Laser desorption time-of-flight mass spectrometry of fluorocarbon films synthesized by C4F8/H2 plasmas

Abstract

Molecular structures of fluorocarbon films synthesized by C4F8/H2 plasmas were analyzed by laser desorption time-of-flight mass spectrometry (LD-TOFMS). Mass peaks of positive and negative ions with m/z up to 250 were observed in the mass spectra. Most of these ions were assigned as atomic hydrogen, atomic fluorine, carbon clusters, hydrocarbon clusters, fluorocarbon clusters, and hydrofluorocarbon clusters. The mass spectra changed sensitively with the partial pressure of H2. The LD-TOFMS analysis showed that the films changed from a polytetrafluoroethylene-like film into crosslinked carbon- and hydrogen-rich one by the addition of H2. The change in the chemical composition of the mass spectrum was consistent with the analyses by conventional x-ray photoelectron spectroscopy and Fourier transform infrared absorption spectroscopy. It is emphasized that LD-TOFMS can be used for the analysis of the degree of polymerization, which is an advantage of LD-TOFMS over the conventional analysis methods.