Bimetallic Thermal Resists Potential for Double Exposure Immersion Lithography and Grayscale Photomasks

摘要

Double exposure/patterning is considered the best candidate for extending 195nm optical lithography below 40nm resolution However, double exposure techniques require a resist where the exposures do not add linearly to produce the final result. A class of negative thermal resists that show this effect are bimetallic thin-films consisting of Bi/In or Sn/In. The films are bi-layered structured until sufficiently heated by a laser exposure pulse (7 mJ/sq. cm for 4 nsec). Experiments with interference lithography at 266nm in air demonstrated that Bi/In resists have a resolution limit <42nm, the exposure system limit. As a first investigation into the resist's potential for immersion lithography, the response of bimetallic resists to immersion lithography was examined. The Sn/In film used demonstrated successful development as thermal resist for immersion exposures and the power level required to convert the film was only slightly higher than the level required for exposing the film in air.