Changes in Structure and Composition of Silicon Oxide Thin Films Induced by Ultraviolet Illumination

The transformation of silicon oxide thin films at room-temperature by UV-photons provided by a Xe2* incoherent excimer lamp (λ = 172 nm, Δλ = 14 nm) was studied. Films were produced at low-temperature (T = 260 °C) by ArF laser-induced CVD (LCVD) in parallel configuration from a silane/nitrous oxide/argon gas mixture. The silicon oxide films were irradiated in several consecutive steps to follow-up the modifications with the illumination time. Rutherford backscattering (RBS), infrared (IR) and X-ray photoelectron (XPS) spectroscopies, ellipsometry, and elastic recoil detection analysis (ERDA) were used to characterize the effects of the irradiation on the structure, composition, density, and hydrogen content. Under the UV illumination the as-deposited film evolves from a suboxide film (SiO1.6) to a stoichiometric silicon dioxide (SiO2), and its originally strained structure changes towards a relaxed tetrahedral configuration. The UV irradiation is able to anneal at room temperature the silicon oxide films breaking the Si-H bonds and incorporating new SiO and hydroxyl groups in a relaxed network. The hydrogen does not effuse out, but remains in the film as molecular hydrogen and/or forming silanol or water groups.