HIGH-RATE AND HIGHLY SELECTIVE SIO2 ETCHING EMPLOYING INDUCTIVELY-COUPLED PLASMA

Plasma and SiO2 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 CHF3 plasma shows an increase in negative fluorine ions in the downstream regions. The intensity ratio of C2 (516.5 nm)/F(685.6 nm) also indicates high carbon-concentration in the downstream region. Further more, addition of H-2 to C4F8, which has more carbon species, yielded higher C2/F ratio. Accordingly, it was found that selectivity of SiO2/Si Si was remarkably enhanced by adding a higher concentration of H-2 to C4F8 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 highly selective SiO2 etching.