Patent Publication Number: US-2011064545-A1

Title: Substrate transfer mechanism with preheating features

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/242,924 (Attorney Docket No. 13300L), filed Sep. 16, 2009, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention relate to apparatus and methods for processing substrates. Particularly, embodiments of the present invention provide apparatus and methods for transferring substrates during processing. 
     2. Description of the Related Art 
     In manufacturing of semiconductor devices, substrates sometimes are processed at high temperatures. In existing systems, substrates generally remain in the processing chamber to cool off after processing at high temperatures to avoid breaking from thermal shock. Cooling off the substrates in the processing chamber takes away production time from the processing chamber causing cost of ownership to increase. Additionally, cooling off substrates in the processing chamber requires frequent cooling down and heating up of the processing chamber causing temperature swings in the processing chamber. The temperature swings in the processing chamber may cause deposits or films formed on internal surfaces of the processing chamber to flake off and increase particle contamination. Frequent cooling and heating of the processing chamber also increases energy cost. 
     Embodiments of the present invention provide methods and apparatus for substrate transferring before, after or between high temperature processing to avoid thermal shock, increase efficiency of processing chambers, and reduce energy consumption. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention generally provide apparatus and methods for transferring substrate during processing. More particularly, embodiments of the present invention provide a substrate transfer mechanism for heating substrates and/or controlling temperature of substrates during transferring. 
     One embodiment of the present invention provides a robot blade assembly for supporting a substrate or a substrate carrier thereon. The robot blade assembly comprises a base plate, an induction heating assembly disposed on the base plate, and a top plate disposed above the induction heating assembly. 
     Another embodiment of the present invention provides a cluster tool. The cluster tool comprises a transfer chamber having a transfer volume, a load lock coupled to transfer chamber, and one or more processing chambers coupled to the transfer chamber. The one or more processing chambers are configured to processing substrates at elevated temperature. The cluster tool further comprises a substrate transfer mechanism disposed in the transfer volume and configured to transfer substrates among the load lock and the one or more processing chambers, and an induction heating assembly configured to heat substrates being transferred by the substrate transfer mechanism. 
     Yet another embodiment of the present invention provides a method for processing one or more substrates. The method comprises transferring the one or more substrates from a first chamber to a second chamber by a transfer mechanism while heating the one or more substrates using an induction heating element to a first temperature, and processing the one or more substrates in the second chamber at a second temperature. The first temperature is substantially close to and lower than second temperature. 
    
    
     
       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. 1  is a schematic view of a cluster tool in accordance with one embodiment of the present invention. 
         FIG. 2A  is a schematic top view of a robot in accordance with one embodiment of the present invention. 
         FIG. 2B  is a schematic top view of a robot blade supporting a substrate carrier. 
         FIG. 3  is a schematic section view of an end effector for a robot according to one embodiment of the present invention; 
         FIG. 4A  is an exploded view of an end effector with one embodiment of the present invention. 
         FIG. 4B  is a sectional side view of the end effector of  FIG. 4A . 
         FIG. 4C  is a sectional view of a coil for an induction heating element in accordance with one embodiment of the present invention. 
         FIG. 5  is a coil arrangement in accordance with one embodiment of the present invention. 
         FIG. 6  schematically illustrates a coil arrangement in accordance with one embodiment of the present invention. 
         FIG. 7  is a sectional view of a transfer chamber with one or more induction heating elements according to one embodiment of the present invention. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
     DETAILED DESCRIPTION 
     Embodiments of the present invention generally provide apparatus and methods for transferring substrates during processing. More particularly, embodiments of the present invention provide a substrate transfer mechanism for heating substrates and/or controlling temperature of substrates during transferring. 
     Embodiments of the present invention provide apparatus and methods for transferring substrates at high temperature without thermal shock, therefore, improving throughput by eliminating cooling and heating periods during processing. 
