Study on deposition of amorphous hydrogenate DLC films on germanium substrates by RF-PECVD

Abstract

This paper aims to research the influence of hydrogen on the variation of mechanical properties and microstructure of diamond-like carbon (DLC) films synthesized by radio frequency plasma chemical vapor deposition (RF-PECVD). The DLC films were deposited on germanium substrates as protective layers with butane-hydrogen mixture gas. The films obtained are polycrystalline and texture-growth, the surface of the thin films is grain-like and dispersing incompact. The synthesis and post-plasma etching treatment of DLC films were prepared with low-temperature methods (T<150°C). The reactant gas is a high pure mixture of butane (99.9%) and hydrogen (99.99%). The effect of deposition parameters on the structure and properties of DLC thin films has been studied. DLC films deposited are studied by atomic force microscopy (AFM), Raman, Fourier-transform infrared (FTIR), nanoindentation and nanoscratch. Test results show the transmissivity of deposited DLC films from 8μm and 12μm region is higher than 60% averagely, which closees to theory value firstly. Secondly, with the increase of deposition voltage, the content of sp3C in the DLC thin films increases, the roughness of thin films decreases. Thirdly, with the increase of deposition frequency, the content of sp3C in the DLC thin films increases, the roughness of the thin films decreases. Finally, as the film thickness increases, the ratio of I(D)/I(G) increases and the hardness decreases. This indicates as the film thickness increases, the bonding is towards graphite structure and reducing hardness. The high sp2 fraction and low hardness explain the poor adhesion of large film thickness. The results reveal that increasing the concentration of hydrogen, thickness and roughness decreases.