Analysis of deprotection reaction for chemically amplified resists by using FT-IR spectrometer with exposure tool

A Fourier transform infrared (FT-IR) spectrometer with built-in exposure tool (248 nm) is used to perform in situ observations of the decomposition of protective groups (deprotection reactions) in chemically amplified resists during exposure, with the exposure ambient temperature varied. In addition, the activation energy and the prefactor of deprotection reaction necessary for lithography simulation are determined. Resist polymers used in this experiment are poly (p-hydroxystyrene) (PHS) protected by Ethoxyethyl (EOE) or by tert-Butoxycarbonyl (t-BOC), and its copolymers. The activation energy is compared at room temperature (23 degreesC). As a result, the activation energy for EOE deprotection reaction is 8.90 kcal/mol, while for t-BOC deprotection reaction is 23.65 kcal/mol. The activation energy for EOE resist is much lower than for t-BOC resist. Progress of the deprotection reaction in EOE resist during exposure at room temperature can be explained in terms of differences in activation energies. In the copolymer resist, introduction of EOE into PHS protected by t-BOC resulted in a decrease in the activation energy required for the t-BOC deprotection. reaction. From this it is found that in a resist composed of PHS copolymer with heterogeneous protection groups attached, the interaction affect between protection groups deprotection reactions. Lithography simulations of resist profiles are performed with the activation energy and the prefactor varied, and the effect of the activation energy on the resist profile is investigated. The results indicate that patterning is possible for an exposure ambient temperature of 20 degreesC or higher for EOE resist, and that of 70 degreesC or higher for t-BOC resist.