Air gap with inverted t-shaped lower portion extending through at least one metal layer, and related method

A radio frequency semiconductor-on-insulator (RFSOI) switch, comprising:

• a transistor gate in a semiconductor-on-insulator (SOI) device layer of an SOI substrate, the transistor gate includes a silicide layer over a gate body;
• at least one metal layer over the SOI device layer, the at least one metal layer including a dielectric with a conductor therein;
• and
• an air gap extending through the dielectric of the at least one metal layer, wherein a lower portion of the air gap contacts the silicide layer over the gate body and has an inverted T-shape over the gate body.

A method, comprising:

• forming an opening through a dielectric of at least one metal layer over a transistor gate, the opening exposing an etch stop layer (ESL) over a silicide layer over a gate body of the transistor gate;
• enlarging the opening over the transistor gate to remove the ESL and expose the silicide layer over the transistor gate, the enlarging of the opening undercutting the dielectric over the transistor gate;
• and
• forming an air gap by forming a dielectric layer over the opening to seal the opening, wherein a lower portion of the air gap contacts the silicide layer over the gate body and has an inverted T-shape over the gate body.