Patent ID: 6875699

Claim:
A method of forming a damascene structure above a substrate, comprising the steps of: forming a low-k dielectric layer over the substrate, wherein the low-k dielectric layer does not have an intermediate trench etch stop layer; etching a plurality of vias through the low-k dielectric layer; forming via plugs in the plurality of vias; forming a poison free trench pattern, etching a plurality of trenches into the low-k dielectric layer, wherein the etching removes fences caused by the via plugs, wherein the etching the plurality of trenches, comprises: etching with a first etchant gas which comprises a polymerized mixture to form fence formations around the via plugs; and etching with a second etchant gas subsequent to etching with the first etchant gas, wherein the second etchant gas comprises a lower polymerizing mixture, which etches away the fence formations; and stripping the via plugs.