CHARACTERIZATION OF SILICON DIOXIDE FILMS DEPOSITED AT LOW-PRESSURE AND TEMPERATURE IN A HELICON DIFFUSION REACTOR

Silicon dioxide films have been deposited at low pressure (a few millitorr) and low substrate temperature ( < 200-degrees-C) by oxygen/silane helicon diffusion radio frequency plasmas. High deposition rates (20-80 nm/min) are achieved at 800 W rf source power. The effect of the oxygen/silane flow rate ratio (R) on the film properties has been investigated: characterization of the deposited films has been carried out by in situ ellipsometry, ex situ Fourier transform infrared spectroscopy, Rutherford backscattering, x-ray photoelectron spectroscopy (XPS), and chemical etch rate measurements (P etch) and the results have been compared to thermally grown oxide. The deposition kinetics has a great effect on the internal film structure: for films presenting a good stoichiometry ([O]/[Si] greater-than-or-equal-to 1.95 for R greater-than-or-equal-to 3), a decrease in the deposition rate is accompanied by a decrease of the refractive index, P-etch rate and XPS line width and by an increase of the Si-O stretching peak frequency toward the thermal oxide respective values. A sufficient oxygen/silane flow rate ratio (R = 10) leads to stoichiometric films which exhibit good optical properties. Small differences in the P-etch rate, XPS linewidth, and infrared stretching peak frequency are still observed between our stoichiometric plasma deposited film and a thermally grown oxide film.