Resist and Sidewall Film Removal after Al Reactive Ion Etching (RIE) Employing F+H2O Downstream Ashing

The sidewall residue seen after Al etching and via-hole etching on an Al pattern was investigated. X-ray photo-electron spectroscopy (XPS) after O2 plasma ashing revealed that this sidewall residue contained a large number of Al atoms sputtered from the Al film surface. A downstream ashing technique employing F atoms and water vapor has already been developed to remove the persistent resist after plasma processing or ion implantation, but even this downstream ashing could not remove the sidewall residue containing Al. It has been found that the downstream process changed Al and Al oxide in the residue to Al fluoride, a water-soluble compound. Thus, rinsing with DI water successfully removed the sidewall residue after downstream ashing.