Dielectric inner spacers in multi-gate field-effect transistors

Abstract

A method includes forming a structure having a dummy gate stack over a fin protruding from a substrate. The fin includes an ML of alternating semiconductor layers and sacrificial layers. The method further includes forming a recess in an S/D region of the ML, forming a recess of the ML, and forming inner spacers on sidewalls of the sacrificial layers. Each inner spacer includes a first layer embedded in the sacrificial layer and a second layer over the first layer. The method further includes forming an S/D feature in the recess, such that the second layer of the inner spacers is embedded in the S/D feature. The method further includes removing the dummy gate stack to form a gate trench, removing the sacrificial layers from the ML, thereby forming openings interleaved between the semiconductor layers, and subsequently forming a high-k metal gate stack in the gate trench and the openings.