Highly insulating alumina films by a bipolar reactive MF sputtering process with special arc handling

Aluminum oxide (Al2O3) thin films are used in microelectronics and sensor applications due to their good insulating properties. Usually, RF sputtering processes are used to produce insulating coatings for sensors, but this process has major drawbacks, mainly, a very low deposition rate which leads to higher production costs. AC reactive sputtering processes present higher deposition rates, but issues regarding arcing and creation of defects in the films need to be addressed. In this work, an AC power supply with a new concept for fast arc handling and limited current output was investigated. Alumina films were produced by means of a bipolar reactive sputtering process, using large area double rotatable cathodes. The process was very stable and arc counts are as low as 3-10 arcs/h in the best deposition conditions. High deposition rates were also observed, reaching 2-3 μm/h. The films obtained excellent insulating properties with breakdown voltages higher than 3 kV for films with thicknesses between 2 and 3 μm and a corresponding breakdown strength of 1.5 kV/μm (15 MV/cm).