Characterization of CO2 plasma ashing for less low-dielectric-constant film damage

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The mechanism of CO2 plasma ashing process was evaluated. CO2 plasma is a good candidate for the ashing process for photoresists because it generates a lot of CO2 ions. These ions can ash equivalent amounts of carbon film with less low-k damage than can oxygen radicals. A high ratio of CO2 ions to oxygen radicals in CO2 plasma can make the ashing process efficient with less low-k damage. The ratio can be controlled by changing the CO2 flow rate, chamber pressure, and radio frequency (RF). When a lower RF frequency of 2 MHz as a plasma generator was used, the authors reduced sidewall low-k damage in patterned structures. CO2 ions can perform anisotropic ashing because the velocity distribution of CO2 ions is directional due to acceleration with a plasma sheath.