     In one embodiment of the present invention, a substrate transfer mechanism comprises a transfer blade having an induction heating assembly configured to provide induction heating to substrates and/or substrate carriers being transferred. In one embodiment, the induction heating assembly comprises one or more planar spiral coils configured to heat substrates and/or a carrier of substrates with inductive energy. In one embodiment, the transfer blade further comprises a reflective foil configured to reflect the electromagnetic field towards the substrate and/or carrier being heated. In one embodiment, the transfer blade comprises an infrared reflective film to avoid heating of the transfer blade and the one or more spiral planar coils. 
     In another embodiment, heating elements are disposed in a transfer path of the substrates, for example, in a transfer chamber, to heat the substrates or maintain the substrates at a high temperature during transfer. In one embodiment, one or more induction heating elements are disposed over a chamber lid of a transfer chamber. 
     Substrate transfer mechanisms of the present invention can be used to rapidly heat substrates and/or maintain substrates at a high temperature while transferring the substrates. In one embodiment, a substrate transfer mechanism with induction heating elements is used to preheat substrates during transfer to a hot processing chamber to avoid thermal shock. In another embodiment, a substrate transfer mechanism with induction heating elements is used to retrieve substrates at a high temperature without thermal shock by maintaining the substrates at a high temperature using induction heating. In another embodiment, one or more portions of the substrate transfer path, such as a transfer chamber, are heated to prevent thermal shock to substrates during transfer. 
       FIG. 1  is a schematic view of a cluster tool  100  in accordance with one embodiment of the present invention. The cluster tool  100  is configured to process substrates using two or more processing chambers. Each processing chamber may be used to perform the same or different processes. In one embodiment, the cluster tool  100  is configured to form nitride compound structures for light emitting diodes (LED). 
     The cluster tool  100  comprises a transfer chamber  106  having a transfer region  107 . The cluster tool  100  comprises a first processing chamber  102  and a second processing chamber  104  coupled to the transfer chamber  106 . In one embodiment, the processing chambers  102 ,  104  may be configured to deposit layers for a LED structure. The processing chambers  102 ,  104  may be a hydride vapor phase epitaxial (HVPE) chamber or a metal organic chemical vapor deposition (MOCVD) chamber. 
     A robot assembly  117  is disposed in the transfer region  107  and configured to transfer substrates to and from the first and second processing chambers  102 ,  104 . In one embodiment, the robot assembly  117  comprises a heating element and is configured to transfer substrates while heating the substrates to a high temperature or maintaining the substrate at a high temperature. 
     The cluster tool  100  further comprises a load lock chamber  108  coupled with the transfer chamber  106  and a load station  110  coupled with the load lock chamber  108 . The load lock chamber  108  and the load station  110  are configured to load substrates to the first processing chamber  102  and the second processing chamber  104  through the transfer chamber  106 . In one embodiment, the cluster tool  100  further comprises a batch load lock chamber  109 , configured for storing a plurality of substrate carriers, coupled with the transfer chamber  106 . 
     The load station  110  is configured as an atmospheric interface to allow an operator to load a plurality of substrates for processing into the confined environment of the load lock chamber  108 , and to unload a plurality of processed substrates from the load lock chamber  108 . In one embodiment, substrates for processing may be grouped in batches and transported by a conveyor tray  111  on a carrier plate  112 . In another embodiment, the load station  110  may be an automatic loading station configured to transfer substrates between carrier plates and transferring cassettes. 
     The load lock chamber  108  provides an interface between the atmospheric environment of the load station  110  and the controlled environment of the transfer chamber  106 . Substrates are transferred between the load lock chamber  108  and the load station  110  via the slit valve and between the load lock chamber  108  and the transfer chamber  106  via another slit valve. In one embodiment, the load lock chamber  108  may comprise multiple carrier supports that are vertically stacked. The carrier supports may be vertically movable to facilitate loading and unloading of a carrier plate  112 . 
     The load lock chamber  108  is coupled to a pressure control system (not shown) which pumps down and vents the load lock chamber  108  to facilitate passing the substrate between the vacuum environment of the transfer chamber  106  and the substantially ambient (e.g., atmospheric) environment of the load station  110 . In addition, the load lock chamber  108  may also comprise features for temperature control. 
