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

In this work, technological conditions for SiOFC layers formation by PECVD method using TEOS (Tetra-ethyl orthositicate) 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 difluoride 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.