Influence of thermal annealing on structural properties and oxide charge of LiNbO3 films

C-oriented polycrystalline lithium niobate (LiNbO3) films have been deposited on Si substrate by the radio-frequency magnetron sputtering method in an Ar atmosphere and Ar + O2 gas mixture. All as-grown LiNbO3 films manifested positive fixed oxide charge regardless of the sputtering conditions. Donor centers are formed in Si substrate because of diffusion of O2 molecules during sputtering process. Thermal annealing (TA) of the deposited films leads to increase in the surface roughness and grain size as well as formation of LiNb3O8 phase in the studied films. Also, TA resulting in the decline of positive oxide charge due to the diffusion of oxygen molecules into LiNbO3 films from air and out-diffusion from Si substrate.