US Patent 11171040 Removing polymer through treatment

A method includes depositing a mask layer over a dielectric layer, patterning the mask layer to form a trench, applying a patterned photo resist having a portion over the mask layer, and etching the dielectric layer using the patterned photo resist as an etching mask to form a via opening, which is in a top portion of the dielectric layer. The method further includes removing the patterned photo resist, and etching the dielectric layer to form a trench and a via opening underlying and connected to the trench. The dielectric layer is etched using the mask layer as an additional etching mask. A polymer formed in at least one of the trench and the via opening is removed using nitrogen and argon as a process gas. The trench and the via opening are filled to form a metal line and a via, respectively.