Focused ion beam XeF2 etching of materials for phase-shift masks

Abstract

Phase-shift masks (PSMs) for photolithography are emerging as a very important technology for integrated circuit manufacture at 0.35 μm design rules and below using conventional optical step and repeat cameras at 365 and 248 nm. One of the biggest issues which remains unresolved in the fabrication of PSMs is defect repair. The sensitivity to printing of defects is much worse for phase defects than defects on conventional photomasks. In addition, the repair of defects in transparent dielectric materials at high-spatial resolution presents many challenges. Focused ion beams (FIBs) offer the necessary spatial resolution for PSM repair. This article discusses the addition of etchant gas to the FIB process for enhanced etch rates, decreased optical effects from implanted ions and possible etch selectivity for process control.