Structure and method for multigate devices with suppressed diffusion

Abstract

A method includes forming a fin that includes a first semiconductor layers and a second semiconductor layers alternatively disposed; forming a gate stack on the fin and a gate spacer disposed on a sidewall of the gate stack; etching the fin within a source/drain region, resulting in a source/drain trench; recessing the first semiconductor layers in the source/drain trench, resulting in first recesses underlying the gate spacer; forming inner spacers in the first recesses; recessing the second semiconductor layers in the source/drain trench, resulting in second recesses; and epitaxially growing a source/drain feature in the source/drain trench, wherein the epitaxially growing further includes a first epitaxial semiconductor layer extending into the second recesses; and a second epitaxial semiconductor layer on the first epitaxial semiconductor layer and filling in the source/drain trench, wherein the first and second epitaxial semiconductor layers are different in composition.