| Supercritical CO2(scCO2) has been tried to use for photoresist removal in semiconductor manufacturing because it is easy to infiltrating into microhole and nano-scale trench owing to its zero surface tension and high diffusivity. However, ScCO2 microemulsions containing toxic fluorous surfactants are usually employed for the photoresist removal due to the high solubility of fluorous surfactants in ScCO2. Few investigations with hydrocarbon-based surfactants and co-solvent in ScCO2 have been reported. In this paper, the removal property of hard baking photoresist and high-dose ion-implanted (HDIM) photoresist in different supercritical conditions with different hydrocarbon-based co-solvents and surfactants has been studied. The influencing factors including type of co-solvents, type of surfactants, temperature, pressure, time and so on have been investigated in detail.The major work and results are as follows:1. The effect of two kinds of co-solvents in ScCO2 cleaning was comparedTwo kinds of co-solvents isopropanol and dimethyl sulfoxide (DMSO) were used to assist ScCO2 to remove hard baking photoresist on two kinds of substrates (polished silicon wafer and patterned silicon wafer). The baking temperature was 100℃,150℃,170℃and 200℃. The dose of co-solvent was ranging from 0 to 8ml. Characterization of surface of the processed samples via metaloscope revealed that hard baking above 150℃led to hardened photoresist, and the adhesion between photoresist and substrates increased significantly.4ml DMSO was enough to improve the photoresist removal efficiency from 15% to 85%, more dose did not cause visible higher efficiency. Comparing with isopropanol, DMSO was more effective to strip the hard baking photoresist under the same condition.2. The effect of two kinds of surfactants in ScCO2 cleaning was researchedIn this study, two hydrocarbon-based nonionic surfactants polyethylene-2,6,8-trimethyl-4-nonyl ether (TMN-3) and 2-ethyl hexanol polyoxyethylene-polyoxypropylene (EH-3) were used to form ScCO2 microemulsions. The results of surface characterization and composition analysis for the processed samples by SEM, FTIR and XPS revealed that comparing with TMN-3, EH-3 was more effective to strip the HDIM photoresist under the same condition. Furthermore, the optium concentration and optium WEH-3/Wwater ratio was got through experiments.3. The effect of temperature, pressure in ScCO2 cleaning was studiedThe post-etch HDIM photoresist was removed in the ScCO2 microemulsions under the pressure of 10-25 MPa at 40-80℃. The results revealed that the removal rate increased with the cleaning temperature when the temperature was lower than 60℃. The removal rate of 90% was achieved at 60℃and then it gradually decreased as the temperature went higher than 60℃due to the lower photoresist solubility in ScCO2 arising from the lower ScCO2 density at higher temperature. The photoresist removal efficiency improved from 40% to 85% with the cleaning pressure changing from 10 MPa to 25 MPa.4. The effect of time and magnetic stirring in ScCO2 cleaning was investigatedThe post-etch HDIM photoresist was removed in the ScCO2 microemulsions under different magnetic agitation conditions-without magnetic agitation, with low-speed magnetic agitation and with high-speed magnetic agitation. A sharp increase of photoresist removal efficiency appeared during the first 10 min, and then it gradually leveled off. Significant promoting of magnetic agitation to the photoresist removal efficiency was observed.5. The performance of traditional cleaning method has been compared with our methodComparing with traditional wet cleaning method, ScCO2 cleaning did not lead to any collapse or deformation and the cleaning efficiency was significantly higher. The same surfactant showed better cleaning efficiency in ScCO2 microemution system than in aqueous solution.Comparing with the existing ScCO2 cleaning method, this study allows dramatic reduction in water and chemical consumptions. Moreover, it is more environment-friendly for it substitutes biodegradable hydrocarbon-based co-solvents and surfactants for toxic fluorous surfactants. The magnetic stirring during ScCO2 cleaning helps ScCO2 microemution evenly mixed, and it generates a bigger physical force on the sample surface. After the cleaning process, pure ScCO2 is used to replace the mixture in cleaning chamber before pressure relief to avoid redeposition of stripped photoresist. |
PDF Full Text Request