Development of High Frequency-High Power Impulse Magnetron Sputtering Power Supply and Its Diamond-Like Carbon Film Properties

Diamond-like carbon (DLC) films formation using the high power impulse magnetron sputtering (HiPIMS) method has large energies carbon ions (C⁺) and argon ions (Ar⁺) than conventional direct current magnetron sputtering (dcMS) method [1]. Therefore, the HiPIMS method can form higher density DLC films than dcMS method [1]. However, the deposition rate of the HiPIMS method is lower than that of the dcMS method. We have developed high frequency (HF)-HiPIMS method as a new power supply to improve the deposition rate of HiPIMS method. In this paper, we report on the deposition rate and film properties of DLC films using this power supply.<br/>A standard circular magnetron ion source was operated with a graphite target 3 inch in diameter. Prior to the experiments, the chamber was evacuated to a base pressure below 5×10⁻⁴ Pa. Discharge conditions were performed from a working pressure of 0.5 Pa, Ar flow rate of 5 sccm, a target to substrate distance of 100 mm and the substrate was rotated at 5 rpm. The pulse conditions of HF-HiPIMS method were a frequency of 200 Hz, a pulse duration under negative voltage of 20 μs (T1 pulse), a pause period of 10 μs (T2 pulse), a pulse duration under negative voltage of 50 μs (T3 pulse), a pulse of 3 μs is turned on and off six times (HF pulses) and negative voltage of −780 V to −870 V. As a comparison, experiments were also performed with the unipolar HiPIMS method, where the pulse conditions were a frequency of 200 Hz, a pulse duration under negative voltage of 50 μs (T3 pulse) and negative voltage of −770 V to −850 V.<br/>The peak discharge current and peak power density in this experiment were 120 A (3.0 A/cm²) and 1.8 kW/cm². It was discharged HiPIMS mode with a peak power density more than 0.5 kW/cm² [2]. In the HF-HiPIMS method, the T1 pulse is applied to start up the discharge of the T3 pulse more quickly. The average power of the HF-HiPIMS method is increased over the unipolar HiPIMS method due to the power input to the T1 and HF pulses also start up the discharge of the T3 pulse. In each method, the deposition rate showed a proportional trend to the peak power density. By comparing these results, the deposition rate of the HF-HiPIMS method was increased by 37% the unipolar HiPIMS method. It is considered that the influence of the increase in average power. As film properties of the DLC films, the film structure was measured by Raman spectroscopy and the film density by X-ray reflectometry (XRR). A D (disorder) peak around 1400 cm⁻¹ and a G (graphite) peak around 1560 cm⁻¹ were observed for all samples, confirming that they are typical DLC films. The full width at half maximum of the G peak (FWHM (G)) was positively correlated to the film density [3]. The FWHM (G) represents the degree of crystallinity due to <i>sp²</i> bonding, with larger values indicating more disordered bonding. It has been reported that the film density and Young's modulus of DLC films increase as the crystallinity is disturbed by <i>sp²</i> bonding, which is consistent with this report. Furthermore, the maximum film density by each deposition method increased by 11% for HF-HiPIMS compared to unipolar HiPIMS. This is inferred to be due to the increase in the average current, which increased the number of ions entering the film and increased the film density.<br/>In this paper, we reported on the deposition rate and film properties of DLC films using HF-HiPIMS method. This HF-HiPIMS method achieved higher deposition rate and higher film density compared to the conventional unipolar HiPIMS method.<br/>References:<br/>[1] K. Sarakinos <i>et al</i>., <i>Surface and Coatings Technology</i>, 206, 2706-2710 (2012).<br/>[2] J. T. Gudmundsson <i>et al</i>., <i>Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films</i>, 30, 030801 (2012).<br/>[3] C. Casiraghi <i>et al</i>., <i>Physical Review B</i>, 72, 085401 (2005).