Chromeless phase-shifted masks: A new approach to phase-shifting masks

This paper introduces a novel concept, "chromeless phase-shifting", that eliminates the need for the use of chrome to form patterns in optical lithography. Chromeless phase-shifting uses 180° phase-shifters on transparentglass to define patterns. The method relies on the destructive interference between phase-shifters and clear areas at the edges of the phase-shifters to define dark or opaque areas on the mask. Gratings sufficiently small will produce sufficient interference to completely inhibit the transmission of light (these gratings are thus named dark-field gratings). The combination of these effects makes it possible to form a wide range of patterns, from line-space patterns to isolated bright or dark areas. In this study, the lithography simulators SPLAT and SAMPLE were used to understand the principles behind this new scheme, and to verify various pattern designs. Simulation and experimental results are presented to demonstrate the concept.