Dissolution phenomena of phenolic molecular glass photoresist films in supercritical CO2

Abstract

The dissolution characteristics of small molecule photoresist films in supercritical CO₂ are measured using laser interferometry. These small molecule photoresists, referred to as molecular glasses, have shown impressive CO₂ solubility in recent reports, and in order to understand this behavior the structure–property relationships that control thin-film dissolution of phenolic molecular glasses are explored. Fully tert-butoxycarbonyl-protected versions of these molecular glasses are tested, and they show relatively fast (>500 nm min⁻¹) dissolution rates that depend primarily on molecular weight and not on the number of carbonyl groups. Material glass transition temperature also plays a role, as those films that are not sufficiently plasticized by the supercritical CO₂ have much slower dissolution rates than films of comparable molecular size and type. Small molecules containing up to two unprotected polar hydroxyl groups still show significant dissolution rates in supercritical CO₂.