Semiconductor device structure with work function layer and method for forming the same

A semiconductor device structure, comprising:

• a substrate;
• a first fin structure and a second fin structure disposed over the substrate;
• a first gate stack disposed over the substrate and overlapping the first fin structure, wherein the first gate stack comprises a first gate dielectric layer, a first work function layer, a second work function layer, and a first gate electrode sequentially stacked over the first fin structure, and a first topmost surface of the second work function layer is higher than a second topmost surface of the first work function layer and is lower than a third topmost surface of the first gate dielectric layer;
• and
• a second gate stack disposed over the substrate and overlapping the second fin structure, wherein the second gate stack is wider than the first gate stack.

A semiconductor device structure, comprising:

• a substrate;
• a first fin structure and a second fin structure disposed over the substrate;
• a first gate stack disposed over the substrate and overlapping the first fin structure, wherein the first gate stack comprises a first gate dielectric layer, a first work function layer, a second work function layer, and a first gate electrode, and the second work function layer covers a first topmost surface of the first work function layer and exposes an upper portion of a sidewall of the first gate dielectric layer;
• and
• a second gate stack disposed over the substrate and overlapping the second fin structure, wherein the second gate stack comprises a second gate dielectric layer, a third work function layer, and a second gate electrode sequentially stacked over the second fin structure, and the second gate electrode is wider than the first gate electrode.