PROCESS FOR ETCHING TUNGSTEN SILICIDE OVERLYING POLYSILICON ESPECIALLY IN A FLASH MEMORY

摘要

A process for etching tungsten silicide covering polysilicon especially in a flash memory is provided to perform a long over-etching process, reduce a micro loading, increase selectivity to silicon and prevent undercutting of a tungsten material. A method for plasma etching tungsten silicide over polysilicon(50) is performed to be particularly useful in fabricating a flash memory having both a densely packed area(46) and an open(iso) area(48) requiring a long over-etching due to micro loading. Wafer biasing is decreased in the over etch. The principal etchant includes NF3 and Cl2. Argon is added to prevent undercutting at the dense/iso interface. To increase etch selectivity and straightens the etch profile, oxygen and nitrogen oxidize any exposed silicon.