Semiconductor device structure with nanostructure 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 gate stack wrapping around the fin and the nanostructure;
• a first source/drain structure and a second source/drain structure over the fin, wherein the gate stack is between the first source/drain structure and the second source/drain structure;
• an inner spacer layer covering a sidewall of the first source/drain structure and partially between the gate stack and the first source/drain structure, wherein the inner spacer layer surrounds the nanostructure between the gate stack and the first source/drain structure;
• and
• a dielectric structure over the gate stack, wherein the dielectric structure has an extension portion extending toward the first source/drain structure, and the inner spacer layer surrounds the extension portion.

A method for forming a semiconductor device structure, comprising:

• providing a substrate, a first nanostructure, a second nanostructure, an inner spacer layer, a first source/drain structure, a second source/drain structure, a dielectric layer, and a gate stack, wherein the first nanostructure is between the second nanostructure and the substrate, the gate stack surrounds the first nanostructure and the second nanostructure, the gate stack is between the first source/drain structure and the second source/drain structure, the inner spacer layer is between the gate stack and the first source/drain structure, and the dielectric layer is over the first source/drain structure and the second source/drain structure;
• removing a first portion of the gate stack over the second nanostructure to form a trench in the dielectric layer;
• removing a second portion of the second nanostructure under the trench;
• removing a third portion of the second nanostructure over the inner spacer layer through the trench;
• and
• forming a dielectric structure in the trench.