Abstract:
This disclosure describes systems, methods, and apparatuses for making a non-contact measurement of a substrate in a plasma processing chamber that accounts for stray blackbody radiation. In particular, a photocurrent is calculated that can be attributed to the stray blackbody radiation based upon a temperature of the stray blackbody radiation, a reflectance of a target substrate, and a temperature of the substrate. Knowing the photocurrent attributable to the stray blackbody radiation, a non-contact temperature measurement can be made, and the photocurrent attributable to the stray blackbody radiation can be subtracted out to arrive at a more accurate non-contact substrate temperature measurement.

Description:
FIELD OF THE DISCLOSURE 
       [0001]    The present invention relates generally to plasma processing. In particular, but not by way of limitation, the present invention relates to systems, methods and apparatuses for non-contact optical temperature measurements of a semiconductor substrate within a plasma processing chamber. 
       BACKGROUND 
       [0002]    Radiation pyrometers are known and commercially available. Typically, pyrometers are used to optically measure the temperature of an object or “target.” Pyrometers are particularly useful when the target is difficult to measure via conductive means (e.g., a thermocouple) because the target is very hot or very delicate, contacting the target could affect the temperature measurement, or because the target is difficult to access due to the hostility of the environment. 
         [0003]    Pyrometers tend to be of two types: brightness or ratio devices. Brightness and ratio pyrometers both utilize a solution of a form of the Planck Radiation Equation to calculate the target&#39;s measured temperature. The Planck Radiation Equation for spectral radiation emitted from an ideal blackbody is: 
         [0000]    
       
         
           
             
               
                 
                   
                     L 
                      
                     
                       ( 
                       λ 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           2 
                            
                           
                               
                           
                            
                           
                             hc 
                             2 
                           
                         
                         
                           λ 
                           5 
                         
                       
                       [ 
                       
                         
                            
                           
                             hc 
                             
                               λ 
                                
                               
                                   
                               
                                
                               
                                 k 
                                 B 
                               
                                
                               T 
                             
                           
                         
                         - 
                         1 
                       
                       ] 
                     
                     
                       - 
                       1 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
         [0004]    where L(λ)=radiance in energy per unit area per unit time per steradian per unit wavelength interval, and where 
         [0005]    h=Plank&#39;s constant, 
         [0006]    c=the speed of light, 
         [0007]    λ=the wavelength of the radiation, 
         [0008]    k B =Boltzman&#39;s constant, and 
         [0009]    T=the absolute temperature. 
         [0010]    For non-blackbodies, the radiance L(λ) can be modified by emissivity ε to give a radiance as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     H 
                      
                     
                       ( 
                       λ 
                       ) 
                     
                   
                   = 
                   
                     
                       ε 
                        
                       
                           
                       
                        
                       
                         L 
                          
                         
                           ( 
                           λ 
                           ) 
                         
                       
                     
                     = 
                     
                       ε 
                        
                       
                         
                           
                             
                               2 
                                
                               
                                   
                               
                                
                               
                                 hc 
                                 2 
                               
                             
                             
                               λ 
                               5 
                             
                           
                           [ 
                           
                             
                                
                               
                                 hc 
                                 
                                   λ 
                                    
                                   
                                       
                                   
                                    
                                   
                                     k 
                                     B 
                                   
                                    
                                   T 
                                 
                               
                             
                             - 
                             1 
                           
                           ] 
                         
                         
                           - 
                           1 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
         [0011]    Equation 2 can be rewritten in terms of photocurrent to derive Equation 3, which describes the photocurrent detected by a pyrometer: 
         [0000]    
       
         
           
             
               
                 
                   
                     P 
                      
                     
                       ( 
                       λ 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           
                             c 
                             1 
                           
                            
                           ε 
                            
                           
                               
                           
                            
                           α 
                         
                         
                           λ 
                           5 
                         
                       
                        
                       
                         [ 
                         
                           
                              
                             
                               
                                 c 
                                 2 
                               
                               
                                 
                                   λ 
                                    
                                   
                                       
                                   
                                    
                                   T 
                                 
                                  
                                 
                                     
                                 
                               
                             
                           
                           - 
                           1 
                         
                         ] 
                       
                     
                     
                       - 
                       1 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     3 
                   
                   ) 
                 
               
             
           
         
       
     
         [0012]    Where C 1  is a constant equal to 2/π*h*c 2 , which is 3.74177*10 −16  W/m 2 , and C 2  is a constant equal to 
         [0000]    
       
         
           
             
               hc 
               
                 k 
                 B 
               
             
             . 
           
         
       
