Integrated circuit structure with backside interconnection structure having air gap

An integrated circuit (IC) structure, comprising:

• a transistor comprising a source/drain epitaxial structure;
• a front-side interconnection structure electrically connected to a front-side of the source/drain epitaxial structure of the transistor;
• a backside via electrically connected to a backside of the source/drain epitaxial structure of the transistor;
• and
• a backside interconnection structure comprises:
• a dielectric layer;
• and
• a power rail embedded in the dielectric layer and electrically connected to the backside via, wherein an air gap is between the dielectric layer and the power rail.

A method for manufacturing an integrated circuit (IC) structure comprising:

• forming a transistor comprising a dummy plug over a substrate;
• removing the substrate to expose the dummy plug;
• forming an isolation material to surround the dummy plug;
• replacing the dummy plug with a backside via;
• forming a dielectric layer over the backside via;
• forming an opening in the dielectric layer to expose the backside via;
• forming a dummy spacer at a sidewall of the opening of the dielectric layer;
• forming a conductive feature in the opening;
• and
• removing the dummy spacer to form an air gap between dielectric layer and the conductive feature.