Investigation of simultaneous fluorine and carbon incorporation in a silicon oxide dielectric layer grown by PECVD

In this work, technological conditions for SiOFC layers formation by PECVD method using TEOS (Tetra-ethyl ortho-silicate) and C2F6 chemistry were identified, and the effect of simultaneous fluorine (F) and carbon (C) incorporation into SiO2 network was studied. Optical and structural properties of the deposited layers as a function of RF (Radio Frequency) power and gas flow were investigated by ellipsometric, XPS (X-ray Photoelectron Spectroscopy), and FTIR (Fourier Transform Infrared Spectroscopy) methods. It was found that RF power and gas flow have complex impact on SiOFC layers: C in the films was observed only at low C2F6 flow, and decreased when the flow increased; increased RF power increases amount of F, simultaneously decreasing C content; both dopants, F and C, substitute O in SiO2 network; presence of terminal bonds creates high-order rings in the oxide network that serve as nano-voids; increased RF power converts di-fluoride tetrahedra into mono-fluoride units, and substantially decreases OH content of the films. These changes led to a decreasing of film density, refractive index and dielectric constant.