Microstructure and nanomechanical properties of nitrogenated amorphous carbon thin films synthesized by reactive radio frequency sputtering

Thin films of nitrogenated amorphous carbon (a-CNx) were deposited on Si(10 0) substrates by reactive radio frequency sputtering using a gas mixture of Ar and N-2 at a total working pressure of 3 mTorr. X-ray photoelectron spe ctroscopy (XPS) showed that the films consisted of amorphous carbon (a-C) c ontaining a beta-C3N4-like phase with N atoms bonded to C atoms in tetrahed ral coordination (sp(3)) and a graphite-like phase with N atoms bonded to C atoms in trigonal coordination (sp(2)). Analysis of the XPS spectra reveal ed a strong effect of the N-2 partial pressure on the concentration and com position of each constituent. The thickness and nanohardness of the a-CNx f ilms were in the ranges of 7-35 nm and 12.5-40 GPa, respectively, depending on the fraction of N-2 in the sputtering gas. Conversely to the chemical c omposition, the growth rate (thickness), microstructure, and nanomechanical properties of the a-CNx films were found to depend on the total mass flow rate. While the N/C atomic ratio increased with the N-2 partial pressure, t he film nanohardness and in-plane elastic modulus decreased due to the redu ced energetic ion bombardment on the growing film surface and the incorpora tion of soft phases in the sputtered films. Nanoindentation and XPS results are presented to elucidate the deposition kinetics and to interpret the de pendence of the resulting film microstructure and nanomechanical properties on the plasma conditions. (C) 1999 American Institute of Physics. [S0021-8 979(99)06005-3].