Quantitative infrared analysis of the stretching peak of SiO2 films deposited from tetraethoxysilane plasmas

Abstract

Infrared transmission spectra of silicon dioxide (SiO2) thin films (∼4500 Å) prepared by plasma-enhanced chemical-vapor deposition have been quantitatively analyzed. The films were deposited at different substrate temperatures (30–450 °C) using tetraethoxysilane (TEOS)/He, TEOS/He/O2, and TEOS/O2 gas mixtures in a parallel-plate radio-frequency reactor. The infrared transmission fits prove to be very accurate showing evidence of deconvolution into three separated Gaussian profiles to account for the asymmetric line-shape feature of the infrared stretching peak between 950 and 1300 cm−1. The examination of the Fourier transform infrared spectroscopy spectra in the complete frequency range (400–4000 cm−1) and ex situ x-ray photoelectron spectroscopy spectra indicates that some extra structures originate from the incorporation of carbon and hydrogen impurities in the film. As the substrate deposition temperature is increased, impurities are gradually removed from the growing layer. Films deposited at high substrate temperatures reveal a better stoichiometry and present similar deconvolution bands regardless of the gas-phase composition; the corresponding frequencies are shifted to lower energies compared to thermal oxides. In addition, the intensity of the first Gaussian profile, associated with the low-energy asymmetry of the stretching peak, increases with the substrate deposition temperature while the intensity of the third Gaussian profile associated with the presence of the high-energy peak shoulder decreases. The vibrational properties of the film seem to be strongly related to the deposition conditions.