Patent Publication Number: US-10330535-B2

Title: Pyrometer background elimination

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/522,858, filed Oct. 24, 2014, which claims benefit of U.S. Provisional Patent Application No. 61/903,079, filed Nov. 12, 2013, both of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Field 
     Embodiments described herein generally relate to thermal processing of substrates. More specifically, embodiments provided herein relate to an apparatus for pyrometer background elimination. 
     Description of the Related Art 
     A number of applications involve thermal processing of semiconductor and other materials, which require precise measurement and control of the temperature of the materials being thermally processed. For instance, processing of a semiconductor substrate requires precise measurement and control of the temperature over a wide range of temperatures. One example of such processing is rapid thermal processing (RTP), which is used for a number of fabrication processes, including rapid thermal annealing (RTA), rapid thermal cleaning (RTC), rapid thermal chemical vapor deposition (RTCVD), rapid thermal oxidation (RTO), and rapid thermal nitridation (RTN). 
     Temperature uniformity across the surface of the substrate is important for thermal processing. For example, it is desirable to have temperature variations of less than about 3° across the surface of the substrate to improve thermal processing results. Conventional substrate supports that support a substrate in RTP processes generally contact the substrate around the circumference of the substrate. The contact between the substrate support and the substrate can create temperature non-uniformities near the edge of the substrate. To overcome the temperature non-uniformities associated with the physical contact between the substrate support and the substrate, various other methods which minimize contact between the support and the substrate may be utilized. However, these methods allow for excess background radiation to propagate beyond the substrate. The excess radiation may interfere with temperature metrology devices and skew temperature measurements of the substrate. 
     Thus, what is needed in the art are apparatuses for supporting a substrate with minimal physical contact and for reducing or eliminating background radiation to improve temperature measurement of an RTP system. 
     SUMMARY 
     In one embodiment, an apparatus for reducing background radiation is provided. The apparatus includes a chamber body defining a processing volume and a radiation source may be coupled to the chamber body. One or more pyrometers may be coupled to the chamber body opposite the radiation source. A support ring may be disposed within the processing volume and an edge ring may be disposed on the support ring. A radiation shield may be disposed above the edge ring and an inner diameter of the radiation shield may extend radially inward over a substrate support member of the edge ring. 
     In another embodiment, an apparatus for reducing background radiation is provided. The apparatus includes a chamber body defining a processing volume and a radiation source may be coupled to the chamber body. A window may separate the processing volume from the radiation source and the radiation source may be coupled to the chamber body below the window. One or more pyrometers may be coupled to the chamber body opposite the radiation source. A support ring may be disposed within the processing volume and an edge ring may be disposed on the support ring. A radiation shield may be disposed above the edge ring and an inner diameter of the radiation shield may extend radially inward over a substrate support member of the edge ring. An absorptive coating may be disposed on the chamber body adjacent a region where the pyrometers are coupled to the chamber body and the absorptive coating comprises a dielectric material selected to absorb or reflect radiation within a desired wavelength. 
     In yet another embodiment, an apparatus for reducing background radiation is provided. The apparatus comprises a chamber body defining a processing volume and a radiation source coupled to the chamber body. A window may separate the processing volume from the radiation source and the radiation source may be coupled to the chamber body above the window. One or more pyrometers may be coupled to the chamber body opposite the radiation source. A support ring may be disposed within the processing volume and an edge ring may be disposed on the support ring. An absorptive coating may be disposed on a bottom of the chamber body adjacent a region where the pyrometers are coupled to the chamber body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, 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 disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. 
         FIG. 1  schematically illustrates a thermal processing chamber. 
         FIG. 2  illustrates a schematic, cross-sectional view of a thermal processing chamber having a radiation shield and absorbing surface disposed therein. 
         FIG. 3  is a schematic, plan view of  FIG. 2  illustrating a substrate and lift pins with the radiation shield removed. 
         FIG. 4A  is a partial, schematic cross-sectional view of the thermal processing chamber illustrating background radiation propagation paths. 
         FIG. 4B  illustrates a partial, schematic cross-sectional view of the thermal processing chamber of  FIG. 2 . 
         FIG. 5  illustrates a schematic, cross-sectional view of a thermal processing chamber having a radiation shield and absorbing surface disposed therein. 
