Stripping of photoresist on silicon wafer by CO2 supercritical fluid

Supercritical CO2-based fluid is not only being considered as environmentally benign medium for photoresist (PR) removal in electronic device manufacture, but also capable of challenging feature dimensions. Despite many attractive properties, clear supercritical CO2 has little solvating power for PR. Here, two acetate modifiers were selective to add in the CO2 and evaluated individual contribution to the overall stripping rate by factorial experiment design, which included four other factors with four level ranges for each one and concluded the best 90% extraction efficiency would be obtained under the optimized parameters: 2.5 min static time, 35 min dynamic time, 1.25 ml ethylacetate spiked, 125 °C oven temperature and 480 atm CO2 pressure. As analyzing the variances of these contributors to this system, it disclosed that dynamics controlled the stripping mechanism before near 35 min purging but thermodynamics took over after then; and that increasing pressure was more competent for removing PR than increasing temperature. All supercritical extracts were from two commercial PR coated on two substrates and analyzed by UV absorption spectrometry. Removing PR coated on silicon oxide layer was easier than that on Al–Cu alloy one.