Deposition of nanostructured crystalline alumina thin film by twin targets reactive high power impulse magnetron sputtering

Abstract

In order to suppress the arcs in reactive sputtering deposition process, twin targets reactive high power impulse magnetron sputtering (TTR-HiPIMS) was proposed, and alumina (Al2O3) thin films were synthesized on silicon (1 0 0) substrates by this method under various argon/oxygen gas flow rates and substrate temperatures. The deposition rate of alumina films decreased from 110 to 85 nm/h when the oxygen flow rate was increased from 8 to 16 sccm. The elemental composition of the films was analyzed by both energy dispersive spectroscopy and X-ray photoelectron spectroscopy, and the results revealed that the suitable argon/oxygen gas flow rate for depositing a stoichiometric alumina film was 50/14. Grazing incidence X-ray diffraction (GIXRD) results indicated that all the as-deposited films were polycrystalline γ-Al2O3. The GIXRD patterns also confirmed that under optimum process conditions, crystalline alumina films can be obtained at temperatures as low as 300 °C, and the intensity of the diffraction peaks increased with the substrate temperature. Scanning electron microscopy showed that all the films have a smooth surface, which indicated that the arc events were almost completely suppressed in the sputtering process. The films prepared at substrate temperatures ranging from 300 to 500 °C contained fine nanocrystals of sizes in the range 15–25 nm. Furthermore, atomic force microscopy results revealed that the root-mean-square roughness of the films increased from 2.06 to 4.24 nm when the substrate temperature was raised from 300 to 500 °C. The results suggest that the new developed TTR-HiPIMS technique is a simple and effective method for the reactive deposition of nanostructured crystalline alumina films at relatively low substrate temperature.