     
         [0000]    The variable α represents a sensor factor multiplied by a view factor, where the sensor factor represents a calibration of the pyrometer (e.g., the percentage of light that passes through optics of the pyrometer and/or optics of a view window of a processing chamber), and the view factor represents a percentage of all radiation from a source that is incident on a particular angular area. In other words, α is a variable that accounts for various factors that affect a ratio of the intensity of blackbody radiation emitted by an object divided by the intensity of blackbody radiation detected by the pyrometer (assuming blackbody-to-pyrometer radiation without reflections). 
         [0013]    In the brightness method of pyrometry, H(λ) and ε are measured at a known wavelength, λ, and, therefore, T can be calculated. Brightness devices rely upon capturing a known fraction of the radiation from a source in a particular solid angle. Brightness pyrometers tend to depend on knowing the emissivity of the target, as required by Equation 3, supra. Emissivity ε is the ratio of the radiation emitted by the target to the radiation emitted by a perfect blackbody radiator at the same temperature. Typically, emissivity is unknown or estimated to a low degree of accuracy. Additionally, the emissivity is often a function of the target temperature, wavelength of radiation examined, and history of the target. These factors greatly limit the utility of brightness pyrometry. For repetitive processing of uniformly prepared and controlled substrates, such as polished silicon wafers, this limit of repeatable temperature measurement is relieved somewhat. 
         [0014]    In practice, it is left to the user of a brightness pyrometer to estimate the target emissivity, usually based upon an analysis of the target&#39;s composition. The target&#39;s thermal and environmental history can alter the emissivity to an unkown degree, as well as current environmental factors such as gases that absorb certain wavelengths of radiation en route from the target to the pyrometer. 
         [0015]    Ratio pyrometers depend upon graybody behavior. A graybody is an energy radiator which has a blackbody energy distribution, times an emissivity, throughout a wavelength interval being examined. Ratio pyrometers detect the radiation intensity at two known wavelengths and, utilizing Planck&#39;s Equation, calculate a temperature that correlates to the radiation intensity at the two specified wavelengths. 
       SUMMARY 
       [0016]    The present invention relates to systems, methods and apparatuses that can include, in one aspect, a method of making a non-contact temperature measurement of a target in a processing chamber. The method can include measuring a temperature of a reference target in the processing chamber, measuring a first temperature of the stray blackbody radiation, and measuring a reflectance of the reference target. The reference target can be replaced with a target, and a non-contact temperature measurement of the target can be made. The non-contact temperature measurement can include measuring a second temperature of the stray blackbody source, measuring a reflectance of the target, and with these two values, calculating a temperature of the target using at least the first temperature of the stray blackbody source, the second temperature of the stray blackbody source, the temperature of the reference target, the reflectance of the reference target, and the reflectance of the target. 
         [0017]    In another aspect of the invention, a non-contact temperature-measuring device is described. This device can include a light beam source, a light beam detector, a first temperature monitor, a second temperature monitor, and a control module. The light beam source can emit a light beam having an emitted intensity. The light beam detector can detect: a first reflected intensity from the light beam reflecting off a reference target; and a second reflected intensity from the light beam reflecting off a target. The first temperature monitor can measure a first temperature of a stray blackbody source during a calibration phase, and can measure a second temperature of the stray blackbody source during a non-contact measurement phase. The second temperature monitor can measure a temperature of the reference target. The control module can determine the following: a first reflectance of the reference target as a ratio of the first reflected intensity over the emitted intensity; a second reflectance of the target as a ratio of the second reflected intensity over the emitted intensity; and a temperature of the target based on at least the first temperature, the second temperature, the third temperature, the first reflectance, and the second reflectance. 
         [0018]    In yet another aspect of the invention a non-contact temperature measuring system can comprise a means for measuring a temperature of a reference target. The system can also comprise a means for measuring a first temperature of a stray blackbody radiation source during a calibration phase and measuring a second temperature of the stray blackbody radiation source during a non-contact temperature measurement phase. The system can further comprise a means for measuring a reflectance of the reference target and a reflectance of the target. The system can also include a means for calculating a temperature of the target based on at least: the temperature of the reference target; the first temperature of the stray blackbody radiation source; the second temperature of the stray blackbody radiation source; the reflectance of the reference target; and the reflectance of the target. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Various objects and advantages and a more complete understanding of the present invention are apparent and more readily appreciated by referring to the following detailed description and to the appended claims when taken in conjunction with the accompanying drawings: 
           [0020]      FIG. 1  illustrates an embodiment of a pyrometer measuring a substrate temperature. 
           [0021]      FIG. 2  illustrates a detailed view of an exemplary embodiment of the pyrometer of  FIG. 1 . 
           [0022]      FIG. 3  illustrates a method of performing a non-contact temperature measurement. 
           [0023]      FIG. 4   a  illustrates an overhead view of an embodiment of a pyrometer having a baffles. 
           [0024]      FIG. 4   b  illustrates a side view of the embodiment of the pyrometer illustrated in 
           [0025]    
         FIG. 4 
         a.  
       
