Investigation of work function tuning using multiple layer metal gate electrodes stacks for complementary metal-oxide-semiconductor applications

Metal gate electrodes consisting of three layered stacks of metals are investigated for complementary metal-oxide-semiconductor device applications. It was observed that the effective work function of the entire gate electrode stack was dominated by the work function of the first metal layer (50 Å of tantalum nitride) contacting the gate dielectric. No significant difference in the effective oxide thickness was observed in devices with and without the initial tantalum nitride layer. The potential reasons for this, based on the penetration of an electron wave function from the gate electrode to the gate dielectric and gate depletion due to longer Debye length of electrons in tantalum nitride, will be discussed.