Vertical gate-all-around device

A method, comprising:

• forming a vertically protruding structure, the vertically protruding structure including a substrate, a first silicon germanium layer disposed over the substrate, a silicon layer disposed over the first silicon germanium layer, and a second silicon germanium layer disposed over the silicon layer;
• forming a first dielectric spacer below the silicon layer and a second dielectric spacer above the silicon layer at least in part by removing a portion of the first silicon germanium layer and removing a portion of the second silicon germanium layer and depositing a dielectric material in place of the removed first silicon germanium layer and the removed second silicon germanium layer;
• laterally trimming the silicon layer, thereby forming a laterally-facing recess that exposes a side surface of the silicon layer;
• and
• forming, after the silicon layer has been laterally trimmed, a gate structure laterally adjacent to the silicon layer, wherein the gate structure includes a gate dielectric and a gate electrode that is surrounded by the gate dielectric in 360 degrees in a cross-sectional side view.

A method, comprising:

• forming a vertically protruding structure, the vertically protruding structure including a substrate, a first semiconductor layer disposed over the substrate, a channel layer disposed over the first semiconductor layer, and a second semiconductor layer disposed over the channel layer, wherein the first semiconductor layer and the second semiconductor layer each contain a first type of semiconductive material (e.g., SiGe), and wherein the channel layer contains a second type of semiconductive material (e.g., Si) different from the first type;
• forming first recesses in the first semiconductor layer and the second semiconductor layer, wherein each of the first recesses protrudes laterally inward;
• filling the first recesses with dielectric spacers;
• laterally trimming the channel layer and the substrate, wherein remaining portions of the channel layer and the dielectric spacers define second recesses that protrude laterally inward;
• and
• forming gate structures in the second recesses.