     The transfer chamber  106  is generally maintained at a vacuum state or a low pressure state. In one embodiment, the transfer chamber  106  may have a controlled environment maintained by an inert gas, such as helium gas and nitrogen gas, a reducing gas, such as ammonia, or combinations thereof. 
     The robot assembly  117  is operable to transfer substrates among the load lock chamber  108 , the batch load lock chamber  109 , the processing chamber  104  and the processing chamber  102 . In one embodiment, the robot assembly  117  may comprise heated end effectors configured to keep the substrates at elevated temperature during transfer. In one embodiment, the robot assembly  117  is configured to keep substrates at a temperature higher than about 350° C. during transfer among the processing chambers. In one embodiment, the robot assembly  117  is configured to heat the substrates to higher than about 700° C. In another embodiment, the robot assembly  117  is configured to heat the substrates between about 700° C. and about 1100° C. 
     The batch load lock chamber  109  having a cavity for storing a plurality of substrates placed on the carrier plates  112  therein. A storage cassette may be moveably disposed within the cavity. The storage cassette may comprise a plurality of storage shelves supported by a frame. In one embodiment, the batch load lock chamber  109  may be configured to clean the substrates prior processing. In one embodiment, the batch load lock chamber  109  may have one or more heaters configured to heat the substrates disposed therein and may be connected to an inert gas source and/or a cleaning gas source to perform a thermal cleaning of the substrates prior to processing. 
     During an operation, for example manufacturing LED devices, a carrier plate  112  containing a batch of substrates is loaded on the conveyor tray  111  in the load station  110 . The conveyor tray  111  is then moved through a slit valve into the load lock chamber  108 , placing the carrier plate  112  onto the carrier support inside the load lock chamber  108 , and the conveyor tray returns to the load station  110 . While the carrier plate  112  is inside the load lock chamber  108 , the load lock chamber  108  is pumped and purged with an inert gas, such as nitrogen, in order to remove any remaining oxygen, water vapor, and other types of contaminants. 
     After the batch of substrates have been conditioned in the batch load lock chamber  109 , the robot assembly  117  may pick up the carrier plate  112  and transfer the carrier plate  112  to the processing chamber  102  for a MOCVD or HVPE process. In one embodiment, the robot assembly  117  heats the carrier plate  112  and the substrates thereon to a temperature close to the temperature in the processing chamber  102  during transfer so that the carrier plate  112  can be disposed on the heated processing chamber  102  without thermal shock. Induction heating may be used to achieve rapid heating and without heating up the robot assembly  117  itself. During processing, such as in HVPE processing, the substrates may be heated in the processing chamber  102  to a temperature up to about 1100° C. 
     After processing in the processing chamber  102 , the robot assembly  117  picks up the carrier plate  112  from the processing chamber  102  without waiting for the carrier plate  112  to cool down. To avoid thermal shock to the carrier plate  112  and the substrates, the induction heating element in the robot assembly  117  is activated to maintain the high temperature of the carrier plate  112  and the substrates and to prevent dramatic temperature drop. In one embodiment, an RF power source is applied to the induction heating element in the robot assembly  117  and the current and/or duration of the RF power may be adjusted to maintain the carrier plate  112  at a desired temperature range. 
     The carrier plate  112  is transferred from the processing chamber  102  to the processing chamber  104  for another process, for example a MOCVD process. In one embodiment, the processing chamber  104  may be heated at a temperature about 800° C., and the carrier plate  112  may be maintained at a temperature between 700° C. to about 800° C. during transferring. Similarly, after processing in the processing chamber  104 , the robot assembly  117  picks up the carrier plate  112  from the processing chamber  104  without waiting for the carrier plate  112  to cool down. The induction heating element in the robot assembly  117  is activated to maintain the high temperature of the carrier plate  112  and the substrates and to prevent dramatic temperature drop. 
