Aqueous base soluble polymer

A new class of aqueous-base soluble polymer, poly[4-(2-hydroxyhexafluo-roisopropyl)styrene] (Fig. 20), has been reported as a replacement of PHOST for 248 nm lithography, which was also protected with the fBOC group [114]. The tBOC-protected polymer can be synthesized by radical polymerization of... 

The t-BOC protection group chemistry has been extended to other aqueous-base soluble polymers such as poly[styrene-co-N-(4-hydroxyphenyl)maleimide], ° poly(styrene-co-maleimide), poly(4-hydroxystyrene sulfone), and poly(4-hydroxy-a-methylstyrene) used in lithographic applications. Even novolac resins have been successfully protected with the t-BOC group,which has resulted in significant reduction of the DUV absorption of these resins. ... 

Fig. 28. Traditional duv-resist design using derivatives of polyhydroxystyrene. Monomer (a) contributes hydrophilic character to the polymer, and its acidic phenol group enhances aqueous base solubility monomer (b) provides acid-labile pendent groups.

Acid-catalyzed silanol condensation to form insoluble networks has been also utilized in the design of aqueous base developable negative resist systems [419]. An aqueous base soluble silicone polymer was synthesized by a sol-gel reaction of a mixture of phenyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane. This polymer contained a high concentration of silanol OH groups and thus was soluble in aqueous base. 

One reported approach to improving the etch resistance of PBS resists was the incorporation of novolac resins into the formulation, as in the poly(methylpentene sulfone) (PMPS) resist developed at Bell Laboratories and the sulfone/novolac system (SNS) resists developed at IBM in the 1980s. Incorporation of novolac resins into this resist system imparted etch stability and aqueous base solubility to these resists. The olefin sulfone acted as a dissolution inhibitor in the unexposed regions, while the scissioned polymer in the exposed regions enhanced the solubility of the phenolic matrix in the base. Unfortunately, the SNS materials were less sensitive than PBS resists because the novolac matrix ahsorhed a substantial portion of the incident exposing electrons, making them unavailable for chain scission reactions by the olefin sulfones. ... 

Alternate protective groups and parent polymers have been utilized in the design of chemically amplified resists. Generally, thermally stable, add labfle substituents are desirable as protective groups for aqueous base soluble parent polymers. Some typical examples that have been employed indude rerf-butyl (46, 47), tetrahydropyranyl (48-52), and a,a-dimethylbenzyl (49, 53, 54). In situations where adequate moisture is expected to be present in the film, hydrotyzable groups such as trimethylsilyl have also been utilized (55). As mentioned above. 

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. 

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cycHzed mbber resist systems led the semiconductor industry to shift to a class of imaging materials based on diazonaphthoquinone (DNQ) photosensitizers. Both the chemistry and the imaging mechanism of these resists (Fig. 10) differ in fundamental ways from those described thus far (23). The DNQ acts as a dissolution inhibitor for the matrix resin, a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac (24). The phenoHc stmcture renders the novolac polymer weakly acidic, and readily soluble in aqueous alkaline solutions. In admixture with an appropriate DNQ the polymer s dissolution rate is sharply decreased. Photolysis causes the DNQ to undergo a multistep reaction sequence, ultimately forming a base-soluble carboxyHc acid which does not inhibit film dissolution. Immersion of a pattemwise-exposed film of the resist in an aqueous solution of hydroxide ion leads to rapid dissolution of the exposed areas and only very slow dissolution of unexposed regions. In contrast with crosslinking resists, the film solubiHty is controUed by chemical and polarity differences rather than molecular size. 

Screenable inks have a resin or polymer base and are of three types organic solvent soluble, aqueous alkah soluble, and permanent. Primarily because of pollution requirements and higher solvent costs, the aqueous types have come into greater use. The permanent types are used as solder masks or for marking the boards. Uv-curable inks are also in use. 

The proceeding discussion of polymer composition was based on the assumption that essentially all polymer is formed in the organic phases of the reaction mixture. If a water-soluble monomer, such as some of the functional monomers, is used, the reactions taking place in the aqueous phase can contribute to variation in polymer composition. In fact, in extreme cases, water soluble polymer can be formed in the aqueous phase. This can happen in batch, semi-continuous or continuous reactors. The fate of functional monomers could be considerably different among the different reactor types, but detailed studies on this phenomenon have not been reported. 

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