*A.P. Ehiasarian¹‚  P.Eh. Hovsepian¹‚ D.A. Loch¹,  A. Oniszczuk², P. Rozanski^2
1Sheffield Hallam University; ²TRUMPF Huettinger Sp. z o.o., Zielonka, Poland
High density transparent oxide layers on polymers and glass can improve the environmental viability of photovoltaics‚ quality of displays‚ gate dielectrics for thin film transistors and low emissivity layers in glazing. High Power Impulse Magnetron Sputtering (HIPIMS) produces high density microstructures and high hardness due to the delivery of an ionised metal and dissociated oxygen deposition flux to the substrates. SiO_x films were produced by reactive HIPIMS of a pair of Si targets in an Argon-Oxygen atmosphere. Dual-magnetron bipolar sputtering and single-target with reverse voltage operation were evaluated. The HIPIMS process was carried out by controlling the current ramp within the pulse. This resulted in the elimination of stability issues associated with runaway currents and arcing. Arcing rates were lowest in the bipolar mode of operation and were significantly reduced using positive (reverse) voltage pulsing due to the discharging of the target surface. In single-target operation, the delay between the switch off of the pulse and the application of the reverse voltage had a strong influence on arcing rates. SiO_x was deposited at a peak current density of 0.5 Acm^-2 in a plasma dominated by Si¹⁺ ions (61%) and Ar1+ ions (14%) as shown by energy- and mass- resolved spectrometry. Dissociated oxygen was twice the amount of molecular oxygen at 7% and 3% respectively. The pulse duration was up to 20 microseconds. However plasma persisted to more than 150 µs after the pulse switch off as evidenced by the Ar neutral (Ar I) optical emission signal. Application of the reverse voltage immediately at the end of the pulse and before the decay of the plasma efficiently neutralised the target and eliminated arcing. SiO_x films deposited without additional heating or substrate biasing had a refractive index of 1.43-1.48, similar to bulk glass. A transparency of 97 % and k-value of 1e-3 for 200 nm thick films indicated low defect density achieved at the lowest arc rate. The nanohardness of 1 µm thick films was 10±1 GPa and Young's modulus 77±9 GPa, representing a 10% increase against the bulk glass substrate.