       FIG. 2A  is a schematic top view of a robot assembly  117  in accordance with one embodiment of the present invention. The robot assembly  117  includes arms  202   a ,  202   b  coupled to rotatable two hubs  201 . The hubs  201  are connected to an actuator configured to rotate the hubs  201 . A transfer blade  204  is mounted on the arms  202   a ,  202   b . The transfer blade  204  is configured to support and secure a substrate or a substrate carrier thereon. The transfer blade  204  comprises an induction heating assembly configured to heat the substrate and/or the substrate carriers disposed thereon. The arms  202   a ,  202   b  extend and retract when the hubs  201  rotate relative to one another along opposite direction. The hubs  201  rotate at the same speed along the same direction, the arms  202   a ,  202   b  and the transfer blades  204  rotate about the hubs  201 . 
       FIG. 2B  is a schematic top view showing the robot blade  204  supporting a substrate carrier. The robot blade  204  has a wrist end  203  configured to mount to an arm assembly, such as the arms  202   a ,  202   b  and the hubs  201 . The robot blade  204  also has a supporting end  207  configured to support substrates and/or substrate carriers thereon. The supporting end  207  comprises one or more induction heating elements configured to provide induction heating energy towards the substrates and/or substrate carrier during transferring. In one embodiment, the supporting end  207  may have one or more slits  208  formed therethrough to allow lifting pins configured to pick up and drop off the substrates and substrate carriers. The blade  204  has raised areas functioning as stops configured to secure a substrate/carrier thereon. In one embodiment, the blade  204  may have two sets of stops configured to secure a squared carrier  205  and a circular carrier  206  respectively. The carriers  205 ,  206  are configured to support and secure a plurality of substrates  209 . 
       FIG. 3  is a schematic section view of the blade  204  for transferring substrates according to an embodiment of the invention. The blade  204  comprises a base plate  241  configured to provide structural support, an induction heating assembly  243  disposed on the base plate  241 , and a top plate  245  disposed over the induction heating assembly  243 . The top plate  245  may have a plurality of bumpers  246  formed on a top surface  245   a . The bumpers  246  are small raised areas on the top plate  245 . The plurality of bumpers  246  are configured to be in contact with a substrate or a carrier plate  112  and to position the carrier plate  112  at a distance  254  away from the top plate  245 . Because there is only minimal contact between the top plate  245  and the carrier plate  112  at the bumpers  240 , thermal conduction between the blade  204  and the carrier plate  112  can be mostly prevented and the blade  204  can remain cool while the carrier plate  112  and the substrates  113  are heated to a high temperature from induction heating from the induction heating assembly  243 . 
     The base plate  241  may be formed from a dielectric material, or any material that is not responsive to induction heating. In one embodiment, the base plate  241  is formed from quartz material. 
     In an embodiment, the base plate  241  may comprise an infrared reflective coating  242  on surfaces facing the induction heating assembly  243 . The infrared reflective coating  242  is configured to reflect infrared energy from the induction heating assembly  243  and the heated substrate  113 /carrier plate  112  to prevent the base plate  241  from heating up by the infrared energy. In an embodiment, the infrared reflective coating  242  comprises a titanium nitride film. The titanium nitride film may be about 0.5 mm in thickness. In another embodiment, the infrared reflective coating  242  may comprise a gold film. 
     In one embodiment, the blade  204  further comprises a ferrite liner  244  disposed under the induction heating assembly  243 . The ferrite liner  244  is configured to shield the inductive field of the induction heating assembly  243  from the base plate  241 , therefore, preventing any induction heating of the base plate  241 . In one embodiment, the ferrite line  244  is a foil made of ferrite material with a thickness about 2 mm. 
     The induction heating assembly  243  generally comprises one or more coils  255  disposed over the base plate  241 . Each coil  255  is connected to a RF power source  248  which provides high frequency alternating current to the coil  255 . The induction heating assembly  243  further comprises a capacitor  249  coupled to the RF power source  248  in a parallel manner. In one embodiment, the capacitor  249  may be cooled by a fluid coolant, such as water. In one embodiment, the capacitor  249  may be used to adjust the phase of the RF power applied to the one or more coils  255 . 
