Effects of working pressure on the deposition of diamond-like carbon films prepared by bipolar-type plasma based ion implantation

Abstract

Diamond-like carbon (DLC) films are prepared by a bipolar-type plasma based ion implantation (PBII), and the deposition rate and the microstructure of the films are examined as a function of working pressure (P) in the range of 0.08–0.5Pa. The positive and negative pulse voltages are fixed at +2kV and −5kV, respectively. The optical emission spectra on the bipolar pulse plasma are also examined. It is found that the deposition rate is increased with increasing P. Raman analysis shows that the intensity ratio of D peak to G peak, ID/IG, suggesting the amount of graphite-like structure, is not significantly changed in this pressure range. However, ion beam analysis reveals that the density of the films is slightly decreased with increasing P, probably due to the increase of H concentration in the films. In addition, the hardness and elastic modulus of the films are also gradually decreased with increasing P. On the other hand, optical emission peaks from H, CH and C radicals are clearly observed. These peaks, especially CH radical, are increased in intensity with increasing P, indicating that the plasma density is increased. This result in the increase of the deposition rate and the results suggest that the rapid increase of CH radicals (and CH ion flux) at higher P presumably causes the slight reduction of the density and mechanical properties of DLC films due to the increase of H concentration.