A high ion energy and high pressure O2/CO-based plasma for ashing field photoresist material subsequent to via-level damascene processing. The optimized plasma ashing process is performed at greater than approximately 300 mT pressure and ion energy greater than approximately 500 W conditions with an oxygen partial pressure of greater than approximately 85%. The rapid ash rate of the high pressure/high ion energy process and minimal dissociation conditions (no “source” power is applied) allow minimal interaction between the interlevel dielectric and ash chemistry to achieve minimal overall sidewall modification of less than approximately 5 nm.