     The induction heating assembly  243  is configured to rapidly heat a substrate or a substrate carrier made of electrically conducting material by applying a RF current to the one or more coils  255 . During heating, the high frequency alternating current in the one or more coils  255  causes eddy currents within an electrically conducting object being heated. The resistance to the eddy current in the electrically conducting object leads to Joule heating of the object. 
     Embodiments of the present invention comprise controlling induction heating by controlling one or more of operating parameters, such as the frequency of the RF power source  248 , duration of the RF power applied, power of the RF power source  248 , spacing between the one or more coils  255  and the object being heated, such as the carrier plate  112 , and spacing between neighboring wires of the coil  255 . In one embodiment, the frequency of the RF power source is about 40 kHz to about 100 kHz. In another embodiment, the frequency of the RF power source is about 45 kHz to about 65 kHz. In another embodiment, the frequency of the RF power source is below about 50 kHz. In one embodiment, the power of the RF power source is about 10 kW. In one embodiment, a carrier plate  112  may be heated by the coils  255  to about 1000° C. in about 20 seconds. 
     The carrier plate  112  may be made from a material subject to induction heating. In one embodiment, the carrier plate  112  is made of graphite. In another embodiment, the carrier plate  112  is made of graphite coated with silicon carbide. In another embodiment, the carrier plate  112  is made of silicon carbide. 
     Each of the one or more coils  255  is a planar spiral coil wound from a cable having a plurality of wires individually wrapped in an insulator. In one embodiment, each planar spiral coil may have about 10 turns. In another embodiment, neighboring planar spiral coils may be wound along opposite directions so that, when RF power of the same phase is applied to the neighboring coils, the currents within outer portion of the neighboring planar spiral coils are of the same direction, therefore, do not cancel one another. Alternatively, neighboring planar spiral coils may be wound along the same direction, and a phase alternating capacitor may be used within the circuit of one of the coil to make sure that currents within wires of the neighboring coils are not off opposite directions. 
     The top plate  245  is generally fabricated from a dielectric material which is not subject to induction heating. In one embodiment, the top plate  245  is also made of an infrared transparent material. In one embodiment, the top plate  245  is made of quartz. In one embodiment, the top plate  245  is also coated with an infrared reflective coating, such as a titanium nitride film or a gold film. 
       FIG. 4A  is an exploded view of the blade  204  according to an embodiment. The base plate  241  includes sidewalls  247  extending upwards along the outer edge. The sidewalls  247  and the bottom of the base plate  241  form a cavity  241   a . The base plate  241  may be coated with infrared reflective coating on the inner surfaces thereof. As one example, a ferrite liner  244  may be disposed on the bottom of the base plate  241 . Two planar spiral coils  255  are disposed on the ferrite liner  244 . The two planar spiral coils  255  may be wound in opposite directions. The top plate  245  rests on the sidewalls  247  of the base plate  241 . The top plate  245  has a plurality of bumpers  246  and stops  250  formed thereon. The bumpers  246  are configured to provide support to object being heated with minimal contact. The stops  250  are higher than the bumpers  246  and are configured to secure an object being heated from lateral motions. 
       FIG. 4B  is a sectional side view of the blade  204  of  FIG. 4A . The bumpers  246  define a supporting plane  246   a . In one embodiment, the bumpers  246  have a height of about 0.5 mm and the stops  250  are about 0.75 mm higher than the supporting plane  246   a . In one embodiment, the top plate  245  may have a thickness of about 1 mm. The cavity  241   a  may have a height of about 10.5 mm. 
       FIG. 4C  is a sectional view of the coil  255  for the induction heating assembly  243  in accordance with one embodiment of the present invention. The coil  255  may be wound by a bundled wire to obtain increased surface area for RF current capacity. In one embodiment, the coil  255  includes a plurality of wires  252  each wrapped in an insulator  253 . The plurality of wires  252  are bundled in an insulator  251 . In one embodiment, the coils  255  are wound using Litz wires. In one embodiment, the wire of the coils  255  may have a diameter of about 8 mm. 
