Impact of F species on plasma charge damage in a RF asher

Resist stripping and cleaning is evaluated on a RF asher. A combination of RF and MW power can be used to enhance the stripping efficiency in the asher. The RIE components of a plasma are capable of producing plasma damage (can be observed in structures such as thin gate oxide underneath poly lines). In this evaluation, both metal antenna structures and Charm-2 wafers were used to monitor plasma charging. No plasma charging was observed using the standard O₂/N₂H₂ plasma, but high plasma charge voltages could be observed with NF₃ addition. The plasma characteristics were studied using optical emission spectroscopy. Analysis of the results suggests that plasma charging can be induced by a combination of RF and free fluorine species in the plasma.