Characterization of Diamond like Carbon film Fabricated by ECR Plasma CVD at room Temperature
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Mat. Res. Soc. Symp. Proc. Vol. 504 © 1998 Materials Research Society
Plasma
Substrate
Substrate holder L
To the vacuum
S-pump
Bias indicator Microwave-Nort Ar Now
Magnetic coils CH4
RF source(13.56MHz)
Fig. 1. Schematic view of experimental apparatus. at 200W, and bias voltage was varied from 0 to 150V by adjusting the RF power to control the ion impinging energy to the substrate. RESULTS Dependence of substrate temperature and film hardness on bias voltage Figure 2 shows the dependence of substrate temperature and film hardness on the bias voltage. The substrate temperature was measured with a thermocouple in contact with the substrate surface after deposition of 250nm thick films. As the bias voltage was increased, the substrate temperature gradually increased. The reason for the increased substrate temperature was considered to be ion impingement on the substrate throughout the process; however, it was nearly at the room temperature level around 50'C. On the other hand, the hardness of the films drastically increased up to 3000Hv by applying a bias voltage of 50V and then remained nearly constant as the bias voltage was increased to 150V. In order to investigate the structures of the films fabricated at the bias voltages of OV and 50V, Raman spectroscopy and scanning electron microscopy were performed. The results are shown in Fig. 3. By applying a bias voltage, there clearly emerged a typical spectrum
"- 100
4000
U
3000 U
S50
2000
U
U.
1000
,
0
-0
.0 80 120 Bias voltage (-V)
160
Fig. 2. Dependences of substrate temperature and film hardness on bias voltage. 254
Surface
Surface Film
F
Si substrate
Si substrate
500nm
500nm
"'
U
2000
.,
1600 1200 Wave number (cm-1) (a) Bias voltage:OV
800
2000
1600 1200 Wave number (cm-1) (b) Bias voltage:50V
800
Fig. 3. Raman spectra and scanning electron micrographs of films fabricated on Si(100) substrates at bias voltages of OV(a) and 50V(b). corresponding to DLC, which had a peak at around 1530cm-1, called the graphite band (G-band), with a shoulder at around 1400cm-', called the disorder band (D-band)[4]. Furthermore, the film exhibited a minute structure and a smooth surface. Accordingly, this result suggests that impingement with ions energized by a bias voltage of 50V is fundamentally required in the growth of DLC films and that DLC films with a hardness of more than 3000Hv can be fabricated at about 50"C. Effect of bias voltage on structural change of DLC films It was impossible to study the effect of ion impingement on the properties of DLC films fabricated above the bias voltage of 50V through the hardness test, as shown in Fig. 2. Therefore, optical and electrical measurements were performed for DLC films fabricated on a glass substrate. The optical gaps were calculated by the Tauc's plot[7]. Evaporated Al electrodes were used in a gap cell configuration of 0.5mm width for the electrical resistivity measurement. Figures 4 and 5 show the dependence of the electrical resistivity and the optical gap on bias voltage, which was v
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