Semiconductor device

A semiconductor device, comprising:

• a first gate structure and a second gate structure extending along a first direction on a substrate;
• a first contact plug extending along the first direction adjacent to one side of the first gate structure;
• a second contact plug extending along the first direction adjacent to another side of the second gate structure;
• and
• a dummy contact plug extending along the first direction between the first gate structure and the second gate structure, wherein
• at least one of the first gate structure and the second gate structure comprises a metal gate, the metal gate comprising a gate dielectric layer, a high-k dielectric layer on the gate dielectric layer, and a work function metal (WFM) layer on the high-k dielectric layer,
• the gate dielectric layer comprises a first thickness at a first end of the metal gate and a second thickness at a second end of the metal gate, the first thickness is less than the second thickness to form a step profile,
• the high-k dielectric layer is conformal to the step profile,
• the WFM layer comprises a third thickness at the first end of the metal gate and a fourth thickness at the second end of the metal gate, the third thickness is greater than the fourth thickness.