Mechanism of Highly Selective SiO2 to Si3N4 Etching Using C4F8 + CO Magnetron Plasma

Highly selective SiO2 to Si3N4 etching was achieved using C4F8 + CO magnetron plasma when the CO gas-mixing ratio exceeded 75%. The analyses of fluorocarbon radicals in the plasma showed a higher carbon-to-fluorine ratio with increasing CO ratio. In particular, a drastic increase in the C radicals was observed, which corresponded to the increase in electron density. The reaction mechanism of CO in the C4F8 + CO plasma was investigated utilizing CO composed of the 13C isotope. CO supplied the carbon by electron-impact dissociation and scavenged fluorine by forming COF x . The carbon-implanted Si3N4 film clarified the role of carbon on Si3N4 etching. The decrease in the Si3N4 etching rate and the increase in the fluorocarbon film thickness on the surface were observed with increasing carbon dose. CO addition thus realizes the high selectivity to Si3N4 in SiO2 etching.