Effects of Fresnel Diffraction on Resolution and Linewidth Control in Synchrotron Radiation Lithography

Abstract

To investigate the influence of Fresnel diffraction on resolution and linewidth control in synchrotron radiation (SR) lithography, a detailed analysis is performed that takes X-ray phase shift in the absorber into account. The phase shift for 0.65-µm-thick Ta absorber is estimated to be -180°. It becomes clear that the phase shift plays a important role in limiting pattern resolution and linewidth control, especially for replicating fine (<0.3 µm) patterns. The conditions for replicating 0.2-µm lines-and-spaces resist patterns under practical conditions-i.e., with a mask contrast of 7 and a proximity gap of around 30 µm-are described. Designing a Ta absorber that is slightly narrower (<0.05 µm) than 0.2 µm is a great advantage for replicating 0.2-µm patterns because the dose-margin for replicating the patterns faithfully is improved.