Abstract:
A method for multi-step temperature control of a substrate includes selecting a first set-point temperature and a second set-point temperature for the substrate, and selecting a first PID parameter set including a first proportional constant K P1 , a first integral constant K I1  and a first derivative constant K D1 , and selecting a second PID parameter set including a second proportional constant K P2 , a second integral constant K I2  and a second derivative constant K D2 . The substrate is placed on a substrate holder, the temperature of the substrate is adjusted to the first set-point temperature and the substrate is processed for a first period of time at the first set-point temperature. The temperature of a region of the substrate is changed from the first set-point temperature to the second set-point temperature using the first PID parameter set for a first ramp period of time and using the second PID parameter set for a second ramp period of time, the second ramp period of time following the first ramp period of time. The substrate is then processed for a second period of time at the second set-point temperature.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is related to co-pending U.S. patent application Ser. No. 10/551,236, entitled “Method and System for Temperature Control of a Substrate”, filed on Sep. 27, 2005; co-pending U.S. patent application Ser. No. 11/525,818, entitled “High Temperature Substrate Holder for a Substrate Processing System” (ES-108), filed on even date herewith; co-pending U.S. patent application Ser. No. 11/526,119, entitled “Method for Multi-step Temperature Control of a Substrate” (ES-112), filed on even date herewith; and co-pending U.S. patent application Ser. No. 11/525,815, entitled “High Temperature Substrate Holder with Non-homogeneous Insulation Layer for a Substrate Processing System” (ES-098), filed on even date herewith. The entire contents of these applications are herein incorporated by reference in their entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method for temperature control of a substrate, and more particularly to a method of using a substrate holder for temperature control of a substrate. 
   2. Description of Related Art 
   It is known in semiconductor manufacturing and processing that various processes, including for example etch and deposition processes, depend significantly on the temperature of the substrate. For this reason, the ability to control the temperature of a substrate and controllably adjust the temperature of the substrate is becoming an essential requirement of a semiconductor processing system. The temperature of a substrate is determined by many processes including, but not limited to, substrate interaction with plasma, chemical processes, etc., as well as radiative and/or conductive thermal exchange with the surrounding environment. Providing a proper temperature to the upper surface of the substrate holder can be utilized to control the temperature of the substrate. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a system for controlling the temperature of a substrate. 
   According to one embodiment, a method of using a substrate support is described, the substrate support comprising one or more heating elements separated from one or more cooling elements by a thermal insulator. 
   According to another embodiment, a method for controlling the temperature of a substrate in a substrate processing system is described, the substrate processing system including a substrate holder for supporting the substrate and having a temperature sensor reporting a temperature at a region of the substrate and a heating element heating the region and being controlled by a temperature control system to control the temperature of the substrate using a PID control algorithm. The method includes selecting a first set-point temperature, selecting a second set-point temperature, selecting a first PID parameter set including a first proportional constant K P1 , a first integral constant K I1  and a first derivative constant K D1 , and selecting a second PID parameter set including a second proportional constant K P2 , a second integral constant K I2  and a second derivative constant K D2 . The substrate is placed on the substrate holder, the temperature of the substrate is adjusted to the first set-point temperature and the substrate is processed for a first period of time at the first set-point temperature. The temperature of the region of the substrate is changed from the first set-point temperature to the second set-point temperature using the first PID parameter set for a first ramp period of time and using the second PID parameter set for a second ramp period of time, the second ramp period of time following the first ramp period of time. The substrate is then processed for a second period of time at the second set-point temperature. 
   According to yet another embodiment, a method for controlling the temperature of a substrate in a substrate processing system is described, the substrate processing system including a substrate holder for supporting the substrate and having a plurality of temperature sensors reporting at least a temperature at an inner region and an outer region of the substrate, and first and second heating elements heating respectively the inner region and the outer region, the first and second heating elements being controlled by a temperature control system using a PID controller to maintain the substrate holder at a selectable set-point temperature. The method includes selecting a first inner set-point temperature and a first outer set-point temperature, selecting a second inner set-point temperature and a second outer set-point temperature, selecting a first inner PID parameter set including a first inner proportional constant K Pinner1 , a first inner integral constant K Iinner1  and a first inner derivative constant K Dinner1 , selecting a second inner PID parameter set including a second inner proportional constant K Pinner2 , a second inner integral constant K Iinner2  and a second inner derivative constant K Dinner2 . Also included is selecting a first outer PID parameter set including a first outer proportional constant K Pouter1 , a first outer integral constant K Iouter1  and a first outer derivative constant K Douter1 ; selecting a second outer PID parameter set including a second outer proportional constant K Pouter2 , a second outer integral constant K Iouter2  and a second outer derivative constant K Douter2 . The substrate is placed on the substrate holder and the inner region of the substrate is heated to the first inner set-point temperature and the outer region of the substrate is heated to the first outer set-point temperature, and the substrate is processed for a first period of time at the first inner and outer set-point temperatures. The temperature of the inner region of the substrate is changed from the first inner set-point temperature to the second inner set-point temperature using the first inner PID parameter set for a first inner ramp period of time and using the second inner PID parameter set for a second inner ramp period of time, the second inner ramp period of time following the first inner ramp period of time, and the temperature of the outer region of the substrate is changed from the first outer set-point temperature to the second outer set-point temperature using the first outer PID parameter set for a first outer ramp period of time and using the second outer PID parameter set for a second outer ramp period of time, the second outer ramp period of time following the first outer ramp period of time. The substrate is then processed for a second period of time at the second inner and outer set-point temperatures. 
   Another aspect of the invention includes a method of changing the temperature of a substrate during processing of the substrate. The method includes providing the substrate on a substrate holder, the substrate holder including a temperature controlled substrate support for supporting the substrate, a temperature controlled base support for supporting the substrate support and a thermal insulator interposed between the temperature controlled substrate support and the temperature controlled base support. The method also includes setting the temperature of the base support to a first base temperature corresponding to a first processing temperature of said substrate, setting the substrate support to a first support temperature corresponding to said first processing temperature of said substrate and setting the temperature of the base support to a second base temperature corresponding to a second processing temperature of said substrate. The substrate support temperature is then changed to a second support temperature corresponding to said second processing temperature of said substrate by selecting a first PID parameter set including a first proportional constant K P1 , a first integral constant K I1  and a first derivative constant K D1 , selecting a second PID parameter set including a second proportional constant K P2 , a second integral constant K I2  and a second derivative constant K D2 , and changing the temperature of said substrate from said first set-point temperature to said second set-point temperature using said first PID parameter set for a first ramp period of time and using said second PID parameter set for a second ramp period of time, said second ramp period of time following said first ramp period of time. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
