Patent ID: 8647991

Claim:
A method for forming a dual damascene opening, the method comprising steps of: forming a first hard mask layer with a trench pattern over a material layer; forming a dielectric layer over the first hard mask layer and filling the dielectric layer into an opening of the trench pattern; forming a second hard mask layer with a first via opening pattern over the first hard mask layer and the dielectric layer, so as to make the second hard mask layer at least partially overlapped with the first hard mask layer; performing a first etching process with an etchant containing a fluorocarbon compound (C x F y ) by using the second hard mask layer as an etching mask, so that a via opening is at least formed in the dielectric layer, wherein the second hard mask layer has an etching rate by the etchant lower than that of the dielectric layer; removing the second hard mask layer by a chlorine (Cl 2 ) plasma etching process, wherein the second hard mask layer has an etching rate in the Cl 2 plasma etching process greater than that of the dielectric layer; and performing a second etching process by using the first hard mask layer as an etching mask, so that a trench opening is formed in the material layer and the via opening is further extended into the material layer, wherein the via opening is located within the trench opening.