Source/drains in semiconductor devices and methods of forming thereof

Abstract

A method includes forming a gate structure over a silicon on insulator (SOI) substrate. The SOI substrate comprising: a base semiconductor layer; an insulator layer over the base semiconductor layer; and a top semiconductor layer over the insulator layer. The method further includes depositing a gate spacer layer over a top surface and along a sidewall of the gate structure; etching the gate spacer layer to define a gate spacer on the sidewall of the gate structure; after etching the gate spacer layer, etching a recess into the top semiconductor layer using a first etch process; and after the first etch process, extending the recess further into the top semiconductor layer using a second etch process. The first etch process is different from the second etch process. The method further includes forming a source/drain region in the recess after the second etch process.