Understanding nonlinear dissolution rates in photoresists

This work focuses on understanding the dissolution phenomenon of surface inhibition, which is observed often in the development of novolac based resists. Many theories have been offered to explain this phenomenon, including a concentration gradient of resist components, oxidation of the surface, formation of a gel layer, and surface roughness effects. This work focuses on theories that propose a concentration gradient in resist components. A technique has been established to separate and analyze individual layers of thin films, and the concentration gradient in many resist components (residual solvent, low molecular weight chains, photoactive compound, density) has been compared to the observed dissolution rate. The results indicate that no significant concentration gradients exist in a mum novolac film, and that these hypotheses are inadequate to explain surface inhibition. Several other theories are explored, including oxidation of the surface, surface roughness effects, etc. The critical ionization dissolution model may offer an explanation for why surface inhibition is observed in novolac, but typically not in poly(p-hydroxystyrene).