Patent ID: 7067435

Claim:
A method for etching an etch-stop located over a substrate, comprising: conducting a first etch through a dielectric layer located over an etch-stop layer, the dielectric layer having a photoresist layer located thereover and the first etch being selective to the etch-stop; and conducting a second etch different from the first etch on the etch-stop, the second etch comprising a mixture of gases wherein an etching gas comprises tetrafluoromethane and an etch rate modulator includes a mixture of argon, oxygen and nitrogen and wherein the ratio of a flow rate of tetrafluoromethane to a flow rate of the oxygen is about 3:1, the ratio of the flow rate of tetrafluoromethane to a flow rate of argon is about 3:70, the ratio of the flow rate of tetrafluoromethane to a flow rate of nitrogen is about 3:20, and the weighted average ratio of nitrogen to carbon is greater than about 10:1.