Kim DW  Heo H  Lim KT

Vol. 23,  No. 4, pp. 357-363, Dec.  2017
10.7464/ksct.2017.23.4.357

Supercritical carbon dioxide Co-solvent Negative photoresist n-butyl acetate

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In this study, the supercritical carbon dioxide (scCO2)/ n-butyl acetate (n-BA) co-solvent system was employed to remove an unexposed negative photoresist (PR) from the surface of a silicon wafer. In addition, the selectivity of the scCO2/n-BA co-solvent system was confirmed for the unexposed and exposed negative PR. Optimum conditions for removal of the unexposed PR were obtained from various conditions such as pressure, temperature and n-BA ratio. The n-BA was highly soluble in scCO2 without cloud point and phase separation in mostly experimental conditions. However, the scCO2/n-BA co-solvent was phase separated at 100 bar, above 80 ℃. The unexposed and exposed PR was swelled in scCO2 solvent at all experimental conditions. The complete removal of unexposed PR was achieved from the reaction condition of 160 bar, 10 min, 40 ℃ and 75 wt% n-BA in scCO2, as measured by ellipsometry. The exposed photoresist showed high stability in the scCO2/n-BA co-solvent system, which indicated that the scCO2/n-BA co-solvent system has high selectivity for the PR removal in photo lithograph process. The scCO2/n-BA co-solvent system not only prevent swelling of exposed PR, but also provide efficient and powful performance to removal unexposed PR.