forming a barrier layer over a substrate;

forming a first dielectric layer over the barrier layer;

forming a second dielectric layer over the first dielectric layer, wherein a dielectric constant of the first dielectric layer is higher than a dielectric constant of the second dielectric layer;

forming a mask layer over the second dielectric layer;

forming a first bottom anti-reflection coating layer over the mask layer;

forming a first photoresist layer over the first bottom anti-reflection coating layer;

patterning the first photoresist layer to obtain a patterned first photoresist layer;

etching the first bottom anti-reflection coating layer and a portion of the mask layer by using the patterned first photoresist layer as a mask to obtain a first trench structure, wherein the first trench structure exposes a surface of the mask layer;

removing the patterned first photoresist layer and the first bottom anti-reflection coating layer;

forming a second bottom anti-reflection coating layer to fill the first trench structure and to cover the surface of the mask layer;

forming a second photoresist layer over the second bottom anti-reflection coating layer;

patterning the second photoresist layer to obtain a patterned second photoresist layer;

etching the second bottom anti-reflection coating layer, the mask layer, the second dielectric layer and the first dielectric layer by using the patterned second photoresist layer as a mask to obtain a first via structure, wherein a bottom of the first via structure exposes a surface of the first dielectric layer;

removing the patterned second photoresist layer, the second bottom anti-reflection coating layer and a portion of the mask layer so as to expose a surface of a remaining hard mask; and

synchronously removing a portion of the second dielectric layer and a portion of the first dielectric layer so as to transform the first trench structure and the first via structure into a second trench structure and a second via structure, wherein a bottom of the second via structure exposes a surface of the substrate, and a bottom of the second trench structure exposes a surface of the first dielectric layer.