Microstructural characterization of ion assisted SiO2 thin films by visible and infrared ellipsometry

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Abstract
The complex dielectric function of SiO2 films deposited on silicon substrates by electron-beam evaporation under ion bombardment is determined by infrared ellipsometry between 700 and 5000 cm−1. Analysis of the absorption band associated with the Si–O–Si stretching mode at about 1040 cm−1, the water absorption band at about 3300 cm−1, and knowledge of the visible refractive index determined by visible ellipsometry (in situ and after venting to atmosphere) enable us to model the complex structure of the films, as a densified silica matrix with pores. Depending on the ion assistance conditions, the pores are either mostly connected (allowing water penetration) or largely isolated (no water adsorption). The refractive index of the silica matrix, the pore volume fraction and the pore water filling rate are evaluated as a function of the assistance conditions.