Effect of oxygen ion energy and annealing in formation of tin oxide thin films

Tin oxide (SnO_x) thin films were deposited by ion-assisted deposition (IAD) at various ion beam voltages (V_I) onto amorphous SiO₂/Si substrate at room temperature. Tin oxide thin films with nonstoichiometric/stoichiometric composition were fabricated. The as-deposited SnOi_x films were mostly amorphous, but they exhibited various degrees of crystallinity and fine grain size after annealing at 500°C for 1 h in air. The annealed film deposited using an ion beam energy (E_i) of 300eV showed a preferred orientation along the SnO₂ (110) plane. The preferred orientation changed to SnO₂ (002) for film 1000 (the annealed film deposited with E_I = 1000eV) through an amorphous intermediate structure of film 500 (the annealed film deposited with E_I = 500eV). X-ray photoelectron spectroscopy study showed that the main Sn3d peaks in all samples were similar to the binding energy of Sn⁴⁺ and the atomic ratios for all the films were higher than 1.51. For the film grown under an average energy of 123 eV/atom, the refractive index was 2.0 and the estimated porosity was 5.2% smaller than that of the other films.