       FIG. 1  presents a block diagram of a substrate processing system according to an embodiment of the present invention; 
       FIG. 2A  presents a schematic cross-section view of a substrate holder according to an embodiment of the present invention; 
       FIG. 2B  illustrate exemplary profiles in thermal conductivity and substrate temperature for a substrate holder; 
       FIG. 3  presents a schematic cross-section view of a substrate holder according to another embodiment of the present invention; 
       FIG. 4  presents a schematic cross-section view of a substrate holder according to another embodiment of the present invention; 
       FIG. 5  presents a schematic cross-section view of a substrate holder according to another embodiment of the present invention; 
       FIG. 6  presents a schematic cross-section view of a substrate holder according to another embodiment of the present invention; 
       FIGS. 7A and 7B  illustrate exemplary time traces of temperature; and 
       FIG. 8  illustrates a flow chart of a method of adjusting a substrate temperature according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   In the following description, for purposes of explanation and not limitation, specific details are set forth, such as a particular geometry of the substrate holder for a substrate processing system and descriptions of various components and processes. However, it should be understood that the invention may be practiced in other embodiments that depart from these specific details. 
   According to an embodiment of the present invention, a material processing system  1  is depicted in  FIG. 1  that includes a process tool  10  having a substrate holder  20  and a substrate  25  supported thereon. The substrate holder  20  is configured to provide temperature control elements for adjustment of substrate temperature. Additionally, the temperature control elements may be spatially arranged in order to ensure a uniform or non-uniform substrate temperature. A controller  55  is coupled to the process tool  10  and the substrate holder  20 , and is configured to monitor, adjust and control the substrate temperature as will be further discussed below. 
   In the illustrated embodiment depicted in  FIG. 1 , the material processing system  1  can include an etch chamber. For example, the etch chamber can facilitate dry plasma etching, or, alternatively, dry non-plasma etching. Alternately, the material processing system  1  includes a photo-resist coating chamber such as a heating/cooling module in a photo-resist spin coating system that may be utilized for post-adhesion bake (PAB) or post-exposure bake (PEB), etc.; a photo-resist patterning chamber such as a photo-lithography system; a dielectric coating chamber such as a spin-on-glass (SOG) or spin-on-dielectric (SOD) system; a deposition chamber such as a vapor deposition system, chemical vapor deposition (CVD) system, plasma enhanced CVD (PECVD) system, atomic layer deposition (ALD) system, plasma enhanced ALD (PEALD) system, or a physical vapor deposition (PVD) system; or a rapid thermal processing (RTP) chamber such as a RTP system for thermal annealing. 
   Referring now to  FIG. 2A , a substrate holder is described according to one embodiment. The substrate holder  100  comprises a substrate support  130  having a first temperature and configured to support a substrate  110 , a temperature-controlled support base  120  positioned below substrate support  130  and configured to be at a second temperature less than the first temperature (e.g. less than a desired temperature of substrate  110 ), and a thermal insulator  140  disposed between the substrate support  130  and the temperature-controlled support base  120 . Additionally, the substrate support  130  comprises one or more heating elements coupled thereto (not shown), and configured to elevate the temperature of the substrate support  130  (e.g. to heat the substrate). It is to be understood that the first temperature may be part of a temperature gradient across the substrate support and the second temperature may be part of a temperature gradient across the temperature controlled base according to embodiments of the invention. 
   According to one embodiment, the thermal insulator  140  comprises a thermal conductivity lower than the respective thermal conductivities of both the substrate support  130  and the temperature-controlled support base  120 . For example, the thermal conductivity of the thermal insulator  140  is less than 1 W/m-K. Desirably, the thermal conductivity of the thermal insulator ranges from approximately 0.05 W/m-K to approximately 0.8 W/m-K and, more desirably, the thermal conductivity of the thermal insulator ranges from approximately 0.2 W/m-K to approximately 0.8 W/m-K. 
   The thermal insulator  140  can comprise an adhesive made of polymer, plastic or ceramic. The thermal insulator  140  may include an organic or an inorganic material. For example, the thermal insulator  140  can comprise a room-temperature-vulcanizing (RTV) adhesive, a plastic such as a thermoplastic, a resin such as a thermosetting resin or a casting resin (or pourable plastic or elastomer compound), an elastomer, etc. In addition to providing a thermal resistance between the substrate support  130  and the temperature-controlled support base  120 , the thermal insulator  140  may provide a bond layer or adhesion layer between the substrate support  130  and the temperature-controlled support base  120 . 
   The thickness and material composition of the thermal insulator  120  should be selected such that, when necessary, adequate radio frequency (RF) coupling between the support base  120  and plasma can be maintained. Furthermore, the thermal insulator  120  should be selected in order to tolerate thermal-mechanical shear driven by thermal gradients and differences in material properties, i.e., coefficient of thermal expansion. For example, the thickness of the thermal insulator  140  can be less than or equal to approximately 10 mm (millimeters), and desirably, the thickness can be less than or equal to approximately 5 mm, i.e., approximately 2 mm or less. 
   Additionally, the material composition of the thermal insulator  140  is preferably such that it demonstrates erosion resistance to the environment within which it is utilized. For example, when presented with a dry plasma etching environment, the thermal insulator  140  should be resistant to the corrosive etch chemistries used during the etching process, as well as the corrosive cleaning chemistries used during an etch system cleaning process. In many etching chemistries and cleaning chemistries, halogen-containing process gases are utilized including, but not limited to, Cl 2 , F 2 , Br 2 , HBr, HCl, HF, SF 6 , NF 3 , ClF 3 , etc. In these chemistries, particularly cleaning chemistries, it is desirable to produce high concentrations of reactive atomic halogen species, such as atomic fluorine, etc. 
   According to one embodiment, the thermal insulator  140  comprises an erosion resistant thermal insulator. In one embodiment, the entire thermal insulator is made from the erosion resistant material. Alternatively, only a portion of the thermal insulator  140 , such as portions exposed to halogen-containing gas, can include the erosion resistant material. For example, the erosion resistant material may be included only at a peripheral exposed edge of the thermal insulator, while the remaining region of the thermal insulator includes a different material composition selected for providing a desired heat transfer co-efficient. 
   The erosion resistant thermal insulator can include an acryl-type material, such as an acrylic-based material or an acrylate-based material. Acrylic-based materials and acrylate-based materials can be formed by polymerizing acrylic or methylacrylic acids through a reaction with a suitable catalyst. Table 1 provides data illustrating the dependence of erosion resistance on material composition. For example, data is provided for silicon-containing adhesives, and a series of acrylic/acrylate-containing adhesives (prepared by various vendors X, Y, Z, Q, R &amp; T). The data includes the erosion amount (mm 3 ) as a function of plasma (or RF power on) hours (hr); i.e, mm 3 /hr. As shown in Table 1, the acrylic/acrylate-containing adhesives exhibit more than an order of magnitude less erosion when subjected to a cleaning plasma (such as a SF 6 -based plasma). 
   