           [0026]      FIG. 5  illustrates an isometric view of a portion of the baffles illustrated in  FIGS. 4   a  and  4   b.    
           [0027]      FIG. 6  illustrates an isometric view of another embodiment of a baffles. 
           [0028]      FIG. 7  illustrates yet another isometric view of another embodiment of a baffles. 
           [0029]      FIG. 8  illustrates a plot of temperature data according to an embodiment of this disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]      FIG. 1  illustrates an embodiment of a semiconductor processing chamber  100  with a pyrometer  105  that measures a temperature of a substrate  102 . The illustrated embodiment shows one way of optically measuring a temperature of a target or substrate  102  (e.g., a semiconductor substrate) within the processing chamber  100  via a non-contact temperature monitoring device (e.g., pyrometer  105 ) that enables non-contact temperature measurements of a semiconducing substrate  102  or other processing target to a degree of accuracy that accounts for or negates stray blackbody radiation. 
         [0031]    In an embodiment, the semiconductor processing chamber  100  can be a plasma processing chamber for etching and deposition on the substrate  102  such as a semiconductor wafer or a photovoltaic polymer substrate. The substrate  102  can rest on a substrate holder  104  (e.g., a wafer chuck), and the pyrometer  105  can measure a temperature of the substrate  102  via transmitting light (e.g., infrared light) through a view window  107  in the processing chamber  100  and reflecting the light off a back or under surface  103  of the substrate  102  and detecting the reflected light that passes through the view window  107  to a light sensor or detector of the pyrometer  105 . 
         [0032]    The pyrometer  105  can include an electronics portion  106  containing electronics for generating, detecting, and analyzing the infrared light. The pyrometer  105  can also include a baffles  108  to reduce stray blackbody radiation from, for instance, the substrate holder  104  and the processing chamber  100  walls. The pyrometer  105  can be in communication with a circuitry or logic  110  by receiving instructions from the circuitry or logic  110  or providing data to the circuitry or logic  110 . In an embodiment, the pyrometer  105  measures a temperature of the substrate  102 , passes temperature data to the circuitry or logic  110 , and the circuitry or logic  110  can modify various parameters of the processing chamber  100  controls (e.g., temperature, gas flow, RF power, to name just a few non-limiting examples). 
         [0033]    The illustrated processing chamber  100  does not show various aspects of typical processing chambers that can be implemented, such as heating elements, gas pressure sensors, gas input and output ports, RF power sources, electrodes, etc. For instance, a heating element can be incorporated into or coupled to the substrate holder  104 , and can be in thermal communication with the substrate  102 . While the pyrometer  105  is centered under the substrate  102 , this is not required. In some embodiments, the pyrometer  105  can be radially offset from the center of the substrate  102  and can direct light at a radially offset point or points on the substrate  102 . Furthermore, while the electronics portion  106  is arranged outside of the processing chamber  100 , in some embodiments, the pyrometer  105  can be arranged partially or completely within the processing chamber  100 , and there may or may not be a view window  107 . Nor is there a requirement that the pyrometer  105  direct light through an opening in the substrate holder  104  as illustrated. In some embodiments, the pyrometer  105  can direct light towards a top surface  101  of the substrate  102  or use mirrors or fiber optics to direct light to the bottom surface  103  of the substrate  102  without passing through the substrate holder  104 . One skilled in the art will also recognize, in view of the specification, that a communication between the pyrometer  105  and the circuits or logic  110  is not required and in some cases the electronics portion  106  can share functionality with the circuits or logic  110 . One skilled in the art will also recognize, in view of the specification, that the pyrometer  105  is not limited to infrared light. 
         [0034]      FIG. 2  illustrates an embodiment of a pyrometer  205 , in communication with temperature monitors  218 ,  220 ,  222 , that makes non-contact temperature measurements of the substrate  202  while accounting for stray blackbody radiation from the substrate holder  204  and other stray blackbody sources. The substrate  202  can rest on or be coupled to the substrate holder  204 , and the pyrometer  205  can be arranged such that a light beam  230  can be directed through a view window  207  of the processing chamber  200  to a bottom surface  203  of the substrate  202  and reflected back to the pyrometer  205  through the view window  207  as a reflected light beam  232 . The pyrometer  205  includes an electronics portion  206  having electronics and devices for generating the light beam  230 , controlling various parameters of the light beam  230 , detecting a reflected light beam  232 , analyzing the reflected light beam  232 , and optionally communicating temperature data to other circuits or logic  210  in communication with the pyrometer  205 . In particular, the electronics portion  206  includes a light beam source  212 , a light beam detector  214 , and an analysis and control module  216 . To cut down on stray blackbody radiation, the pyrometer includes a baffles  208  that blocks a substantial amount of stray blackbody radiation from reaching the light beam detector  214 . The baffles  208  can be cooled in order to reduce stray blackbody radiation from the baffles  208  itself. 
         [0035]    The analysis and control module  216  can instruct the light beam source  212  to project the light beam  230  towards the substrate  202  via control of the power and timing of the light beam  230 . The light beam  230  reflects off the substrate  202  and returns to the pyrometer  205  as the reflected light beam  232 , which is detected by the light beam detector  214 . The light beam detector  214  provides a signal to the analysis and control module  216  giving information regarding the reflected light beam  232  (e.g., photocurrent P(λ)). The analysis and control module  216  can use this information along with information regarding the amount of light generated by the light beam source  212  to determine a reflectance R of the substrate  202 , which also gives an emissivity of the substrate as ε=1−R. Reflectance R of the substrate  202  is given as the ratio of the amount of light detected by the light beam detector  214  over the amount of light directed at the substrate  202  by the light beam source  230  (e.g., reflected intensity of light or second intensity divided by emitted intensity of light or first intensity). The analysis and control module  216  also knows a wavelength λ at which the light beam  230  was generated, and an attenuation factor α that can account for a view factor and a sensor factor (e.g., a percentage of light intensity transmitted through the pyrometer  205  window and/or a view window  207  of the processing chamber  200 ). With these parameters, Equation 3 can be solved for a temperature of the substrate T. 
         [0036]    However, such a temperature measurement can be inaccurate since it does not distinguish between blackbody radiation from the substrate  202  and stray blackbody radiation  234  from stray blackbody sources such as the substrate holder  204 . For purposes of this disclosure, stray blackbody radiation refers to blackbody radiation from anything other than the substrate  202  that reaches the light beam detector  214  whether directly or via one or more reflections. For instance, blackbody radiation from the baffles  208  that directly impinges on the light beam detector  214  as well as blackbody radiation from the baffles  208  that reflects off the substrate  202  and impinges on the light beam detector  214 , are both considered stray blackbody radiation. To account for stray blackbody radiation, a photocurrent for each blackbody source can be added to Equation 3. For instance, Equation 4 has an additional term P(λ) b1  added to the photocurrent of Equation 3 to account for the blackbody radiation from a stray blackbody source such as the substrate holder  204  or a heating element. 
         [0000]    
       
