Mask modification for the shadow effect reduction by Rigorous coupled-wave analysis in extreme ultraviolet lithography

Abstract

Extreme ultraviolet lithography (EUVL) is believed to be the next generation lithography and so it is seriously under study globally. The near-field intensity on the EUVL mask is affected by the mask structure. The absorber and the buffer layer make a shadow since the light is shining on the mask at some angle to the normal on-axis. This shadow effect in the EUVL mask is an important factor that decreases the contrast of the aerial image and, as a result, causes a line width variation and a pattern shift. Among the several possible mask structures, we focused on the mask edge slope variation with a typical incident angle of 5°. We analyzed electromagnetic wave around the mask by rigorous coupled-wave analysis (RCWA) and reflectivity in the modified mask structure.