Fin field effect transistor (finFET) device structure and method for forming the same

A method for forming a fin field effect transistor (FinFET) device structure, comprising:

• forming a fin structure over a substrate;
• forming a polysilicon layer over a first portion of the fin structure;
• forming a dummy gate structure over a second portion of the fin structure;
• removing the polysilicon layer to expose a top surface and a sidewall of the fin structure;
• epitaxially growing a source/drain (S/D) structure over the first portion of the fin structure, wherein the S/D structure has an inner surface in contact with the top surface and the sidewall of the fin structure and an outer surface surrounding the inner surface;
• and
• replacing the dummy gate structure with a gate structure.

A method for forming a fin field effect transistor (FinFET) device structure, comprising:

• forming a fin structure over a substrate;
• forming a polysilicon layer over the fin structure, wherein the polysilicon layer has a plurality of segments;
• forming an opening between two adjacent segments of the polysilicon layer to expose the fin structure;
• forming a dummy gate structure in the opening;
• removing the polysilicon layer to expose a top surface and a sidewall of the fin structure;
• epitaxially growing a source/drain (S/D) structure surrounding the top surface and the sidewall of the fin structure;
• and
• replacing the dummy gate structure with a gate structure.