Mechanical stability of DLC films on metallic substrates: Part I - Film structure and residual stress levels

Hydrogenated diamond-like carbon (DLC) films have been deposited onto aluminium, titanium and silicon substrates using a 13.56 MHz capacitively-coupled RF glow discharge in a methane atmosphere. All of the DLC films, which were prepared with a negative bias voltage in the range 40 V to 345 V and a gas pressure in the range I Pa to 40 Pa, showed strong sp(3)-CHx, FTIR absorbance peaks at 2900 cm(-1) and a broad Raman peak at 1540 cm(-1). Deposition temperatures, which were measured using irreversible self-stick thermax, varied from 25 degrees C to 182 degrees C. Stress levels in the films were measured by monitoring the curvature changes of thin (125 mu m) Ti foil after depositing thick (several mu m) DLC films, using an Al bonding layer. This intrinsic (deposition) stress was compressive and varied from -0.3 GPa to -2.0 GPa. It increased initially with the energy of the bombarding ions, as implantation became more pronounced, reached a maximum and then decreased, as a consequence of thermally-activated structural relaxation. The experimental stress data agree well with predictions from a model proposed by Davis [C.A. Davis, A simple model for the formation of compressive stress in thin film by ion bombardment, Thin Solid Films, 226 (1993) 30-34]. (C) 1998 Elsevier Science S.A.