         
           
             
               
                 
                   
                     P 
                      
                     
                       ( 
                       λ 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           
                             
                               c 
                               1 
                             
                              
                             
                               ε 
                               t 
                             
                              
                             
                               α 
                               t 
                             
                           
                           
                             λ 
                             5 
                           
                         
                          
                         
                           [ 
                           
                             
                                
                               
                                 
                                   c 
                                   2 
                                 
                                 
                                   
                                     λ 
                                      
                                     
                                         
                                     
                                      
                                     T 
                                   
                                    
                                   
                                       
                                   
                                 
                               
                             
                             - 
                             1 
                           
                           ] 
                         
                       
                       
                         - 
                         1 
                       
                     
                     + 
                     
                       
                         P 
                          
                         
                           ( 
                           λ 
                           ) 
                         
                       
                       
                         b 
                          
                         
                             
                         
                          
                         1 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     4 
                   
                   ) 
                 
               
             
           
         
       
     
         [0037]    When P(λ) b1  is expanded, Equation 4 can be written as: 
         [0000]    
       
         
           
             
               
                 
                   
                     P 
                      
                     
                       ( 
                       λ 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           
                             
                               c 
                               1 
                             
                              
                             
                               ε 
                               t 
                             
                              
                             
                               α 
                               t 
                             
                           
                           
                             λ 
                             5 
                           
                         
                         [ 
                         
                           
                              
                             
                               
                                 c 
                                 2 
                               
                               
                                 
                                   λ 
                                    
                                   
                                       
                                   
                                    
                                   
                                     T 
                                     t 
                                   
                                 
                                  
                                 
                                     
                                 
                               
                             
                           
                           - 
                           1 
                         
                         ] 
                       
                       
                         - 
                         1 
                       
                     
                     + 
                     
                       
                         
                           
                             
                               c 
                               1 
                             
                              
                             
                               ε 
                               
                                 b 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                              
                             
                               α 
                               
                                 b 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                              
                             
                               R 
                               t 
                             
                           
                           
                             λ 
                             5 
                           
                         
                         [ 
                         
                           
                              
                             
                               
                                 c 
                                 2 
                               
                               
                                 
                                   λ 
                                    
                                   
                                       
                                   
                                    
                                   
                                     T 
                                     
                                       b 
                                        
                                       
                                           
                                       
                                        
                                       1 
                                     
                                   
                                 
                                  
                                 
                                     
                                 
                               
                             
                           
                           - 
                           1 
                         
                         ] 
                       
                       
                         - 
                         1 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     5 
                   
                   ) 
                 
               
             
           
         
       
     
         [0038]    Equation 5 shows that the stray blackbody radiation P(λ) b1  depends at least on the temperature of the stray blackbody source T b1  along with the wavelength λ of the light beam  230 , a reflectance R t  of the substrate  202  (e.g., the intensity of the reflected light beam  232 , or first intensity, divided by the intensity of the light beam  230 , or second intensity), emissivity ε b1  of the blackbody source, and an attenuation factor α b1  that accounts for at least a sensor factor and a view factor of the blackbody source. View factor is a percentage of light emanating from a source that is incident on a given target. Sensor factor represents a percentage of the light incident on the given target that is detected (e.g., there can be losses due to reflection and absorption in optics of the detector). The terms ε b1 α b1  can be simplified into a term, k b1 . While most terms can be measured during a temperature measurement, k b1  cannot, and thus a calibration is made to determine k b1 , which can then be used in Equation 5 to determine the substrate  202  temperature T t  during a temperature measurement. 
         [0039]    The calibration can be part of a two-phase non-contact measurement of the substrate  202  temperature T t . First, a calibration measurement can be made in a calibration phase and then a non-contact measurement in a non-contact measurement phase. The calibration measurement can involve solving Equation 6 (below) for k b1  (or ε b1 α b1 ), where Equation 6 is the same as Equation 5, but rewritten in terms of k b1  and performed with a reference substrate substituted for the substrate  202 . The reference substrate can be substituted for the substrate  202  during the calibration phase since a contact measurement for temperature could damage the substrate  202 , which may have a variety of delicate films and structures on its surfaces. The reference substrate is thus used in place of the substrate  202  for this measurement, and should have similar if not identical characteristics and quality to that of the substrate  202 . To clearly show that Equation 6 applies to the reference substrate, Equation 6 can be rewritten in terms of reflectance of the reference substrate R ref  and a temperature of the reference substrate T ref , rather than in terms of R t  and T t . 
         [0000]    
       
         
           
             
               
                 
                   
                     P 
                      
                     
                       ( 
                       λ 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           
                             
                               c 
                               1 
                             
                              
                             
                               ε 
                               ref 
                             
                              
                             α 
                           
                           
                             λ 
                             5 
                           
                         
                         [ 
                         
                           
                              
                             
                               
                                 c 
                                 2 
                               
                               
                                 
                                   λ 
                                    
                                   
                                       
                                   
                                    
                                   
                                     T 
                                     ref 
                                   
                                 
                                  
                                 
                                     
                                 
                               
                             
                           
                           - 
                           1 
                         
                         ] 
                       
                       
                         - 
                         1 
                       
                     
                     + 
                     
                       
                         
                           
                             
                               c 
                               1 
                             
                              
                             
