Semiconductor device having a contact plug with an air gap spacer

A semiconductor device comprising:

• a fin protruding from a substrate;
• a gate structure over a channel region of the fin;
• an epitaxial region in the fin adjacent the channel region;
• a first dielectric layer over the gate structure, the first dielectric layer comprising a first region that is doped with a first dopant;
• a contact plug extending through the first dielectric layer and contacting the epitaxial region;
• a second dielectric layer over the first dielectric layer;
• and
• an air gap between the contact plug and the gate structure, wherein an upper region of the air gap is bounded by the first region, and wherein the air gap is separated from the second dielectric layer by the first region.

A device comprising:

• a contact plug over a substrate;
• a spacer adjacent the contact plug, wherein the spacer is isolated from the contact plug by an air gap that extends between a sidewall of the contact plug and a sidewall of the spacer;
• an insulating layer covering the air gap and the spacer, wherein the insulating layer extends along the sidewall of the contact plug, wherein the insulating layer comprises a doped region, wherein a top surface of the insulating layer and a top surface of the contact plug are level;
• and
• a capping layer over the contact plug and the insulating layer, wherein a bottom surface of the capping layer is below the top surface of the insulating layer.