Semiconductor device structure with metal gate stacks

A semiconductor device structure, comprising:

• a substrate;
• a first metal gate stack and a second metal gate stack over the substrate;
• a gate spacer extending along a sidewall of the first metal gate stack;
• a dielectric layer surrounding the first metal gate stack and the gate spacer;
• and
• an insulating structure over the substrate, wherein:
• the insulating structure separating the first metal gate stack from the second metal gate stack, and
• the insulating structure extends towards the dielectric layer to surpass an edge of the gate spacer.

A semiconductor device structure, comprising:

• a substrate;
• a first metal gate stack over the substrate, wherein the first metal stack has a first concave sidewall;
• and
• a second metal gate stack over the substrate, wherein the second metal gate stack has a second concave sidewall facing the first concave sidewall of the first metal gate stack.