DRY ETCHED MOLYBDENUM SILICIDE PHOTOMASKS FOR SUBMICRON INTEGRATED-CIRCUIT FABRICATION

The aim of this paper is to demonstrate a manufacturable molybdenum silicide mask process. Each step of the fabrication of a mask was addressed: lithography, dry etching, cleaning, inspection and repair. SAL601 resist (Shipley) was chosen for the etch mask as dry etch resistance and almost vertical resist profiles are required [J. W. Thackeray, G. W. Orsula, E. Pavelcheck, D. Canistro, L. E. Bogan, A. K. Berry, and K. A. Graziano, Proc. SPIE 1086 (1989)]. Etching experiments of the molybdenum silicide were performed using different fluorinated gas mixtures. Two of them, CF4 + O2, SF6 + O2, were chosen and optimized for selectivity (ratio of molybdenum silicide etch rate versus resist etch rate) using a statistical experimental design approach. Results indicate a higher selectivity for the CF4 + O2 mixture but lower loading effects for SF6 + O2 leading to a better uniformity in the latter case. In both cases, the pressure was chosen low enough (below 200 m Torr to get anisotropic etching conditions even if the selectivity is reduced. Inspection has been performed using standard optical equipment from KLA Instrument Corporation. None of the defects found were related to lithography and dry etching processes. Repair feasibility has been demonstrated with both laser beam and focused ion beam (FIB). Thanks to its fine grain structure, very smooth edges have been obtained, after FIB repair, for molybdenum silicide as compared to chrome.