         FIG. 6  illustrates a partial, schematic cross-sectional view of the thermal processing chamber of  FIG. 5 . 
         FIG. 7  is a schematic, plan view of  FIG. 5  illustrating a substrate and lift pins supported by an edge ring with the radiation shield removed. 
         FIG. 8  illustrates a partial, schematic cross-sectional view of a thermal processing chamber. 
         FIG. 9  is a schematic, bottom view of  FIG. 8  illustrating a substrate and substrate supports with a radiation shield removed. 
         FIG. 10  schematically illustrates a thermal processing chamber. 
         FIG. 11  illustrates a schematic, cross-sectional view of a thermal processing chamber having an edge ring and absorbing surface disposed therein. 
     
    
    
     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 and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. 
     DETAILED DESCRIPTION 
     Embodiments disclosed herein provide an RTP system for processing a substrate. An RTP chamber has a radiation source configured to deliver radiation to a substrate disposed within a processing volume. One or more pyrometers are coupled to the chamber body opposite the radiation source. In one example, the radiation source is disposed below the substrate and the pyrometers are disposed above the substrate. In another example, the radiation source is disposed above the substrate and the pyrometers are disposed below the substrate. The substrate may be supported in varying manners configured to reduce physical contact between the substrate support and the substrate. An edge ring and shield are disposed within the processing volume and are configured to reduce or eliminate background radiation from interfering with the pyrometers. Additionally, an absorbing surface may be coupled to the chamber body to further reduce background radiation interference. 
       FIG. 1  schematically illustrates a processing chamber, such as the VULCAN RTP chamber available from Applied Materials, Inc. of Santa Clara, Calif. A heating apparatus  124  is coupled to the chamber  100  below a window  120  and is configured to heat a substrate  112  during thermal processing. The heating apparatus comprises a plurality of lamps  126 , which may be separated by reflectors  127 . The lamps  126  are configured to rapidly heat the substrate  112  to temperatures between about 800° C. and about 1200° C. or greater. The reflectors  127  comprise an apparatus configured to concentrate radiation towards to the substrate  112 . For example, the reflectors  127  may form a cavity within which the lamp  126  is disposed. 
     The window  120 , which comprises a transparent material such as quartz, separates the heating apparatus  124  from the processing region  118  of the chamber  100 . The substrate  112  to be thermally processed is supported on its periphery by an edge ring  164 . The edge ring  164  is supported by and coupled to a support ring  130 . The edge ring  164  is formed from a material, such as silicon carbide or the like, capable of withstanding the elevated temperatures associated with thermal processing. Although not shown, lift pins extend through the heating apparatus  124  and the window  120  to lift the substrate  112  off of the edge ring  164  during transfer of the substrate  112  into and out of the chamber  100 . During processing, the lift pins are retracted below the edge ring  164  out of contact with the substrate  112 . 
     A magnetic levitation system  105  is also provided. The magnetic levitation system is configured to rotate the support ring  130 , edge ring  164 , and substrate  112  during processing. For example, the magnetic levitation system raises the support ring  130  and edge ring  164 , which is supporting the substrate  112 , above the window  120  and causes the raised components to rotate around a central axis  134 . In certain embodiments, the support ring  130  may be disposed radially outside the window  120 . 
     One or more pyrometers  140  are coupled to the chamber  100  through a chamber ceiling  128 . One or more radiation collecting apparatuses  142 , such as light pipes, extend through the ceiling  128  and are directed toward the substrate  112  to measure a temperature of the substrate  112 . The radiation collecting apparatuses  142  are coupled to the pyrometers  140 , which are further coupled to a controller  144 . The controller  144  receives outputs of the pyrometers  140  and accordingly controls the voltages supplied to the heating apparatus  124 . The pyrometers  140  generally measure light intensity in a narrow wavelength bandwidth of about 30 or 40 nm in a range between about 700 nm to about 1000 nm. The controller  144  converts the light intensity to a temperature through the Plank distribution of the spectral distribution of light intensity radiating from a black body held at that temperature. In this manner, temperature of the substrate  112  can be monitored during thermal processing. 
