UV activated surface preparation of silicon for high-k dielectric deposition

High-k gate materials, such as HfO₂, are unstable on silicon and form low permittivity interfacial oxides when heated. A single layer of silicon nitride grown prior to gate dielectric deposition could serve as a diffusion barrier to prevent oxide formation. A monolayer film of surface amine groups will be chemically similar to surface hydroxyl groups, and could also serve as a seed layer to promote the nucleation of a high-k film. The deposition of amines (≡Si-NH₂ or ≡Si-NH-Si≡) on chlorine and hydrogen terminated Si(100) at low temperature (<100°C) was investigated using x-ray photoelectron spectroscopy (XPS). UV-Cl₂ exposures (0.1-10 Torr Cl₂ at 25-150°C, 10-600 s, 1000 W Xe lamp) were used to terminate Si(100) with Cl atoms. Exposure to NH₃ (0.1-1000 Torr, 75°C, 5-60 min) replaced Cl atoms with up to 0.3 ML of amine groups, as measured by XPS. Cl atoms served as reactive leaving groups, lowering the overall activation energy barrier for nitridation. Alternatively, UV photons with energy greater than 5.7 eV were used to photodissociate NH₃ molecules, yielding NH₂ photofragments that reacted with the H-terminated Si(100) surface. At a UV photon flux of 19 mW/cm², the N coverage increased with time and saturated at ∼1 ML. Significant oxygen was observed on the surface due to H₂O contamination in the source gas.