Multi-gate devices with multi-layer inner spacers and fabrication methods thereof

A method of manufacturing a semiconductor device, comprising:

• forming a stack of a first type and a second type epitaxial layers on a semiconductor substrate, the first type and second type epitaxial layers having different material compositions and the first type and second type epitaxial layers being alternatingly disposed in a vertical direction;
• patterning the stack to form a fin structure;
• forming a sacrificial gate structure over the fin structure;
• removing at least the first type epitaxial layers from a source/drain (S/D) region of the fin structure, which is not covered by the sacrificial gate structure;
• forming a first insulating layer on lateral ends of the first type epitaxial layers, wherein the first insulating layer includes carbon-containing compound;
• forming a second insulating layer on the first insulating layer, wherein the second insulating layer includes oxide-containing compound;
• after the second insulating layer is formed, forming an S/D epitaxial feature in contact with lateral ends of the second type epitaxial layers;
• forming an S/D contact over the S/D epitaxial feature;
• and
• forming a multilayer interconnection over the S/D contact, wherein the first and second insulating layers interpose the S/D epitaxial feature and the first type epitaxial layers, and
• wherein the second insulating layer separates the first insulating layer from physically contacting the S/D epitaxial layer.

A method, comprising:

• forming a stack of a first type and a second type epitaxial layers on a semiconductor substrate, the first type and second type epitaxial layers having different material compositions and the first type and second type epitaxial layers being alternatingly disposed in a vertical direction;
• patterning the stack to form a fin-shape structure;
• forming a sacrificial gate structure over the fin-shape structure;
• etching the fin-shape structure in a region adjacent to the sacrificial gate structure to form a recess;
• laterally etching the first type epitaxial layers from the recess;
• depositing a first insulating layer on lateral ends of the first type epitaxial layers;
• depositing a second insulating layer on the first insulating layer, wherein material compositions of the first and second insulating layers are different;
• depositing a third insulating layer on the second insulating layer, wherein material compositions of the second and third insulating layers are different, and wherein the first and third insulating layers have a same material composition;
• forming an epitaxial feature in the recess and in contact with lateral ends of the second type epitaxial layers, wherein the first, second, and third insulating layers interpose the epitaxial feature and the first type epitaxial layers;
• completely removing the first type epitaxial layers to release the second type epitaxial layers;
• and
• replacing the sacrificial gate structure with a metal gate structure.