Optical lithography into the millennium: sensitivity to aberrations, vibration and polarization

Various factors, such as lens aberrations, system vibration and the choice of illumination polarization can degrade the level of modulation, and hence, image quality. This paper discusses the sensitivity of multiple feature types to these factors. it is shown that aberration sensitivity increases Linearly with decreasing resolution, scaled to the Rayleigh criteria. An analysis of the vibration tolerance is done for transverse and axial vibration planes, where the effects on the process window and CD uniformity are measured. The vibration is shown to decrease the process window greater for low contrast images and is shown to scale directly with the resolution. The new millennium will usher in optical systems with very high NA lenses (>0.75NA) for 248nm, 193nm and 157nm. This paper re-examines the role of the polarization on required specifications of the exposure tool optics. it is found that tight polarization specifications with <10% residual polarization will be needed for future systems.