     
       
             
             
             
           
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
           
         
             
                 
               TABLE 1 
             
           
           
             
                 
                 
             
             
                 
               Silicon 
               Acryl type 
             
           
        
         
             
                 
               type 
               X 
               Y 
               Z 
               Q 
               R 
               T 
             
             
                 
                 
             
           
        
         
             
               Thickness (mm) 
               0.13 
               0.13 
               0.25 
               0.13 
               0.15 
               0.05 
               0.12 
             
             
               Thermal 
               0.25 
               0.35 
               0.6 
               0.37 
               0.3 
               0.6 
               0.2 
             
             
               conductivity 
             
             
               (W/m-K) 
             
             
               Thermal resistance 
               5.2 
               3.7 
               4.2 
               3.5 
               7.5 
               8.3 
               6 
             
             
               (E −4 ) 
             
             
               Erosion ratio 
               5.5 
               0.32 
               0.3 
               0.22 
               0.25 
               0.15 
               0 
             
             
               (mm 3 /hr) 
             
             
                 
             
           
        
       
     
   
   According to yet another embodiment, the thermal insulator  140  comprises a non-uniform spatial variation of the heat transfer coefficient (W/m 2 -K) through the thermal insulator  140  between the temperature controlled support base  120  and the substrate support  130 . For example, the heat transfer coefficient can vary in a radial direction between a substantially central region of the thermal insulator  140  (below substrate  110 ) and a substantially edge region of the thermal insulator  140  (below substrate  110 ). The spatial variation of the heat transfer coefficient may comprise a non-uniform spatial variation of the thermal conductivity (W/m-K) of the thermal insulator  140 , or the spatial variation of the heat transfer coefficient may comprise a non-uniform spatial variation of the thickness of the thermal insulator  140 , or both. As used herein, the term “non-uniform spatial variation” of a parameter means a spatial variation of the parameter across an area of the substrate holder that is caused by design rather than inherent minor variations of the parameter across a substrate holder. Further, the term “substantially central region of the thermal insulator” means a region of the thermal insulator that would overlap a center of the substrate if placed on the substrate holder, and the term “substantially edge region of the thermal insulator” means a region of the thermal insulator that would overlap an edge of the substrate if placed on the substrate holder. 
   As illustrated in  FIG. 2B , the thermal conductivity can vary in a radial direction between a substantially central region of the thermal insulator  140  below substrate  110  and a substantially edge region of the thermal insulator  140  below substrate  110 . For example, the thermal conductivity can vary between a first value between approximately 0.2 W/m-K and approximately 0.8 W/m-K and a second value between approximately 0.2 W/m-K and approximately 0.8 W/m-K. Additionally, for example, the thermal conductivity can be approximately 0.2 W/m-K near a substantially central region of the thermal insulator  140  and the thermal conductivity can be approximately 0.8 W/m-K near a substantially edge region of the thermal insulator  140  . Additionally yet, for example, the variation in the thermal conductivity substantially occurs between approximately the mid-radius region of the thermal insulator  140  and a substantially peripheral region of the thermal insulator  140  . As shown in  FIG. 2B , the temperature may vary from center to edge between a first temperature (T 1 ) and a second temperature (T 2 ). Such variations in thermal conductivity (and temperature) may be imposed to counter excessive heating of the peripheral edge of the substrate by, for instance, the focus ring surrounding the substrate. 
   As illustrated in  FIG. 3 , a substrate holder is described according to another embodiment. The substrate holder  200  comprises a substrate support  230  having a first temperature and configured to support a substrate  210 , a temperature-controlled support base  220  positioned below substrate support  230  and configured to be at a second temperature less than the first temperature (e.g. less than a desired temperature of substrate  210 ), and a thermal insulator  240  disposed between the substrate support  230  and the temperature-controlled support base  220 . Additionally, the substrate support  230  comprises one or more heating elements coupled thereto (not shown), and configured to elevate the temperature of the substrate support  230  (e.g. to heat the substrate). The thermal insulator  240  comprises a non-uniform thickness. 
   As shown, the thickness is less at a substantially center region of the thermal insulator  240  (below substrate  210 ) and it is relatively thicker at a substantially edge region below the substrate  210 . Alternatively, the thickness can be greater at a substantially center region below substrate  210  and it can be relatively thinner at a substantially edge region of substrate  210 . The non-uniform thickness of thermal insulator  240  may be imposed by a non-flat upper surface on support base  220 , or it may be imposed by a non-flat lower surface of substrate support  240 , or it may be imposed by a combination thereof. Alternatively yet, a layer of material having a different thermal conductivity than that of the thermal insulator  240  may be disposed on a portion of either the upper surface of support base  220  or the lower surface of substrate support  230 . For instance, a layer of Kapton®, Vespel®, Teflon®, etc., may be disposed on a substantially central region below substrate  210 , or such a layer may be disposed on a substantially peripheral region below substrate  210 . 
