Plasma reactive ion etching of 193 nm attenuated phase shift mask materials

Abstract

This article gives details on plasma etch process development for potential attenuated phase shift masking materials for use at 193 nm. Masking films investigated include materials based on aluminum nitride, zirconium nitride, molybdenum–silicon oxide, tantalum–silicon nitride, and tantalum–silicon oxide. A variety of halogenated etch plasmas were investigated, including fluorine-based chemistries (CF4 and SF6) and chlorine-based chemistries (Cl2, CCl4) combined with oxygen, argon, and hydrogen. Thin films of TaN, MoSiO, SixNy, and TaO that allow for sufficient volatility in fluorine plasma and processes using SF6 were chosen for optimization. Fluorides of aluminum and zirconium exhibit very low vapor pressure so Cl2+Ar mixtures were chosen for study. Al and Zr chlorides can be made volatile but ion assistance is generally needed to produce sufficiently high etch rates. Because of this, selectivity to resist is generally poor. Of all the materials evaluated, attenuated phase shift mask films of TaN/Si3N4 etched with SF6 allow the largest etch selectivity to both fused silica and resist.