Influence of the mask magnification on imaging in hyper-NA lithography

Argon fluoride laser (ArF) lithography using immersion technology has the potential to extend the application of optical lithography to 45 nm half-pitch and possibly beyond. By keeping the same 4× magnification factor, the dimensions of the structures on masks are becoming comparable to the exposure wavelength or even smaller. The polarization effect induced by mask features is, however, an issue. The introduction of a larger mask magnification should be strongly considered when poor diffraction efficiencies from subwavelength mask features and the resulting image degradation would be encountered in hyper-NA lithography. The dependence of the diffraction efficiencies on mask pitch and illuminating angle are evaluated. The near-field intensity and phase distributions from the mask are calculated. The imaging performance of 4× and 8× masks for the sub-45 nm node are explored. A rigorous coupled-wave analysis is developed and employed to analyze the optical diffraction from the 3D topographic periodic features.