   Referring now to  FIG. 4 , a substrate holder is described according to another embodiment. The substrate holder  300  comprises a substrate support  330  having a first temperature and configured to support a substrate  310 , a temperature-controlled support base  320  positioned below substrate support  330  and configured to be at a second temperature less than the first temperature (e.g. less than a desired temperature of substrate  310 ), and a thermal insulator  340  disposed between the substrate support  330  and the temperature-controlled support base  320 . Additionally, the substrate support  330  comprises one or more heating elements coupled thereto (not shown), and configured to elevate the temperature of the substrate support  330 . 
   As shown in  FIG. 4 , the support base  320  comprises a plurality of protrusions, or ridges  342 , that partially extend into (or fully extend through) the thermal insulator  340 . Furthermore, the number density of protrusions can vary between a substantially central region  344  and a substantially peripheral region  346  of the substrate holder. For example, a higher density of protrusions may be placed at the peripheral region  346 , while a relatively lower density of protrusions may be placed at the central region  344 . Alternatively, for example, a lower density of protrusions may be placed at the peripheral region  346 , while a relatively higher density of protrusions may be placed at the central region  344 . In addition to the variation in density of protrusions, or in lieu of a variation in density, the size or shape or both of the protrusions may be varied. 
   The temperature controlled support base  120  ( 220 ,  320 ) may be fabricated from a metallic material or a non-metallic material. For example, the support base  120  ( 220 ,  320 ) can be fabricated from aluminum. Additionally, for example, the support base  120  ( 220 ,  320 ) can be formed of a material having a relatively high thermal conductivity, such that the temperature of the support base can be maintained at a relatively constant temperature. The temperature of the temperature controlled support base is preferably actively controlled by one or more temperature control elements such as cooling elements. However, the temperature controlled support may provide passive cooling by use of cooling fins to promote enhanced free convection due to the increased surface area with the surrounding environment for example. The support base  120  ( 220 ,  320 ) can further include passages therethrough (not shown) to permit the coupling of electrical power to the one or more heating elements of the substrate support, the coupling of electrical power to an electrostatic clamping electrode, the pneumatic coupling of heat transfer gas to the backside of the substrate, etc. 
   The substrate support  130  ( 230 ,  330 ) may be fabricated from a metallic material or a non-metallic material. The substrate support  130  ( 230 ,  330 ) can be fabricated from a non-electrically conductive material, such as a ceramic. For example, substrate support  130  ( 230 ,  330 ) can be fabricated from alumina. 
   According to one embodiment, the one or more heating elements are embedded within the substrate support  130  ( 230 ,  330 ). The one or more heating elements can be positioned between two ceramic pieces which are sintered together to form a monolithic piece. Alternatively, a first layer of ceramic is thermally sprayed onto the thermal insulator, followed by thermally spraying the one or more heating elements onto the first ceramic layer, and followed by thermally spraying a second ceramic layer over the one or more heating elements. Using similar techniques, other electrodes, or metal layers, may be inserted within the substrate support  130  ( 230 ,  330 ). For example, an electrostatic clamping electrode may be inserted between ceramic layers and formed via sintering or spraying techniques as described above. The one or more heating elements and the electrostatic clamping electrode may be in the same plane or in separate planes, and may be implemented as separate electrodes or implemented as the same physical electrode. 
   Referring now to  FIG. 5 , a substrate holder is described according to another embodiment. The substrate holder  400  comprises a substrate support  430  having a first temperature and configured to support a substrate  410 , a temperature-controlled support base  420  positioned below substrate support  430  and configured to be at a second temperature less than the first temperature (e.g. less than a desired temperature of substrate  410 ), and a thermal insulator  440  disposed between the substrate support  430  and the temperature-controlled support base  420 . Additionally, the substrate support  430  comprises one or more heating elements  431  coupled thereto, and configured to elevate the temperature of the substrate support  430 . Furthermore, the support base  420  comprises one or more cooling elements  421  coupled thereto, and configured to reduce the temperature of the substrate support  430  via the removal of heat from the substrate support  430  through thermal insulator  440 . 
   The one or more heating elements  431  can comprise at least one of a heating fluid channel, a resistive heating element, or a thermoelectric element biased to transfer heat towards the wafer. Furthermore, as shown in  FIG. 5 , the one or more heating elements  431  are coupled to a heating element control unit  432 . Heating element control unit  432  is configured to provide either dependent or independent control of each heating element, and exchange information with a controller  450 . 
   For example, the one or more heating elements  431  can comprise one or more heating channels that can permit a flow rate of a fluid, such as water, Fluorinert, Galden HT-135, etc., therethrough in order to provide conductive-convective heating, wherein the fluid temperature has been elevated via a heat exchanger. The fluid flow rate and fluid temperature can, for example, be set, monitored, adjusted, and controlled by the heating element control unit  432 . 
