A high SiO2 etching rate (more than 5000 A/min) and an extremely high etching selectivity to photoresist (more than 10) have been simultaneously achieved in C2F4/CF3I/Ar plasma using a conventional dual-frequency reactive ion etching system. The etching selectivity increases with increases of Ar dilution in C2F4/CF3I. The carbon/fluorine ratio of the fluorocarbon polymer on the photoresist was drastically increased by Ar dilution and ion bombardment, which caused the etching rate of a photoresist to decrease. Under these conditions, high-aspect-ratio SiO2 contact etching (0.09 μm Φ, more than 10) was achieved. These gas chemistries are promising candidates for use in nano-scale high-aspect-ratio SiO2 etching. © 2003 American Vacuum Society.