Resolution limits due to chemical amplification in resists

While the chemical amplification concept has served the semiconductor industry 

Ito and C.G. Willson, Chemical amplification in the design of dry developing resist materials, Polym. Eng. Sci. 23, 1012 (1983) H. Ito, C.G. Willson, and J.M.J. Frechet, Positive and negative working resist compositions with acid generating photoinitiator and pol3mier with acid labile groups pendant from polymer backbone, U.S. Patent No. 4,491,628 (1985). 

The design concept of chemical amplification is based on generation of a chemically stable catalytic species (commonly referred to as a photoacid and designated as a proton H, as illustrated in Fig. 17.22 for a resist system comprising a copolymer—poly(4-hydroxystyrene-co-4-t-butyloxycarbonyloxystrene)—in 

Schmid, M.D. Stewart, C. Y. Wang, B.D. Vogt, V.M. Prabhu, E.K. Lin, and C.G. Willson, Resolution limitations in chemically amplified photoresist systems, Proc. SPIE 5736, 333 342 (2004). 

As a thermally driven process, the photoacid diffusion length and rate in CARs is temperature dependent, as illustrated in Fig. 17.24 for the diffusion of perfluoro-octane sulfonate photoacid in partially protected poly(4-t-butyloxycarbonyloxy-strene)-based resist. Within normal processing conditions, the higher the PEB temperature, the faster is the rate of the photoacid diffusion and the longer is the diffusion length. Although the PEB temperature can be used to modulate photoacid diffusion and consequently resist sensitivity, it nevertheless involves a trade-off 

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