCRIPTION  
      The present invention generally is a method and apparatus for controlling temperature of a substrate during processing. Although invention is illustratively described in a semiconductor substrate processing apparatus, such as, e.g., a processing reactor (or module) of a CENTURA® integrated semiconductor wafer processing system, available from Applied Materials, Inc. of Santa Clara, Calif., the invention may be utilized in other processing systems, including etch, deposition, implant and thermal processing, or in other application where control of the temperature profile of a substrate or other workpiece is desirable.  
       FIG. 1  depicts a schematic diagram of an exemplary etch reactor  100  having one embodiment of a substrate pedestal assembly  116  that may illustratively be used to practice the invention. The particular embodiment of the etch reactor  100  shown herein is provided for illustrative purposes and should not be used to limit the scope of the invention.  
      Etch reactor  100  generally includes a process chamber  110 , a gas panel  138  and a controller  140 . The process chamber  110  includes a conductive body (wall)  130  and a ceiling  120  that enclose a process volume. Process gasses are provided to the process volume of the chamber  110  from the gas panel  138 .  
      The controller  140  includes a central processing unit (CPU)  144 , a memory  142 , and support circuits  146 . The controller  140  is coupled to and controls components of the etch reactor  100 , processes performed in the chamber  110 , as well as may facilitate an optional data exchange with databases of an integrated circuit fab.  
      In the depicted embodiment, the ceiling  120  is a substantially flat dielectric member. Other embodiments of the process chamber  110  may have other types of ceilings, e.g., a dome-shaped ceiling. Above the ceiling  120  is disposed an antenna  112  comprising one or more inductive coil elements (two co-axial coil elements  112 A and  112 B are illustratively shown). The antenna  112  is coupled, through a first matching network  170 , to a radio-frequency (RF) plasma power source  118 .  
      In one embodiment, the substrate pedestal assembly  116  includes a support member  126 , a thermoconductive layer  134 , a base  114 , a collar ring  152 , a joint ring  154 , a spacer  178 , a ground sleeve  164  and a mount assembly  162 . The mounting assembly  162  couples the base  114  to the process chamber  110 . The base  114  is generally formed from ceramic or similar dielectric material. In the depicted embodiment, the base  114  further comprises at least one optional embedded heater  158  (one heater  158  is illustratively shown), at least one optional embedded insert  168  (one annular insert  168  is illustratively shown), and a plurality of optional conduits  160  fluidly coupled to a source  182  of a heating or cooling liquid. In this embodiment, the base  114  is further thermally separated from the ground sleeve  164  using an optional spacer  178 .  
      The conduits  160  and heater  158  may be utilized to control the temperature of the base  114 , thereby heating or cooling the support member  126 , thereby controlling, in part, the temperature of a substrate  150  disposed on the support member  126  during processing.  
      The insert  168  is formed from a material having a different coefficient of thermal conductivity than the material of the adjacent regions of the base  114 . Typically, the inserts  168  has a smaller coefficient of thermal conductivity than the base  114 . In a further embodiment, the inserts  168  may be formed from a material having an anisotropic (i.e. direction-dependent coefficient of thermal conductivity). The insert  168  functions to locally change the rate of heat transfer between the support member  126  through the base  114  to the conduits  160  relative to the rate of heat transfer though neighboring portions of the base  114  not having an insert  168  in the heat transfer path. Thus, by controlling the number, shape, size, position and coefficient of heat transfer of the inserts, the temperature profile of the support member  126 , and the substrate  150  seated thereon, may be controlled. Although the insert  168  is depicted in  FIG. 1  shaped as an annular ring, the shape of the insert  168  may take any number of forms.  
      The thermoconductive layer  134  is disposed on a chuck supporting surface  180  of the base  114  and facilitates thermal coupling (i.e., heat exchange) between the support member  126  and the base  114 . In one exemplary embodiment, the thermoconductive layer  134  is an adhesive layer that mechanically bonds the support member  126  to member supporting surface  180 . Alternatively (not shown), the substrate pedestal assembly  116  may include a hardware (e.g., clamps, screws, and the like) adapted for fastening the support member  126  to the base  114 . Temperature of the support member  126  and the base  114  is monitored using a plurality of sensors (not shown), such as, thermocouples and the like, that are coupled to a temperature monitor  174 .  
      The support member  126  is disposed on the base  114  and is circumscribed by the rings  152 ,  154 . The support member  126  may be fabricated from aluminum, ceramic or other materials suitable for supporting the substrate  150  during processing. The substrate  150  may rest upon the support member  126  by gravity, or alternatively be secured thereto by vacuum, electrostatic force, mechanical clamps and the like. The embodiment depicted in  FIG. 1 , the support member  126  is an electrostatic chuck  188 .  
      The electrostatic chuck  188  is generally formed from ceramic or similar dielectric material and comprises at least one clamping electrode (not shown) controlled using a power supply  128 . In a further embodiment, the electrostatic chuck  188  may comprise at least one RF electrode (not shown) coupled, through a second matching network  124 , to a power source  122  of substrate bias, and may also include at least one embedded heater (not shown) controlled using a power supply  132 .  