     As discussed above, one or more coils may be used in providing induction heating. The one or more coils may be arranged according to the heating needs. In one embodiment, as shown in  FIG. 5 , a coil assembly  300  comprises six planar spiral coils  303   a ,  303   b ,  303   c ,  303   d ,  303   e , and  303   f  used to provide induction heating to a substantially circular object, such as substrate carrier configured to carry a plurality of sapphire substrates. Each coil  303   a ,  303   b ,  303   c ,  303   d ,  303   e , and  303   f  is substantially triangular with neighboring coils wound in opposite directions. Distance  304  indicates the distance between leading wires of neighboring coils. Distance  305  indicates distance between neighboring wires within a coil. In one embodiment, the distance  304  is greater than the distance  305 . The planar spiral coils  303   a ,  303   b ,  303   c ,  303   d ,  303   e , and  303   f  are coupled to an RF power source  301 . A capacitor  302  is coupled to the RF power source  301  in a parallel manner. 
       FIG. 6  schematically illustrates a coil arrangement in a robot blade  404  in accordance with one embodiment of the present invention. Six coil assemblies  403  are arranged on the robot blade  404 . In one embodiment, each coil assembly  403  may comprise two parallel coils connected to two separate power supplies. In one embodiment, powers with different frequencies are applied to the parallel coils in each coil assembly  403 . 
     Embodiments of the present invention also provide methods and apparatus for inductively heating substrates and/or carriers using induction heating elements positioned along a transfer path, for example in transfer chambers and load locks. In one embodiment, one or more induction heating elements may be disposed outside a transfer chamber and configured to heat substrates or carriers while the substrates and carriers are within the transfer chamber. The one or more induction heating elements may be positioned on a lid of the transfer chamber. 
       FIG. 7  is a sectional view of a transfer chamber  500  with one or more induction heating elements according to one embodiment of the present invention. The transfer chamber  500  is generally used in a cluster tool, such as the cluster tool  100  of  FIG. 1 , to facilitate substrate transferring among load locks and processing chamber. 
     The transfer chamber  500  comprises a chamber bottom  501 , sidewalls  503  disposed over the chamber bottom  501 , and a chamber lid  502  disposed over the sidewalls  503 . The chamber bottom  501 , sidewalls  503  and chamber lid  502  define a transfer volume  504 . A robot  510  is disposed within the transfer volume  504 . The robot  510  has a robot blade  511  configured to support and transfer a carrier plate  112 . In one embodiment, the robot blade  511  comprises induction heating elements, similar to robot blades described above. In another embodiment, the robot blade  511  does not include any heaters. 
     A plurality of slit valve openings  505  are formed through the sidewalls  503 . Each slit valve opening  505  provides an interface with other chambers, such as a processing chamber  102 , and a load lock chamber  109 . Slit valves  507  may be used to selectively open and close the slit valve openings  505  so that the transfer volume  504  can be selectively in fluid communication with the chambers connected to the transfer chamber  500 . When the slit valve  507  is open, the robot blade  511  can extend through the slit valve opening  505  to pick up or drop off a carrier plate  112  in the chamber connected thereto. 
     In one embodiment, a vacuum pump  530  is connected to the transfer volume  504  so that the transfer chamber  500  can be maintained at a vacuum state or a low pressure state. In another embodiment, the transfer volume  504  has a controlled environment maintained by an inert gas, such as helium gas and nitrogen gas, a reducing gas, such as ammonia, or combinations thereof. 
     The transfer chamber  500  comprises an induction heating assembly  509  disposed outside the transfer chamber. In one embodiment, the induction heating assembly  509  is disposed adjacent the chamber lid  502 . The chamber lid  502  has a window  512 . The induction heating assembly  509  is configured to heat substrates on the carrier plate  112  in the transfer chamber  500  through the window  512 . 