       FIG. 2  is a schematic cross-sectional view of a thermal processing chamber  200  having a radiation shield  202  and absorbing surface  250  disposed therein according to one embodiment. The radiation shield  202  rests on a support ring  230  as described above with regard to  FIG. 1  and the radiation shield  264  is configured to support the substrate  112 . A plurality of protrusions  208  extend from a portion  265  of the edge ring  264  which is disposed below the substrate  112 . For example, three or four protrusions  208 , such as pins or posts, contact and support the substrate  112  at discrete locations on a bottom surface of the substrate  112 . It is believed that the minimal physical contact between the substrate  112  and the protrusions  208  reduce thermal discontinuity across the surface of the substrate  112  when compared to traditional edge rings which support the substrate  112  around the entire circumference of the substrate  112 . The protrusions  208  substantially prevent the edge ring  264  from acting as a heat sink which negatively affects temperature uniformity of the substrate  112  during thermal processing. 
     The edge ring  264  is made from a material which is substantially opaque and thus prevents the transmission of light through the edge ring  264 . However, because the protrusions  208  separate the substrate  112  from the edge ring  264 , light may propagate through the space between the substrate  112  and the edge ring  264  towards one or more pyrometers  240 . This stray radiation, or background radiation, adversely affects the temperature measurement of the pyrometers  240  which are configured to measure the temperature of the substrate  112 . 
     To prevent or reduce background radiation, the radiation shield  202  is disposed within the chamber  200 . The radiation shield  202  is substantially ring-like and is made of a thermally stable opaque material, such as silicon carbide or the like. During thermal processing, the radiation shield  202  is supported by the edge ring  264  and at least a portion of the radiation shield  202  is disposed over a top surface of the substrate  112 . The radiation shield  202  has an inner diameter  203  which is less than a diameter of the substrate  112 . Thus, the radiation shield  202  extends over and above an outer portion of the substrate  112 . 
     A first plurality of lift pins  204  are configured to contact the radiation shield  202  and raise the radiation shield  202  from the edge ring  264 . The lift pins  204  extend through one or more voids  210  of the edge ring  164  sized to accommodate the lift pins  204 . Although not shown, the lift pins  204  extend through the window  120  and the heating apparatus  124  and are coupled to an actuator, which is configured to move the lift pins  204  up and down along a vertical path. A second plurality of lift pins  206  are also provided in the chamber  200 . The lift pins  206  are configured to engage the substrate  112  and support the substrate  112  during processing. The lift pins  206  are also configured to raise and lower the substrate  112  to accommodate ingress and egress of the substrate from the processing volume  118 . 
     In operation, the first plurality of lift pins  204  engage the radiation shield  202  and raise the radiation shield above and clear of a plane occupied by the substrate  112  while the substrate  112  is being transferred into the chamber  200 . The second plurality of lift pins  206  are positioned in a raised orientation to accept the substrate  112  from a robot blade (not shown). After the substrate  112  has been engaged by the lift pins  206 , the robot blade is removed from the chamber  200  and the lift pins  206  retract and lower the substrate  112  into a processing position in contact with the protrusions  208 . Subsequently, the lift pins  204  lower the radiation shield  202  into contact with the edge ring  264  such that the radiation shield  202  rests on the edge ring  264 . The lift pins  204  then continue to retract through the voids  210  to a position below the edge ring  264  to enable the support ring  230 , edge ring  264  and radiation shield  202  to be rotated by the magnetic levitation system (not shown). 
     A ceiling  228  of the chamber  200  has an absorbing surface  250  disposed thereon. The absorbing surface  250  is configured to absorb background radiation and prevent or reduce stray background radiation from reaching the pyrometers  240 . In one embodiment, the pyrometers  240  and radiation collecting apparatuses  242  are disposed near a center region of the chamber  200 . In another embodiment, the pyrometers  240  and radiation collecting apparatuses  242  are disposed within the chamber  200  in a region which is above a central region of the substrate  112 . The absorbing surface  250  may be a dielectric coating comprising various materials configured to absorb radiation within a desired wavelength. In one embodiment, the absorbing surface  250  is textured or embossed. In addition to absorbing stray background radiation, the topography of the absorbing surface  250  is configured to direct background radiation away from the pyrometers  240 . For example, a feature of the absorbing surface  250  may reflect stray background radiation not absorbed radially outward toward walls of the chamber  200  away from the pyrometers  240 . 
