We investigate the synergistic effects of a remote rf oxygen plasma source operated simultaneously with rf bias at low temperature and find that the photoresist removal rates substantially exceed those observed with either plasma source alone. When applied to high dose ion-implanted photoresist, optical emission curves show a transition between the hydrogen-devoid crust, where oxygen radical consumption is reduced, and the underlying bulk photoresist, where oxygen radical consumption is substantial. Differences between the reactant and product optical emission traces are indicative of complex mechanisms during the crust removal, which are likely related to crust inhomogeneities observed from scanning electron microscopy (SEM) analysis. Crust removal times are as short as 13-16 s, crust removal rates are 1-1.3 mu m/min or about half the removal rate of unimplanted photoresist, and crust density estimates are similar to the density of graphite. Because photoresist removal rates are comparable to conventional high temperature downstream ashers, a single step low temperature dual-mode plasma process is able to remove both the crust and bulk photoresist in less than 40 s. 0 2006 American Vacuum Society.