There has been a continuing desire in the electronics industry to obtain higher circuit density in microelectronic devices. To achieve the higher degree of integration necessary to meet the ground rules for such devices, the microelectronic industry has sought to develop improved lithographic tools and techniques which in turn have increased the demand for new photoresists which enhance the resolution of lithographic patterns in such photoresist films.
Aqueous base developable photoresist compositions which crosslink through electrophilic aromatic substitution have been disclosed in Reck et al., SPIE Regional Technical Conference on Photopolymers, Ellenville, N.Y., 63 (1988). Such formulations are characterized by having 3 structural components which include (a) an aromatic moiety, such as poly(4-hydroxystyrene) or novolak, which is susceptible to electrophilic aromatic substitution (b) a stable substance which is capable upon reaction with acid, of generating an electrophile, viz., a carbocationic species whose precursor is the acetate of an aryl methylol, and (c) a photo-acid generator which is an onium salt such as triphenylsulfonium hexafluoroantimonate. Upon exposure latent images are formed due to the chemical changes caused by the photoacid generation which include acetate hydrolysis, benzylic carbonium ion formation, and partial crosslinking of the aromatic resin. When the film is baked briefly after exposure, the acid cleaves the acetate group of the latent electrophile to produce a benzylic carbocationic species which reacts immediately with the surrounding phenolic resin to form new carbon-carbon bonds. Such formation of new carbon-carbon bonds results in an increase in molecular weight of the resin or its crosslinking, thereby drastically altering its solubility properties. Subsequent development in dilute base affords a negative-tone image of the mask. (Systems which included novolak resins were said to exhibit an unacceptable high optical density in deep UV).
U.S. Pat. No. 4,810,601 to Allen et al. is concerned with the formation of negative tone patterns by crosslinking an aromatic compound with a monomeric or polymeric source of polyfunctional carbonium ions. Diacetoxymethylbenzene and trisacetoxymesitylene were used with triphenylsulfonium hexafluoroantimonate to crosslink a poly(p-hydroxystyrene) matrix resin. The imaged resist was aqueous base developable. Poly(vinylbenzylacetate) was used as a polymeric polyfunctional carbonium ion generator to crosslink Bisphenol A. The resist patterns formed with these systems were briefly baked and then developed with an organic solvent such as acetone.
European Patent Application No. EP 0 361 907 is directed to photoresist compositions which are useful for deep UV image reversal processes which comprise an organic film-forming material, an oxime sulfonate photoacid generator, and an additive which can crosslink the film-forming material and increase the positive photospeed of the composition. The additives have the general formula RO--CH.sub.2 --A--CH.sub.2 ---OR where A is a monomeric aromatic hydrocarbon having one or more fused or unfused, separated or unseparated rings and each R unit is independently H, (C.sub.1 -C.sub.6) alkyl, (C.sub.3 -C.sub.6)cycloalkyl, aryl or arylalkyl. The additives have the general formula ##STR1## wherein R.sub.1, R.sub.4, R.sub.5, R.sub.6 are independently H, (C.sub.1 -C.sub.6)alkyl, (C.sub.3 -C.sub.6) cycloalkyl, aryl, arylalkyl or OR.sub.2 ; and R.sub.2, R.sub.3 are independently H, (C.sub.1 -C.sub.6)alkyl, (C.sub.3 -C.sub.6)cycloalkyl, aryl, or arylalkyl.
U.S. Pat. No. 4,404,272 to Stalhofen is concerned with aqueous developable light sensitive compositions comprising novolak resins having brominated phenol units. These compositions may includehot curable hydroxymethylphenol deritives to enhance adhesion of the compostion to the substrate. The derivitives include ##STR2## where R is a hydrogen atom, a lower alkyl group, or a lower acyl group, preferable a hydrogen atom, R' is an alkyl, alkoxy, cycloalkyl, aryl, aryloxy, acyl or aralkyl group or a halogen atom, X is a single bond or one of the groups S, O, CO or CR'R.sup.2, preferably a prop-2,2-ylene group, and Y is a hydrogen atom or, preferably, a CH.sub.2 OH group, R.sup.1 and R.sup.2 being identical or different and representing hydrogen atoms or substituted or unsubstituted alkyl groups which can be linked to one another to form a ring, and not more than two of the substituents Y being hydrogen atoms. These results depend upon the cleaveage of an acetate or an orthocarboxylic compound to give positive images.