Effects of Ar gas pressure on microstructure of DLC films deposited by high-power pulsed magnetron sputtering

Diamond-like carbon (DLC) films are prepared on Si substrates by a high-power pulsed magnetron sputtering and the microstructure is examined using Raman spectroscopy as a function of Ar gas pressure in the range of 0.11–0.52 Pa. Compositional analysis is also carried out by Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA). In the Raman spectra, disorder (D) and graphite (G) peaks are observed at around 1370 and 1580 cm−1, respectively, for all samples. The parameters, the intensity ratio of D peak to G peak (I(D)/I(G)), G peak position and full width at half maximum (FWHM) of G peak, are obtained by peak fitting using Gaussian function. The I(D)/I(G) decreases from 3.84 to 3.32 with increasing Ar gas pressure up to 0.3 Pa. At further increase of the pressure, it is nearly constant of 3.3, indicating the sp2 cluster size is not changes. In addition, the G peak position also decreases from 1584 to 1571 cm−1, and the FWHM of G peak increases from 125 to 144 cm−1 with increasing pressure up to 0.3 Pa. These results suggest that the disordering of the films is enhanced up to 0.3 Pa. However, the G peak position shifts to 1578 cm−1 and the FWHM decreases at further increase of the pressure, suggesting that the sp2 clusters increase in amount. Ion beam analysis also reveals that the density of the films increases from 1.66 to 2.03 g/cm3 with increasing pressure up to 0.3 Pa and decreases to 1.79 g/cm3 at higher pressure than 0.3 Pa. H concentration also increases from 10 to 14.9 at% at the pressure more than 0.3 Pa. These results suggest that the densification of DLC films proceeds by varying Ar gas pressure up to 0.3 Pa, but it is suppressed possibly due to the increase in H concentration at further increase of the pressure. In current experiments, the pressure around 0.3 Pa may be suitable for sp2 phase disordering and less sp2 clustering, relating to the increase of sp3 C–C configuration in the films.