Postdeposition annealing on RF-sputtered SrTiO₃ thin films

Understanding of structural, optical, and electrical properties of thin films are very important for a reliable device performance. In the present work, the effect of postdeposition annealing on stoichiometric SrTiO₃ (STO) thin films grown by radio frequency magnetron sputtering at room temperature on p-type Si (100) and quartz substrates were studied. Highly transparent and well adhered thin films were obtained in visible and near infrared regions. As-deposited films were amorphous, while nanocrystalline and polycrystalline phases of the STO thin films formed as a function of annealing temperature. Films annealed at 300 °C showed nanocrystallinity with some amorphous phase. Crystallization started after 15 min annealing at 700 °C, and further improved for films annealed at 800 °C. However, crystallinity reduced for films which were annealed at 900 °C. The optical and electrical properties of STO thin films affected by postdeposition annealing at 800 °C: E_g values decreased from 4.50 to 4.18 eV, n(λ) values (at 550 nm) increased from 1.81 to 2.16. The surface roughness increased with the annealing temperature due to the increased crystallite size, densification and following void formation which can be seen from the scanning electron microscopy images. The highest dielectric constants (46 at 100 kHz) observed for films annealed at 800 °C; however, it was lower for 300 °C annealed (25 at 100 kHz) and as-deposited (7 at 100 kHz) STO films having ∼80 nm thickness.