Ellipsometric Evaluation of the sp³-Bonded Carbon Fraction in Carbon Thin Films

We prepared amorphous carbon films on Si (100) substrates by using a magnetic-field-filtered plasma stream deposition system. Various samples with different sp³-bonded carbon fraction were obtained by changing the bias voltage applied to the substrates. We measured the ellipsometric spectra of various carbon film samples in the photon energy range of 2.0-5.0 eV. We also measured the Raman spectra for comparison. Our results show that the ellipsometric spectra are dependent on the sp³ carbon fraction. We analysed the measured ellipsometric spectra by a simple method, and determined the sp³ carbon fraction semi-quantitatively. The results from the ellipsometry and the Raman spectroscopy show the same tendency of the sp³ carbon fraction as a function of bias voltage. We found that the spectroscopic ellipsometry is a relatively simple, non-destructive method to evaluate the sp³ carbon fraction of the amorphous carbon films.