FOCUSED ION-BEAM BIASED REPAIR OF CONVENTIONAL AND PHASE-SHIFT MASKS

A novel technique, focused ion beam biased sputtering, is used to repa ir opaque defects in both conventional binary intensity masks and phas e shift masks without leaving post-repair residual defects caused by g allium ion staining. The biased repair involves sputter removal of a d efect to an area larger than its original size. The reduction of light transmission due to gallium stain is then effectively compensated by the enlarged repair. Results are presented on the repair of both conve ntional and attenuated phase shift masks using the biased method in co mparison with conventional (no bias) repair. Optimum bias is determine d by computer simulation of optical imaging and resist development. Un like other anti-staining techniques which require additional equipment and process steps, the biased repair method involves only a change of sputtering strategy and can be implemented in any existing focused io n beam mask repair tools. (C) 1996 American Vacuum Society.