Effects of alkyl chain length of <i>n</i>-alkyl acetates on the dissolution of polymer films for lithography: quartz crystal microbalance method

Abstract Aqueous solutions of tetraalkylammonium hydroxides with long alkyl chains are promising alternatives for positive tone development in lithography. In negative tone development, a n -butyl acetate was used to develop negative tones. However, the effects of the alkyl chains are still unclear for n -butyl acetate. In this study, the dissolution of polymer films in n -alkyl acetate developers was investigated to clarify the effects of the alkyl chain length on dissolution kinetics. The dissolution kinetics of 13 polymers in ethyl, n -pentyl, and n -hexyl acetates were measured using a quartz crystal microbalance (QCM). The polymers were chosen to cover the wide range of surface free energy without limiting to those for negative tone development. The obtained QCM charts were analyzed by simulations based on diffusion theory to determine the diffusion constants and hydrodynamic radii of the polymers during development. For partially protected poly(4-hydroxystyrene), the hydrodynamic radii were almost independent of the protection ratio (polymer polarity) and increased with increasing acetate alkyl chain length (decreasing the developer polarity).