Apparatus and method for real time measurement of substrate temperatures for use in semiconductor growth and wafer processing

Abstract

The invention is an optical method and apparatus for measuring the temperature of semiconductor substrates in real-time, during thin film growth and wafer processing. Utilizing the nearly linear dependence of the interband optical absorption edge on temperature, the present method and apparatus result in highly accurate measurement of the absorption edge in diffuse reflectance and transmission geometry, in real time, with sufficient accuracy and sensitivity to enable closed loop temperature control of wafers during film growth and processing. The apparatus operates across a wide range of temperatures covering all of the required range for common semiconductor substrates.

1 . In an apparatus for measuring the temperature of a substrate material by inference from its bandgap measured by diffuse reflectivity comprising lamp means for emitting broad spectrum white light, focusing means for focusing the white light upon a surface of a substrate material, detector means positioned at a non-specular position on the front side of said substrate material and computing means for determining the temperature dependent bandgap absorption from onset wavelength of non-specular reflection from a surface of the substrate material, the improvement comprising: 
 single optical fiber means for collecting non-specularly reflected light detected by said detector means.    
   
   
       2 . The apparatus of  claim 1  which further comprises at least one selectively positionable lens for collecting said non-specularly reflected light from said surface of said substrate, whereby said light is focused by said lens and directed to said optical fiber means.  
   
   
       3 . The apparatus of  claim 1  which further comprises at least one selectively positionable mirror for collecting said non-specularly reflected light from said surface of said substrate, whereby said light is focused by said mirror and directed to said optical fiber means.  
   
   
       4 . The apparatus of  claim 1  which further comprises positioning means on which said detector is mounted whereby said detector scans in the aperture plane of said single optical fiber.  
   
   
       5 . The apparatus of  claim 1  which further comprises a tilt stage on which said detector is mounted whereby said detector may be aligned.  
   
   
       6 . The apparatus of  claim 1  which further comprises laser source means for aligning said detector means.  
   
   
       7 . The apparatus of  claim 1  which further comprises intensity control means for controlling said lamp means.  
   
   
       8 . The apparatus of  claim 1  which further comprises heating means for heating said substrate, switch means for automatically switching from the use of said lamp means to said heating means when its temperature is sufficiently high to emit visible radiation, whereby said heating means emits said light.  
   
   
       9 . The apparatus of  claim 1  which further comprises a quartz rod positioned behind said substrate material for collecting broadband light.  
   
   
       10 . The apparatus of  claim 1 , wherein said lamp means further comprises a lamp condensing mirror.  
   
   
       11 . The apparatus of  claim 1  which further comprises an array spectrometer optimized in predetermined wavelength range coupled to said optical fiber means.  
   
   
       12 . The apparatus of  claim 1  which further comprises condensing optics for the purpose of collecting said reflected light.  
   
   
       13 . The method of measuring the temperature of a substrate material by inference from its bandgap measured by diffuse reflectivity comprising: 
 A. Generating a broad spectrum of light by light-producing means;    B. Directing said light upon a front surface of a substrate material whereby a portion of said light is non-specularly reflected from at least one surface of said substrate;    C. Collecting at least a portion of said non-specularly reflected light at at least one focusing mirror;    D. Selecting at least a portion of said collected light to a single optical fiber means;    E. Transmitting said at least a portion of said non-specularly reflected light through said optical fiber means to a spectrometer; and    F. Analyzing said non-specular reflected light to improve band edge definition.    G. Mapping the surface temperature of the wafer by detector scanning stage means.    
   
   
       14 . The method of measuring the temperature of a substrate material by inference from its bandgap measured by diffuse reflectivity comprising: 
 A. Generating a broad spectrum of light by light-producing means;    B. Directing said light upon a front surface of a substrate material whereby a portion of said light is non-specularly reflected from at least one surface of said substrate;    C. Collecting at least a portion of said non-specularly reflected light at at least one focusing lens;    D. Selecting at least a portion of said collected light to a single optical fiber means;    E. Transmitting said at least a portion of said non-specularly reflected light through said optical fiber means to a spectrometer; and    F. Analyzing said non-specular reflected light to improve band edge definition.    G. Mapping the surface temperature of the wafer by detector scanning stage means.    
   
   
       15 . The invention of  claim 13 , wherein said light-producing means comprises a heater placed in proximity to said substrate.  
   
   
       16 . The invention of  claim 14 , wherein said light-producing means comprises a heater placed in proximity to said substrate.  
   
   
       17 . The invention of claims  1  through  12 , which further comprises feedback means for sensing and controlling the output of said lamp means.