Process for creating an etch mask suitable for deep plasma etches

Abstract

A process, compatible with reduced-pitch masking technology, for creating a metal etch mask that will not erode in a halogenated-plasma etch environment. The process begins by creating an isolation layer (preferably of silicon dioxide) on top of the layer to be etched (typically a silicon substrate). A thin layer of a metal selected from a group consisting of cobalt, nickel, palladium, iron, and copper is then deposited on top of the isolation layer. A hard-material mask (preferably of silicon dioxide) is then created on top of the metal layer as though it were to be the final etch mask. A layer of polysilicon is then blanket deposited on the surface of the in-process wafer. The polysilicon layer must be sufficiently thick to entirely convert exposed regions of the underlying metal layer to silicide during a subsequent elevated temperature step. Only metal in regions not covered by the hard-material mask is converted to silicide. Unreacted polysilicon is then removed with a wet polysilicon etch, followed by the removal of the hard-material mask with a wet etch selective for silicon dioxide over the existent metal silicide, followed by removal of the metal silicide with a wet etch selective for silicide over silicon dioxide to avoid undercutting the oxide isolation layer beneath the metal layer remnants. The metal layer remnants constitute a metal mask which precisely duplicates the pattern of the hard-material mask.