Philipp Dürrenfeld¹, Gayatri Rane¹, Uwe Krause², Denis Shaw^3
1Advanced Energy Industries Inc., Karlstein am Main, Germany
²Advanced Energy Industries Inc., Metzingen, Germany
¹Advanced Energy Industries Inc., Fort Collins, CO
Titanium dioxide (TiO₂) films are widely used in glass coatings, fuel cells, displays, and photovoltaic devices due to their UV opacity, high refractive index, and durability. Modern TiO₂ sputtering processes often use ceramic, sub-stoichiometric (TiO_x) targets for high stability and high sputtering rates.
In a recent field study, we used an industrial-sized drum coater to examine TiO₂ films deposited from dual rotary TiO_x targets of 60 cm in length. Operating in bipolar pulsed-DC mode, the targets alternate as cathode and anode, reversing polarity at frequencies between 0.5 kHz and 50 kHz. The cathodes can also be operated in DC against a separate anode without pulsing, or in dual reverse pulsing (DRP) mode, where the voltage between each target and the shared floating anode is synchronously pulsed. A low pulsing frequency is usually preferred for higher deposition rates because it uses less power for the frequent re-ignition and switching of the plasma.
Our findings reveal that, when compensating for power losses and measuring the power directly at the cathode, the deposition rate is independent of switching frequency. The TiO₂ sputter deposition from TiO_x targets is remarkably robust with low arcing rates, however, the quality of the vacuum, particularly the amount of residual water vapor, impacts the deposition rate and optical properties. This is crucial in batch coater environments where chambers are regularly vented. By utilizing process gas analysis, we have quantified these impacts and disentangled them from frequency-dependent effects.