Doping Induced Internal Stress Reduction in Diamondlike Carbon Films Deposited by Pulsed Laser Ablation

ABSTRACTWe have investigated the effect of dopants on the reduction of internal compressive stress in diamond-like carbon (DLC) films prepared by pulsed laser deposition on Si(100) substrates. A novel target configuration was used to incorporate dopants into DLC films by sequential pulsed laser ablation of two targets. These dopants include copper, titanium and silicon. The thickness of the DLC films deposited was measured in the range 400nm - 600nm using a profilometer. Raman spectroscopy was employed to analyze the chemistry of the films. The shifts of the G-peak position in the Raman spectrum, due to different concentrations of dopant, were used to estimate the internal stress changes. All of the films showed a Raman spectrum typical of DLC films containing a high fraction of sp3 species, with the G-peak centered at around 1510–1560cm−1. The shift of the G-peak due to the presence of dopants was observed for all the DLC films as compared to the undoped one. It was found that Ti has the strongest tendency to reduce the compressive stress of DLC films. This effect increases with increasing concentration of dopants. Silicon was also observed to have this effect, but the G-peak position did not appear to shift with different Si concentrations. Buckling occurred in the as-deposited, undoped DLC film because of the relief of the large compressive stress accumulated in the film, while all the doped DLC films showed good adhesion to the substrate. The results are discussed combining the atomic structure of DLC and the structure and properties of the dopants.