Air gap formation between gate spacer and epitaxy structure

A semiconductor device, comprising:

• a gate structure extending across a semiconductor fin;
• source/drain epitaxial regions on the semiconductor fin and spaced apart from the gate structure at least by air-containing regions;
• and
• a dielectric structure between a first one of the source/drain epitaxial regions and a first one of the air-containing regions, the dielectric structure having a gradient density.

A semiconductor device, comprising:

• an n-type transistor comprising a first gate structure and n-type source/drain regions on opposite sides of the first gate structure, the first gate structure being spaced apart from the n-type source/drain regions at least by first air-containing regions;
• and
• a p-type transistor comprising a second gate structure and p-type source/drain regions on opposite sides of the second gate structure, the second gate structure being spaced apart from the p-type source/drain regions at least by second air-containing regions,
• wherein the n-type source/drain regions have inner surfaces facing the first air-containing regions, and the p-type source/drain regions have inner surfaces facing the second air-containing regions, and the inner surfaces of the n-type source/drain regions are rougher than the inner surfaces of the p-type source/drain regions.