Methods of forming interconnect structures of semiconductor device

An interconnect structure, comprising:

• a first dielectric layer;
• an etching stop layer on the first dielectric layer;
• a second dielectric layer on the etching stop layer;
• an insert layer between the etching stop layer and the second dielectric layer;
• and
• a conductive feature in the second dielectric layer, the insert layer, the etching stop layer, and the first dielectric layer,
• wherein a material of the insert layer is different from the first dielectric layer, the second dielectric layer, and the etching stop layer.

A method of forming an interconnect structure, comprising:

• forming an etching stop layer;
• forming an insert layer on the etching stop layer;
• forming a dielectric layer on the insert layer;
• patterning the dielectric layer, the insert layer and the etching stop layer to form a plurality of trench openings, comprising:
• performing a first etching process on the dielectric layer and the insert layer to form a plurality of first openings exposing the etching stop layer;
• and
• performing a second etching process to remove the etching stop layer exposed by the first openings to form the plurality of trench openings;
• and
• forming a plurality of conductive lines in the plurality of trench openings.