                               k 
                               
                                 b 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                              
                             
                               R 
                               ref 
                             
                           
                           
                             λ 
                             5 
                           
                         
                         [ 
                         
                           
                              
                             
                               
                                 c 
                                 2 
                               
                               
                                 
                                   λ 
                                    
                                   
                                       
                                   
                                    
                                   
                                     T 
                                     
                                       b 
                                        
                                       
                                           
                                       
                                        
                                       1 
                                     
                                   
                                 
                                  
                                 
                                     
                                 
                               
                             
                           
                           - 
                           1 
                         
                         ] 
                       
                       
                         - 
                         1 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     6 
                   
                   ) 
                 
               
             
           
         
       
     
         [0040]    Solving Equation 6 for k b1  can involve first measuring the first temperature T ref  of the reference substrate via the temperature monitor  218 , the first temperature T b1  of the stray blackbody source (e.g., the substrate holder  204 ) via one of the temperature monitors  220 ,  222 , and the first reflectance R ref  of the reference substrate via the light beam source  212 , the light beam detector  214 , and the control module  216 . The emissivity ε ref  of the reference substrate is given as ε ref =1−R ref , the attenuation factor α of the substrate term can be a value determined by the manufacturer for each pyrometer produced, and the wavelength λ is the wavelength of the light beam  230 . 
         [0041]    With the value of k b1 , or at least having made the measurements of the reference substrate temperature T ref , the first blackbody source temperature T b1 , and the reference substrate reflectance R ref , the non-contact measurement can be made in the non-contact measurement phase. If a reference substrate was used, then the reference substrate can be replaced with the substrate  202  intended for processing and the temperature monitor  218  can be removed or decoupled from the reference substrate. In an alternative embodiment in which a reference substrate is not used, the temperature monitor  218  can be decoupled from the substrate  202 . A second temperature T′ b1  of the stray blackbody source can be measured via a temperature monitor (e.g.,  220  or  222 ) coupled to the stray blackbody source (e.g., the substrate holder  204 , the baffles  208 , or a heating element, to name three non-limiting examples) since the stray blackbody source likely increased in temperature when the temperature in the processing chamber increased. Also, a reflectance R t  of the substrate  202  (or target) can be determined as a ratio of intensity of the light detected by the light beam detector  214  (e.g., photocurrent in the light beam detector  214 ), the second intensity, divided by an intensity of light emitted by the light beam source  212 , the first intensity. These values can be substituted into Equation 7 (below) and Equation 7 can be solved for the temperature of the substrate T t . 
         [0000]    
       
         
           
             
               
                 
                   
                     P 
                      
                     
                       ( 
                       λ 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           
                             
                               c 
                               1 
                             
                              
                             
                               ε 
                               t 
                             
                              
                             α 
                           
                           
                             λ 
                             5 
                           
                         
                         [ 
                         
                           
                              
                             
                               
                                 c 
                                 2 
                               
                               
                                 
                                   λ 
                                    
                                   
                                       
                                   
                                    
                                   
                                     T 
                                     t 
                                   
                                 
                                  
                                 
                                     
                                 
                               
                             
                           
                           - 
                           1 
                         
                         ] 
                       
                       
                         - 
                         1 
                       
                     
                     + 
                     
                       
                         
                           
                             
                               c 
                               1 
                             
                              
                             
                               k 
                               
                                 b 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                              
                             
                               R 
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                             λ 
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                                   λ 
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         [0042]    Although the reference substrate and the substrate  202  can be similar if not identical materials, a reflectance measurement for both (R ref  and R t ) can still be made. For instance, this may be desired where the substrate  202  is at a higher temperature than the reference substrate. In an alternative embodiment, a single reflectance measurement can be taken, either on the substrate  202  or the reference substrate, and the value can be used in both Equations 6 and 7. 
         [0043]    In an alternative embodiment, rather than solving for k b1  and then substituting k b1  into Equation 7, the values for the reflectance of the reference substrate R ref , the first temperature of the stray blackbody source T b1 , and the temperature of the reference substrate T ref , can be measured, followed by a replacement of the reference substrate with the substrate  202 , a ramping of the temperature, and then measurements of reflectance R t  of the substrate  202  and second temperature of the stray blackbody source T′ b1 . Then the temperature of the substrate T t  can be calculated using Equations 6 and 7 in combination with these measured values to solve for the temperature of the substrate T t  via a single calculation. In other words, equation 6 can be solved for k b1 , and the solution for k b1  can be substituted into Equation 7 and then solved for the temperature of the substrate T t . 
         [0044]    The calibration measurement can be made using a reference substrate—a substrate other than the one that will be measured during the non-contact measurement. Alternatively, the calibration measurement can be performed on the substrate  202  to be processed, but at a temperature at which a contact measurement can be made via the temperature monitoring device  218  (e.g., via thermocouple). Once the calibration measurement has been performed, the temperature monitoring device  218  can be decoupled from the substrate  202  and processing of the substrate  202  can begin. 
         [0045]    The substrate  202  and reference substrate are embodiments of a target and reference target. The target and reference target can include objects to be processed that include, but are not limited to substrates and reference substrates. For instance, a polymer or glass sheet for photovoltaic manufacturing can be a target or reference target. 
         [0046]    Equations 4-7 account for the blackbody radiation of a single source. Such a source can typically be a heating element that is at a much greater temperature than any other objects in the processing chamber  200 . Thus, there may not be a need to account for any more than one stray blackbody source. However, in the event that more than one stray blackbody source is to be accounted for, one skilled in the art will recognize that Equation 4 can be expanded beyond two terms, with each additional term accounting for a separate stray blackbody source. For instance, in Equation 8 (below) two photocurrent terms P(λ) b1  and P(λ) b2  are added to the target photocurrent term P(λ) t  to account for two different stray blackbody radiation sources (e.g., the substrate holder  204  and a heating element). 
         [0000]        P (λ)= P (λ) t   +P (λ) b1   +P (λ) b2   (Equation 8)
 
