LOW-TEMPERATURE SYNCHROTRON-RADIATION-EXCITED ETCHING OF SILICON DIOXIDE WITH SULFUR-HEXAFLUORIDE ADSORPTION

Ultralarge-scale integration circuits now require innovative microfabr ication processes in order to achieve gigabit-scale integration. One a pproach is to use soft x rays, because they can give excellent spatial resolution by their short wavelength and high-reaction selectivity by core-electron excitation. Synchrotron-radiation (SR) -excited etching of SiO2 and Si is studied from the viewpoints of pattern replicabilit y and analysis of etching selectivity between two layers. Deep-submicr on patterns of SiO2 are formed by cooling the specimen with liquid N2 and adsorbing SF6 reaction gas during SR irradiation. Photon-stimulate d desorption ions from SF6-adsorbed SiO2 and Si surfaces are first inv estigated. As a result, ion species such as SiF(n)+ and SO(n)+, which are etching products from the surface, are obtained only from SiO2, an d this selective etching of SiO2 is also investigated by x-ray photoel ectron spectroscopy. In this selective etching mechanism, constraint o f Si-etching by passivation of photofragment S+ ions is most likely. T he higher selectivity of this reaction can be used not only for bulk S iO2 etching, but also for Si-surface cleaning by eliminating native ox ide.