Goos-Hanchen compensation in autofocus systems

Abstract

A new and useful method is provided for Goos-Hanchen compensation in an optical autofocus (AF) system that uses light reflected from a substrate to determine changes in the z position of a substrate. According to the method of the invention reflected light from the substrate is provided at a plurality of wavelengths and polarizations, detected and used to make corrections that compensate for the errors due to the Goos-Hanchen effect.

1 . A method for compensating for errors due to the Goos-Hanchen effect in an optical autofocus system that uses light reflected from a substrate to determine changes in the z position of the substrate, comprising directing reflected light from the substrate at a plurality of wavelengths and polarizations, detecting the reflected light at the plurality of wavelengths and polarizations, and using the detected light at the plurality of wavelengths and polarizations to compensate for the errors due to the Goos-Hanchen effect. 
     
     
         2 . The method of  claim 1 , wherein broadband light is directed at the substrate, and reflected light from the substrate is broken into different polarizations and wavelengths that are then detected. 
     
     
         3 . The method of  claim 2 , wherein broadband light reflected from the substrate is refracted by a pair of prisms, a first prism that spreads the reflected light as collimated light in angles by wavelengths, and a second prism that is displaced from the first prism along the z axis, and makes the collimated rays at all the wavelengths parallel, so that the wavelengths are spatially separated. 
     
     
         4 . The method of  claim 3 , wherein detection of the light comprises fringe detection. 
     
     
         5 . The method of  claim 1 , wherein broadband light reflected from the substrate is refracted by a pair of prisms, a first prism that spreads the reflected light as collimated light in angles by wavelengths, and a second prism that is displaced from the first prism along the z axis, and makes the collimated rays at all the wavelengths parallel, so that the wavelengths are spatially separated. 
     
     
         6 . The method of  claim 5 , wherein detection of the light comprises fringe detection. 
     
     
         7 . The method of  claim 1 , wherein light at a plurality of wavelengths is directed at the substrate, the light at the plurality of wavelengths is reflected from the substrate and broken into different polarizations, and then detected. 
     
     
         8 . The method of  claim 7 , wherein detection of the light comprises fringe detection. 
     
     
         9 . The method of  claim 1 , where separate light sources of finite spectral width are incident at different angles such that they can be separated in angle space. 
     
     
         10 . The method of  claim 9 , wherein detection of the light comprises fringe detection. 
     
     
         11 . The method of  claim 1 , wherein light is directed at the substrate comprises light from an illumination source that produces light sequentially at a plurality of wavelengths and a plurality of polarizations, and light at the plurality wavelengths and polarizations is detected sequentially. 
     
     
         12 . The method of  claim 11 , wherein detection of the light comprises fringe detection. 
     
     
         13 . The method of  claim 1 , wherein the light reflected by the substrate is used to determine changes in the z position of the substrate by applying a weighting average to the set of z measurements at the different wavelengths and polarizations, and using the weighting average to make corrections in the z position that account for the Goos-Hanchen effect. 
     
     
         14 . The method of  claim 13 , wherein the weighting average is produced by a linear least squares regression estimate of the coefficients of the first order position of the substrate. 
     
     
         15 . The method of  claim 14 , wherein the linear least squares regression estimate of the coefficients of the first order position of the substrate uses reflectance values as a function of wavelength. 
     
     
         16 . The method of  claim 13 , wherein applying a weighting average to the set of z measurements at the different wavelengths and polarizations, and using the weighting average to make corrections in the z position that account for the Goos-Hanchen effect uses reflectance values as a function of wavelength.