Spectro-ellipsometric studies of defective diamond films deposited by MPECVD

Abstract

Abstract Novel diamond films, which were deposited by microwave plasma enhanced chemical vapour deposition (MPECVD) method using various mixtures of methane and hydrogen gases, and exhibited excellent electron-emission characteristics, have been investigated by X-ray diffraction, Raman spectroscopy, atomic force microscopy, scanning electron microscopy and spectroscopic ellipsometry. The structural investigation has shown that these films are nanocrystalline diamond films and that there are distorted sp 3 -bonded carbons and sp 2 -bonded carbons in the grain boundaries. Moreover, the methane-concentration and the depth-dependent distributions of sp 2 -bonded carbons have been quantified nondestructively by fitting the measured ellipsometric spectra to the three-layer model of the surface layer (diamond+void), the bulk-like layer (diamond+glassy carbon), and the interface layer (diamond+glassy carbon). Interestingly, the relative glassy-carbon fraction in each layer has been found almost invariant for given methane concentration regardless of the thickness. However, regardless of the methane concentration, the interface layers have been found to have a higher glassy-carbon fraction, while the rough surface layers are free from glassy carbon. Finally, it has been found that both the film growth rate and the glassy-carbon fraction increase as a function of methane concentration.