     An interior surface  229  of the ceiling  228  radially outward of the pyrometers  240  and radiation collecting apparatuses  242  may be coated with the absorbing surface  250 . However, portions  227  of the chamber ceiling  228  between the locations where the radiation collecting apparatuses  242  extend through the ceiling  228  are not coated with the absorbing surface  250  to prevent measurement errors of the substrate  112  temperature by the pyrometers  240 . The absorbing surface  250  may be disposed over the entire interior surface  229  radially outside the portions  227  or may be disposed only on a portion of the interior surface  229 . For example, the absorbing surface  250  may be disposed on the interior surface  229  at locations where the majority of stray background radiation contacts the ceiling  228 . 
     It is believed that utilizing the radiation shield  202  in combination with the absorbing surface  250  may substantially reduce or eliminate stray background radiation from reaching the pyrometers. As a result, the temperature measurement of the substrate  112  by the pyrometers  240  may be increased and a more accurate temperature measurement may be achieved. 
       FIG. 3  is a schematic plan view of  FIG. 2  illustrating the substrate  112  and lift pins  204  with the radiation shield  202  removed according to one embodiment. The lift pins  204 , which are configured to engage the radiation shield  202  (not shown), are disposed in a configuration such that the substrate  112  has an unobstructed path into and out of the chamber  200 . For example, the lift pins  204  are disposed beyond an outer diameter of the substrate  112  and outside of the path of travel (indicated by the dashed lines and arrow) of the substrate  112 . In this manner, the radiation shield  202  is raised above the plane of travel of the substrate  112  and the substrate  112  can be positioned by the robot blade (not shown) where the substrate  112  is engaged by the lift pins  206  (not shown). 
       FIG. 4A  is a partial schematic cross-sectional view of the thermal processing chamber  100  of  FIG. 2  according to one embodiment. Stray background radiation from the heating apparatus  124  propagating around the edge of the substrate  112  and toward the pyrometers  240  may propagate along various propagation paths  475 . As illustrated, the propagation paths  475  may reflect from the backside of the substrate  112 , the edge ring  264 , the radiation shield  202 , and the absorbing surface  250 . Thus, the background radiation propagation paths  475  are altered by the presence and location of the radiation shield  202  and the absorbing surface  250 . 
     For example, radiation traveling along the propagation path A may be absorbed by the absorbing surface  250  or reflected away from the pyrometers  240 . Any radiation not absorbed or reflected away from the pyrometers  240  by the absorbing surface  250  travels along propagation path B. Along this path, the radiation is directed back towards a top surface of the substrate  112  and may then reflect upward to the pyrometers  240 . Assuming the pyrometers  140  incorporate an optical system to reduce the field of view and the minimal view angle  490  of the pyrometers  240  to the substrate  112  is less than between about 25° and about 50°, such as less than about 30°, stray background radiation measured by the pyrometers  240  may be substantially reduced. 
       FIG. 4B  is a partial schematic cross-sectional view of the thermal processing chamber  100  of  FIG. 2  according to one embodiment. As previously discussed, the background radiation propagation paths are altered by the radiation shield  202  and the absorbing surface  250  to reduce the incidence of background radiation from being detected by the pyrometers  240 . The relationships between the various components of the chamber  200  are generally responsible for determining the propagation paths of the background radiation. 
     In one embodiment, the radiation shield  202  extends laterally inward over an edge of the substrate  112  a first distance  406 . A second distance  404 , measured from an inner surface  201  of the radiation shield  202  to a location on the ceiling  228  where the radiation collecting apparatus  242  is disposed, is greater than the first distance  406 . The absorbing surface  250  may be disposed over a portion of or over the entire distance  404  on the interior surface  229  of the ceiling  228 . In another embodiment, the radiation shield  202  is disposed a third distance  402  above the substrate  112 . A fourth distance  408 , measured from the interior surface  229  of the ceiling  228  to the substrate  112  in a processing position, is greater than the third distance  402 . The spatial relationships between the radiation shield  202 , ceiling  228 , radiation collecting apparatuses  242  and pyrometers  240 , and the substrate  112  provide for the reduction or elimination of stray background radiation being measured by the pyrometers  240 . 
