Residual stress measurement in DLC films deposited by PBIID method using Raman microprobe spectroscopy

Diamond-like carbon (DLC) films were prepared and their residual stresses were measured nondestructively using Raman microprobe spectroscopy. The plasma-based ion implantation and deposition (PBIID) method was used to coat the DLC films on thin glass substrates using acetylene, a mixture of acetylene and toluene, or only toluene gas at 1.0 Pa. Peaks in the Raman spectra of the DLC films were assigned as the D′(disordered) or C-C bonding peaks at 1150 cm− 1. The phonon deformation potentials (a′) of the films were estimated from data for the phonon deformation potentials for pure graphite and diamond and calculated using the sp3/sp2 bonding ratio and the hydrogen content of the films. Thus, a relation was observed between the Raman shift of the G peak (ωG) and the residual stress (σc) in each film. The Raman shifts (ω0) of the G peak for the films with no deformation were 1554, 1556, and 1562 cm− 1 for the films deposited using acetylene, a mixture gas and toluene gas. Moreover, only toluene had stress constants of − 0.378, − 0.384, and − 0.391 GPa/cm− 1. The residual stresses constant in each film using (8.2 × 10− 4·a′)− 1 ω0− 1 were estimated as − 0.379, − 0.384, and − 0.391 GPa/cm− 1. The Raman shift of the D peak remained stationary as the compressive σc in the films increased but changed when the deposition gas was varied. The distance the D peak moved from 1420 cm− 1 corresponded to that of the G peak from 1560 cm− 1 in the Raman spectra of the films in the stress-free state. In addition, the compressive residual stress in the DLC film had a major impact on the hardness.