Semiconductor structure and method for forming the same

A method for forming a semiconductor structure, comprising:

• forming a first FET device and a second FET device over a substrate;
• forming a first gate trench in the first FET device and a second gate trench in the second FET device;
• forming a first high-k dielectric layer in the first gate trench and a second high-k dielectric layer in the second gate trench;
• forming a first work function metal layer in the first gate trench and a second work function metal layer in the second gate trench;
• removing a portion of the first work function metal layer from the first gate trench;
• forming a first intervening metal layer in the first gate trench and a second intervening metal layer in the second gate trench;
• and
• filling the first gate trench with a first gap-filling metal layer and filling the second gate trench with a second gap-filling metal layer,
• wherein the first intervening metal layer is in contact with the first high-k dielectric layer, and the second intervening metal layer is separated from the second work function metal layer and the second high-k dielectric layer.

A method for forming a semiconductor structure, comprising:

• forming a first FET device and a second FET device over a substrate;
• forming a first gate trench in the first FET device and a second gate trench in the second FET device;
• forming a first high-k dielectric layer in the first gate trench and a second high-k dielectric layer in the second gate trench;
• forming a first metal layer in the first gate trench and a second metal layer in the second gate trench, wherein a thickness of the first metal layer is less than a thickness of the second metal layer;
• forming a third metal layer over the first metal layer and a fourth metal layer over the second metal layer, wherein a thickness of the third metal layer is equal to a thickness of the fourth metal layer;
• removing a portion of the first metal layer and a portion of the third metal layer from the first gate trench and removing a portion of the second metal layer and a portion of the fourth metal layer from the second gate trench;
• forming a first intervening metal layer in the first gate trench and a second intervening metal layer in the second gate trench, wherein the second intervening metal layer is in contact with a topmost portion of the second metal layer and a topmost portion of the fourth metal layer;
• and
• filling the first gate trench with a first gap-filling metal layer and filling the second gate trench with a second gap-filling metal layer,
• wherein a width of a top surface of the first gap-filing metal layer is greater than a width of a top surface of the second gap-filling metal layer.