      The electrostatic chuck  188  may further comprise a plurality of gas passages (not shown), such as grooves, that are formed in a substrate supporting surface  176  of the chuck and fluidly coupled to a source  148  of a heat transfer (or backside) gas. In operation, the backside gas (e.g., helium (He)) is provided at controlled pressure into the gas passages to enhance the heat transfer between the electrostatic chuck  188  and the substrate  150 . Conventionally, at least the substrate supporting surface  176  of the electrostatic chuck is provided with a coating resistant to the chemistries and temperatures used during processing the substrates.  
      In one embodiment, the support member  126  comprises at least one embedded insert  166  (one annular insert  166  is illustratively shown) formed from at least one material having a different coefficient of thermal conductivity than the material(s) of adjacent regions of the support member  126 . Typically, the inserts  166  are formed from materials having a smaller coefficient of thermal conductivity than the material(s) of the adjacent regions. In a further embodiment, the inserts  166  may be formed from materials having an anisotropic coefficient of thermal conductivity. In an alternate embodiment (not shown), at least one insert  166  may be disposed coplanar with the substrate supporting surface  176 .  
      As with the inserts  168  of the base  114 , the thermal conductivity, as well as the shape, dimensions, location, and number of inserts  166  in the support member  126  may be selectively chosen to control the heat transfer through the pedestal assembly  116  to achieve, in operation, a pre-determined pattern of the temperature distribution on the substrate supporting surface  176  of the support member  126  and, as such, across the diameter of the substrate  150 .  
      The thermoconductive layer  134  comprises a plurality of material regions (two annular regions  102 ,  104  and circular region  106  are illustratively shown), at least two of which having different coefficients of thermal conductivity. Each region  102 ,  104 ,  108  may be formed from at least one material having a different coefficient of thermal conductivity than the material(s) of adjacent regions of the thermoconductive layer  134 . In a further embodiment, one or more of the materials comprising the regions  102 ,  104 ,  106  may have an anisotropic coefficient of thermal conductivity. For example, coefficients of thermal conductivity of materials in the layer  134  in the directions orthogonal or parallel to the member supporting surface  180  may differ from the coefficients in at least one other direction. The coefficient of thermal conductivity between the regions  102 ,  104 ,  106  of the layer  134  may be selected to promote laterally different rates of heat transfer between the chuck  126  and base  114 , thereby controlling the temperature distribution across the diameter of the substrate  150 .  
      In yet further embodiment, gaps  190  (as shown in  FIG. 2A ) maybe provided between at least two adjacent regions of the thermoconductive layer  134 . In the layer  134 , such gaps  190  may form either gas-filled or vacuumed volumes having pre-determined form factors. A gap  190  may alternatively be formed within a region of the layer  134  (as shown in  FIG. 1C ).  
       FIG. 2  depicts a schematic cross-sectional view of the substrate pedestal taken along a line  2 - 2  in  FIG. 1A . In the depicted embodiment, the thermoconductive layer  134  illustratively comprises the annular regions  102 ,  104  and the circular region  106 . In alternate embodiments, the layer  134  may comprise either more or less than three regions, as well as regions having different form factors, for example, the regions may be arranged as grids, radially oriented shapes, and polar arrays among others. The regions of the thermoconductive layer  134  may be composed from materials (e.g., adhesive materials) applied in a form of a paste that is further developed into a hard adhesive compound, as well as in a form of an adhesive tape or an adhesive foil. Thermal conductivity of the materials in the thermoconductive layer  134  may be selected in a range from 0.01 to 200 W/mK and, in one exemplary embodiment, in a range from 0.1 to 10 W/mK. In yet another embodiment, the adjacent regions have a difference in thermal conductivities in the range of about 0.1 to 10 W/mK, and may have a difference in conductivity between an inner most and out most regions of the layer  134  of about 0.1 to about 10 W/mK. Examples of suitable adhesive materials include, but not limited to, pastes and tapes comprising acrylic and silicon based compounds. The adhesive materials may additionally include at least one thermally conductive ceramic filler, e.g., aluminum oxide (Al 2 O 3 ), aluminum nitride (AlN), and titanium diboride (TiB 2 ), and the like. One example of an adhesive tape suitable for the conductive layer  134  is sold under the tradename THERMATTACH®, available from Chomerics, a division of Parker Hannifin Corporation, located in Wolburn, Mass.  
      In the thermoconductive layer  134 , the thermal conductivity, as well as the form factor, dimensions, and a number of regions having the pre-determined coefficients of thermal conductivity may be selectively chosen to control the heat transfer between the electrostatic chuck  126  and the base  114  to achieve, in operation, a pre-determined pattern of the temperature distribution on the substrate supporting surface  176  of the chuck and, as such, in the substrate  150 . To further control the heat transfer through the conductive layer  134  between the base  114  and support member  126 , one or more channels  108  are provided to flow a heat transfer medium therethrough. The channels  108  are coupled through the base  114  to a source  150  of heat transfer medium, such as a cooling gas. Some examples of suitable cooling gases include helium and nitrogen, among others. As the cooling gas disposed in the channels  108  is part of the heat transfer path between the chuck  126  and base  114 , the position of the channels  108 , and the pressure, flow rate, temperature, density and composition of the heat transfer medium of cooling gas provided, provides enhanced control of the heat transfer profile through the pedestal assembly  116 . Moreover, as the density and flow rate of gas in the channel  108  may be controlled in-situ during processing of substrate  150 , the temperature control of the substrate  150  may be changed during processing to further enhance processing performance. Although a single source  156  of cooling gas is shown, it is contemplated that one or more sources of cooling gas may be coupled to the channels  108  in a manner such that the types, pressures and/or flow rate of cooling gases within individual channels  108  may be independently controller, thereby facilitating an even greater level of temperature control.  
