Methods of forming different gate structures in nmos and pmos regions and gate structures so formed

Abstract

A method of forming transistor gate structures in an integrated circuit device can include forming a high-k gate insulating layer on a substrate including a first region to include PMOS transistors and a second region to include NMOS transistors. A polysilicon gate layer can be formed on the high-k gate insulating layer in the first and second regions. A metal silicide gate layer can be formed directly on the high-k gate insulating layer in the first region and avoiding forming the metal-silicide in the second region. Related gate structures are also disclosed.