In this paper, the effects of ultraviolet (UV) annealing on films deposited by photo-induced chemical vapour deposition (photo-CVD) have been investigated using ellipsometry and Fourier transform infrared spectroscopy (FTIR) measurements. It was found that SiO2 could be formed at UV annealing temperatures above 350°C and its thickness (several nm) depends on annealing time, temperature and annealing gas such as N2 and O2 as well as the Ta2O5 thickness. X-ray photoelectron spectroscopy (XPS) and HF etching confirmed that the SiO2 formed on the surface of the Ta2O5 after the UV annealing step. Results show that the active oxygen species play an important role in the improvement of layer properties during UV annealing.