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

The mechanical stability of amorphous carbon (a-C) films deposited on ultra smooth Si(100) substrates by radio-frequency sputtering under different ene rgetic ion bombardment conditions was investigated in light of results obta ined from aging and annealing experiments. The a-C films were annealed at 4 95 degreesC in the high-vacuum chamber of an x-ray photoelectron spectrosco py (XPS) system with a base pressure of 10(-8) Torr. The annealing process consisted of three sequential heating cycles of temperature 495 degreesC an d duration 5, 10, and 70 min, respectively. Atomic force microscopy and XPS studies were conducted to reveal possible changes in the surface topograph y, microstructure, and composition of the a-C films. To investigate the eff ect of annealing on the nanomechanical properties of the a-C films, nanoind entation experiments were performed with a surface force microscope. Only s ubtle changes in the surface topography, microstructure, composition, and n anomechanical properties of the a-C films were observed after aging for abo ut two years. Film agglomeration during annealing due to residual stress re laxation was found to strongly depend on the kinetics of film deposition. I t is shown that the stability of the a-C films is affected by residual stre sses produced from the energetic ion bombardment during film growth. The ma gnitude of the residual stress and the film thickness exhibits a pronounced effect on the thermodynamics and kinetics of film agglomeration. The exper imental results demonstrate that increasing the residual stress and/or film thickness decreases the mechanical stability of the a-C films. (C) 2001 Am erican Institute of Physics.