Preparation of Al-O-N coatings by r.f. reactive sputtering

The influence of sputtering conditions on the microstructure and mechanical properties of Al-O-N films was investigated using XRD, TEM and nano-indentation. The targets of sintered Al₂O₃ plate were sputtered in a mixture of argon and nitrogen using an r.f. sputtering apparatus of facing target-type sputtering. Nitrogen gas flow rate was controlled from 0 to 40 sccm under the fixed Ar gas flow rate (10 sccm). The substrate was heated up to ∼ 300 °C. The highest hardness of 27 GPa was obtained for the Al-O-N film deposited at 300 °C under 30 sccm of the nitrogen gas flow rate, which value is almost twice that of Al-O films. XRD and SAED analysis of Al-O-N films suggested the existence of some phases; hcp-AlN, AlON and ι- Al ₂O₃ phase may presented in the film. The dark-field TEM images of the Al-O-N films revealed that the film consists of very fine grains of ∼ 6 nm in diameter. The Al-O-N film having the highest hardness has higher transparency of visible light than that of Al-O films. Even if the Al-O-N films was annealed up to 800 °C for 1 hour in the air, mechanical properties were not changed, but decreased drastically after the annealing at 900 °C.