Room temperature deposition of silicon dioxide films by ion-assisted plasma enhanced chemical vapor deposition

Silicon dioxide (SiO2) thin films were deposited on silicon wafers at 25 degrees C using varying degrees of ion energy flux (IEF) in a 13.56 MHz, RF driven asymmetric plasma reactor from a gas mixture of tetraethoxysilane (TEOS), Ar, and O-2. On-line mass spectrometer (MS) and optical emission spectroscopy (OES) were used to analyze the plasma chemistry while the films were analyzed by Fourier transform infrared (FTIR) and Rutherford backscattering spectroscopy (RES). The MS and OES results showed that the decomposition of TEOS was enhanced as the power input was increased and that the role of O-2 was to oxidize the hydrocarbon molecules to carbon oxides (CO and CO2) and water; which lead to fewer hydrocarbon impurities in the film. The refractive index and the density of the film increased while the etching rate of the film decreased with increasing IEF. The low p-etch rates of the films prepared at high IEF (>17 mW/cm(2)) suggested that the films have quality close to that of thermal oxide. From the FTIR spectra, the observed reduction in film porosity at high IEF coincides with the decreases in SiO-H and C=O peak intensities; and the decreasing shoulder of Si-O-Si antistretching mode in the range of 1260 similar to 1100 cm(-1). Also, the downward shift of the maximum peak of the Si-O-Si stretching suggested that the intrinsic stress of the films increased with increasing IEF. The surface topology measured by an atomic force microscopy was very flat even at a high degree of IEF (average roughness of less than 10 Angstrom).