Vibrational spectroscopy characterization of low-dielectric constant SiOC:H films prepared by PECVD technique

Low-dielectric constant SiOC:H films were prepared by plasma enhanced chemical vapour deposition (PECVD) from trimethyl-silane (H-Si-(CH ₃)₃) and ozone (O₃) gas mixture. The samples were preliminarily annealed at 400°C in N₂ atmosphere and then in N₂ + He plasma. Afterwards, they were treated in vacuum at some fixed temperatures in the range between 400 and 900°C. Structural investigations of the annealed films were carried out by means of vibrational spectroscopy techniques. FT-IR spectrum of a preliminarily treated sample shows absorption bands due to stretching modes of structural groups like Si-CH ₃ at ∼1270cm^-1, Si-O-Si at 1034 cm^-1 and C-H_x in the region between 2800 and 3000 cm^-1. No significant spectral change was observed in the absorption spectra of samples annealed up to 600°C, indicating that the preliminarily treated film retains a substantial structural stability up to this temperature. Above 600°C, absorption spectra show a strong quenching of H-related peaks while the band due to Si-O-Si anti-symmetric stretching mode shifts towards higher energy, approaching the value observed for thermally grown SiO₂. Raman spectra of samples treated at temperatures T≥ 500°C exhibit both D and G bands typical of sp²-hybridised carbon, due to the formation of C-C bonds within the film which is accompanying the release of hydrogen. The intensity of D and G bands becomes more pronounced in samples annealed at higher temperatures, thus suggesting a progressive precipitation of carbon within the oxide matrix.