Semiconductor device and manufacturing method thereof

Abstract

A method includes forming a plurality of first semiconductor layers and a plurality of second semiconductor layers in an alternate manner over a substrate; patterning the first and second semiconductor layers and the substrate to form a fin structure, in which the fin structure includes a base portion protruding from the substrate and remaining portions of the first and second semiconductor layers; etching the fin structure to form a first recess extending through the remaining portions of the first and second semiconductor layers and into the base portion; epitaxially growing a first epitaxy layer in the first recess; epitaxially growing a second epitaxy layer over the first epitaxy layer; oxidizing the first epitaxy layer, wherein the second epitaxy layer remains unoxidized after the first epitaxy layer is oxidized; and after oxidizing the first epitaxy layer, forming a source/drain epitaxy structure on the second epitaxy layer.