       FIG. 5  is a schematic cross-sectional view of a thermal processing chamber  200  having a radiation shield  504  and absorbing surface  250  disposed therein according to one embodiment. The chamber  200  and components disposed therein are substantially similar to the chamber  200  and components described with regard to  FIG. 2 . However, the radiation shield  504  is coupled to and supported by a third plurality of lift pins  502 . The lift pins  502  are configured and function similarly to the lift pins  204  described with regard to  FIGS. 2 and 3 , but in this embodiment, the lift pins are  502  disposed radially outward of the support ring  230  and an edge ring  564 . The radiation shield  202  extends from the lift pins  502  radially inward over the substrate  112  such that the inner diameter  203  of the radiation shield  202  is the same as the inner diameter  203  described with regard to  FIG. 2 . 
       FIG. 6  is a partial schematic cross-sectional view of the thermal processing chamber  200  of  FIG. 5  according to one embodiment. The distances  402 ,  404 ,  406  and  408  are similar to and described in greater detail with regard to  FIG. 4B . Here, the lift pins  502  are not disposed through the edge ring  564 , which reduces the complexity of manufacturing the edge ring  564  and the necessity of the lift pins  204  to extend through the edge ring  564 . For example, the edge ring  564  does not have voids formed therethrough to allow for passage of lift pins, which allows the edge ring  564  to more effectively prevent the propagation of background radiation from reaching the substrate  112 . 
       FIG. 7  is a schematic plan view of  FIG. 5  illustrating the substrate  112  supported by the edge ring  564  and the lift pins  502  with the radiation shield  504  removed according to one embodiment. As illustrated, the substrate  112  is supported by the protrusions  208  (not shown) of the edge ring  564 . The lift pins  502 , which are configured to engage the radiation shield  504  (not shown), are disposed in a configuration such that the substrate  112  has an unobstructed path into and out of the chamber  200 . For example, the lift pins  502  are disposed beyond an outer diameter of the edge ring  564  and outside of the path of travel (indicated by the dashed lines and arrow) of the substrate  112 . In this manner, the radiation shield  504  is raised above the plane of travel of the substrate  112  and the substrate  112  can be positioned by the robot blade (not shown) where the substrate  112  is engaged by the lift pins  206  (not shown). In this embodiment, the lift pins  502  are disposed radially outward of the edge ring  564 . 
       FIG. 8  is a partial schematic cross-sectional view of the thermal processing chamber  200  according to one embodiment. In this embodiment, supports  802  of the radiation shield  202  support the substrate  112  instead of an edge ring  864 . The edge ring  864 , which is supported by the support ring  230 , supports the radiation shield  202 . The supports  802  are coupled to the radiation shield  202  and extend below the radiation shield  202 . The supports  802  comprise a first member  804  which extends downward from the radiation shield  202 , a second member  806  which extends substantially horizontally from the first member  804 , and one or more protrusions  808 . The supports  802  may be a separate apparatus coupled to the radiation shield  202  or may be an integral part of a unitary body with the radiation shield  202 . The supports  802  may comprise the same material as the radiation shield  202 , which is a material capable of withstanding thermal processing conditions, such as silicon carbide. In one embodiment, the supports  802  may be a transparent material, such as quartz, which may prevent shadowing of radiation from the heating apparatus  124  to prevent cold spots from forming on the substrate  112  during processing. 
     In one embodiment, three supports  802  may be utilized to support the substrate  112 . The first member  804  extends from the radiation shield  202  from a location radially outwards from the circumference of the substrate  112  when the substrate is located in the processing position. The second member  806  extends from the first member  804  such that at least a portion of the second member  806  is disposed beneath the substrate  112  when the substrate  112  is in a processing position. The protrusions  808  extend from the second member  806  and contact the substrate  112 . In this example, only the protrusions  808  contact the substrate  112  so as to minimize physical contact between the substrate  112  and the supports  802 . 
     The first plurality of lift pins  204  function as described with regard to  FIG. 2 . By utilizing the supports  802 , no lift pins to support the substrate  112  are necessary as the supports  802  are coupled to the radiation shield  202 . It is contemplated that the spacing and relationship between the first member  804 , second member  806 , and protrusions  808  are configured to allow for a robot blade to place and retrieve the substrate  112  without utilizing any additional apparatuses for separating the substrate  112  from the protrusions  808 . Thus, no lift pins for the substrate  112  are necessary which reduces the complexity of the chamber  200 . Further, the distances  402 ,  404 ,  406  and  408  are similar to those described with regard to  FIGS. 4B and 6  although the manner of supporting the substrate  112  is different. 
