Semiconductor device with a core-shell feature and method for forming the same

A device, comprising:

• a semiconductor substrate;
• a first stack of channel layers and a second stack of channel layers each vertically arranged above the semiconductor substrate and extending in parallel with each other;
• a dielectric fin between the first stack of channel layers and the second stack of channel layers;
• and
• a gate structure extending across a top surface of the first stack of channel layers, the second stack of channel layers, and the dielectric fin,
• wherein the dielectric fin includes a fin top having a bottom surface extending along or above a topmost channel layer, and
• wherein the fin top includes a first dielectric material surrounding a second dielectric material on at least four sides.

A semiconductor device, comprising:

• a substrate;
• a first plurality of channel layers vertically stacked and suspended above the substrate;
• a second plurality of channel layers vertically stacked and suspended above the substrate;
• an isolation structure disposed on the substrate and between the first plurality of channel layers and the second plurality of channel layers;
• and
• a dielectric fin disposed on the isolation structure and between the first plurality of channel layers and the second plurality of channel layers,
• wherein:
• the dielectric fin includes a fin bottom and a fin top,
• the fin bottom includes a first outer layer of a first dielectric constant and a first inner layer of a second dielectric constant that is smaller than the first dielectric constant, and
• the fin top includes a second outer layer of a third dielectric constant and a second inner layer of a fourth dielectric constant that is smaller than the third dielectric constant.