M. Khan et al., REVISITING PHASE-SHIFTING MASKS IN X-RAY-LITHOGRAPHY, Journal of vacuum science & technology. B, Microelectronics and nanometer structures processing, measurement and phenomena, 15(6), 1997, pp. 2255-2258
In this article, we describe a framework for selecting the materials f
or phase shift masks (PSMs) in x-ray lithography to yield the optimal
exposure latitude. Traditional design of PSMs involves choosing the th
ickness of the material to produce a pi phase shift, as in the case of
clear phase shifting masks, or to produce the sufficient contrast nee
ded for imaging with a requisite phase shift to improve linewidth cont
rol, as in the cases of attenuated phase shifting masks and half-tone
phase shifting masks. We instead find the optical constants of a theor
etical material that yield optimal exposure latitude, and try to find
combinations or alloys of various materials that have the requisite op
tical constants. (C) 1997 American Vacuum Society.