Optoelectronic properties of fluorine-doped silicon nitride thin films

Plasma-enhanced chemical vapor deposition (PECVD) of fluorine-doped silicon nitride (SiNx:F) has been investigated with a small amount of tetrafluorosilane (SiF4) added into the SiH4–NH3 gas mixture. The influence of preparation conditions on the optical and electrical properties of the SiNx:F films has been systematically studied by XPS, FT-IR and UV–visible spectroscopy for optical property and current–voltage ramping measurement for electron conduction mechanism. It has been found that low radio frequency plasma power and the appropriate amount of SiF4 addition favor the improvement of film properties to minimize the side effect for high quality film deposition such as etching effect from the dissociated SiFx and F radicals. Remarkably, deposition rate and optical band gap are higher than that in SiH4–NH3 gas chemistry even in the case of NHx radical deficient deposition conditions. SiNx:F films have lower hydrogen content and show rather rough and porous microstructure. However, the improvement of dielectric property can be obtained with high optical band gap (∼5.5 eV), resistivity (>1017 Ω cm) and barrier height (>1.6 eV) for the trapped electron conduction even in the Si-rich nitride films.