Resolution enhancement of stepper by complementary conjugate spatial filter

An ultra-high resolution stepper is proposed, which combines annular illumination and a complementary conjugate spatial filter. This technique reproduces deep submicron complex non-repeated patterns by relatively emphasizing the diffracted light from high spatial-frequency patterns. Images of several patterns are simulated for a conventional stepper, a stepper with phase shifting, and for the proposed technique. The results indicate that this technique has the potential to pattern 0.3-|im images using an i-line stepper with 0.5 N.A. with conventional masks. It should enable stepper ranges to be extended to the next generation of DRAMs.