Fabrication of advanced La-incorporated Hf-silicate gate dielectrics using physical-vapor-deposition-based in situ method and its effective work function modulation of metal/high-k stacks

Lanthanum (La) incorporation into Hf-silicate high-permittivity (high-k) gate dielectrics was conducted using a physical-vapor-deposition (PVD)-based in situ method. PVD-grown metal Hf, La, and Hf-La alloys on base SiO2 oxides received in situ annealing to form high-quality HfLaSiO dielectrics, and subsequent deposition of metal gate electrodes was carried out to fabricate advanced metal/high-k gate stacks without breaking vacuum. The in situ method was found to precisely control La content and its depth profile and to tune the effective work function of metal/high-k stacks. Remarkable leakage current reduction of almost seven orders of magnitude compared with conventional poly-Si/SiO2 stacks and excellent interface properties comparable to an ideal SiO2/Si interface were also achieved at an equivalent oxide thickness of around 1.0 nm. Our x-ray photoelectron spectroscopy analysis revealed that, as previously suggested, effective work function modulation due to La incorporation is attributed to the interface dipole (or localized sheet charge) at the bottom high-k/SiO2 interface, which is crucially dependent on the La content at the interface. Moreover, it was found that high-temperature annealing causing interface oxide growth leads to redistribution of La atoms and forms the uppermost La-silicate layer at the metal/high-k interface by releasing the dipole moment at the bottom high-k/SiO2 interface. Based on these physical and electrical characterizations, the advantages and process guidelines for La-incorporated dielectrics were discussed in detail.