      In the embodiment depicted in  FIG. 1A , the channels  108  are depicted as formed in the member supporting surface  180 . However, it is contemplated that the channels  108  may be formed at least partially in the member supporting surface  180 , at least partially in the bottom surface of the support member  126 , or at least partially in the thermally conductive layer  134 , along with combinations thereof. In one embodiment, between about 2 to 10 channels  108  are disposed in the pedestal assembly  116  and provide with the selectivity maintained at a pressure between about 760 Torr (atmospheric pressure) to about 10 Torr. For example, at least one of the channels  108  may be partially or entirely formed in the electrostatic chuck  126 , as illustrated in  FIGS. 3-4 . More specifically,  FIG. 3  depicts a schematic diagram of a portion of the substrate pedestal assembly  116  where the channels  108  are formed entirely in the electrostatic chuck  126 .  FIG. 4  depicts a schematic diagram of a portion of the substrate pedestal assembly  116  where the channels  108  are partially formed in the base  114  and, partially, in the electrostatic chuck  126 .  FIG. 5  depicts a schematic diagram of a portion of the substrate pedestal assembly  116  where the channels  108  are formed in the thermoconductive layer  134 . Although in  FIG. 5  the channels are shown disposed between different regions  102 ,  104 ,  106  of the thermoconductive layer  134 , the one or more of the channels may be formed through one or more of the regions  102 ,  104 ,  106 .  
      Returning to  FIG. 1A , at least one of the location, shape, dimensions, and number of the channels  108  and inserts  166 ,  168  as well as the thermal conductivity of the inserts  166 ,  168  and gas disposed in the channels  108 , may be selectively chosen to control the heat transfer between the support member  126  to the base  114  to achieve, in operation, a pre-determined pattern of the temperature distribution on the substrate supporting surface  176  of the chuck  126  and, as such, control the temperature profile of the substrate  150 . In further embodiments, the pressure of the cooling gas in at least one channel  108 , as well as the flow of the cooling liquid in at least one conduit  156  may also be selectively controlled to achieve and/or enhance temperature control of the substrate. The heat transfer rate may also be controlled by individually controlling the type of gas, pressure and/or flow rate between respective channels  108 .  
      In yet further embodiments, the pre-determined pattern of the temperature distribution in the substrate  150  may be achieved using individual or combinations of the described control means, e.g., the thermoconductive layer  134 , the inserts  166 ,  168 , channels  108 , conduits  160 , the pressure of cooling gas in the channels  108 , and the flow of the cooling liquid in the conduits  160 . Furthermore, in the discussed above embodiments, pre-determined patterns of the temperature distribution on the substrate supporting surface  176  and in the substrate  150  may additionally be selectively controlled to compensate for non-uniformity of the heat fluxes originated, during processing the substrate  150 , by a plasma of the process gas and/or substrate bias.  
       FIG. 6  depicts a flow diagram of one embodiment of an inventive method for controlling temperature of a substrate processed in a semiconductor substrate processing apparatus as a process  600 . The process  600  illustratively includes the processing steps performed upon the substrate  150  during processing in the reactor  100  described in the embodiments above. It is contemplated that the process  600  may be performed in other processing systems.  
      The process  600  starts at step  601  and proceeds to step  602 . At step  602 , the substrate  150  is transferred to the pedestal assembly  116  disposed in the process chamber  110 . At step  604 , the substrate  150  is positioned (e.g., using a substrate robot, not shown) on the substrate supporting surface  176  of the electrostatic chuck  188 . At step  606 , the power supply  132  engages the electrostatic chuck  188  to clamp the substrate  150  to the supporting surface  176  of the chuck  188 . At step  608 , the substrate  150  is processed (e.g., etched) in the process chamber  110  in accordance with a process recipe executed as directed by the controller  140 . During step  608 , the substrate pedestal assembly  116  facilitates a pre-determined pattern of temperature distribution in the substrate  150 , utilizing one or more of the temperature control attributes of the pedestal assembly  116  discussed in reference to  FIGS. 1-5  above. Optionally, the rate and/or profile of heat transferred through the chuck  114  during step  608  may be adjusted in-situ by changing one or more of the characteristics of the gas present in one or more of the channels  108 . Upon completion of processing, at step  610 , the power supply  132  disengages the electrostatic chuck  188  and, as such, de-chucks the substrate  150  that is further removed from the process chamber  110 . At step  612 , the process  600  ends.  
      While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.