Electrochemical Cleaning of Post-Plasma Etch Fluorocarbon Residues Using Reductive Radical Anion Chemistry

Abstract

A process for cleaning post-etch fluorocarbon residues based on reductive radical ion chemistry has been developed and modified for use in semiconductor processing. Conventional liquid cleaning processes or oxidative processes may be incompatible with emerging low-dielectric constant materials. X-ray photoelectron spectroscopy results indicate that radical anion solutions, based on sodium-naphthalenide, are capable of defluorinating model fluorocarbon etch residues at a rate of 27 nm/min. To eliminate sodium, which is a semiconductor contaminant, radical naphthalene ions can be generated electrochemically without sodium. Comparable defluorination of fluorocarbon materials was observed. A selective carbon-carbon bond cleavage using aqueous ozone was necessary to complete the removal of the defluorinated residue. Semiconductor process compatibility was evaluated using three interlevel dielectric materials. Both silicon dioxide and Coral demonstrated good chemical and etch resistance to the process. Minimal oxidation of methylsilsesquioxane was observed during the ozone treatments.