Methods and apparatus for generating a library of spectra

Abstract

A method of generating a library from a reference substrate for use in processing product wafers is described. The method includes measuring substrate characteristics at a plurality of well-defined points of a reference substrate, measuring spectra at plurality of measurement points of the reference substrate, there being more measurement points than well-defined points, and associating measured spectra with measured substrate characteristics.

1 . A method of generating a library for use in processing product wafers, the method comprising:
 measuring substrate layer thickness at a first well-defined point and a second well-defined point of a reference substrate with a first metrology system;   measuring a spectrum at a measurement point of the reference substrate with a second monitoring system other than the first metrology system;   determining a closer well-defined point of the first well-defined point and the second well-defined point to the measurement point; and   storing an association of the spectrum with the substrate layer thickness of the closer well-defined point.   
     
     
         2 . The method of  claim 1 , wherein substrate layer thickness is measured prior to measuring the spectrum. 
     
     
         3 . The method of  claim 1 , wherein measuring the spectrum comprises scanning a sensor across the reference substrate and measuring a plurality of spectra at a plurality of measurement points including the spectrum at the measurement point. 
     
     
         4 . The method of  claim 3 , further comprising measuring substrate layer thicknesses of the reference substrate at a plurality of well-defined points with the first metrology system, the plurality of well-defined points including the first well-defined point and the second well-defined point. 
     
     
         5 . The method of  claim 4 , further comprising determining a closest well-defined point of the plurality of well-defined points for each of the plurality of measurement points. 
     
     
         6 . The method of  claim 5 , further comprising, for each spectrum from the plurality of spectra, storing an association of the spectrum from the plurality of spectra with a substrate layer thickness of the closest well-defined point. 
     
     
         7 . The method of  claim 6 , further comprising:
 scanning a product substrate other than the reference substrate with an optical monitoring system to generate a measured spectrum of the product substrate;   determining a best matching spectrum from the plurality of spectra to the measured spectrum of the product substrate; and   determining a substrate layer thickness associated with the best matching spectrum.   
     
     
         8 . The method of  claim 7 , wherein second monitoring system is the optical monitoring system. 
     
     
         9 . The method of  claim 1 , wherein the first well defined point and the second well defined point are in different dies on the reference substrate. 
     
     
         10 . The method of  claim 9 , wherein the first well defined point and the second well defined point are at the same relative position within the different dies. 
     
     
         11 . A computer program product, tangibly stored on machine readable storage device, for generating a library for use in processing product wafers, the product comprising instructions operable to cause a processor to:
 cause substrate layer thickness to be measured at a first well-defined point and a second well-defined point of a reference substrate with a first metrology system;   cause a spectrum to be measured at a first measurement point of the reference substrate with a second monitoring system other than the first metrology system;   determine a closer well-defined point of the first well-defined point and the second well-defined point to the first measurement point; and   store an association of the spectrum with the substrate layer thickness of the closer well-defined point.   
     
     
         12 . A method of generating a library for use in processing product wafers, the method comprising:
 measuring a first value of a substrate layer characteristic at a first well-defined point of a reference substrate with a first metrology system and measuring a second value of the substrate layer characteristic at a second well-defined point of the reference substrate with the first metrology system;   measuring a spectrum at a measurement point of the reference substrate with a second monitoring system other than the first metrology system;   determining a first distance from the measurement point to the first well-defined point and a second distance from the measurement point to the second well-defined point;   calculating a third value from the first value, the second value, the first distance and the second distance; and   storing an association of the spectrum with the third value.   
     
     
         13 . The method of  claim 12 , wherein the substrate layer characteristic comprises a layer thickness. 
     
     
         14 . The method of  claim 12 , wherein calculating the third value comprises calculating a weighted average of the first value and the second value with weighting based on the first distance and the second distance. 
     
     
         15 . The method of  claim 12 , further comprising measuring the substrate layer characteristic of the reference substrate at a plurality of well-defined points with the first metrology system to generate a plurality of values, the plurality of well-defined points including the first well-defined point and the second well-defined point. 
     
     
         16 . The method of  claim 14 , wherein the first well-defined point and the second well defined point are the closest well-defined points of the plurality of well-defined points to the measurement point. 
     
     
         17 . The method of  claim 15 , wherein measuring the spectrum comprises scanning a sensor across the reference substrate and measuring a plurality of spectra at a plurality of measurement points including the spectrum at the measurement point. 
     
     
         18 . The method of  claim 16 , further comprising, for each spectrum from the plurality of spectra, determining distances from the measurement point to two of the plurality of well-defined points and calculating a value from values of the substrate layer characteristic at the two of the plurality of well-defined points and the distances. 
     
     
         19 . The method of  claim 17 , further comprising:
 scanning a product substrate other than the reference substrate with an optical monitoring system to generate a measured spectrum of the product substrate;   determining a best matching spectrum from the plurality of spectra to the measured spectrum of the product substrate; and   determining the value of the substrate layer characteristic associated with the best matching spectrum.   
     
     
         20 . The method of  claim 12 , wherein the first well defined point and the second well defined point are in different dies on the reference substrate. 
     
     
         21 . The method of  claim 19 , wherein the first well defined point and the second well defined point are at the same relative position within the different dies. 
     
     
         22 . A computer program product, tangibly stored on machine readable storage device, for generating a library for use in processing product wafers, the product comprising instructions operable to cause a processor to:
 cause a first value of a substrate layer characteristic to be measured at a first well-defined point of a reference substrate with a first metrology system and cause a second value of the substrate layer characteristic to be measured at a second well-defined point of the reference substrate with the first metrology system;   cause a spectrum to be measured at a measurement point of the reference substrate with a second monitoring system other than the first metrology system;   determine a first distance from the measurement point to the first well-defined point and a second distance from the measurement point to the second well-defined point;   calculate a third value from the first value, the second value, the first distance and the second distance; and   store an association of the spectrum with the third value.