SILICA DEPOSITION BY EXCIMER-LASER-INDUCED CHEMICAL-VAPOR-DEPOSITION IN PERPENDICULAR CONFIGURATION

Silicon oxide films have been deposited on silicon wafers at low tempe rature by irradiation of the substrates with an ArF (lambda = 193 nm) excimer laser beam in a SiH4 and N2O atmosphere. A systematic study of the growth rate and properties of the films as a function of the proc essing parameters (gas composition, substrate temperature, laser pulse energy, pulse repetition rate, total pressure and gas flow rate) has been performed. The process is photolytically activated in the gas pha se and the diffusion of photodecomposed precursor species towards the surface plays an important limiting role. The N2O/SiH4 ratio mainly co ntrols the film composition; for ratios above 40, stoichiometric silic a may be obtained, as confirmed by Rutherford backscattering (RES) mea surements. The role of the surface temperature in the growth kinetics is not critical, so that deposition of films is possible down to subst rate temperatures as low as 70 degrees C. Nevertheless, the density of the films varies greatly with the substrate temperature. The fact tha t no Si-H vibration was detected with Fourier transform infrared (FTIR ) spectrophotometry is surprising, since hydrogen incorporation is a v ery typical phenomenon encountered in most silane systems. This effect is probably associated with the ultraviolet photon irradiation of the adsorbed species and the film as it grows, thus breaking bonds and af fecting the bond structure of the film.