Stable reactive deposition of amorphous Al2O3 films with low residual stress and enhanced toughness using pulsed dc magnetron sputtering with very low duty cycle

• A high density discharge with short pulses and high repetition frequency was used.
• Stable arc-free deposition in transition mode of sputtering was achieved.
• Transparent Al2O3 films with n550 = 1.67 at a rate of ≈30 nm/min were prepared.
• Amorphous films exhibit a hardness of 11.5 GPa and a low residual stress (±200 MPa).
• High fracture toughness of 2.7 MPa m−1/2 was observed.

Alumina films are attractive due to their interesting optical and tribomechanical properties. However, stable arc-free reactive deposition process of dense Al2O3 films at a high deposition rate is challenging. Inspired by recent activities on HiPIMS, we used a reactive discharge with short pulses of 10 μs at a high repetition frequency of 10 kHz using an Al target and deposition onto unheated and unbiased glass and silicon substrates. We achieved stable deposition in the sputtering transition mode and produced transparent amorphous Al2O3 films with a hardness of up to 11.5 GPa and a low residual stresses of ±200 MPa at a relatively high deposition rate of ≈30 nm/min. The Al2O3 films prepared under optimized deposition conditions exhibit a high fracture toughness of 2.7 MPa m−1/2. The results suggest that the 10 kHz short-pulse deposition technique is very beneficial for the reactive deposition of dielectric materials such as metal oxides.