Blends and Dissolution Inhibitors

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]. 

Although it is generally difficult to find polymer pairs that mix homogeneously, PHOST partially protected with THP or tert-butoxycarbonylmethyl group has been reported to be miscible with a novolac resin or PHOST and to function as a dissolution inhibitor [124,132]. Another acid-labile polymeric dissolution inhibitor is a terpolymer of tert-butyl methacrylate (TBMA), methyl methacrylate (MMA), and methacrylic acid (MAA), which is miscible with a novolac resin [179] while PTBMA is not [159]. This methacrylic terpolymer is only marginally miscible with PHOST but more compatible with C- and 

O-methylated PHOST [179]. This terpolymer was originally developed as a chemically amplified laser resist for circuit board application [180] and then as a single layer 193 nm positive resist [181], which will be described in more detail later. Another interesting three-component approach is the use of a N-acetal polymer as a dissolution inhibitor of poly(3-methyl-4-hydroxystyrene) [182]. A deep UV resist consisting of poly(3-methyl-4-hydroxystyrene-co-4-hydroxystyrene), poly(N,0-acetal), bis(arylsulfonyl)diazomethane, and a photobase was reported from Hoechst (currently Clariant). The function of the photobase is described later. A copolymer of 4-hydroxystyrene with styrene was also employed as a matrix resin. 

Hexakis(4-ter -butoxycarbonylphenoxy)cyclotriphosphazene was employed as a dissolution inhibitor of a novolac resin for a design of a three-component positive resist [183]. 

The copolymer and blend approaches have been combined to design three-component chemical amplification positive resists, which consist of PHOST partially protected with an acid-labile group (see Fig. 31), an acid-labile dissolution inhibitor, and PAG [124,157,158]. In this scheme both the matrix polymer and 

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