Acid-catalyzed deprotection

Fig. 23. Representative protecting groups for phenolic and carboxylic acid-based systems, (a) The polymer-based protecting groups are fisted in order of increasing activation energy for acid-catalyzed deprotection, (b) Acid-labile monomeric dissolution inhibitors, a bifunctional system based on protected bisphenol A. (c) Another system that combines the function of dissolution inhibitor and PAG in a single unit.

Gronowitz and associates coupled 2-(2-trimethylstannyl-3-thienyl)-l,3-dioxolane (75) with tert-butyl N- (o/t/io-bromo tbienyl)carbamate (127) to give the Stille adduct, which underwent acid-catalyzed deprotection and cyclization to deliver dithienopyridine 128 [112]. The... 

In this paper, we report an alternative approach to the design of deep UV resist systems combining the desired properties, which involves copolymerization of methacrylic ester with styrenic comonomer and the use of the acid-catalyzed deprotection chemistry. 

Since only Ta and Nb catalysts, which are not tolerant to polar groups, are available for the polymerization of disubstituted acetylenes, it is generally difficult to synthesize disubstituted acetylene polymers having such a highly polar substituent as a hydroxy group. Recently, synthesis of poly[l-phenyl-2-( -hydroxyphenyl)acetylene] has been achieved by the polymerization of 1-phenyl-2-(p-siloxyphenyl)acetylene and the subsequent acid-catalyzed deprotection reaction. 

Figure 23 lists representative acid-labile protecting groups that have been incorporated in positive-tone CA resist systems. These groups can be pendent to the matrix polymer chain, can be attached to a monomeric or polymeric additive that acts as a dissolution inhibitor (64—66), or can even be appended to the PAG structure (67). The kinetics of acid-catalyzed deprotection vary significantly with structure. In particular, the activation energy,... 

Fig. 31. An acrylic terpolymer designed for chemically amplified resist applications. The properties each monomer contributes to the final polymeric structure are for MMA, PAG solubility, low shrinkage, adhesion and mechanical, strength for TBMA acid-catalyzed deprotection and for MMA, aqueous...

In 2007, Wiles et al. (2007c) demonstrated the ability to employ solid-supported catalysts in series within an EOF-based microreactor. As summarized in Scheme 39, the model reaction sequence involved combining a previously investigated acid-catalyzed deprotection with a base-catalyzed condensation reaction to enable the synthesis of a,(3-unsaturated carbonyl compounds from dimethyl acetals. 

Scheme 1 Acid-catalyzed deprotection reaction. In the postexposure bake, the acid generated by the photoacid generator molecules (PAG) in a photochemical reaction catalyzes a deprotection reaction that cleaves the pendant group of the insoluble polymer, resulting in a polymer that is soluble in the developer...

Figure 4.28. Molecular structures and photoinduced reactions of common photoresists. Shown (top) is the positive tone resist containing the active diazonapthoquinone (DNQ) chromophore group. Chemical amplification (CAM) reactions are illustrated in (i)-(iii). Reaction (i) represents photoinduced acid generation step (ii) is an acid-catalyzed deprotection mechanism (positive tone resist) and step (iii) is an acid-catalyzed crosslinking mechanism (negative tone resist).

SCHEME 12.3 Acid catalyzed deprotection of a poly(r T-butoxycarbonyloxy styrene) PTBOCST resists by the strong Bronsted acid formed in the prior photolysis reaction of a PAG. 

Fig. 12 Acid-catalyzed deprotection for polarity change (fBOC resist)...

The conversion of PBOCST to PHOST in the solid state can be conveniently monitored by IR spectroscopy because the fBOC carbonyl absorption at 1755 cm-1 shrinks in intensity, accompanied by appearance of a phenolic hydroxyl absorption at 3500 cm 1 as the acid-catalyzed deprotection proceeds (Fig. 15). Because this is the most classical and simplest form of the chemical... 

Fig. 19 Photochemically induced acid-catalyzed deprotection and subsequent base-catalyzed deacetylation during development...

A new type of copolymer resist named ESCAP (environmentally stable chemical amplification photoresist) has recently been reported from IBM [163], which is based on a random copolymer of 4-hydroxystyrene with tert-butyl acrylate (TBA) (Fig. 37), which is converted to a copolymer of the hydroxystyrene with acrylic acid through photochemically-induced acid-catalyzed deprotection. The copolymer can be readily synthesized by direct radical copolymerization of 4-hydroxystyrene with tert-butyl acrylate or alternatively by radical copolymerization of 4-acetoxystyrene with the acrylate followed by selective hydrolysis of the acetate group with ammonium hydroxide. The copolymerization behavior as a function of conversion has been simulated for the both systems based on experimentally determined monomer reactivity ratios (Table 1) [164]. In comparison with the above-mentioned partially protected PHOST systems, this copolymer does not undergo thermal deprotection up to 180 °C. Furthermore, as mentioned earlier, the conversion of the terf-butyl ester to carboxylic acid provides an extremely fast dissolution rate in the exposed regions and a large... 

The deprotection chemistry has been incorporated into the acid generator structure itself [177]. Phenolic hydroxyl groups pendant from triphenylsulfonium salts were protected with tBOC (Fig. 43). This dissolution inhibiting PAG mixed with PHOST becomes base soluble through photochemically-induced acid-catalyzed deprotection and thus the exposed area dissolves rapidly in aqueous base, which was named SUCCESS and promoted by BASF. A similar approach has been later reported on o-nitrobenzyl sulfonate acid generators, in which a tert-butyl ester was attached to the benzene ring for acid-generation and acid-catalyzed deprotection on one molecule (Fig. 43) [178]. 

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