Automated overlay metrology system

Abstract

Non-imaging measurement is made of misalignment of lithographic exposures by illuminating periodic features of a mark formed by two lithographic exposures with broadband light and detecting an interference pattern at different wavelengths using a specular spectroscopic scatterometer including a wavelength dispersive detector. Misalignment can be discriminated by inspection of a spectral response curve and by comparison with stored spectral response curves that may be empirical data or derived by simulation. Determination of best fit to a stored spectral curve, preferably using an optimization technique can be used to quantify the detected misalignment. Such a measurement may be made on-line or in-line in a short time while avoiding tool induced shift, contact with the mark or use of a tool requiring high vacuum.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is as follows:  
     
         1 . A method of measuring overlay alignment of sequential lithographic exposures, said method including steps of 
 forming first separated features on a surface,    forming second separated features on said surface interleaved between said first separated features, and    illuminating said first and second separated features and detecting an interference pattern.    
     
     
         2 . A method as recited in  claim 1 , including the further step of calculating a spectrographic response corresponding to said interference pattern.  
     
     
         3 . A method as recited in  claim 1 , wherein said illuminating and detecting step is performed with a specular spectroscopic scatterometer.  
     
     
         4 . A method as recited in  claim 3  wherein said scatterometer is of the reflectometer type.  
     
     
         5 . A method as recited in  claim 3  wherein said scatterometer is of the ellipsometer type.  
     
     
         6 . A method as recited in  claim 5 , wherein said ellipsometer measures complex reflectivity spectral ratio for two orthogonal polarizations with broadband illumination.  
     
     
         7 . A method as recited in  claim 1  wherein said illumination is broadband light.  
     
     
         8 . A method as recited in  claim 1  wherein said detection measures amplitude and phase.  
     
     
         9 . A method as recited in  claim 1 , wherein said illumination and detection step results in measured spectral curves and including the further steps of 
 modelling said first arid second features by simulation to obtain simulated spectral curves, and    comparing said measured spectral curves with said simulated spectral curves.    
     
     
         10 . A method as recited in  claim 9 , wherein said comparing step includes use of an optimization technique to determine best fit and to quantify a misalignment value.  
     
     
         11 . A test mark including 
 a plurality of marks formed by a lithographic exposure,    a mark formed between said plurality of marks by another lithographic exposure,    said mark and said plurality of marks forming a periodic structure.    
     
     
         12 . A non-imaging metrology apparatus comprising 
 means for storing spectral curves,    a specular spectroscopic scatterometer for measuring reflection from a plurality of marks formed by two lithographic exposures and forming a periodic structure, and    means for comparing processed signals output from said specular spectroscopic scatterometer with said spectral curves to evaluate misalignment of said two lithographic exposures.