DLC Coating by HiPIMS: The Influence of Substrate Bias Voltage

Abstract

Carbon-related materials are prepared using various physical vapor deposition (PVD) methods. High-power impulse magnetron sputtering is a PVD method that uses glow plasma and this method is employed to prepare diamond-like carbon (DLC) films. The densities of the glow current and the consumed power for an effective area of plasma generation are 1.4 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm A}/{\rm cm}^{2}$</tex></formula> and 1.2 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${\rm kW}/{\rm cm}^{2}$</tex></formula> , respectively. A pulsed bias is applied to the substrate (subsequently called substrate bias voltage). The pressures of the background gas and the substrate bias voltages influence the surface morphology and the roughness of the deposited films. It is discovered that a critical pressure of 0.3 Pa and a critical bias voltage of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 100}~{\rm V}$</tex></formula> is needed to change the DLC film characterization. A drastic change in these characteristics is seen for pressures <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${&lt;}{\rm 0.3}~{\rm Pa}$</tex></formula> ; a bumping surface and dumpling-like aggregations are produced. In addition, there is a bias-voltage dependency on these films, as smoother surfaces are seen in a bias-voltage range that is higher than <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 100}~{\rm V}$</tex></formula> . This phenomenon may be related to the DLC structure, which is evaluated by Raman parameters of the deposited films. It is found that the position and the full width at half maximum of the graphite peak show a minimum and a maximum, respectively, at a bias voltage of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 100}~{\rm V}$</tex></formula> . The results of X-ray photoemission spectroscopy reveal that the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm sp}^{3}$</tex> </formula> bond ratio indicates a maximum at a pressure of 0.3 Pa and at a bias voltage of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 100}~{\rm V}$</tex></formula> . Thus, it is clear that the gas pressure of 0.3 Pa and the bias voltage of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 100}~{\rm V}$</tex></formula> are critical values that change the pressure and bias dependence of the film characteristics.