QUANTITATIVE INFRARED-ANALYSIS OF THE STRETCHING PEAK OF SIO2-FILMS DEPOSITED FROM TETRAETHOXYSILANE PLASMAS

Infrared transmission spectra of silicon dioxide (SiO2) thin films (ap proximately 4500 angstrom) prepared by plasma-enhanced chemical-vapor deposition have been quantitatively analyzed. The films were deposited at different substrate temperatures (30-450-degrees-C) using tetraeth oxysilane (TEOS)/He, TEOS/He/O2, and TEOS/O2 gas mixtures in a paralle l-plate radio-frequency reactor. The infrared transmission fits prove to be very accurate showing evidence of deconvolution into three separ ated Gaussian profiles to account for the asymmetric line-shape featur e of the infrared stretching peak between 950 and 1300 cm-1. The exami nation of the Fourier transform infrared spectroscopy spectra in the c omplete frequency range (400-4000 cm-1) and ex situ x-ray photoelectro n 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 g radually removed from the growing layer. Films deposited at high subst rate temperatures reveal a better stoichiometry and present similar de convolution bands regardless of the gas-phase composition; the corresp onding frequencies are shifted to lower energies compared to thermal o xides. In addition, the intensity of the first Gaussian profile, assoc iated with the low-energy asymmetry of the stretching peak, increases with the substrate deposition temperature while the intensity of the t hird Gaussian profile associated with the presence of the high-energy peak shoulder decreases. The vibrational properties of the film seem t o be strongly related to the deposition conditions.