WC-based thin films obtained by reactive radio-frequency magnetron sputtering using W target and methane gas

Abstract

Deposition of tungsten carbide (WC) films was investigated by radio-frequency reactive sputtering using a tungsten target and methane gas. The effect of some processing parameters (pressure, power, CH4-to-Ar gas flow ratio) upon the chemical and structural properties of the films has been investigated. The evolution of the chemical composition has been analyzed by photoemission, the microstructure has been studied through electron microscopy techniques and the crystallographic structure was investigated by X-ray diffraction as well as Raman spectroscopy. This study demonstrates that the formation of tungsten carbide is highly dependent on the deposition conditions: thin films are composed of either metallic tungsten or carbon for a total gas pressure of 0.5Pa while for higher total gas pressure (5Pa), tungsten carbide films are deposited for a large power range (50–180W) but a narrow range of methane flow rate (2–8%). In this latter case, no changes are observed in microstructure and crystallography of tungsten carbide films with processing parameters: all films present a columnar growth and are mainly formed of cubic sub-stoichiometric WC1−x nanocrystallites embedded in amorphous carbon. However, as function of process parameters, a strong variation in chemical composition of the films is revealed and is attributed to the defective structure of cubic sub-stoichiometric WC1−x phase.