Method of manufacturing a semiconductor device

A method of manufacturing a semiconductor device, comprising:

• forming a precursor structure comprising:
• a substrate having a top surface, a bottom surface, and a via hole penetrating the substrate;
• a liner on a sidewall of the via hole, the top surface and the bottom surface of the substrate;
• a conductor in the via hole;
• a seed layer between the liner and the conductor;
• a first insulating layer and a second insulating layer respectively on the top surface and the bottom surface of the substrate, wherein the first insulating layer and the second insulating layer respectively have a first hole and a second hole exposing the conductor;
• and
• a first redistribution layer and a second redistribution layer respectively in contact with the conductor through the first hole and the second hole;
• forming a first opening and a second opening respectively in the first insulating layer and the second insulating layer to expose a portion of the liner;
• etching the liner through the first opening and the second opening to form an air gap surrounding the conductor;
• and
• filling the first opening and the second opening to seal the air gap.