Amplified deep-UV resists

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. 

H. Iwasaki, T. Itani, M. Fujimoto, and K. Kasama, Acid size effects of chemically amplified negative resist on lithographic performance, Proc. SPIE 2195, 164 172 (1994) U. Schedeli, N. Miinzel, H. Holzwarth, S.G. Slater, and O. Nalamasu, Relationship between physical properties and lithographic behavior in a high resolution positive tone deep UV resist, Proc. SPIE 2195, 98 110 (1994). 

A chemically amplified deep UV photoresist system based on acetal chemistiy is reported. Acetal-protected pol vinylphenols) were prepared either by free radical polymerization of the monomers or chemical modification of poly(vinylphenol). In the presence of an add as a catalyst, the polymers thermally decomposed to aqueous base soluble po vinylphenol) and some small molecules. Therefore, the resists were formulated with the acetal-protected polymers and a photoadd generator such as triphei lsulfonium hex-afluoroantimonate. Positive-tone image could be resolved 1 exposing the resist film in deep UV region, post-baking, and developing in tetramethylam-monium hydroxide solutions. 

Recently, nonionic acid precursors based on nitrobenzyl ester photochemistry have been developed for chemically amplified resist processes (78-80). These ester based materials (Figure 8) exhibit a number of advantages over the onium salt systems. Specifically, the esters are easily synthesized, are soluble in a variety organic solvents, are nonionic in character, and contain no potential device contaminants such as arsenic or antimony. In addition, their absorption characteristics are well suited for deep-UV exposure. 

The chemically amplified resists reported here for deep-UV applications require a post-exposure thermal treatment process step to effect the deprotection reaction. This step has proven to be critical, and in order to understand the processing considerations it is instructive to discuss, qualitatively, the various primary and secondary reactions that occur with these systems during both exposure and PEB, ie ... 

Recent progress has been made in microelectronic device fabrication, particularly in microlithography used to manufacture the high-resolution circuit elements of integrated circuit (Ref. 96). Deep-UV photolithography based on chemically amplified resist is likely to be the first technology that met the severe performance criteria required. The best known chemically amplified resist is based on poly (4-t-butoxycarbonyloxy styrene) or copolymers (Ref. 97). 

Typical resists include cyclized polyisoprene with a photosensitive crosslinking agent (ex bisazide) used in many negative photoresists, novolac resins with diazoquinone sensitizers and imidazole catalysts for positive photoresists, poly(oxystyrenes) with photosensitizers for UV resists, polysilanes for UV and X-ray resists, and polymethacrylates and methacrylate-styrenes for electron-beam resists (Clegg and Collyer, 1991). Also note the more recent use of novolac/diazonaphthoquinone photoresists for mid-UV resists for DRAM memory chips and chemically amplified photoacid-catalysed hydroxystyrene and acrylic resists for deep-UV lithography (Choudhury, 1997). 

Nalamasu et al., Development of a chemically amplified positive resist material for single layer deep UV lithography, Proc. SPIE 1262, 32 (1990). 

A new family of chemically amplified positive resists based on methaaylate terpolymers has been developed. The three different monomers each perform a separate function in the terpolymer. These resists were original designed for use in printed circuit board (PCB) fabrication. The flexibility of this approach in the design of positive resists has recently been demonstrated in the development of several new integrated circuit (IC) positive resists for deep UV (248 nm) and deep, deep UV (193 nm) lithography. These advances demonstrate that resists for wide application can be designed from a common platform of materials technology. 

In the deep UV region, exposure tools which use the conventional Hg lamps require fast resists (< 15 mj/cm ) in order to provide short exposure times and sufficient throughput. To meet the photospeed requirements, resists based on the incorporation of TBOC groufis onto the PHOST backbone pioneered the era of acid catalyzed amplified tems. Both negative, positive, and top surface imaging (TSI) resists based on TBOC have been formulated for the deep UV region (3, 5). 

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