Structural Evolution of Rare-Earth Terbium Oxide Thin Films as Influenced by Growth Parameters and Post-Deposition Annealing Treatment

Terbium oxide (Tb4O7) thin films were deposited on silicon (Si) substrates by RF magnetron sputtering and subjected to low-temperature post-deposition annealing at 450 °C in an argon (Ar) atmosphere. Structural and surface analyses, using GIXRD, FESEM–EDX, and AFM, showed that annealing significantly improved the film's crystallinity and morphology. The crystallite size increased from 14.06 nm to 24.58 nm, accompanied by a reduction in lattice parameter toward the cubic Tb4O7 reference value. Grain growth, surface densification, and a decrease in RMS roughness from 1.85 nm to 1.44 nm were observed. EDX revealed increased oxygen content after annealing, indicating reduced oxygen vacancy (Vo) concentration. These results confirm that low-temperature Ar annealing effectively produces dense, uniform, and highly crystalline Tb4O7 thin films suitable for Si passivation and other low-thermal-budget semiconductor applications.