Semiconductor device structure with contact structure and method for forming the same

A method for forming a semiconductor device structure, comprising:

• providing a substrate and a nanostructure stack, wherein the substrate has a base and a fin over the base, and the nanostructure stack is over the fin;
• forming a gate stack wrapped around the nanostructure stack;
• forming a source/drain structure in the nanostructure stack and adjacent to the gate stack;
• removing the gate stack, the nanostructure stack and the fin under the gate stack to form a trench passing through the nanostructure stack and the fin;
• forming a dielectric isolation structure in the trench;
• and
• forming a contact structure over the source/drain structure, wherein the contact structure has a wide strip portion and a narrow strip portion, and the wide strip portion is closer to the dielectric isolation structure than the narrow strip portion in a top view of the contact structure and the dielectric isolation structure.

A semiconductor device structure, comprising:

• a substrate having a base and a fin over the base;
• a nanostructure over the fin;
• a first source/drain structure passing through the nanostructure;
• a dielectric structure over the first source/drain structure and the base;
• a dielectric isolation structure passing through the dielectric structure, the nanostructure, and the fin;
• a gate stack wrapped around the nanostructure, wherein the first source/drain structure is between the dielectric isolation structure and the gate stack;
• and
• a first contact structure over the first source/drain structure, wherein the dielectric isolation structure is closer to the first contact structure than the gate stack.