Chemical-mechanical photoresist drying in supercritical carbon dioxide with hydrocarbon surfactants

Abstract

Supercritical CO2 containing hydrocarbon surfactants was utilized to remove water from photoresists without pattern collapse due to capillary forces. The addition of highly branched hydrocarbon surfactants to CO2 reduces the amount of solvent required for drying, and lowers the interfacial tension from 20 mN/m to approximately 1 mN/m, thus reducing pattern collapse. The drying time and amount of solvent were further reduced in a chemical/mechanical method, in which solvent, drained by gravity forces, is removed by hydrodynamic forces resulting from flowing CO2. In situ ellipsometry measurements show that the resist films swollen with CO2 return to their original thickness upon depressurization, indicating CO2 is compatible with these resists.