         [0047]    The term P(λ) t  is the photocurrent of the substrate  202  as given by Equation 3, the term P(λ) b1  is the photocurrent attributable to a first stray blackbody source and equals 
         [0000]    
       
         
           
             
               
                 
                   
                     
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                       k 
                       
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             , 
           
         
       
     
         [0000]    and the term P(λ) s2  is the photocurrent attributable to a second stray blackbody source and equals 
         [0000]    
       
         
           
             
               
                 
                   
                     
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         [0000]    As seen, the photocurrent of each of the stray blackbody sources depends at least in part on a temperature of each stray blackbody source T b1  and T b2 , respectively. The emissivity and attenuation factor of the first stray blackbody source are represented by k b1  and by k b2  for the second stray blackbody source. The reflectance R represents that of the reference substrate or the substrate  202 , depending on whether Equation 8 is being used in the calibration or the non-contact measurement phase. In embodiments such as that modeled by Equation 8 where there are multiple stray blackbody sources and thus two or more k values, a matrix of results can be determined, which can then be interpolated based on weighing of the two or more stray blackbody sources to determine the two or more k values. 
         [0048]    Referring to Equation 6, in various alternative embodiments, once k is determined, an array or table of substrate  202  temperatures T t  can be calculated as a function of reference substrate temperature T ref , stray blackbody source temperature T b , wavelength λ, reference substrate reflectance R ref , and substrate  202  reflectance R t . In such embodiments, the temperature of the substrate T t  is essentially pre-calculated such that during the non-contact measurement, the temperature of the substrate T t  can be looked up in the array or table. 
         [0049]    An array or table can lead to discontunity between values. In other words, given changing conditions or temperatures in the processing chamber, the calculated value of the substrate temperature T t  does not change smoothly, but jumps between values in the array or table. This can be challenging for a control system to handle and for a human engineer to analyze if looking for continuous data trends. Thus, in the alternative to using a table or array, a polynomial can be used in combination with a least squares fit to the polynomial to solve for the substrate  202  temperature T t . In a particular embodiment, a second or fourth-order polynomial can be used to model a temperature to be subtracted from the measured temperature (also known as an error function) in order to arrive at a substrate  202  temperature T t  that accounts for the bias of stray blackbody radiation. In other words, the polynomial can predict measured substrate temperature (e.g., based on a pyrometer readout) as a function of actual substrate temperature. Performing a least squares fit to a polynomial (e.g., a fourth-order polynomial) enables a smooth and continuous accounting of the temperature component attributable to stray blackbody radiation. The data points used to perform the fit comprise one or more pyrometer temperature readings for a reference substrate as a function of different substrate temperatures.  FIG. 8 , illustrates one exemplary set of data where a polynomial  802  is fitted to data points  804  representing pyrometer temperature reading error (in units of temperature) for different reference substrate temperatures. To arrive at this data set, the reference substrate temperature can be set to a first value, and a difference between the temperature measured by the pyrometer and a temperature of the reference substrate as measured by a thermocouple can be calculated. This difference is plotted as a function of the reference substrate temperature. The reference substrate temperature is then either increased or decreased, and another difference calculated. This procedure continues thus generating the set of temperature differences or errors  804  as a function of reference substrate temperature. The polynomial  802  can then be fitted to the data points  804  via a least squares algorithm. 
         [0050]    In another embodiment, the non-contact temperature of the target is determined in a two-phase process. First in a calibration phase, a value for k is determined. Then, in a non-contact measurement phase, the temperature of the target T t  is measured. The non-contact measurement phase can include measuring a reflected intensity of the reflected light beam  232 , and subtracting from the reflected intensity an intensity of light attributable to the stray blackbody radiation, for instance by subtracting photocurrents P(λ) b1  and P(λ) b2  as defined with reference to Equation 8. The non-contact measurement phase can then include calculating or recalculating the target temperature T t  based on the reflected intensity of light minus the intensity of light attributable to the stray blackbody radiation. 
         [0051]    The baffles  208  is viewed in cross section, and as illustrated is a tube that can be made from a variety of preferably light-absorbing materials, although reflective and light-scattering materials can also be used. In an embodiment, the baffles  208  can have a textured surface that helps scatter and absorb stray blackbody radiation  234  such that less of the stray blackbody radiation  234  reaches the light beam detector  214 . The baffles  208  can be arranged as close to the substrate  202  as possible without contacting the substrate  202  so that an amount of stray blackbody radiation  234  reaching the light beam detector  214  is reduced. The baffles  208  is shown as being separated from the substrate holder  204 —passing through an opening, hole, or gap in the substrate holder  204 . However, in some embodiments, the baffles  208  can be coupled to the substrate holder  204  via an insulating material or device such as a washer. The baffles  208  can be coupled to a view window  207  of the processing chamber  200 . 
