Process for etching tungsten silicide overlying polysilicon particularly in a flash memory

摘要

A method of plasma etching tungsten silicide over polysilicon particularly useful in fabricating flash memory having both a densely packed area and an open (iso) area requiring a long over etch due to microloading. Wafer biasing is decreased in the over etch. The principal etchant include NF₃ and Cl₂. Argon is added to prevent undercutting at the dense/iso interface. Oxygen and nitrogen oxidize any exposed silicon to increase etch selectivity and straightens the etch profile. SiCl₄ may be added for additional selectivity.