   Alternatively, for example, the one or more heating elements  431  can comprise one or more resistive heating elements such as a tungsten, nickel-chromium alloy, aluminum-iron alloy, aluminum nitride, etc., filament. Examples of commercially available materials to fabricate resistive heating elements include Kanthal, Nikrothal, Akrothal, which are registered trademark names for metal alloys produced by Kanthal Corporation of Bethel, Conn. The Kanthal family includes ferritic alloys (FeCrAl) and the Nikrothal family includes austenitic alloys (NiCr, NiCrFe). For example, the heating elements can comprise a cast-in heater commercially available from Watlow (1310 Kingsland Dr., Batavia, Ill., 60510) capable of a maximum operating temperature of 400 to 450 C, or a film heater comprising aluminum nitride materials that is also commercially available from Watlow and capable of operating temperatures as high as 300 C and power densities of up to 23.25 W/cm 2 . Additionally, for example, the heating element can comprise a silicone rubber heater (1.0 mm thick) capable of 1400 W (or power density of 5 W/in 2 ). When an electrical current flows through the filament, power is dissipated as heat, and, therefore, the heating element control unit  432  can, for example, comprise a controllable DC power supply. A further heater option, suitable for lower temperatures and power densities, are Kapton heaters, consisted of a filament embedded in a Kapton (e.g. polyimide) sheet, marketed by Minco, Inc., of Minneapolis, Minn. 
   Alternately, for example, the one or more heating elements  431  can comprise an array of thermoelectric elements capable of heating or cooling a substrate depending upon the direction of electrical current flow through the respective elements. Thus, while the elements  431  are referred to as “heating elements,” these elements may include the capability of cooling in order to provide rapid transition between temperatures. Further, heating and cooling functions may be provided by separate elements within the substrate support  430 . An exemplary thermoelectric element is one commercially available from Advanced Thermoelectric, Model ST-127-1.4-8.5M (a 40 mm by 40 mm by 3.4 mm thermoelectric device capable of a maximum heat transfer power of 72 W). Therefore, the heating element control unit  432  can, for example, comprise a controllable current source. 
   The one or more cooling elements  421  can comprise at least one of a cooling channel, or a thermoelectric element. Furthermore, as shown in  FIG. 5 , the one or more cooling elements  421  are coupled to a cooling element control unit  422 . Cooling element control unit  422  is configured to provide either dependent or independent control of each cooling element  421 , and exchange information with controller  450 . 
   For example, the one or more cooling elements  421  can comprise one or more cooling channels that can permit a flow rate of a fluid, such as water, Fluorinert, Galden HT-135, etc., therethrough in order to provide conductive-convective cooling, wherein the fluid temperature has been lowered via a heat exchanger. The fluid flow rate and fluid temperature can, for example, be set, monitored, adjusted, and controlled by the cooling element control unit  422 . Alternately, during heating for example, the fluid temperature of the fluid flow through the one or more cooling elements  421  may be increased to complement the heating by the one or more heating elements  431 . Alternately yet, during cooling for example, the fluid temperature of the fluid flow through the one or more cooling elements  421  may be decreased. 
   Alternately, for example, the one or more cooling elements  421  can comprise an array of thermoelectric elements capable of heating or cooling a substrate depending upon the direction of electrical current flow through the respective elements. Thus, while the elements  421  are referred to as “cooling elements,” these elements may include the capability of heating in order to provide rapid transition between temperatures. Further, heating and cooling function may be provided by separate elements within the temperature controlled support base  420 . An exemplary thermoelectric element is one commercially available from Advanced Thermoelectric, Model ST-127-1.4-8.5M (a 40 mm by 40 mm by 3.4 mm thermo-electric device capable of a maximum heat transfer power of 72 W). Therefore, the cooling element control unit  422  can, for example, comprise a controllable current source. 
   Additionally, as shown in  FIG. 5 , the substrate holder  400  can further comprise an electrostatic clamp (ESC) comprising one or more clamping electrodes  435  embedded within substrate support  430 . The ESC further comprises a high-voltage (HV) DC voltage supply  434  coupled to the clamping electrodes  435  via an electrical connection. The design and implementation of such a clamp is well known to those skilled in the art of electrostatic clamping systems. Furthermore, the HV DC voltage supply  434  is coupled to controller  450  and is configured to exchange information with controller  450 . 
   Furthermore, as shown in  FIG. 5 , the substrate holder  400  can further comprise a back-side gas supply system  436  for supplying a heat transfer gas, such as an inert gas including helium, argon, xenon, krypton, a process gas, or other gas including oxygen, nitrogen, or hydrogen, to the backside of substrate  410  through at least one gas supply line, and at least one of a plurality of orifices and channels (not shown). The backside gas supply system  436  can, for example, be a multi-zone supply system such as a two-zone (center/edge) system, or a three-zone (center/mid-radius/edge), wherein the backside pressure can be varied in a radial direction from the center to edge. Furthermore, the backside gas supply system  436  is coupled to controller  450  and is configured to exchange information with controller  450 . 