         [0052]    Although illustrated as a hollow tube, in an embodiment, the baffles  208  can be a solid cylinder of waveguide material (e.g., a fiber optic or tube of sapphire or glass). Such a waveguide material could further prevent stray blackbody radiation  234  from reaching the light beam detector  214  since some stray blackbody radiation  234  able to reflect off the substrate  202  and enter the tubular baffles  208  illustrated in  FIG. 2 , would partially reflect off an end of a waveguide baffles (e.g., when incident at greater than the critical angle for total internal reflection). This affect is attributable to the higher index of refraction of the waveguide baffles (e.g., glass or sapphire) versus the vacuum or processing chamber gas in which the stray blackbody radiation  234  travels through before impinging on the waveguide baffles. Such a waveguide baffles may also have the benefit of allowing the electronics portion  206  to be located further from the substrate  202  or the processing chamber  200  (e.g., where a fiber optic feeds from a pyrometer  205  outside the processing chamber to the substrate  202  within the processing chamber). A waveguide baffles could also have a light-reflecting or light-absorbing coating or material on an outer surface to prevent stray light and blackbody radiation  234  from entering the waveguide baffles via a side of the waveguide baffles. 
         [0053]    In some variations, the baffles  208  can be cooled to below room temperature including temperatures which greatly reduce blackbody radiation emitted in wavelengths overlapping with that of the emitted light beam  230  (e.g., infrared wavelengths). For instance, the baffles  208  can be cooled to between 0 C.° and 20 C.°. The baffles  208  can be cooled via thermal coupling with a cooling device (not illustrated) such as a liquid cooling system, for example. 
         [0054]    The light beam source  212  can be implemented with any number of light generating devices such as diode lasers and light emitting diodes. The light beam  230  can be collimated, can have a narrow or broad wavelength bandwidth, and can change wavelength during measurements in order to perform multi-wavelength non-contact measurements. 
         [0055]    The light beam detector  214  can be implemented with any number of light detecting devices such as photodiodes, photomultipliers, charge-coupled devices, calorimeters, and photodetectors to name just a few non-limiting examples. 
         [0056]    In the illustrated embodiment, the temperature monitors  220 ,  222  coupled to stray blackbody sources can be used to measure the temperature of the substrate holder  204  and the baffles  208 , respectively and the temperature monitor  218  can be used to measure the temperature of a reference substrate, and optionally the substrate  202 . A thermocouple is an exemplary temperature monitor  218 ,  220 ,  222 , although one skilled in the art will recognize that other temperature monitoring devices can also be used. 
         [0057]    One skilled in the art will also recognize that the light beams  230 ,  232  and stray blackbody radiation  234  are not drawn to scale, and the angles of the beams may not be entirely accurate. For instance, the light beam  230  and the reflected light beam  232  may be substantially parallel. One skilled in the art will also recognize that the arrangement of components within the electronics portion  206  is merely illustrative. For instance, the light beam source  212  and light beam detector  214  need not be separated as illustrated, but could be coupled to each other, adjacent to each other, overlapping, or even built into a single device or circuit board or system-on-a-chip. The light beam source  212 , light beam detector  214 , and analysis and control module  216  can all be built into a single device or circuit board, or system-on-a-chip. 
         [0058]      FIG. 3  illustrates a method  300  of making a non-contact temperature measurement of a substrate inside a processing chamber that accounts for stray blackbody radiation. The method  300  includes a measure a first temperature of a reference target in the processing chamber operation  302 , a measure a temperature of the stray blackbody source operation  304 , a measure a reflectance of the reference target operation  306 , a replace the reference target with the target operation  308 , and a perform a non-contact temperature measurement of the target in the processing chamber operation  310  where the perform operation  310  further includes a measure a second temperature of the stray blackbody source operation  312 , a measure a reflectance of the target operation  314 , and a calculate the temperature of the target operation  316 . 
         [0059]    The measure a temperature of the reference target operation  302  can involve measuring a temperature (e.g., via a thermocouple) of the reference target (e.g., a reference substrate) during a calibration phase where the reference target is not heated to processing temperatures, but rather is measured at temperatures around room temperature. 
         [0060]    The measure a first temperature of the stray blackbody source operation  304  can involve measuring a temperature (e.g., via a thermocouple) of the stray blackbody source (e.g., a heating element, the substrate holder, the chamber walls, to name a few non-limiting examples). 
         [0061]    The measure a reflectance of the reference target operation  306  can involve reflecting a light beam off the reference target and comparing an intensity of reflected light to an intensity of emitted light. For instance, the reflectance can equal a ratio of the reflected light divided by the emitted light. 
         [0062]    The replace the reference target with the target operation  308  can take place after a temperature of the reference target, temperature of the stray blackbody source, and reflectance of the reference target have been measured. A determination of emissivity or an array of emissivities for different stray blackbody source temperatures can be determined prior to the replace operation  308 . 
         [0063]    The perform operation  310  can include a number of sub-operations as discussed in the following. The measure a second temperature of the stray blackbody source operation  312  can involve measuring a temperature (e.g., via a thermocouple) of the stray blackbody source once the processing chamber has been raised to a processing temperature (e.g., 600° C.). The measure a reflectance of the target operation  314  can involve reflecting a light beam off the target and comparing an intensity of reflected light to an intensity of emitted light. For instance, the reflectance can equal a ratio of the reflected light divided by the emitted light. The calculate the temperature of the target operation  316  can calculate the temperature of the target based on or as a function of at least the following: the first temperature of the stray blackbody source, the second temperature of the stray blackbody source, the temperature of the reference target, the reflectance of the reference target, and the reflectance of the target. In one embodiment, an emissivity for the stray blackbody source can be calculated based on the first temperature of the stray blackbody source, the temperature of the reference target, and the reflectivity of the reference target. This emissivity can then be used in concert with the second temperature of the stray blackbody source and the reflectance of the target to calculate the temperature of the target. In yet another embodiment, an array of emissivity values can be determined for different temperatures of the stray blackbody source, and this array can be used to calculate a temperature of the target. 
