Spatial frequency analysis of optical lithography resolution enhancement techniques

A. consistent frequency-space analysis of the effects of optical lithography resolution enhancement techniques including optical proximity correction, off-axis illumination, phase-shift masks, and imaging interferometric lithography is presented. The improvements for each of these techniques are directly related to the enhanced frequency-space coverage afforded. Optical proximity 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 the exposure wavelength enabling kappa(1)'s of similar to 0.45 in the context of the usual Rayleigh resolution equation CD = kappa(1)lambda/NA. There are many possible configurations for off-axis illumination. For a quadrupole oriented at 45 degrees to the (x, y) pattern axes, the maximum spatial frequency is extended to root 2NA/lambda or kappa(1)similar to 0.43. Adding pupil plane filters to ensure a uniform modulation transfer function and orienting 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 emphasize 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) 1999 American Vacuum Society.