Method for forming semiconductor structure

Abstract

A method includes forming top semiconductor channels for a top device over bottom semiconductor channels for a bottom device; forming a high-k gate dielectric layer wrapping around each of the top and the bottom semiconductor channels; forming a first gate metal over the high-k gate dielectric layer; etching back the first gate metal to expose top portions of the high-k gate dielectric layer while bottom portions of the high-k gate dielectric layer remain, wherein the etching back includes dry etching to etch the first gate metal and to generate a co-polymer byproduct that covers the exposed top portions of the high-k gate dielectric layer; and performing a post-cleaning process to remove the co-polymer byproduct, the post-cleaning process comprising a first wet cleaning to remove silicon oxide components of the co-polymer byproduct and a second wet cleaning to remove metal oxide components of the co-polymer byproduct.