         [0064]      FIGS. 4   a  and  4   b  illustrate a top and side view, respectively, of an embodiment of the baffles  408  of a pyrometer  405 . Non-contact temperature measurements as disclosed herein typically take place in an environment devoid of non-blackbody light sources (e.g., with the lights off or obstructed). The baffles  408  can prevent stray blackbody radiation from passing through it and striking the light beam detector  414 . However, some stray blackbody radiation  450  can reflect off the substrate  402 , then off an end of a baffles  410 , off the substrate  402  again, and then impinge on the light beam detector  414  (more than one reflection of an end of a baffles  410  is also possible). 
         [0065]    To reduce this stray blackbody radiation  450 , the baffles  408  can have a light-absorbing end  410 . For instance, the baffles  408  can be made of a plurality of concentric rings of tubes coupled to each other or arranged adjacent to each other (as viewed from above in  FIG. 4   a ), and arranged such that light cannot pass through the baffles  408  from a side of the baffles. However, these tubes are also of such a diameter (e.g., 2-10 mm) that when the stray blackbody radiation  450  impinges on the end of the baffles  410 , the stray blackbody radiation  450  scatters off the tubes and generally is directed downward in  FIG. 4   b  towards the electronics portion  406  rather than reflecting back towards the substrate  402  (the stray blackbody radiation  450  is illustrated to show the reflections off of a non-absorbing end of a baffles rather than a light-absorbing baffles as discussed in this paragraph). As the stray blackbody radiation  450  scatters back and forth between the tubes, each scattering results in absorption, and eventually the stray blackbody radiation  450  is absorbed or substantially absorbed in the tubes. In other words, the tubes act as a near-perfect light absorber. While three concentric rings of tubes are illustrated, more or less than three concentric rings of tubes can also be implemented. 
         [0066]    In an embodiment, a similar effect to using tubes for the baffles  408  can be achieved by coating the end  410  of the baffles  408  with a light-absorbing textured material such as gold black. 
         [0067]    The baffles  408  is coupled to an electronics portion  406  that houses at least a light beam source  412  (e.g., a laser diode) and a light beam detector  414  (e.g., photodiode). The light beam source  412  and light beam detector  414  can be adjacent to a center of the baffles  408  (as viewed from above in  FIG. 4   a ), but can also be arranged in any number of other configurations. 
         [0068]      FIG. 5  illustrates a close-up isometric view of a portion of the tubes  408  of  FIG. 4 . The spacing between each concentric ring of the tubes  408  is not limited, however it will depend on the wavelength of infrared light emitted from the light beam source  412 . The spacing between tubes  408  in a given concentric ring can also depend on the wavelength of light emitted from the light beam source  412 . For shorter wavelengths of light, the tubes  408  can be more closely arranged. The tubes can be hollow or solid cylinders. 
         [0069]    The concept behind the baffles  408  made of tubes in  FIG. 4  is that a structure that is very tall relative to its diameter presents little surface area for light reflection, and presents a large area for scattering and redirecting the light in substantially the same direction that the light was originally traveling. Other shapes can also achieve a similar affect, and some non-limiting examples are discussed with reference to  FIGS. 6-7 . 
         [0070]      FIG. 6  illustrates a close-up view of a portion of an end of an embodiment of a baffles  608  with a single concentric ring of round-ended or needle-tipped tubes. The round-ended or needle-tipped tubes may have less reflective area provided to stray blackbody radiation than concentric rings of tubes as in  FIGS. 4   a ,  4   b , and  5 . Only one ring of needle-tips is illustrated, but in other embodiments there can be a plurality of concentric rings of needle-tips. 
         [0071]      FIG. 7  illustrates a close-up view of a portion of an end of an embodiment of a baffles  708  made with a plurality concentric rings. These concentric cylinders act similarly to the tubes of  FIGS. 4   a ,  4   b , and  5  in that light has very little surface area to reflect off of and instead a majority of light scatters off of sides of each ring in a direction generally opposite to the direction of the substrate until enough scattering has occurred to substantially absorb all of the stray blackbody radiation. 
         [0072]      FIGS. 6-7  show just two examples of the myriad forms that such a light-absorbing baffles can take. The general idea being that the baffles comprise a structure presenting very little surface area for reflections of stray blackbody radiation back towards the substrate, and instead cause stray blackbody radiation to scatter off sides of the structure and be absorbed by the structure during a plurality of scattering events such that the stray blackbody radiation is substantially absorbed rather than reflected from an end of the baffles. 
         [0073]    In conclusion, the present invention provides, among other things, a method, system, and apparatus that enables non-contact temperature measurements of a semiconducting substrate or other processing target to a degree of accuracy that accounts for or negates stray blackbody radiation. Those skilled in the art can readily recognize that numerous variations and substitutions may be made in the invention, its use, and its configuration to achieve substantially the same results as achieved by the embodiments described herein. Accordingly, there is no intention to limit the invention to the disclosed exemplary forms. Many variations, modifications, and alternative constructions fall within the scope and spirit of the disclosed invention.