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.