Effect of insert mid-frequency pulses on I-V characterisation, deposition rates and properties of nc-WC/a-C:H films prepared by superimposed HiPIMS process

Unipolar superimposed high-power impulse magnetron sputtering (HiPIMS) was successfully used to deposit nc-WC/a-C:H thin films. The concept of unipolar superimposition is to insert unipolar MF pulses during the off-time of the unipolar HiPIMS pulsing to enhance the deposition rate of thin films. In this work, nc-WC/a-C:H films were deposited using the unipolar superimposed HiPIMS technique employing various MF pulses from 0 to 30 counts. The effects of inserting MF pulses on the current-voltage (I-V) characteristics of discharging with a tungsten (W) target, deposition rate, microstructure and mechanical properties of nc-WC/a-C:H thin films were investigated. The results indicated that the I-V characteristics of discharging with a W target were affected by the introduced C2H2 reaction gas because of the impedance change from the plasma condition. The deposition rate can be enhanced to be 1.23 times higher than the unipolar HiPIMS output via inserting an MF output because of the extra power output of 1 kW direct current (DC). However, the deposition rate was mainly affected by the extra MF power output rather than by the inserted MF pulse counts. In addition, the hardness values were decreased, and the feature of carbon based a-C, a-C:H and nc-Me/a-C:H (DLC) films (nc-WC/a-C:H) was weakened by increasing the inserted MF pulse, due to the fact that the W content was increased in the films because of the plasma condition difference in the degree of ionisation, which in different peak power density.