Interfacial interaction between cerium oxide and silicon surfaces

The interaction of cerium oxide films with Si substrates is investigated by means of X-ray photoelectron spectroscopy. Cerium oxide films of different thickness have been grown at room temperature by reactive deposition on different Si surfaces, namely Si(111), Si(100) and thermally oxidized Si(100). We show that cerium oxide and silicon form a silicate phase of subnanometric thickness and that the interfacial phase composition and thickness is similar on the (111) and (100) Si surfaces. The silicate phase formed at the interface contains cerium in the 3+ oxidation state, while silicon presents different oxidation states up to 4+. With a thermal annealing in O2 at 1040 K the interface reaction proceeds and the silicate phase evolves in stoichiometry. We demonstrate the stability of the silicate phase towards oxidation after exposure to atomic or molecular oxygen or air. The presence of a thick thermal oxide layer on the Si surface partially limits the extent of the reaction.