US Patent 11855178 Semiconductor devices having air-gap

A semiconductor device is provided. The semiconductor device includes a fin protruding from a semiconductor substrate and a gate structure formed across the fin. The semiconductor device also includes a gate spacer formed over a sidewall of the gate structure. The gate spacer includes a sidewall spacer and a sealing spacer formed above the sidewall spacer. In addition, an air gap is vertically sandwiched between the sidewall spacer and the sealing spacer. The semiconductor device further includes a hard mask formed over the gate structure and covering a sidewall of the sealing spacer.