XPS and laser Raman analysis of hydrogenated amorphous carbon films

Hydrogenated amorphous carbon films were deposited in an RF parallel plate plasma reactor using various values of process pressure (10-50 mTorr) and DC self-bias (0-300 V). The films were then analysed by laser Raman spectroscopy (LRS) at 514.5 nm and X-ray photoelectron spectroscopy (XPS). Values for the ratio of sp(2):sp(3) bonded carbon in the various films were obtained by suitable fitting of the XPS carbon Is energy peaks, using a three-curve fitting procedure, which recognises a portion of the peak attributable to CO surface bonding. The sp(3) content was found to depend upon the DC self bias (and hence the ion impact energy) during deposition, peaking at a value of 81% at approximately 150 V The softer films grown at lower DC bias values still had an sp(3) content of approximately 70%. Microcombustion analysis showed that films deposited with low DC bias contained 7 at.% H compared to less than 2 at.% for films deposited at biases greater than 100 V. This high sp(3) content can be explained by H-termination of dangling bonds, suggesting that sp3 content alone is not a reliable indication of film properties. Curve-fittings of LRS spectra of the films showed that the Breit-Wigner-Fano lineshape is inappropriate for use with hydrogen containing films. Fitting using a Gaussian profile gave precise values for the FWHM, intensity, and Stokes' shift of the G and D-peaks. A linear relationship between the intensity ratio of the D to G peaks and the width of the G peak was found for films deposited at high DC bias (with low H content), but not for films deposited at low DC bias. This is consistent with the increased H content of the films causing a change in the elastic constants and/or affecting the stress levels within the films. (C) 2003 Elsevier Science B.V. All rights reserved.