       FIG. 9  is a schematic bottom view of the embodiments shown in  FIG. 8  illustrating the substrate  112  and supports  802  with a radiation shield  202  removed according to one embodiment. As illustrated, the substrate  112  is supported by the supports  802 . The first member  804  extends vertically (into the page) and the second member  806  extends horizontally from the first member  804 . The first member of each support  802  is disposed beyond the path of travel (indicated by the dashed lines and arrow) of the substrate  112 . The second member  806  of each of the supports  802  extends to a position inside the diameter of the substrate  112  to allow the substrate  112  to rest on the protrusions  808  (not shown) extending from the second member  806 . The substrate  112  travels above the second member  806  and is lowered onto the protrusions  808  of the second member  806  by the robot blade which is then retracted along the substrate  112  travel path. Although not shown, the radiation shield  202  is spaced a distance from the second member  806  configured such that the robot blade and substrate  112  are unobstructed while positioning and moving the substrate  112 . 
       FIG. 10  schematically illustrates a processing chamber  1100 , such as the RADIANCE® RTP chamber available from Applied Materials, Inc. of Santa Clara, Calif. A heating apparatus  124  is coupled to the chamber  1100  above a window  120  and is configured to heat a substrate  112  during thermal processing. The heating apparatus  124  comprises a plurality of lamps  126 , which may be separated by reflectors  127 . The lamps  126  are configured to rapidly heat the substrate  112  to temperatures between about 800° C. and about 1200° C. or greater. The reflectors  127  comprise an apparatus configured to concentrate radiation towards to the substrate  112 . For example, the reflectors  127  may form a cavity within which the lamp  126  is disposed. 
     The window  120 , which comprises a transparent material such as quartz, separates the heating apparatus  124  from the processing region  118  of the chamber  1100 . The substrate  112  to be thermally processed is supported on its periphery by an edge ring  1064 . The edge ring  1064  is supported by and coupled to a support ring  1030 . The edge ring  1064  is formed from a material, such as silicon carbide or the like, capable of withstanding the elevated temperatures associated with thermal processing. Although not shown, lift pins extend through a bottom  1017  of the chamber  1100  to lift the substrate  112  off of the edge ring  1064  during transfer of the substrate  112  into and out of the chamber  1100 . During processing, the lift pins are retracted below the edge ring  1064  out of contact with the substrate  112 . 
     A magnetic levitation system  105  is also provided. The magnetic levitation system  105  is configured to rotate the support ring  1030 , edge ring  1064 , and substrate  112  during processing. For example, the magnetic levitation system  105  raises the support ring  1030  and edge ring  1064 , which is supporting the substrate  112 , within the processing volume  118  and causes the raised components to rotate around a central axis  134 . In certain embodiments, the support ring  1030  may be disposed radially outside the window  120 . 
     One or more pyrometers  1040  are coupled to the chamber  1100  through the chamber bottom  1017 . One or more radiation collecting apparatuses  1042 , such as light pipes, extend through the chamber bottom  1017  and are directed toward the substrate  112  to measure a temperature of the substrate  112 . The radiation collecting apparatuses  1042  are coupled to the pyrometers  1040 , which are further coupled to a controller  1044 . The controller  1044  receives outputs of the pyrometers  1040  and accordingly controls the voltages supplied to the heating apparatus  124 . The pyrometers  1040  generally measure light intensity in a narrow wavelength bandwidth of about 30 or 40 nm in a range between about 700 nm to about 1000 nm. The controller  1044  converts the light intensity to a temperature through the Plank distribution of the spectral distribution of light intensity radiating from a black body held at that temperature. In this manner, temperature of the substrate  112  can be monitored during thermal processing. 
