Bottom self-aligned via

A method for an interconnect structure including: forming a hard mask layer on a semiconductor substrate having a wiring line; patterning the hard mask layer to form a patterned hard mask layer having a hard mask layer opening; depositing a dielectric stack on the patterned hard mask layer and in the hard mask layer opening; patterning the dielectric stack to form a via opening aligned with the hard mask layer opening and to expose the wiring line through the via opening and the hard mask layer opening, a bottom of the via opening defined by the hard mask layer having the hard mask layer opening; and filling the via opening and the hard mask layer opening with a metal to form a via in contact with the wiring line.