Transistor gate structures and methods of forming the same

Abstract

In an embodiment, a method includes: forming a gate dielectric layer on a channel region of a semiconductor feature; depositing a work function tuning layer on the gate dielectric layer, the work function tuning layer including a first work function tuning element; depositing a capping layer on the work function tuning layer with atomic layer deposition, the capping layer formed of an oxide or a nitride; performing an anneal process while the capping layer covers the work function tuning layer, the anneal process driving the first work function tuning element from the work function tuning layer into the gate dielectric layer; removing the capping layer to expose the work function tuning layer; and depositing a fill layer on the work function tuning layer.