Fin field-effect transistor and method of forming the same

A method, comprising:

• forming a semiconductor fin over a substrate;
• forming a dielectric fin over the substrate and adjacent the semiconductor fin;
• forming an isolation structure to separate the semiconductor fin from the dielectric fin;
• forming a dummy gate structure over the semiconductor fin and the dielectric fin, including implementing a first etching process using a first etchant and subsequently implementing a second etching process using a second etchant, the first etchant being different from the second etchant in composition;
• forming source/drain features adjacent the dummy gate structure;
• and
• replacing the dummy gate structure with a metal gate structure that is interposed between the source/drain features.

A semiconductor structure, comprising:

• a first semiconductor fin extending from a substrate;
• a second semiconductor fin extending from the substrate and elongated parallel to the first semiconductor fin;
• a dielectric fin extending from the substrate and interposed between the first semiconductor fin and the second semiconductor fin;
• isolation regions surrounding the first semiconductor fin, the dielectric fin, and the second semiconductor fin;
• source/drain features over the each of the first semiconductor fin and the second semiconductor fin;
• and
• a metal gate structure interposed between the source/drain features to engage with the first semiconductor fin, the second semiconductor fin, and the dielectric fin, wherein a first portion of the metal gate structure disposed between the first semiconductor fin and the dielectric fin has a first gate length along a bottom surface of the metal gate structure and a second portion of the metal gate structure disposed between the second semiconductor fin and the dielectric fin has a second gate length along the bottom surface of the metal gate structure, the second gate length being less than the first gate length.