Effects of deposition conditions on residual stress in DLC films prepared by UBM sputtering

Abstract

Effects of deposition conditions for residual stress in DLC films consisted of a-C:H layer and Cr/C inclined interlayer were studied. Residual stresses in upper and lower film were calculated respectively by our developed Stoney's equation in order to apply double layer film. a-C:H layer and Cr/C inclined interlayer were prepared by UBM sputtering onto SUS304 substrate as a function of process parameters:substrate bias voltage, deposition temperature, gas mixture ratio [CH4]/{[Ar]+[CH4]}, and total gas pressure. Applying a bias voltage to a substrate brought a rapid increase in the compressive stress of a-C:H layer. However, over -300V voltage brought a slightly decrease in the compressive stress. Compressive stress in a-C:H layer increased with deposition temperature under 501K, and decreased over 501K. An increase of gas mixture ratio brought a gradual decrease of compressive stress. Compressive stress in a-C:H layer decreased with total gas pressure. Meanwhile, deposition conditions brought different changes of residual stress in Cr/C inclined interlayer from that in a-C:H layer. Compressive stresses in a-C:H layer were compared with N/S ratio obtained by Raman spectrum, which seemed to indicate hydrogen contents in the films. In group of films having small compressive stresses, compressive stresses in a-C:H layer approximately decreased with increase of N/S ratio. And in group of films having large compressive stresses, Ar ion assist affected to rapid increase of compressive stress in a-C:H layer deposited as a function over -100V substrate bias voltage and under total gas pressure 0.25Pa. Higher substrate temperature at the end of deposition over approximately 530K brought a decrease of compressive stress in a-C:H layer. © 2008 The Society of Materials Science.