Photolithographic Patterning in Supercritical Carbon Dioxide: Application to Patterned Light-emitting Devices

Photolithography is a high-throughput, cost-effective patterning technology. However, the application to organic electronic devices has been restricted because of its chemical compatibility issue with delicate organic materials. In this study we propose a new photolithography technique which utilizes supercritical carbon dioxide (scO₂) as an organic electronic materials-benign development solvent. Supercritical carbon dioxide is a fluid that exists above its critical pressure and temperature (P_c=73.8 bar and T_c=31.1degC). Apart from the environmental advantages, useful process benefits result from the fact that most non-fluorinated organic materials are not damaged in contact with scCO₂. A polymeric material composed of perfluorodecyl methacrylate (FDMA) and tert-butyl methacrylate (TBMA) was synthesized as a negative-tone photoresist, processible in scCO₂. Micron-sized resist patterns on a Si wafer were successfully processed under i-line (lambda=365 nm) exposure conditions. The resist showed a capability to make patterns on the conductive poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) film. The resulting resist pattern was finally applied to fabricate patterned polymer light-emitting devices.