High Rate and Highly Selective SiO₂ Etching Employing Inductively Coupled Plasma

Abstract

Plasma and SiO 2 etching characteristics employing inductively coupled plasma (ICP) were studied with respect to distance from an antenna. Measurement of the ratio of electron to ion saturation currents in CHF 3 plasma shows an increase in negative fluorine ions in the downstream regions. The intensity ratio of C 2 (516.5 nm)/F(685.6 nm) also indicates high carbon-concentration in the downstream region. Further more, addition of H 2 to C 4 F 8 , which has more carbon species, yielded higher C 2 /F ratio. Accordingly, it was found that selectivity of SiO 2 /Si was remarkably enhanced by adding a higher concentration of H 2 to C 4 F 8 in the downstream region. The favorable results are due to the sheetlike characteristics of ICP. Since the plasma is confined near a quartz plate, HF molecules generated from the reaction of H atoms with F atoms do not undergo dissociation in the diffusive region. Thus high-speed pumping of HF is considered to suppress Si etching and in turn, to allow highiy selective SiO 2 etching.