Hardmask structure and method of forming semiconductor structure

A method of forming a semiconductor structure, comprising:

• forming a conductive layer on a substrate;
• forming a first ashable hardmask on the conductive layer, wherein a stress of the first ashable hardmask is from −100 MPa to 100 MPa;
• forming a first dielectric antireflective coating on the first ashable hardmask;
• forming a second ashable hardmask on the first dielectric antireflective coating;
• etching the first ashable hardmask, the first dielectric antireflective coating, and the second ashable hardmask to transfer a first pattern to at least the first ashable hardmask;
• etching the conductive layer according to the first ashable hardmask to form a patterned conductive layer;
• forming a porous dielectric layer on the conductive layer;
• and
• etching the porous dielectric layer using the first ashable hardmask having the first pattern as a mask.