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Effects of Rate Constant for Deprotection on Latent Image Formation in Chemically Amplified Extreme Ultraviolet Resists

The resolution of chemically amplified extreme ultraviolet (EUV) resists has reached sub-30 nm. However, the sensitivity and the reduction in the line edge roughness of such resists is still inadequate for the realization of EUV lithography. The pattern formation of chemically amplified resists is based on chemical reactions, which start with energy deposition from exposure tools and are terminated by quenchers or by cutting the heat supply for chemical reactions. In this study, the effects of rate constant for deprotection on latent image formation in chemically amplified EUV resists were investigated from the viewpoint of the difference between high- and low-activation-energy (Ea)-type resists. In chemically amplified resists, neutralization and deprotection competitively proceed. In high-Ea-type resists, in which neutralization proceeds before deprotection, the contrast of pattern edges is improved by suppressing deprotection in the low-dose region. In low-Ea-type resists, in which a fast deprotection is expected, the difference in the extent of deprotection between the high- and low-dose regions can be enhanced by promoting deprotection over neutralization. For the improvement in high- or low-Ea-resist performance, it is effective to enhance or balance all advantages of chemical reactions.