       FIG. 11  is a schematic cross-sectional view of the thermal processing chamber  1110  having the edge ring  1164  and absorbing surface  250  disposed therein according to one embodiment. The edge ring  1164  rests on the support ring  1130  as described above and the edge ring  1164  is configured to support the substrate  112 . The plurality of protrusions  208  extend from the portion  1165  of the edge ring  1164  which is disposed below the substrate  112 . For example, three or four protrusions  208 , such as pins or posts, contact and support the substrate  112  at discrete locations on a bottom surface of the substrate  112 . It is believed that the minimal physical contact between the substrate  112  and the protrusions  208  reduce thermal discontinuity across the surface of the substrate  112  when compared to traditional edge rings which support the substrate  112  around the entire circumference of the substrate  112 . The protrusions  208  substantially prevent the edge ring  1164  from acting as a heat sink, which negatively affects temperature uniformity of the substrate  112  during thermal processing. 
     The edge ring  1164  is made from a material which is substantially opaque and thus prevents the transmission of light through the edge ring  1164 . However, because the protrusions  208  separate the substrate  112  from the edge ring  1164 , light may propagate through the space between the substrate  112  and the edge ring  1164  towards the pyrometers  1140 . This stray radiation, or background radiation, adversely affects the temperature measurement of the pyrometers which are configured to measure the temperature of the substrate  112 . 
     A plurality of lift pins  206  are provided in the chamber  1110 . The lift pins  206  are configured to engage the substrate  112  and support the substrate  112  during processing. The lift pins  206  are also configured to raise and lower the substrate  112  to accommodate ingress and egress of the substrate  112  from a processing position. In operation, the plurality of lift pins  206  are positioned in a raised orientation to accept the substrate  112  from a robot blade (not shown). After the substrate  112  has been engaged by the lift pins  206 , the robot blade is removed from the chamber  110  and the lift pins  206  retract and lower the substrate  112  into a processing position in contact with the protrusions  208 . The lift pins  206  retract further to a position out of contact with the substrate  112  to enable the support  1130  and edge ring  1164  to be rotated by the magnetic levitation system (not shown). 
     The bottom  1117  of the chamber  1110  has the absorbing surface  250  disposed thereon. The absorbing surface  250  is configured to absorb background radiation and prevent or reduce stray background radiation from reaching the pyrometers  1140 . The absorbing surface  250  may be a dielectric coating comprising various materials configured to absorb radiation within a desired wavelength. In one embodiment, the absorbing surface  250  is textured or embossed. In addition to absorbing stray background radiation, the topography of the absorbing surface  250  is configured to direct background radiation away from the pyrometers  1140 . For example, a feature formed by roughening or embossing the absorbing surface  250  may reflect stray background radiation not absorbed radially outward toward the support ring  1130  away from the pyrometers  1140 . 
     An interior surface  1151  of the bottom  1117 , disposed radially outward of the pyrometers  1140  and radiation collecting apparatuses  1142 , may be coated with the absorbing surface  250 . However, portions  1153  of the chamber bottom  1117  between the locations where the radiation collecting apparatuses  1142  extend through the chamber bottom  1117  are not coated with the absorbing surface  250  to prevent measurement errors of the substrate  112  temperature by the pyrometers  1140 . The absorbing surface  250  may be disposed over the entire interior surface  1151  radially outside the portions  1153  or may be disposed only on a portion of the interior surface  1151 . For example, the absorbing surface  250  may be disposed on the interior surface  1151  at locations where the majority of stray background radiation contacts the bottom  1117 . 
     It is believed that utilizing the absorbing surface  250  may substantially reduce or eliminate stray background radiation from reaching the pyrometers  1140 . As a result, the temperature measurement of the substrate  112  by the pyrometers  1140  may be increased and a more accurate temperature measurement may be achieved. 
     Embodiments described herein utilize a radiation shield and absorbing surface, either alone or in combination to reduce the negative effects of stray background radiation on pyrometer temperature measurement. Methods of supporting the substrate to reduce heat discontinuity across the surface of the substrate are utilized in concert with the radiation shield and absorbing surface. As a result, accuracy of substrate temperature measurement by the pyrometers can be improved by removing the interfering background radiation. Embodiments described herein may be utilized on chambers which incorporate heating apparatuses either above or below the substrate. For example, embodiments described herein may be especially useful in the RADIANCE® and VULCAN processing chambers available from Applied Materials, Inc., Santa Clara, Calif. However, it is contemplated that the embodiments described herein may also advantageously be incorporated on processing chambers from other manufacturers. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.