Solid-state nuclear magnetic resonance spectroscopy of low dielectric constant films from pulsed hydrofluorocarbon plasmas

Solid-state nuclear magnetic resonance (NMR) spectroscopy is applied to the study of films from pulsed plasma enhanced chemical vapor deposition from two hydrofluorocarbon gases, CHF₂CHF₂ and CH₂F₂. Beyond confirming the relative CF_x fractions obtained from X-ray photoelectron spectroscopy, NMR offered greater structural insight into the plasma film network. ¹⁹F NMR identified various network sequences, three CF₃ (CF*₃ C, CF*₃ CF, CF*₃ CF₂), five CF₂ (CF₂CF*₂CF₂, CF₂CF*₂CF₃, CF₂CF*₂CHF₂, CF₂CF₂CHF*₂, CF_xCF*₂CF_x), and three CF (CF*, CH₂F*, CF* = C<) segments, based on differences in next nearest neighbor attachment. ¹³C NMR distinguished between sp³ and sp² bond configurations, with further separation of unsaturated nonfluorinated carbons into two distinct types. One is attributed to aromatic or graphitic carbon structures while the other is due to unsaturated carbons in closer proximity to fluorines. NMR also allowed changes in structure to be probed upon film thermal decomposition. The film from CHF₂CHF₂ showed both precursor desorption and CF₃ detachment, while that from CH₂F₂ showed only CH₂F loss.