Spin coating and photolithography using liquid and supercritical carbon dioxide

This thesis details work on the utilization of dense phase carbon dioxide (CO₂) in semiconductor processing. In particular, work is presented on the formulation of CO₂ soluble photoresists and the spin coating of those photoresists using only liquid CO₂ as a solvent. As part of this spin coating work, a novel high-pressure CO₂ spin coater was designed and constructed, and the theoretical equations governing its performance were derived. Also discussed in this thesis are 248 and 193 nm exposures of these CO₂ spun films and subsequent development in supercritical CO₂. Resist stripping was also performed in CO₂. In short, this thesis details the first steps towards a complete replacement of all aqueous and organic solvents in the conventional photolithographic processes of spin coating, developing, and resist stripping. This change not only confers significant environmental advantages, but opens up many new avenues in resist chemistry and promises improvements in large scale film uniformity, elimination of feature collapse, elimination of extraneous processing steps, and improved control of the lithographic process.