Isotropic silicon etch process that is highly selective to tungsten

摘要

A back end of the line dry etch method is disclosed. Etching of a mask oxide and temporary (sacrificial) silicon mandrel occurs following the formation of gate stacks and tungsten studs. The mask oxide is etched selectively to tungsten and silicon through the use of a polymerizing oxide etch. The silicon is etched selectively to both silicon nitride, silicon oxide, and tungsten. The process removes the silicon mandrel and associated silicon residual stringers by removing backside helium cooling, while using HBr as the single species etchant, and by adjusting the duration, the pressure, and the electrode gaps during the silicon etch process. The silicon may be undoped polysilicon, doped polysilicon, or single crystal silicon.