Semiconductor device with air gaps between metal gates and method of forming the same

A semiconductor device comprising:

• a first semiconductor fin and a second semiconductor fin extending from a substrate;
• a gate stack formed over the first semiconductor fin and the second semiconductor fin;
• a separation feature cutting into the gate stack and separating the gate stack into a first portion over the first semiconductor fin and a second portion over the second semiconductor fin, wherein the separation feature includes a protection layer and a filling layer defining an air gap therebetween;
• and
• a sealing layer disposed over the protection layer and the filling layer and covering an opening of the air gap.

A device comprising:

• a first fin and a second fin disposed on a substrate;
• an dielectric isolation structure extending from the first fin to the second fin;
• a first gate stack disposed over the first fin and a second gate stack disposed over the second fin;
• a separation feature extending into the dielectric isolation structure between the first and second gate stacks such that the separation feature interfaces with the first and second gate stacks, wherein the separation feature includes a protection layer and a filling layer defining an air gap therebetween;
• and
• a sealing layer disposed on a interfacing with at least one the protection layer and the filling layer.