Characterization of Low-Temperature PECVD Silicon Dioxide Films

Silicon dioxide (SiOx, x ≤ 2) films were plasma-deposited at a pressure of 1 Torr and low substrate temperature (≤ 300°C) by N20/lSiH4 flow. Deposition rates in the range 20–50 nm/min were achieved at 20 W rf source power. Deep level transient spectroscopy showed that no significant defect levels were introduced in the Si substrates at this low source power. The effects of flowrate ratio, R, of N2O/SiH4 and substrate temperature on film properties were determined using ex-situ spectroscopic ellipsometry, prism coupler, Rutherford backscattering spectroscopy (RBS), secondary ion mass spectrometry (SIMS), Fourier transform infrared spectroscopy (FTIR) and chemical etching (P-etch). Near-stoichiometric oxide layers were obtained for R ≥ 1, and a decrease in deposition rate with increasing R was observed. The increase in refractive index for R ≤ 1 has been correlated to compositional changes in the thin films. Complementary results were obtained from FFIR and P-etch measurements. Nitrogen was present in the films deposited using R = 4.4, for which the depostion rate showed an Arrhenius-like relationship to substrate temperature. No OH-related bands were observed in our films.