Chemically Amplified Imaging Mechanisms

The original chemical amplification scheme reported in the early 1980s contained three mechanisms [25] depolymerization for positive imaging, deprotection for dual tone imaging, and polymerization for negative imaging. Since then numerous imaging mechanisms based on photochemically-induced acid 

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H. Ito, Chemical amplification resists for microlithography, Adv. Polym. Set, 172, 149 (2005). Ito, Y. Maekawa, R. Sooriyakumaran, and E.A. Mash, Acid catalyzed dehydration A new mechanism for chemically amplified lithographic imaging, Polymers for Microelectronics, ACS Symp. Series 537, L.F. Thompson, C.G. Willson, and S. Tagawa, Eds., p. 64, American Chemical Society, Washington, DC. (1994). 

As with all chemically amplified resists, a major concern is, however, the latent image stabflity and the susceptibility to environmental conditions. With t-BOC deprotecdon systems, the influence of airborne nudeophilic contaminants has been recently demonstrated (23) the observadon of surface residues in a number of such materials (23, 24) may be traced back to the presence of ppb amounts of volatile bases. In the case of the acetal systems (19-21), the influence of trace bases is less pronounced, as even amine hydrochlorides are sdll sufficiendy addic to have some catatydc activity. Linewidth dianges with the interval between exposure and post exposure bake have been observed for both the t-BOC and the acetal systems. In the case of the t-BOC tystems, long intervals (several hoius) between exposure and post-e]q)osure bake will lead to a decrease of apparent sensidvity, which manifests itself as a linewidth inCTease, or, in extreme cases, as faUure to open the imaged areas. These effects are normally due to contaminadon by base traces, or, in cases where the presence of even ppb amounts of bases can be excluded, may be assumed to be the result of the same, unspecified chain terminadon (add annihilation) mechanism which is responsible for the containment of the calalytic reacdon to the immediate vicinity of the imaged resist. 

Theories suggesting the spontaneous formation of biological asymmetry are based on two-component chemical systems, which are symmetric for the two components (mirror-image reaction systems). Fluctuations in the initial conditions are amplified by the kinetic mechanism leading to macroscopic asymmetry. (For a review of critical evaluation of models for the amplification of chirality see Fajszi Czege (1981).) The measure of the asymmetry can be expressed by... 

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