| CPC H10D 64/679 (2025.01) [H01L 21/02068 (2013.01); H01L 21/302 (2013.01); H01L 21/311 (2013.01); H10D 30/0225 (2025.01); H10D 62/115 (2025.01); H10D 64/015 (2025.01); H10D 64/256 (2025.01); H10D 64/671 (2025.01); H10D 30/797 (2025.01); H10D 62/822 (2025.01)] | 20 Claims |

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1. A semiconductor device, comprising:
two source/drain (S/D) regions over a substrate;
a gate stack over the substrate and between the two S/D regions, the gate stack having a gate dielectric layer and a gate electrode layer over the gate dielectric layer;
a spacer layer covering sidewalls of the gate stack;
an S/D contact metal over one of the two S/D regions;
a first dielectric layer covering sidewalls of the S/D contact metal and an upper surface of the two S/D regions; and
a second dielectric layer covering the first dielectric layer, the spacer layer, and the gate stack, and defining an air gap, wherein an extent of a first sidewall of the air gap from a bottommost point to an uppermost point is a sidewall of the first dielectric layer, a second sidewall of the air gap is a sidewall of the spacer layer, a top surface of the air gap defines the uppermost point and is a bottom surface of the second dielectric layer, wherein a material of the first sidewall of the air gap is different from material of the top surface of the air gap, and a material of the second sidewall of the air gap is different from the material of the top surface of the air gap, wherein a top surface of the first dielectric layer and a top surface of the gate electrode layer are coplanar, and a top surface of the S/D contact metal is above the top surface of the gate electrode layer and the top surface of the first dielectric layer.
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