Fluorinated a-C:H films investigated by thermal-induced gas effusion

Abstract

Using thermal-induced gas effusion the decomposition of plasma deposited fluorinated a-C:H films has been investigated. The main contributions to the effusion spectra were found to come from hydrogen, hydrocarbons, CF 4 and HF. It is observed that hydrogen-related effusion is progressively substituted by the effusion of CF 4-related species as the fluorine content is increased, confirming that fluorine atoms substitute hydrogen in the amorphous network. At low fluorine contents (<10 at.%) the material is relatively compact and the effusion of hydrogen-related species (hydrogen molecules and hydrocarbons) dominate. For high enough fluorine concentrations a strong change in the effusion characteristics indicates that an interconnected network of voids is present. Strong effusion of CF 4-related species is found to be consistent with a surface desorption process and can be observed when CF n bonds are present in the film microstructure and the void network dimensions are large enough, i.e. for films with the highest fluorine contents (∼20 at.%). The effusion results can be correlated to a structural transition from diamond-like to polymer-like film.