Effect of copolymer composition on acid-catalyzed deprotection reaction kinetics in model photoresists

The kinetics of the deprotection reaction in model photoresist materials was measured as a function of copolymer composition with Fourier transform infrared (FTIR) spectroscopy. A mathematical model was developed to analyze the deprotection kinetics in terms of the coupled reaction rate and acid-diffusion processes. The first-order reaction rate constant decreases as the non-reactive comonomer content increased. Additionally, the extent of reaction appears to saturate to different levels as a function of reaction temperature. The resulting composition-dependent reaction constant arises from a dramatically reduced acid transport rate due to a strong interaction of the acid with the increasing polar resist matrix. The reduced acid transport is consistent with the observed hydrogen bonding between the photoacid and methacrylic acid reaction product. These results provide important insight into the effect of the changing polymer composition on the acid-catalyzed reaction kinetics.