Influence of the plasma pressure on the microstructure and on the optical and mechanical properties of amorphous carbon films deposited by direct current magnetron sputtering

Abstract

The influence of the plasma pressure on the microstructure and on the mechanical and optical properties of amorphous carbon films deposited by dc-magnetron sputtering was investigated. A modified version of the computer code TRIM 98.01 was employed to simulate the thermalization of the sputtered carbon atoms. In this way, it provided the efficiency of transport and the amount of energy deposited at the growing surface per sputtered carbon atom as a function of the plasma pressure and according to Sigmund’s energy distribution of sputtered particles. Several techniques were employed to characterize the films properties: ion beam analysis provided the composition and areal density; profilometry provided the thickness and film/substrate bending, with which the internal stress could be calculated through Stoney’s equation, and nanoindentation provided the film hardness. In addition, the disorder of the amorphous network was characterized by Raman spectroscopy, while infrared spectroscopy provided information about chemical bonding. Transmission and reflection spectroscopies were carried out in the 400–2500 nm range, and the optical gap was obtained through the Tauc plot. The index of refraction was obtained at 1.3 μm according to the Abelès method. All these quantities were related to the growing conditions, providing a clear picture of the growth of polymer-like or diamond-like films. Finally, the present models for a-C films are reviewed in light of experimental results.