Depth of focus (DOF) for trench-first-via-last (TFVL) damascene processing with hard mask and low viscosity photoresist

A method is provided, the method comprising forming a dielectric layer above a structure layer, forming a hard mask layer above the dielectric layer, and forming at least one trench opening and at least one upper portion of a first via opening in the dielectric layer through the hard mask layer. The method also comprises forming a low viscosity photoresist layer above the at least one trench opening and the at least one upper portion of the first via opening in the dielectric layer.