     The induction heating assembly  509  generally comprises one or more coils  520 . The coils  520  may be planar spiral coils. In one embodiment, the coils  520  include two parallel rows as shown in  FIG. 7 . Alternative, the coils  520  may include a single row. The coils  520  may have a circular shape. In one embodiment, the coils  520  are sized appropriately to match diameter of the carrier plate  112  being heated. 
     The coils  520  may comprise two or more coils for uniform heating. In one embodiment, the coils  520  comprises an inner heating element  522  and an outer heating element  521 . The outer heating element  521  is coupled to a first power source  524  and a first heating station  523 . The inner heating element  522  is coupled to a second power source  526  and a second heating station  525 . Both the first power source  524  and the first heating station  523  are separate and distinct from the second power source  526  and the second heating station  525 . The heating elements  522 ,  521  operate independently from each other so that collectively, a wide range of precise temperature tuning is possible. The heating elements  521 ,  522  may be spaced from the top of the substrate or the top of the carrier plate  112  by a distance of between about 0.2 inches and about 0.8 inches. 
     The outer heating element  521  may comprise an induction coil that has between about 8 turns and about 11 turns. In one embodiment, the outer heating element  521  may be arranged in two substantially parallel rows and have an outer diameter of between about 12 inches and about 15 inches. The inner heating element  522  may comprise an induction coil that has between about 6 turns and about 9 turns. In one embodiment, the inner heating element  522  may be arranged in two substantially parallel rows and have an outer diameter of between about 3 inches and about 6 inches. The number of turns and heating element  521 ,  522  size is not limited to those shown or described. For example, for heating a bigger carrier plate  112 , the size and shape of the heating elements  521 ,  522  can be adjusted accordingly so the concept is not limited to the particular sizes discussed above. 
     The first heating station  523  and power source  524  may be arranged to supply between about 30 kW of power and about 45 kW of power while the second heating station  525  and power supply  526  may be configured to supply between about 10 kW and about 17 kW of power. In one embodiment, the frequency of the first power source  524  and second power supply  526  may be different. 
     The inner heating element  522  and the outer heating element  521  are disposed outside of the chamber lid  502  adjacent the window  512 . The window  512  is optically transparent. In one embodiment, the window  512  is made of transparent or opaque quartz. In another embodiment, the window  512  may comprise a dielectric material that is electromagnetically transparent. In another embodiment, the window  512  may be a metallic window with slits to reduce eddy currents. 
     In one embodiment, a coating  508  may be present on the transparent window  512  to reflect heat back into the transfer chamber  500 . In one embodiment, the coating  508  may comprise titanium nitride. In another embodiment, the coating  508  may comprise gold. In another embodiment, the coating  508  may comprise tungsten, or any other reflective material that has high reflectivity in the infrared region. In one embodiment, the coating  508  may be present inside of the transfer chamber  500  as shown in  FIG. 7 . In another embodiment, the coating  508  may be present on outside the transfer chamber  500  on an outside surface of the window  512 . The coating  508  may have a thickness of between about 0.5 micrometers and about 2.0 micrometers. The coating  508  permits the heat to enter the transfer  500  with minimal reflectance back to the induction heating assembly  509 . The coating  508  also functions to reflect any heat within the transfer chamber  500  back into the transfer chamber  500  to minimize the amount of heat loss. 
     In operation, the induction heating assembly  509  may be activated to heat substrates or maintaining hot substrates at high temperature while the substrate are in the transfer chamber  500  in transit. The induction heating assembly  509  may be used independently or in combination with induction heating in the robot blade  511 . 
     The induction heating in the transfer chamber  500  are advantageous because they are induction heating elements rather than resistive heating elements. The induction heating elements are more efficient than resistive heating elements because they utilize less energy and are powered by an RF power source. The induction heating elements do not heat all of the material (such as the entire chamber), but rather, the heat is focused onto the predetermined area (such as the substrates and the carriers). 
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
     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.