Patent ID: 7754610

Claim:
A method of etching a tungsten-containing layer overlying a silicon layer, comprising the steps of: placing onto an electrode in a plasma reaction chamber a substrate containing the tungsten-containing layer and an etching mask overlying the tungsten-containing layer, wherein the silicon layer consists principally of silicon; a first step of flowing into the chamber a first gas mixture comprising an etching gas comprising NF 3 and Cl 2 and an oxidizing gas comprising oxygen gas and nitrogen gas; biasing the electrode with a first level of RF power; applying a second level of RF power to excite the first gas mixture into a first plasma to thereby etch at least the tungsten-containing layer sufficiently that at least some of the silicon layer is exposed; a subsequent second step of flowing into the chamber a second gas mixture comprising the etching gas having a smaller fraction of NF 3 than in the first step and the oxidizing gas having a larger fraction of nitrogen gas than in the first step; biasing the electrode with a third level of RF power greater than the first level; and applying a fourth level of RF power to excite the second gas mixture into a second plasma to thereby etch possibly remaining portions of the tungsten-containing layer remaining before the second gas mixture had been excited into the second plasma.