Patent attributes
Provided are methods for fabricating a semiconductor device. A gate dielectric layer is formed on a substrate including first through third regions. A first functional layer is formed on only the first region of the first through third regions. A second functional layer is formed on only the first and second regions of the first through third regions. A threshold voltage adjustment layer is formed on the first through third regions. The threshold voltage adjustment layer includes a work function adjustment material. The work function adjustment material is diffused into the gate dielectric layer by performing a heat treatment process with respect to the substrate.