Semiconductor device with air gap on gate structure and method for forming the same

A semiconductor device structure, comprising:

• a fin structure over a semiconductor substrate;
• a source/drain feature formed in the fin structure;
• a first gate structure and a second gate structure across the fin structure and on both sides of the source/drain feature, wherein each of the first gate structure and the second gate structure comprises:
• a gate electrode layer formed over the fin structure;
• and
• a conductive capping layer covering the gate electrode layer;
• an insulating cap structure formed over the conductive capping layer of the first gate structure;
• and
• a conductive via structure formed over the conductive capping layer of the second gate structure,
• wherein a lower surface of the insulating cap structure is higher than a lower surface of the conductive via structure, and an upper surface of the insulating cap structure is substantially level with an upper surface of the conductive via structure.

A method for forming a semiconductor device structure, comprising:

• forming two neighboring gate spacers over a semiconductor substrate;
• forming a gate stack between the gate spacers, wherein the gate stack comprises:
• a gate electrode layer;
• and
• a conductive capping layer formed over the gate electrode layer;
• covering the gate stack with a sacrificial layer, wherein upper surfaces of the gate spacers protrude above an upper surface of the sacrificial layer;
• successively forming a first insulating layer and a second insulating layer to cover the upper surfaces of the gate spacers and the upper surface of the sacrificial layer;
• removing portions of the first insulating layer and the second insulating layer to expose the upper surfaces of the gate spacers;
• and
• removing the sacrificial layer after the upper surfaces of the gate spacers are exposed, so that a lower surface of the first insulating layer faces and is separated from an upper surface of the gate stack.