Rapid technological advances have presented several environmental issues and call for the use of environmentally
friendly processes. Supercritical carbon dioxide (scCO<sub>2</sub>) is a widely used solvent that can enhance processing
performance in photolithography, especially in the development step. Supercritical CO<sub>2</sub> is a good solvent for many nonpolar
molecules with low molecular weights. However, it is generally a very poor solvent for high molecular-weight
photoresists. Recently researchers have reported the ability to develop conventional polymeric resists in scCO<sub>2</sub> using
tailored soluble additives. The mechanism of dissolution of a polymer photoresist in scCO<sub>2</sub> in the presence of these
additives is clearly at a very early stage of understanding. To understand this mechanism in more detail, we synthesized
a series of scCO<sub>2</sub> compatible quaternary ammonium salts (QAS) and used them as additives in the dry development of
model and commercially available photoresists. In this paper, we describe the various interactions that the QAS additive
has with the different functional groups on the polymer resist to assist its dissolution in scCO<sub>2</sub>. Using contact analysis
plots we report the dominant interactions between the additive and the resist material. We report the results with two
salts (QAS-I and QAS-II) to show the structure-property relation of these amphiphilic additives with an ESCAP resist.
Finally, we report the lithographic evaluation of a commercial EUV resist using an appropriate scCO<sub>2</sub> compatible QAS
after development in scCO<sub>2</sub>.