Semiconductor device structure and method for forming the same

A semiconductor device structure, comprising:

• a substrate having a base and a fin over the base;
• a nanostructure over the fin;
• a metal gate stack wrapped around the nanostructure and the fin, wherein the metal gate stack comprises a gate dielectric layer, a work function layer, and a gate electrode layer sequentially stacked over the nanostructure and the fin;
• and
• a cap layer over the metal gate stack, wherein the work function layer is closer to the cap layer than the gate dielectric layer.

A method for forming a semiconductor device structure, comprising:

• forming a gate stack over a substrate;
• forming a spacer over a first sidewall of the gate stack;
• forming a dielectric layer over the substrate;
• removing the gate stack, wherein a trench is formed in the spacer after removing the gate stack;
• forming a metal gate stack in the trench, wherein the metal gate stack comprises a gate dielectric layer, a work function layer, and a gate electrode layer, and the gate electrode layer is over the work function layer;
• removing a top portion of the metal gate stack, wherein a recess is formed and is surrounded by the spacer and adjacent to the metal gate stack;
• and
• forming a cap layer in the recess, wherein the cap layer has a plurality of first layers, each first layer comprises boron, nitrogen, and carbon, and the cap layer interfaces with the work function layer.