   Further yet, as shown in  FIG. 5 , the substrate holder  400  can further comprise one or more temperature sensors  462  coupled to a temperature monitoring system  460 . The one or more temperature sensors  462  can be configured to measure the temperature of substrate  410 , or the one or more temperature sensors  462  can be configured to measure the temperature of substrate support  430 , or both. For example, the one or more temperature sensors  410  may be positioned such that the temperature is measured at the lower surface of the substrate support  430  as shown in  FIG. 5 , or positioned such that the temperature of a bottom of the substrate  410  is measured. 
   The temperature sensor can include an optical fiber thermometer, an optical pyrometer, a band-edge temperature measurement system as described in pending U.S. patent application Ser. No. 10/168544, filed on Jul. 2, 2002, the contents of which are incorporated herein by reference in their entirety, or a thermocouple (as indicated by the dashed line) such as a K-type thermocouple. Examples of optical thermometers include: an optical fiber thermometer commercially available from Advanced Energies, Inc., Model No. OR2000F; an optical fiber thermometer commercially available from Luxtron Corporation, Model No. M600; or an optical fiber thermometer commercially available from Takaoka Electric Mfg., Model No. FT-1420. 
   The temperature monitoring system  460  can provide sensor information to controller  450  in order to adjust at least one of a heating element, a cooling element, a backside gas supply system, or an HV DC voltage supply for an ESC either before, during, or after processing. 
   Controller  450  includes a microprocessor, memory, and a digital I/O port (potentially including D/A and/or A/D converters) capable of generating control voltages sufficient to communicate and activate inputs to substrate holder  400  as well as monitor outputs from substrate holder  400 . As shown in  FIG. 5 , controller  450  can be coupled to and exchange information with heating element control unit  432 , cooling element control unit  422 , HV DC voltage supply  434 , backside gas supply system  436 , and temperature monitoring system  460 . A program stored in the memory is utilized to interact with the aforementioned components of substrate holder  400  according to a stored process recipe. One example of controller  450  is a DELL PRECISION WORKSTATION 640™, available from Dell Corporation, Austin, Tex. 
   The controller  450  may also be implemented as a general purpose computer, processor, digital signal processor, etc., which causes a substrate holder to perform a portion or all of the processing steps of the invention in response to the controller  450  executing one or more sequences of one or more instructions contained in a computer readable medium. The computer readable medium or memory is configured to hold instructions programmed according to the teachings of the invention and can contain data structures, tables, records, or other data described herein. Examples of computer readable media are compact discs, hard disks, floppy disks, tape, magneto-optical disks, PROMs (EPROM, EEPROM, flash EPROM), DRAM, SRAM, SDRAM, or any other magnetic medium, compact discs (e.g., CD-ROM), or any other optical medium, punch cards, paper tape, or other physical medium with patterns of holes, a carrier wave, or any other medium from which a computer can read. 
   Controller  450  may be locally located relative to the substrate holder  400 , or it may be remotely located relative to the substrate holder  400  via an internet or intranet. Thus, controller  450  can exchange data with the substrate holder  400  using at least one of a direct connection, an intranet, or the internet. Controller  450  may be coupled to an intranet at a customer site (i.e., a device maker, etc.), or coupled to an intranet at a vendor site (i.e., an equipment manufacturer). Furthermore, another computer (i.e., controller, server, etc.) can access controller  450  to exchange data via at least one of a direct connection, an intranet, or the internet. 
   Optionally, substrate holder  400  can include an electrode through which RF power is coupled to plasma in a processing region above substrate  410 . For example, support base  420  can be electrically biased at an RF voltage via the transmission of RF power from an RF generator through an impedance match network to substrate holder  400 . The RF bias can serve to heat electrons to form and maintain plasma, or bias substrate  410  in order to control ion energy incident on substrate  410 , or both. In this configuration, the system can operate as a reactive ion etch (RIE) reactor, where the chamber and upper gas injection electrode serve as ground surfaces. A typical frequency for the RF bias can range from 1 MHz to 100 MHz and is preferably 13.56 MHz. 
   Alternately, RF power can be applied to the substrate holder electrode at multiple frequencies. Furthermore, an impedance match network can serve to maximize the transfer of RF power to plasma in the processing chamber by minimizing the reflected power. Various match network topologies (e.g., L-type, π-type, T-type, etc.) and automatic control methods can be utilized. 
   Referring now to  FIG. 6 , a substrate holder is described according to another embodiment. The substrate holder  500  comprises a substrate support  530  having a first temperature and configured to support a substrate  510 , a temperature-controlled support base  520  positioned below substrate support  530  and configured to be at a second temperature less than the first temperature (e.g. less than a desired temperature of substrate  510 ), and a thermal insulator  540  disposed between the substrate support  530  and the temperature-controlled support base  520 . Additionally, the substrate support  530  comprises a center heating element  533  (located at a substantially center region below substrate  510 ) and an edge heating element  531  (located at a substantially edge, or peripheral, region below substrate  510 ) coupled thereto, and configured to elevate the temperature of the substrate support  530 . Furthermore, the support base  520  comprises one or more cooling elements  521  coupled thereto, and configured to reduce the temperature of the substrate support  530  via the removal of heat from the substrate support  530  through thermal insulator  540 . 
