New radical-injection method for high-performance dielectric 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 the main polymer precursor. In a conventional gas plasma, however, the CF₂ radicals and other radicals (high-molecular-weight-radicals: C_xF_y) lead to polymerization. This causes microloading and etching-stop in high-aspect contact-hole patterning due to the sidewall polymerization during SiO₂ etching processes. By using new fluorocarbon gases (C₂F₄ and CF₃I), however, we were able to generate CF₂ radicals selectively and to eliminate high-molecular-weight-radicals. This made possible microloading-free and etching-stop-free high-aspect-ratio contact-hole patterning of SiO₂. The higher-molecular-weight radicals play an important role in the sidewall polymerization in contact holes because they have a sticking coefficient higher than that of 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.