Low-temperature crystallization and hardness enhancement of alumina films using the resputtering technique

In this study, alumina thin films were deposited on Si (100) substrates by reactive magnetron sputtering in an Ar-O₂ atmosphere. The resputtering technique without any separated ion source was applied, as well as various substrate biases and deposition temperatures. Suitable oxygen/argon gas flow rate ratio was obtained to deposit stoichiometric Al₂O ₃ films. As investigated by grazing incidence X-ray diffraction (GIXRD) and nanohardness measurements, the amorphous characteristics and hardness values of alumina films aren't altered with the various substrate biases up to - 120 V at the temperatures up to 600 C. The microstructure of alumina films with thin crystalline Al₂O₃ layer between the amorphous layers was achieved with the resputtering technique at elevated temperatures (≤ 300 C). This suggests that the reactive magnetron sputtering with the resputtering technique is a simple and effective method of preparing crystalline alumina films at relatively low temperature. The existence of thin crystalline Al₂O₃ layers between the amorphous layers makes the film harder than the amorphous films. In general, increasing the deposition temperature with the resputtering technique increased the hardness of the films, thus the crystalline-volume fraction of the films. However, the hardness was not a monotonic function of the deposition temperature.