   As shown in  FIG. 6 , the center heating element  533  and the edge heating element  531  are coupled to a heating element control unit  532 . Heating element control unit  532  is configured to provide either dependent or independent control of each heating element, and exchange information with a controller  550 . 
   Additionally, as shown in  FIG. 6 , the substrate holder  500  can further comprise an electrostatic clamp (ESC) comprising one or more clamping electrodes  535  embedded within substrate support  530 . The ESC further comprises a high-voltage (HV) DC voltage supply  534  coupled to the clamping electrodes  535  via an electrical connection. The design and implementation of such a clamp is well known to those skilled in the art of electrostatic clamping systems. Furthermore, the HV DC voltage supply  534  is coupled to controller  550  and is configured to exchange information with controller  550 . 
   Furthermore, as shown in  FIG. 6 , the substrate holder  500  can further comprise a back-side gas supply system  536  for supplying a heat transfer gas, such as an inert gas including helium, argon, xenon, krypton, a process gas, or other gas including oxygen, nitrogen, or hydrogen, to the center region and the edge region of the backside of substrate  510  through two gas supply lines, and at least two of a plurality of orifices and channels (not shown). The backside gas supply system  536 , as shown, comprises a two-zone (center/edge) system, wherein the backside pressure can be varied in a radial direction from the center to edge. Furthermore, the backside gas supply system  536  is coupled to controller  550  and is configured to exchange information with controller  550 . 
   Further yet, as shown in  FIG. 6 , the substrate holder  500  further comprises a center temperature sensor  562  for measuring a temperature at a substantially center region below substrate  510  and an edge temperature sensor  564  for measuring a temperature at a substantially edge region below substrate  510 . The center and edge temperature sensors  562 ,  564  are coupled to a temperature monitoring system  560 . 
   Referring now to  FIG. 8 , a flowchart describing a method  700  of controlling the temperature of a substrate on a substrate holder in a processing system is presented according to another embodiment. For example, the temperature control scheme can pertain to multiple process steps for a process in a processing system having a substrate holder such as one of those described in  FIGS. 1 through 6 . The method  700  begins in  710  with disposing a substrate on a substrate holder. 
   The substrate holder comprises a plurality of temperature sensors reporting at least a temperature at an inner region and an outer region of the substrate and/or substrate holder. Additionally, the substrate holder comprises a substrate support having a first heating element and a second heating element heating the inner region and the outer region respectively, and a support base having a cooling element for cooling the inner region and the outer region. The first and second heating elements and the cooling element are controlled by a temperature control system to maintain the substrate holder at a selectable set-point temperature. Furthermore, the substrate holder comprises a thermal insulator disposed between the substrate support and the support base. 
   In  720 , the substrate is set to a first temperature profile. Using the temperature control system, a first base temperature for the base support (that is less than the first temperature profile (e.g. the substrate temperature), and a first inner set-point temperature and a first outer set-point temperature are selected. Thereafter, the temperature control system adjusts the cooling element and the first and second heating elements to achieve the selected temperatures described above. 
   In  730 , the substrate is set to a second temperature profile. Using the temperature control system, a second base temperature for the base support, and a second inner set-point temperature and a second outer set-point temperature are selected. Thereafter, the temperature control system changes the substrate temperature from the first temperature profile (i.e., first inner and outer set-point temperatures) to the second temperature profile (i.e., second inner and outer set-point temperatures) by optionally adjusting the cooling element to change the first base temperature to the second base temperature and adjusting the inner and outer heating elements until the second inner and outer set-point temperatures are achieved. 
   In one example, the substrate temperature is increased (or decreased) from the first temperature profile to the second temperature profile, while the second base temperature remains the same as the first base temperature. The power delivered to the inner and outer heating elements is increased (or decreased) in order to heat (or cool) the substrate from the first temperature profile to the second temperature profile. 
   In another example, the substrate temperature is increased (or decreased) from the first temperature profile to the second temperature profile, while the second base temperature is changed to a value different from the first base temperature. The power delivered to the inner and outer heating elements is increased (or decreased) in order to heat (or cool) the substrate from the first temperature profile to the second temperature profile, while the power delivered to the cooling element is increased (or decreased) in order to change the first base temperature to the second base temperature. Thus, according to one embodiment of the invention, the temperature of the support base is varied to assist the substrate support in controlling the temperature of the substrate. The present inventors have recognized that this varying of the support base temperature can provide more accurate and/or rapid temperature transitions of the substrate. 
   The temperature control system utilizes a control algorithm in order to stably adjust temperature(s) in response to measured values provided by the temperature monitoring system. The control algorithm can, for example, include a PID (proportional, integral and derivative) controller. In a PID controller, the transfer function in the s-domain (i.e., Laplacian space) can be expressed as:
 
