Imaging interferometric lithography: approaching the resolution limits of optics

The resolution limits of conventional optical lithography reflect the low-p ass spatial-frequency [numerical aperture (NA)/lambda] filter characteristi cs of the imaging system. Imaging interferometric lithography extends the r esolution of optical lithography to the spatial-frequency limits of optics (2/lambda). Off-axis illumination downshifts the high-frequency components of the mask pattern. An interferometric beam at the wafer upshifts these fr equency components back to their original spatial frequencies following the lens. 2x reduction imaging interferometric lithography experiments demonst rate a continuous frequency coverage up to similar to 3N.A./lambda with a c onsequent threefold resolution enhancement. (C) 1999 Optical Society of Ame rica.