Carbon nitride thin films were deposited on Si(l 0 0) substrate by microwave plasma-enhanced chemical vapor deposition (PECVD). Hexamethylenetetramine (HMTA) was used as carbon and nitrogen source while N, gas was used as both nitrogen source and carrier gas. The sp -bonded C-N structure in HMTA was considered significantly in the precursor selection. X-ray diffraction analysis indicated that the film was a mixture of crystalline alpha- and beta-C3N4 as well as araphitic-C3N4 and beta-Si3N4 which were not easily distinguished. Raman spectroscopy also suggested the existence of alpha- and P-C3N4 in the films. X-ray photoelectron spectroscopy study indicated the presence of sp(2_) and sp(3) -bonded C-N structures in the films while (SPC)-C-3-N bonding structure predominated to the sp(2) C-N bonding structure in the bulk composition of the films. N was also found to be bound to Si atoms in the films. The product was, therefore. described as CNx:Si, where x depends on the film depth, with some evidences of crystalline C3N4 formation. (C) 2004 Elsevier B.V. All rights reserved.