A soft Plasma Enhanced-Chemical Vapor Deposition process for the tailored synthesis of SiO2 films

The availability of soft synthetic processes for the preparation of SiO2 films with tailored features plays a key role for several technological applications, from optics to electronics, from surface modifications to barrier coatings. In such context, this work presents the development and optimization of a Plasma Enhanced-Chemical Vapor Deposition route towards high-purity SiO2 films at near room temperature. Depositions were performed from Ar and Ar/O2 plasmas using tetramethoxysilane as precursor, devoting particular attention to the interplay between film properties and process parameters (RF- (Radio Frequency-) power, total pressure, O2/(Ar+O2) ratio and precursor vaporization temperature). Real-time information on the growth process was gained by Laser Reflection Interferometry, while the chemical composition and bonding structure of the obtained layers were analyzed by Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy. Scanning Electron and Atomic Force Microscopies were adopted to analyze the surface and cross-sectional film morphology. The system structural and optical properties were investigated by means of Glancing Incidence X-Ray Diffraction and UV-Vis spectroscopy. Finally, nanoindentation measurements were performed to investigate film hardness. Under optimized conditions, very pure silica films, characterized by a remarkable optical transparency and favorable mechanical properties, were obtained even at RF-power values as low as 5 W and in the absence of O2 in the plasma.