Photoacidity

Fig. 21. Representative nonionic photoacid generators. A variety of photochemical mechanisms for acid production ate represented. In each case a sulfonic acid derivative is produced (25,56,58—60). (a) PAG that generates acid via 0-nitrobenzyl rearrangement (b) PAG that generates acid via electron transfer with phenohc matrix (c) PAG that is active at long wavelengths via electron-transfer sensitization (d) PAG that generates both carboxylic acid and...

To achieve the best overall resist performance, the optimum PAG for a given resist system, whether ionic or nonionic, must balance the functional properties Hsted eadier in this section. The development of new photoacid generators, and the characterization of their functional properties, ate considered key to the design of resists with increased levels of performance. 

Photoresist appHcations in the microelectronics industry have also been disclosed (340). Thermally stable ben2yl sulfonate esters based on 2-methyl-3-nitroben2otrifluoride [6656-49-1] can serve as nonionic photoacid generators to promote a cascade of reactions during irradiation of the resist. 

Phosphoms pentoxide-methanesulfonic acid (PPMA), 315 Phosphorylation, 187 Photoacid generator (PAG), 317 Photoluminescence, 490 Photosensitive polyimides, 270-271, 292 PHRRs. See Peak heat release rates (PHRRs)... 

Products from the photolysis of the cyclopropyl ketone (44) are dependent on the pH of the solvent.(42) In aqueous dioxane only the 2,3-diphenyl-phenol (45) is formed along with the photoacid (46). Bond cleavage at c takes place via both the singlet and triplet states, whereas bond cleavage at a with phenol formation takes place in the triplet state ... 

Proton dissociation in the excited states commonly occurs much easier than in the ground states, and the great difference in proton dissociation constants by several orders of magnitude is characteristic for photoacids [47]. These dyes exist as neutral molecules and their excited-state deprotonation with the rate faster than the emission results in new red-shifted bands in emission spectra [48]. Such properties can be explored in the same manner as the ground-state deprotonation with the shift of observed spectral effect to more acidic pH values. 

Tolbert LM, Solntsev KM (2002) Excited-state proton transfer from constrained systems to super photoacids to superfast proton transfer. Acc Chem Res 35 19-27... 

Nonionic latexes (latices), 19 855 Nonionic photoacid generators, 15 167-168 Nonionic polymers... 

PhoStrip process, as advanced wastewater treatment, 25 907 Photoablation, 20 278 Photoacid generators (PAGs), 10 521 ... 

This basic approach to chemical amplification was subsequently extended by Ito et al. [3] through resist formulations incorporating appropriately chosen triaryl sulfonium or diaryliodonium salt. For example, end-capped poly(phthalaldehyde) used in combination with an onium salt photoacid generator is an excellent self-... 

The imaging process involving polymers or 1 used in combination with a photoacid generating compound is outlined in Figure 6. Spin-coated films of polymer ... 

In this paper we report on the use of trifluoro-methanesulfonates (Table 1) of 4-N, N-dimethylamino-benzenediazonium (Dl) and 4-methoxybenzene-diazonium (D2) as CEL dyes, negative working sensitizers, and photoacid generators for chemical amplification resist systems(11). 

Photoacid generator. D1 (4 wt%) was mixed with poly(glycidyl methacrylate) (PGMA) (20 wt%) in ethyl cellosolve acetate. The mixture was spin-coated on a silicon wafer and baked at 80V for 1 minute. Exposure was performed with a 600-W Xe-Hg lamp in conjunction with a UVD2 filter. The resist was developed in a mixture of methyl ethyl ketone to ethanol (7/1 w/w). 

Fig. 7 Novel patternable block copolymers to achieve spatially controlled nanostructures, a An asymmetric PaMS-fc-PHS copolymer/photoacid generator/crosslinker solution was spin-coated on a silicon substrate and formed vertical PaMS cylinders due to rapid solvent evaporation, b 248 nm stepper exposure and subsequent development to form micropatterns with features as small as 400 nm. c Strong UV irradiation under high vacuum to remove PaMS, thus generating patterned nanochannels...

An interesting question then arises as to why the dynamics of proton transfer for the benzophenone-i V, /V-dimethylaniline contact radical IP falls within the nonadiabatic regime while that for the napthol photoacids-carboxylic base pairs in water falls in the adiabatic regime given that both systems are intermolecular. For the benzophenone-A, A-dimethylaniline contact radical IP, the presumed structure of the complex is that of a 7t-stacked system that constrains the distance between the two heavy atoms involved in the proton transfer, C and O, to a distance of 3.3A (Scheme 2.10) [20]. Conversely, for the napthol photoacids-carboxylic base pairs no such constraints are imposed so that there can be close approach of the two heavy atoms. The distance associated with the crossover between nonadiabatic and adiabatic proton transfer has yet to be clearly defined and will be system specific. However, from model calculations, distances in excess of 2.5 A appear to lead to the realm of nonadiabatic proton transfer. Thus, a factor determining whether a bimolecular proton-transfer process falls within the adiabatic or nonadiabatic regimes lies in the rate expression Eq. (6) where 4>(R), the distribution function for molecular species with distance, and k(R), the rate constant as a function of distance, determine the mode of transfer. 

In recent years, there have been many significant advances in our models for the dynamics for proton transfer. However, only a limited number of experimental studies have served to probe the validity of these models for bimolecular systems. The proton-transfer process within the benzophenone-AL A -di methyl aniline contact radical IP appears to be the first molecular system that clearly illustrates non-adiabatic proton transfer at ambient temperatures in the condensed phase. The studies of Pines and Fleming on napthol photoacids-carboxylic base pairs appear to provide evidence for adiabatic proton transfer. Clearly, from an experimental perspective, the examination of the predictions of the various theoretical models is still in the very early stages of development. 

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