Methods for producing nanowire stack GAA device with inner spacer

A method of forming a semiconductor device comprising:

• forming a fin structure extending from a substrate, the fin structure comprising alternating layers of first semiconductor layers and second semiconductor layers, the first semiconductor layers being formed of a first material, the second semiconductor layers being formed of a second material;
• forming a sacrificial gate structure over the fin structure;
• forming an outer spacer along a sidewall of the sacrificial gate structure;
• forming a dielectric layer over the fin structure adjacent the outer spacer;
• forming a first opening in the dielectric layer, wherein the fin structure is exposed in the first opening;
• removing first portions the first semiconductor layers exposed in the first opening, second portions of the first semiconductor layers under the sacrificial gate structure remaining, wherein a sidewall of the second portions of the first semiconductor layers are concave;
• forming an inner spacer layer in the first opening, the inner spacer layer extending along the sidewall of the second portions of the first semiconductor layers, along sidewalls of the outer spacer, and over the second semiconductor layers in the first opening;
• removing the inner spacer layer from surfaces of the second semiconductor layer in the first opening, thereby forming inner spacers, each of the inner spacers adjacent to a corresponding one of the second portions of the first semiconductor layers;
• epitaxially growing a source/drain region in the first opening, the source/drain region contacting the second semiconductor layers;
• removing the sacrificial gate structure to form a second opening;
• removing the second portions of the first semiconductor layers in the second opening;
• and
• forming a gate structure in the second opening, wherein at least a portion of the gate structure extends over the inner spacers, wherein an interface between the gate structure and each of the inner spacers is non-planar.