Effects of low-molecular-weight radicals for reduction of microloading in high-aspect contact-hole etching

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: C_xF_y) 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 CF₂ 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 C_xF_y radicals are thus necessary to eliminate microloading and etching-stop in the formation of high-aspect-ratio contact holes.