A novel process of etching EUV masks for future generation technology

Abstract

Studies on pattern transfer of next generation lithographic (EUV) photomask were carried out. Based on current absorber layer material candidates, thermodynamic calculations were performed and plasma etch gas system and composition were investigated. The gas systems have the advantage of all etch products being in volatile condition. This is helpful to keep the etch process and etch chamber clean. For etch CD bias challenge in EUV photomask etch, self-mask concept was investigated, which makes anti-reflective (AR) sub-layer of the absorber layer function as a hard mask for the bulk absorber layer beneath. It significantly reduces etch CD bias and improves pattern transfer fidelity. For common candidates of EUV mask absorber layers such as TaBO/TaBN and TaSiON/TaSi, reactive gas systems were proposed according to thermodynamic calculations with all products volatile. AR sub-layers were etched in one gas composition with volatiles. Once the AR sub-layer is etched through, gas composition was changed so that the bulk absorber sub-layer beneath is etched selectively with volatile products. Excellent results in profiles, CD bias, CD uniformity, and underneath buffer/capping layer impact have been demonstrated.