Evaluation of carbon bonding of DLC films using HF-HiPIMS method by Raman spectroscopy

A double-pulse high-power impulse sputtering (HiPIMS) method has deposited DLC films with higher hardness than conventional unipolar HiPIMS method. We have developed high frequency (HF)-HiPIMS method as a new power supply to improve the film properties of HiPIMS method. However, the carbon bonding of DLC films deposited by the HF-HiPIMS method has not been clarified. In this study, we report on the carbon bonding of DLC films using the HF-HiPIMS method by Raman spectroscopy. Raman spectra were deconvoluted into five active bonds (N, D, G⁻, G⁺, D’) using the Voigt function. The film density was measured by X-ray reflectometry (XRR). In this study, the discussion will focus on the relationship between film density and G⁻/G⁺ area rate. The film density was negatively correlated the G⁻/G⁺ area rate (r = −0.87). This G⁻/G⁺ area rate is related to the quantity of strained constituents in the films. Also, when the CH₄/Ar ratio is high, the quantity of strained constituents are high and the matrix sea (DLC) is sparse. It is considered that the DLC films are dense when the quantity of strained constituents are low. Therefore, the G⁻/G⁺ area rate decreased and the film density increased.