High rate deposition of mixed oxides by controlled reactive magnetron-sputtering from metallic targets

The use of mixed tailored optical materials opens new fields for the design and optimization of thin film properties. For example the refractive index may be tuned between the higher and the lower value while the stress is decreased. Therefore new designed materials are of great interest for optical applications. Magnetron sputtering with radiofrequency excitation and the use of ceramic targets is one of the most widely spread techniques. However, this process suffers from low deposition rate and difficult up-scaling. Mid-frequency pulsed reactive magnetron sputtering from metallic targets improves the situation but the process control is more complicated because of superimposed hysteresis effects. In case of cosputtering of different materials in a dual magnetron setup each target has its own hysteresis. Lambda probe measurements allow only a description of the coupled process since the inertia time is too long and a limited spatial resolution is given. To control each target individually an optical emission spectroscopy system with separated optical fibers was built up and integrated in a closed-loop control system. An embedded proportional integral controller modifies the pulse pattern to reach and stabilize the emission intensity setpoint of pre-selected wavelengths. In this way the composition of the resulting films can be adjusted while the process is controlled in the high-rate transition mode. Besides the process control system different mixtures of hafnium-aluminium-oxide and zirconiumaluminium- oxide prepared in this way will be presented. Optical and mechanical film properties of the mixtures are compared to the properties of single homogeneous films.