Abstract
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 (O
3) gas mixture. The samples were preliminarily annealed at 400
°C in N
2 atmosphere and then in N
2+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 ∼1270
cm
−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 SiO
2. Raman spectra of samples treated at temperatures
T⩾500
°C exhibit both D and G bands typical of sp
2-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.