Spatial frequency analysis of optical lithography resolution enhancement techniques

A. consistent frequency-space analysis of the effects of optical lithograph y resolution enhancement techniques including optical proximity correction, off-axis illumination, phase-shift masks, and imaging interferometric lith ography is presented. The improvements for each of these techniques are dir ectly related to the enhanced frequency-space coverage afforded. Optical pr oximity correction extends the frequency coverage out to similar to 1.2-1.3 x NA/lambda where NA is the optical system numerical aperture and lambda t he exposure wavelength enabling kappa(1)'s of similar to 0.45 in the contex t of the usual Rayleigh resolution equation CD = kappa(1)lambda/NA. There a re many possible configurations for off-axis illumination. For a quadrupole oriented at 45 degrees to the (x, y) pattern axes, the maximum spatial fre quency is extended to root 2NA/lambda or kappa(1)similar to 0.43. Adding pu pil plane filters to ensure a uniform modulation transfer function and orie nting the quadrupole along the pattern axes allows extension to frequencies of 2NA/lambda or K(1)similar to 0.3. Phase shifts at the mask plane emphas ize the high frequency image components by increasing the importance of the quadratic imaging terms and allow frequencies to 2NA/lambda and K-1's out to similar to 0.35. Imaging interferometric lithography further extends the frequency coverage out to either ( 1 + NA)/lambda or 3NA/lambda depending on the details with corresponding kappa(1)'s of similar to 0.23-0.2. (C) 19 99 American Vacuum Society.