Dissolution behavior of novolak resins

Novolak and polyhydroxystyrene (PHS) constitute the film forming polymers of positive resists. Laser interferometry was used to study the dissolution and film morphology of spun cast films. PHS forms uniform films with polymer chains preferentially orientated. Novolak resins exhibit disruption of ordering throughout the depth of the film. Thicker (greater than 1 micrometer) films of novolak are more disordered. Casting solvents can also alter film morphology. Micron thick films of novolak resins, except for monodisperse fractions, show disruption of order, especially in layers at the vicinity of the substrate. Thicker novolak films exhibit more disorder due to solvent/surface tension gradients. PHS films of higher Tg are not sensitive to coating disruptions. The addition of surfactants eliminates global radial phase separation of diazoquinone and novolak and restores uniform orientation in plane of dissolution by neutralizing surface tension driven gradients.