Fabrication of smooth amorphous carbon micro-cantilevers by lift-off

Abstract

The amorphous carbon films prepared by filtered cathodic vacuum arc (FCVA) deposition system are superior in nature with very smooth surface morphology, relatively high hardness, exceptional tribological behavior and excellent bio-compatibility. These exceptional qualities make them suitable for many device applications. However, these superior quality films prepared at relatively lower substrate bias such as −80 V exhibits high compressive stress. The stress reduction is achieved by preparing the film in conjunction with high substrate pulse biasing. In the present study, pure a-C films of about 1 μm in thickness were prepared, on highly doped n-type 〈1 0 0〉 Si wafer, using FCVA system in conjunction with high substrate pulse biasing of −5 kV, 600 Hz and 25 μs. The intrinsic compressive stress in the film, calculated from the change in radius of curvature from the substrate and film-substrate sandwich is approximately 300 MPa. Free-standing amorphous carbon (a-C) film structures were successfully fabricated by photolithography technique together with anisotropic wet etching of Si in 40% KOH. However, it has been noticed that etching in KOH for a longer duration at room temperature or for a relatively shorter duration at higher temperatures creates relatively larger holes on the surface of the film. This directed us also to analyze the micro-structural and morphological changes of pure a-C films as a function of etching temperature and duration, for two different concentrations (20 and 40%) of KOH and which are discussed in detail.