Stoichiometry control during deposition by ion beam sputtering

Ion beam sputtering of chemical compounds is in general nonstoichiometric. The problem is especially severe for inorganic insulators because target charging and ionic emission render sputtering rates unstable. This study reports on the influence of target charging on ion beam sputtering of Al ₂O ₃ and LiNbO ₃ films on Si and Al ₂O ₃/Si substrates. It was found that undesirable ionic emission could be minimized by eliminating target charging, controlled via electron to ion neutralization ratio of the incident beam. Experimental data suggest that the stoichiometric sputtering corresponds to zero target charging and thus can be used as an effective feedback parameter during deposition. When the target charging was minimal, high quality stoichiometric Al ₂O ₃ films were obtained without the need for oxygen supplied to the deposition chamber. The dependence of refractive index, residual stress, and specific resistance on neutralization ratio showed abrupt change in the vicinity of zero target charging. In a separate experiment, minimization of the target charging helped to maintain stoichiometry during ion beam sputtering of LiNbO ₃, suggesting that this method is also beneficial for sputtering of ternary compounds.