 G   c ( s )= K   P   +K   D   s+K   I   s   −1 ,  (1)
 
   where K P , K D , and K I , are constants, referred to herein as a set of PID parameters. The design challenge for the control algorithm is to select the set of PID parameters to achieve the desired performance of the temperature control system. 
   Referring to  FIG. 7A , several exemplary time traces of temperature are shown to illustrate how different sets of PID parameters lead to a different temperature response. In each case, the temperature is increased from a first value to a second value. A first time trace of temperature  601  illustrates a relatively aggressive control scheme having a relatively low value for K I , for example, wherein the time trace exhibits “overshoot” and a series of oscillations following the overshoot. A second time trace of temperature  602  illustrates a relatively less aggressive control scheme having a relatively higher value for K I , for example, wherein the time trace exhibits a relatively slow, gradual increase to the second temperature. A third time trace of temperature  603  illustrates a desired moderately aggressive control scheme having a value for K I  between that of time trace  601  and time trace  602 , for example, wherein the time trace exhibits a relatively faster increase to the second temperature without overshoot. However, the present inventors have recognized that the use of only one PID parameter set is not sufficient to provide a desired condition for stability and rise rate. 
   According to one embodiment, two or more PID parameter sets are utilized to achieve a rapid and stable adjustment of the temperature between an initial value and a final value.  FIG. 7B  illustrates an exemplary time trace of temperature  600  utilizing two sets of PID parameters. A first set of PID parameters is used for a first time duration  622 , and a second set of PID parameters is used for a second time duration  624 . The first time duration  622  can be determined by setting a temperature offset  620  from the final value of the temperature. For example, the temperature offset can range from approximately 50% to 99% of the temperature difference between the initial value and the final value. Additionally, for example, the temperature offset can range from approximately 70% to 95% of the temperature difference between the initial value and the final value, and desirably, the temperature offset can range from approximately 80% to 95%. 
   For example, a relatively aggressive PID parameter set may be used for the first time duration  622 , while a relatively less aggressive PID parameter set may be used for the second time duration  624 . Alternatively, for example, the PID parameter K D  can be increased from the first PID set to the second PID set, the PID parameter K I  can be decreased from the first PID set to the second PID set, or a combination thereof. 
   Although only certain embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.