a. Field of the Invention
This invention relates to a novel hydroxycarboxylic acid resin, and also to its production process and use. The hydroxycarboxylic acid resin according to the present invention is useful inter alia as a photoresist resin composition with excellent sensitivity and resolving power, as a metal chelate resin with excellent flexibility, oxidation resistance and waterproofness, as a color-developing agent for pressure-sensitive copying paper or an intermediate therefor, and as an epoxy resin curing agent.
b. Description of the Related Art
As photoresist resins, phenol or cresol novolak resins are used in general. A composition formed of a diazidonaphthoquinonesulfonate and a novolak resin is used as a positive resist, because when exposed to light of 300-500 nm, quinone diazide groups are decomposed into carboxyl groups and the diazidonaphthoquinonesulfonate is hence converted from the alkaline-solution-insoluble form into an alkaline-solution-soluble form. This positive resist features far superior resolving power to negative resists and is used for the fabrication of integrated circuits such as ICs and ISIs. With respect to integrated circuits, miniaturization has progressed in recent years, keeping step with the high densification, so that formation of patterns on the order of submicrons is now demanded. As a result, still better resolving power is required even for positive resists. In the case of a resist material formed of a diazidonaphthoquinonesulfonate and a novolak resin, there is a limitation to the improvement of the resolving power as long as conventional available materials are combined. An improvement in resolving power might be contemplated, for example, by increasing the content of the quinone diazide compound. An increase in the content of the quinone diazide compound however is accompanied by serious drawbacks such as a reduction in sensitivity and an increase in development residue. There is hence a limitation to the improvement of the resolving power, resulting in the demand for a base resin as a substitute for phenol or cresol novolak resins.
There have also been attempts to improve the sensitivity and developability of a resist composition by adding a specific compound thereto. For example, Japanese Patent Laid-Open No. 141441/1986 discloses a positive composition containing trihydroxybenzophenone. A problem with this trihydroxybenzophenone-containing positive photoresist however is that the heat resistance is deteriorated by the addition of trihydroxybenzophenone, although the sensitivity and developability have been improved. Further, Japanese Patent Laid-Open Nos. 44439/1989, 177032/1989, 280748/1989 and 10350/1990 disclose techniques for increasing the sensitivity without reducing the heat resistance by the addition of aromatic polyhydroxy compounds other than trihydroxybenzophenone. However, these techniques are not considered to be sufficient with respect to the improvement of developability.
On the other hand, salicylic acid novolak resins have already been known as metal chelate resins, cement dispersants, metal coating thickeners, fiber treatments, color-developing materials for pressure-sensitive copying paper, and the like. Resins of this type are each produced by reacting salicylic acid with formaldehyde in the presence of an acid catalyst [for example, Journal of Organic Chemistry (J. Org. Chem.), 27, 1424(1962); publications in which the former publication is referred to.]. Further, Japanese Patent Laid-Open Nos. 164716/1987 and 176875/1987 disclose novel salicylic acid resins, i.e., xylok resins. Like novolak resins represented by phenol-formaldehyde resin, however, salicylic acid novolak resins are accompanied by such drawbacks as low flexibility and susceptibility to oxidation and deterioration. To meet the high physical properties required in recent years, there is increasing recognition that improvements to the resins themselves are indispensable. Further, the salicylic-acid-base xylok resins are accompanied by the drawback that they have low waterproofness.