Reactive pulsed magnetron sputtering of SiO2 - influence of process parameters on layer properties
Reactive magnetron sputtering of SiO2, Al2O3, TiO2, Nb2O5 was applicable for mass production of optical layer stacks onto large substrate size since the development of dual magnetron systems (DMS) with powering of the magnetron discharge in the 10 to 70 kHz frequency range. To improve the long-term behavior of the reactive process for the deposition of highly insulating, low refractive and transparent SiO2 from silicon targets in an argon/oxygen atmosphere, there have been developed sine wave and pulse power supplies with arc detection and extinguishing units. The innovative concept of pulse packet switching presents a new opportunity of stepwise changing the operating point from unipolar pulsed mode to bipolar pulsed mode. It is characterized by two operating frequencies-pulse and polarity changing frequency. As discharge characteristics change with different pulse parameters, the properties of the deposited layers change, as well. Deposition rate, residual stress and surface roughness in relation to the pulse parameters have been investigated. The residual stress of SiO2 films deposited in pulse packet mode was found to be reduced to 53% compared to the stress obtained from samples produced in bipolar mode.