XPS and laser Raman analysis of hydrogenated amorphous carbon films

• Published in: Diamond and related materials Vol. 12; no. 3; pp. 974 - 978
• Main Authors: Filik, J., May, P.W., Pearce, S.R.J., Wild, R.K., Hallam, K.R.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01.03.2003; Elsevier
• Subjects: Composition and phase identification; Condensed matter: structure, mechanical and thermal properties; Diamond-like carbon; Exact sciences and technology; Film composition; Laser Raman analysis; Physics; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology; XPS; Film composition; Diamond-like carbon; XPS; Laser Raman analysis; Raman spectra; Films; Amorphous state; Experimental study; Carbon; Diamond lattices; Nonmetals; Amorphous hydrogenated material; Chemical preparation; Chemical bonds; Chemical composition; X-ray photoelectron spectra
• ISSN: 0925-9635; 1879-0062
• DOI: 10.1016/S0925-9635(02)00374-6

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 1s 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 sp 3 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.