Effect of mask pattern correction for off-axis incident light in extreme ultraviolet lithography

摘要

The effect of mask pattern correction for off-axis incident light on the pattern fidelity of a model pattern with 22 nm wide lines and spaces was investigated. Corrections were made to the edges of mask patterns, because off-axis incident light produces an asymmetric aerial image. The corrections were found to compensate effectively for the degradation in pattern fidelity due to the influence of off-axis incident light and optical proximity effects. Off-axis incident light causes asymmetry in the positions of pattern edges, the mask error enhancement factor, and pattern edge contrast, even when a symmetric mask pattern layout is designed. It was found that these asymmetries could be suppressed by employing thin buffer and absorber films and a large numerical aperature of projection optics.