Tetrahedral amorphous carbon films prepared by magnetron sputtering and dc ion plating

Highly tetrahedral, dense amorphous carbon (ta-C) films have been deposited using rf sputtering of graphite by an unbalanced magnetron with intense dc Ar-ion plating at low temperatures (<70 degrees C). The ratio of the argon ion flux to neutral carbon flux Phi(i)/Phi(n) is about 5. The film density and compressive stress are found to pass through a maximum of 2.7 g/cm(3) and 16 GPa, respectively, at an ion plating energy of about 100 eV. Experiments with higher ion flux ratios of Phi(i)/Phi(n) = 10 show that it is possible to deposit carbon films with densities up to 3.1 g/cm(3) and sp(3) contents up to 87%. Deposition of ta-C in this experiment when the energetic species is Ar appears to require a minimum stress of 14 GPa to create significant sp(3) bonding, which contrasts with the continuous increase in sp(3) content with stress when the energetic species is C ions themselves. These results are used to discuss possible deposition mechanisms. (C) 1996 American Institute of Physics.