The kinetics of an acid-catalyzed deprotection reaction in model photoresist materials was studied as a function of copolymer composition with Fourier Transform Infrared spectroscopy. A mathematical model was developed to analyze the acid catalyzed deprotection kinetics with respect to coupled reaction rate and acid-diffusion processes. The first order reaction rate constant decreases as a non-reactive comonomer content is increased. Additionally, the extent of reaction appears self-limiting as verified by a slowing down necessitating an acid-trapping chemical equation to model the data. This composition-dependent reaction constant indicates a strong interaction of the acid with the increasing polar resist matrix that drastically reduces the acid transport rate. The severely reduced acid transport is consistent with hydrogen bonding between photoacid and methacrylic acid product. These results demonstrate a correlation between polymer microstructure and acid catalyzed kinetics.
Pub Type: Journals
copolymer, diffusion, FTIR, outgassing, photoacid, photolithography, photoresists, reaction rate constant