Gate-all-around field-effect transistor device

A method of forming a semiconductor device, the method comprising:

• forming semiconductor strips protruding above a substrate;
• forming isolation regions between adjacent ones of the semiconductor strips;
• forming hybrid fins on the isolation regions, the hybrid fins comprising dielectric fins and dielectric structures over the dielectric fins;
• forming a dummy gate structure over the semiconductor strips and the hybrid fins;
• forming source/drain regions over the semiconductor strips and on opposing sides of the dummy gate structure;
• forming nanowires under the dummy gate structure, wherein the nanowires are over and aligned with respective semiconductor strips, and the source/drain regions are at opposing ends of the nanowires, wherein the hybrid fins extend further from the substrate than the nanowires;
• after forming the nanowires, reducing widths of center portions of the hybrid fins while keeping widths of end portions of the hybrid fins unchanged, wherein the center portions of the hybrid fins are under the dummy gate structure, and the end portions of the hybrid fins are beyond boundaries of the dummy gate structure;
• and
• forming an electrically conductive material around the nanowires.

A semiconductor device comprising:

• a semiconductor strip protruding above a substrate;
• a first isolation region and a second isolation region on opposing sides of the semiconductor strip;
• nanowires over and aligned with the semiconductor strip;
• source/drain regions at opposing ends of the nanowires;
• a first dielectric fin on the first isolation region;
• and
• a metal gate around the nanowires and around a center portion of the first dielectric fin, wherein the center portion of the first dielectric fin is disposed between a lower surface of the metal gate and the substrate, wherein the lower surface of the metal gate faces the substrate and physically contacts the center portion of the first dielectric fin, wherein end portions of the first dielectric fin are disposed on opposing sides of the metal gate, wherein the end portions of the first dielectric fin are wider than the center portion of the first dielectric fin.