Cross-linking negative electron

Poly(glycidyl methacrylate) (PGMA), a well-known negative electron beam resist first reported by Hirai et al. (55), actually functions as a positive-tone resist upon DUV exposure (Table 3.1) (56). The epoxide functionality responsible for cross-linking under electron beam exposure does not absorb in the DUV region, and the response of PGMA to DUV radiation is determined by the absorption due to the n — tt transition of the carbonyl chromo-... 

Examples of such photochemical acid generators are shown in Chart 3.2. These onium salts, which are cationic photoinitiators originally developed for curing of epoxy resins (i09), can be used to formulate cross-linking negative resist materials (JOS), are very sensitive to electron beam and X-ray (JOS, 107, 108) radiation, and can be sensitized to longer wavelength radiation (JOS, 110, 111). 

After the absorption step, it appears that the cross-linking or degradation chemistries of X-ray and e-beam resists are similar. This is demonstrated in Figure 9 where the sensitivities of several polymer resists to both 20 keV electron beam exposures and Mo (5.41 A) X-rays are plotted. Both degrading (positive) and cross-linking (negative) polymers are included in this plot. 

Fig. 8. HK97 assembly and maturation. (A) Negatively stained electron micrograph of a mature dsDNA-filled capsid, with noncontractile tail and accessory proteins. (B) Steps in capsid assembly and maturation (see text in vitro conditions are in boldface, and in vivo conditions or components that differ from the in vitro conditions are in italic) (Conway et al, 1995). (C) Chemistry of the cross-linking reaction.

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