providing a substrate having a conductive layer, a first etching stop layer, a dielectric layer, and a first photoresist layer positioned on the surface of the substrate in order;

patterning the first photoresist layer so as to defined a via pattern on the first photoresist layer;

performing a first etching process to remove a portion of the dielectric layer through the via pattern, until the etching stop layer is exposed so as to form a via hole structure in the dielectric layer;

performing a first ash process to remove the first photoresist layer by providing a gas comprising carbon monoxide (CO-containing gas);

filling gap-fill polymer (GFP) materials into the via hole structure;

forming a second photoresist layer on the substrate;

patterning the second photoresist layer to define a trench pattern;

performing a second etching process to etch the dielectric layer though the trench pattern so as to form a trench structure on the upper portion of the dielectric layer, the trench structure exposing the via hole structure;

removing the second photoresist layer and the GFP materials in the via hole structure; and

removing the first etching stop layer exposed by the via hole structure.