Thickness dependence of the structure of a-C:H thin films prepared by rf-CVD evidenced by Raman spectroscopy

Polymeric hydrogenated amorphous carbon (a-C:H) thin films of different thickness were prepared by radio frequency chemical vapor deposition method from benzene using low ion energies. The dependence of the bonding configuration on the thickness of the layers was investigated by infrared excited Raman spectroscopy. It was found that the shape of the spectra changes significantly as the thickness increases. While 60 nm thick layer consists of sp clusters built mainly of chains, an increased thickness of up to 500 nm results in the formation of an amorphous carbon matrix containing distorted or partially destroyed benzene rings. Additionally, the Raman spectra provide evidence for the presence of an increasing amount of intact substituted benzene rings in the structure. Above 500 nm, the bonding configuration of the films does not show significantly dependence on thickness. (c) 2006 Elsevier B.V. All rights reserved.