Sacrificial layer for channel surface retention and inner spacer formation in stacked-channel fets

A method for forming a field effect transistor, comprising:

• forming a stack of alternating layers of channel material and sacrificial material, with a layer of sacrificial material forming a top layer of the stack;
• forming an initial spacer on sidewalls of the dummy gate;
• selectively etching the sacrificial material to form recesses in the sacrificial material layers;
• etching away the initial spacer;
• forming crescent-shaped spacers in the recesses in the sacrificial material layers, with at least one pair of spacers being formed in recesses above an uppermost layer of channel material, each of the at least one pair of spacers extending vertically;
• forming merged source and drain regions at respective ends of the layers of channel material, said merged source and drain regions covering the spacers in the recesses in the sacrificial material layers;
• etching away the sacrificial material with an isotropic etch to expose the layers of channel material;
• and
• forming a gate stack over, around, and between the layers of channel material.