Synthesis and characteristics of nc-WC/a-C:H thin films deposited via a reactive HIPIMS process using optical emission spectrometry feedback control

Abstract

A high-power impulse magnetron sputter deposition system with feedback control using an optical emission spectrometer (OES) is used to deposit nc-WC/a-C:H thin films using a tungsten (W) target material reaction with C2H2 gas in a reactive mode. The plasma emission intensity of W+ ions at an emission wavelength of 429.6 nm is monitored, and the amount of reactive C2H2 gas is precisely controlled in order to maintain stable emission intensity during the deposition process. By controlling the input flow rate of C2H2 and using different W+ ion optical emission intensity set points, various nc-WC/a-C:H thin films are obtained at a fixed duty cycle of 2% and pulse frequency of 133 Hz between deposition temperatures of 70 °C and 75 °C. The characteristics and mechanical properties of the obtained thin films are investigated. The highest peak current and peak power density of 189 A and 706 W/cm2, respectively, are obtained at an OES set point of 10%, which corresponds to a high amount of C2H2 gas injection. When the OES set point is <80%, a phase change from α-W2C to WC1−xis clearly identified using the XRD data. Raman analysis also depicts that a W-doped diamond-like carbon structure (nc-WC/a-C:H) is obtained below an OES set point of 30%. Additionally, the concentration of carbon in the nc-WC/a-C:H thin films is observed to gradually increase from 16.9 to 93.8 at.%, whereas the concentration of tungsten decreases from 78.1 to 5.4 at.% as the OES set point decreases from 90% to 10%. The highest hardness of 32.6 GPa was obtained at an OES set point of 90% when the film was composed of an α-W2C phase. However, the hardness values are observed to decrease as the OES set points decrease.