Thermal stability and bonding configuration of fluorine-modified low-k SiOC:H composite films

Fluorine-modified organosilicate glass (F-SiOC:H) and unmodified organosilicate glass (OSG) films were deposited for comparison at various temperatures (200-400 deg. C) by plasma enhanced chemical vapor deposition (PECVD) method using mixed precursors of tetrafluorosilane, trimethelysilane and oxygen. Subsequently, the films were investigated by examining bonding configuration, index of refraction, surface composition, hardness, leakage current density and breakdown field strength with various annealing cycles, where each cycle represents annealing at 400 deg. C for 30 min followed by cooling to room temperature. The absorption spectra of Fourier transform infrared (FTIR) spectroscopy show that the frequency of Si-O stretching vibration mode in the as-deposited F-SiOC:H films shifted to higher wave number (blueshift) with fluorine incorporation compared with the OSG films, while that shifted to lower wave number (redshift) upon annealing. The FTIR results also show the reduction of fluorine and methyl group upon annealing, which coincided with X-ray photoelectron spectroscopy (XPS) analysis. The dielectric constant of the annealed F-SiOC:H films is higher than that of the as-deposited films. However, this is still lower than the annealed OSG films. The higher hardness and breakdown voltage strength were achieved in the F-SiOC:H films due to fluorine introduction and more perfect network structures. Comparing these results to those obtained OSG films shows that the mechanical and electrical strength of the F-SiOC:H films was improved by introducing of fluorine incorporation and annealing treatment, while maintaining or lowering a dielectric constant