Stability of ultrathin amorphous carbon films deposited on smooth silicon substrates by radio frequency sputtering

Abstract

The mechanical stability of amorphous carbon (a-C) films deposited on ultrasmooth Si(100) substrates by radio-frequency sputtering under different energetic ion bombardment conditions was investigated in light of results obtained from aging and annealing experiments. The a-C films were annealed at 495 °C in the high-vacuum chamber of an x-ray photoelectron spectroscopy (XPS) system with a base pressure of 10−8 Torr. The annealing process consisted of three sequential heating cycles of temperature 495 °C and duration 5, 10, and 70 min, respectively. Atomic force microscopy and XPS studies were conducted to reveal possible changes in the surface topography, microstructure, and composition of the a-C films. To investigate the effect of annealing on the nanomechanical properties of the a-C films, nanoindentation experiments were performed with a surface force microscope. Only subtle changes in the surface topography, microstructure, composition, and nanomechanical properties of the a-C films were observed after aging for about two years. Film agglomeration during annealing due to residual stress relaxation was found to strongly depend on the kinetics of film deposition. It is shown that the stability of the a-C films is affected by residual stresses produced from the energetic ion bombardment during film growth. The magnitude of the residual stress and the film thickness exhibits a pronounced effect on the thermodynamics and kinetics of film agglomeration. The experimental results demonstrate that increasing the residual stress and/or film thickness decreases the mechanical stability of the a-C films.