Influence of different physical factors on microstructure and properties of magnetron sputtered amorphous carbon films

Abstract

Structure evolution of amorphous carbon (a-C) films deposited by dc magnetron sputtering of graphite in argon was investigated as a function of substrate temperature T_s (20–800°C) and dc substrate bias voltage U_b (floating — −175 V). Film structure was studied by transmission electron microscopy, selected area electron diffraction, reflective high energy electron diffraction and Raman spectroscopy. Film resistivity in two directions — parallel and perpendicular to the substrate — was also measured. The results obtained allow for the assumption that the film structure is based on coexistence of D- and G-phases formed of sp² bonded carbon atoms. G-phase consists of small graphite-like ordered areas embedded in continuous uniform amorphous D-phase. The evolution of a-C film structure in 20−450°C interval occurs by temperature induced graphite-like ordering of small areas within D-phase (G-phase nucleation). In the 500–800°C range the change of C-film growth mechanism takes place. Instead of nucleation of the G-phase within the D-phase the initial nuclei of graphite phase appears on the substrate. The changes of a-C film microstructure under the ion bombardment in the range of −20≤U_b≤−150 V are accompanied by decreasing of G-phase clusters size and simultaneous certain disordering in their internal structure. At U_b>−150 V the cluster structure tends to be more ordered towards it graphitization. The effect of graphite-like clusters ‘texturing’ revealed in a-C films under the ion bombardment is discussed.