US Patent 10923565 Self-aligned contact air gap formation

In one example aspect, a method for integrated circuit (IC) fabrication comprises providing a device structure including a substrate, a source/drain (S/D) feature on the substrate, a gate stack on the substrate, a contact hole over the S/D feature; and a dummy feature over the S/D feature and between the gate stack and the contact hole. The method further comprises forming in the contact hole a contact plug that is electrically coupled to the S/D feature, and, after forming the contact plug, selectively removing the dummy feature to form an air gap that extends higher than a top surface of the gate stack. The method further comprises forming over the contact plug a seal layer that covers the air gap.