Self-aligned contact air gap formation

A device comprising:

• a source/drain feature disposed on a substrate, the source/drain feature including a silicide feature;
• a gate stack disposed on the substrate and associated with the source/drain feature, the gate stack extending to a first height above the substrate;
• an etch stop layer disposed on the gate stack and extending to the source/drain feature such that the etch stop layer interfaces with the source/drain feature;
• a first interlayer dielectric layer disposed over the substrate;
• a contact feature extending through the first interlayer dielectric layer to the silicide feature;
• a nitride layer disposed directly on and extending along a sidewall of the contact feature;
• and
• an air gap disposed between the gate stack and the contact feature, the air gap extending to a second height above the substrate that is greater than the first height of the gate stack, and wherein the etch stop layer, the nitride layer and the first interlayer dielectric layer are exposed to the air gap, wherein the etch stop layer is disposed between the source/drain feature and the air gap thereby preventing the source/drain feature from being exposed to the air gap.

An integrated circuit (IC) device, comprising:

• a substrate;
• a source/drain (S/D) feature disposed on the substrate;
• a contact plug disposed over the S/D feature and electrically coupled to the S/D feature;
• a gate stack disposed on the substrate adjacent to the contact plug;
• an air gap disposed between the contact plug and the gate stack;
• and
• a seal layer covering the air gap, and
• wherein an interface between the seal layer and the air gap is higher than a top surface of the gate stack, wherein the S/D feature is exposed to the air gap, and wherein the gate stack includes a gate electrode layer and a spacer that interfaces with the gate electrode layer, wherein both the spacer and an upper portion of the gate electrode layer are exposed to the air gap.