Anisotropic nitride etch process with high selectivity to oxide and photoresist layers in a damascene etch scheme

Abstract

A process and etchant gas composition for anisotropically etching a trench in a silicon nitride layer of a multilayer structure. The etchant gas composition has an etchant gas including a polymerizing agent, a hydrogen source, an oxidant, and a noble gas diluent. The oxidant preferably includes a carbon-containing oxidant component and an oxidant-noble gas component. The fluorocarbon gas is selected from CF , C F , and C F ; the hydrogen source is selected from CHF , CH F , CH F, and H ; the oxidant is selected from CO, CO , and O ; and the noble gas diluent is selected from He, Ar, and Ne. The constituents are added in amounts to achieve an etchant gas having a high nitride selectivity to silicon oxide and photoresist. A power source, such as an RF power source, is applied to the structure to control the directionality of the high density plasma formed by exciting the etchant gas. The power source that controls the directionality of the plasma is decoupled from the power source used to excite the etchant gas. The etchant gas can be used during a nitride etch step in a process for making a metal oxide semiconductor field effect transistor.