Modification of silicon nitride films to oxynitrides by ArF excimer laser irradiation

An intensive study of the effects induced by the ArF excimer laser irradiation of silicon nitride films has been carried out. Amorphous silicon nitride films were deposited on silicon substrates by CO2 laser-induced chemical vapour deposition (LCVD) in parallel configuration using a SiH4/NH3/Ar gas mixture. Post-deposition UV photon irradiation of the silicon nitride films was performed at room temperature and in an inert gas atmosphere. Changes in composition and refractive index were systematically followed by Fourier transform infrared spectroscopy (FTIR), and single-wavelength ellipsometry. The FTIR studies show that the initial ArF laser pulses provoke the elimination of bonded hydrogen (Si-H, N-H) incorporated in the as-deposited silicon nitride films. By increasing the UV irradiation time, incorporation of oxygen in the him is observed allowing the him composition to be tailored from silicon nitride to silicon oxide. This tendency is confirmed by a gradual decrease in the film refractive index. The proposed film modification mechanism is basically the breaking of Si-H, N-H and Si-N bonds, followed by a reaction with the adsorbed water in the films.