US Patent 11171236 Cut-fin isolation regions and method forming same

A method includes forming a first semiconductor fin and a second semiconductor fin parallel to each other and protruding higher than top surfaces of isolation regions. The isolation regions include a portion between the first and the second semiconductor fins. The method further includes forming a gate stack crossing over the first and the second semiconductor fins, etching a portion of the gate stack to form an opening, wherein the portion of the isolation regions, the first semiconductor fin, and the second semiconductor fin are exposed to the opening, etching the first semiconductor fin, the second semiconductor fin, and the portion of the isolation regions to extend the opening into a bulk portion of a semiconductor substrate below the isolation regions, and filling the opening with a dielectric material to form a cut-fin isolation region.