Transmission of oxygen radicals through free-standing single-layer and multilayer silicon-nitride and silicon-dioxide films

摘要

Free radicals from processing plasmas are known to cause damage to dielectric films used in semiconductor devices. Many radicals are highly reactive and can readily interact with the material exposed to the plasma. This can modify the chemical structure of the material causing deterioration of electrical and mechanical properties of the films. This work detects the transmission of oxygen radicals through single- and double-layer silicon-nitride and silicon-dioxide freestanding films. The films were exposed to oxygen plasma. A fluorophore dye was used to detect the oxygen radicals traversing through the films. By measuring the fluorescence of the dye before and after multiple timed-plasma exposures, the transmission properties of oxygen radicals through the material were found. The results indicate that the absorption length of oxygen radicals increases with increasing plasma exposure times for Si_3N_4 films because the oxygen plasma oxidizes the top layer of the film and forms a less dense silicon oxynitride layer. For SiO_2 films, the absorption length was found to decrease as a function of plasma exposure time because of oxidation of the SiO_2 surface which leads to the formation of a denser oxide layer on the surface of the sample.