OPTICAL-PROPERTIES OF ION-ASSISTED DEPOSITED SIO THIN-FILMS

The application of the ion-assisted deposition (IAD) technique to the evaporation of SiO thin films has been studied. SiO thin films 2700 an d 540 nm thick were evaporated on silicon and sapphire substrates, wit h and without low energy (120 eV) ion bombardment. Transmittance spect ra in the IR region of 1000-5000 nm show that ion assistance has induc ed a clear change in the refractive index of the films. In addition, a new absorption peak at 2900 nm appears in the IAD-grown samples, the intensity of this peak being dependent on the film thickness. This dif ferent optical behaviour has been related to an IAD-induced change in the stoichiometry of the films. Auger depth profiling of the SiO films indicates a decrease of the Si/O Auger intensity ratio by a factor of 2 in the treated samples. This variation implies a change in the atom ic concentrations of oxygen and silicon in the IAD-treated films. The results presented in this work are very promising for application of t he IAD technique to the design of multilayer IR filters.