SiO2 etching is done by using fluorocarbon gases to deposit a fluoropolymer on the underlying silicon. This deposit enhances the etching selectivity of SiO2 over silicon or silicon nitride. CF2 radicals are used as the main gas precursor for polymer deposition. In a conventional gas plasma, however, the CF2 radicals and other radicals (high-molecular-weight radicals: CxFy) lead to polymerization. This condition causes microloading and etching-stop in high-aspect contact-hole patterning due to the sidewall polymerization during SiO2 etching processes. Conversely, by using new fluorocarbon gas chemistries (C2F4/CF3I), we achieved selective radical generation of CF, and eliminated high-molecular-weight radicals. Under this condition, microloading-free and etching-stop-free high-aspect-ratio contact-hole patterning of SiO2 was accomplished. Thus, the higher molecular weight radicals play an important role in the sidewall polymerization in contact holes because these radicals have a higher sticking coefficient than CF2 radicals. Selective generation of CF2 radicals and suppression of CxFy radicals are thus necessary to eliminate microloading and etching-stop in the formation of high-aspect-ratio contact holes.