Физика твердого тела, 2004, том 46, вып. Precursors for CVD growth of nanocrystalline diamond decreases with increase in biasing voltage. Although not shown here, the hardness of NCD films grown by the BEG process at 200 V approaches to the hardness of natural diamond when the thickness increases to 4 µm . The Raman peak ratio In/Ig (the ratio of 1150 cm-1 feature to graphite G band) varies in the same fashion as the hardness of the films indicating that the relative concentration of NCD in the films may be responsible for the hardness of the films.
The stress in the films increases with increasing bias voltage and increases drastically in the film grown at 320 V. The samples grown at 320 V were visibly bent, and accounted for an enormous stress in the films . It should be mentioned that no bending was observed in a sample, in a separate experiment, treated at bias voltage of -320 V for an hour while using only hydrogen, i. e., without any methane in the gas-phase. This means that the bending occurs solely due to stress generating in the carbon film depositing on the wafers. To the best of our knowledge, there is no report of such an enormous amount of stress in carbon films. It may be mainly because the films, deposited Figure 4. XRD patterns of the films deposited at the bias voltage by other groups, if having compressive stress more than of 200 (a) and 320 V (b).
2 GPa, delaminated soon after the deposition due to weak adhesion [37,38]. However, in our case, a strong adhesion of the films to the substrate is developed making it possible to Fig. 3 shows the Raman spectra of the films deposited on Si(100) at the biasing voltages of 200 and 320 V. It should be noted that the deposition didn’t take place when the biasing voltage was lower than 200 V. As can be seen, the intensity of the NCD Raman feature has almost vanished in the films grown at 320 V. Moreover, there is a drastic variation in the position of the graphitic G band in the film grown at 320 V. It appears that relative concentration of spto sp2 carbon of the films decreases with biasing voltage in the films. It suggests that the relative intensity of the NCD Raman feature decreased with increasing the biasing voltage. In fact, the NCD Raman feature appeared to have almost vanished in the films grown at 320 V. Moreover, there was a drastic variation in the position of the graphitic G band in the films grown at 320 V. Overall, it appears that the relative concentration of sp3 to sp2 carbon of the films decreases with biasing voltage in the films. But it should be noted that no peaks associated with graphite could be identified in our films.
XRD patterns of the films at the biasing voltages of 200 and 320 V are shown in Fig. 4. The calculated interplanar spacing corresponding to the peaks at 2 44.05, 75.25 ± 0.20 in the XRD patterns of the films match closely with the inter-planar d-values of (111) and (220) planes of cubic diamond, respectively. It should be noted that the full width at half maximum (FWHM) of the diamond peaks in the films is in general high as compared to the MCD films. This is well correlated with the fact that diamond nanocrystallites are present in our films. It should be noted that no peaks associated with graphite or features related with amorphous carbon could be identified in our films.
Figure 5. Plot of hardness, Raman intensity ratio of NCD (In) to Fig. 5 illustrates the summary of the properties grown graphitic G band (Ig), compressive stress, layer thickness, and rms at different biasing voltages. The hardness of the films surface roughness of the film, as a function of biasing voltage.
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