Structure and formation method of semiconductor device with metal gate stack

A semiconductor device structure, comprising:

• a stack of first channel structures and a stack of second channel structures over a substrate;
• a first metal gate stack wrapped around the first channel structures, wherein the first metal gate stack has a first width;
• and
• a second metal gate stack wrapped around the second channel structures, wherein the second gate stack has a protruding portion extending away from the second channel structures, the protruding portion of the second metal gate stack has a second width, and half of the first width is greater than the second width.

A method for forming a semiconductor device structure, comprising:

• respectively forming a first dummy gate stack and a second dummy gate stack over a first channel structure and a second channel structure, wherein the second dummy gate stack is wider than the first dummy gate stack;
• forming a dielectric layer to surround the first dummy gate stack and the second dummy gate stack;
• removing the first dummy gate stack and the second dummy gate stack to form a first trench and a second trench;
• forming metal gate stack layers with a first portion in the first trench and a second portion in the second trench;
• trimming the second portion of the metal gate stack layers in the second trench;
• and
• forming a protective structure over the second portion after the second portion is thinned.