Effect of incident angle of off-axis illumination on pattern printability in extreme ultraviolet lithography

Abstract

The effect of the incident angle of off-axis illumination on the printability of 22-nm-wide line patterns was investigated for three absorber stack configurations. Shadowing due to off-axis illumination and the absorber wall degrades printability, especially for a dense pattern layout. It was found that the influence of shadowing on resolution and pattern fidelity could be suppressed by employing a small incident angle and thin buffer and absorber films. An incident angle below 6.0° and an absorber stack with an optical density of 2.0 provide a practical level of pattern fidelity. Furthermore, a small incident angle below 5.0° and a thin absorber stack eliminate differences in fidelity for patterns with different orientations with respect to the direction of the off-axis light incident on a mask.