Polyhydroxystyrene has been known as a microlens-forming material. However, polyhydroxystyrene has problems described below and therefore there is scope for improvement. Using polyhydroxystyrene as a microlens-forming material, the microlens is likely to lose its hemispherical shape due to heating at high temperatures, and therefore microlenses of a uniform shape are difficult to be formed. In addition, polyhydroxystyrene is prone to discoloration by heat treatment and tends to deteriorate in transparency, so that the discoloration of the microlens may be observed during use.
A composition for forming anti-reflective coatings that contains a polymer having a triazinetrione structure has been suggested (Patent Document 1), and a photoresist composition and a material to be used for forming a resist protective layer for immersion lithography, both of which contain a maleimide copolymer, and the like have been suggested (Patent Document 2 to Patent Document 4).
In order to develop insulating films for display devices such as liquid crystal displays (LCD) and organic electroluminescent displays, a process for forming an insulating film for a display device, in which a radiation-sensitive resin composition that contains an alkali-soluble copolymer composed of indene, maleimide, and an N-substituted maleimide, a 1,2-naphthoquinonecliazide compound, and a crosslinking agent is used, has been suggested (Patent Document 5).
A maleimide copolymer that contains an unsubstituted maleimide-based monomer structural unit, a styrene-based monomer structural unit, and a (meth)acrylic acid-based monomer structure, and that is very excellent in compatibility with a multifunctional (meth)acrylate, is excellent in alkali solubility, and therefore is expected to be suitably used in various applications requiring such characteristics has been suggested (Patent Document 6).
However, none of these related-art documents are intended to provide applications as a photosensitive resin composition for microlenses, nor suggest specific methods for nor the effects of incorporating, into a photosensitive resin composition for microlenses, a copolymer that is obtained using allyl isocyanurate as a raw material, particularly a copolymer that is obtained using allyl isocyanurate and unsubstituted maleimide and/or an N-substituted maleimide as raw materials.
A radiation-sensitive resin composition that contains [A] a polymer of (a1) an unsaturated carboxylic acid and/or an unsaturated carboxylic anhydride, (a2) an epoxy group-containing unsaturated compound, (a3) a maleimide monomer, and (a4) other olefin unsaturated compound, and [B] a 1,2-quinonediazide compound has been reported (Patent Document 7). The document describes that the radiation-sensitive resin composition reported therein has high radiation-sensitiveness and can easily form a patterned thin film that is excellent in solvent resistance, heat resistance, transparency, and heat discoloration resistance. However, the document suggests neither the profile nor the heat resistance of a pattern that is to be formed from the composition. The documents do not describe maleimide monomer to include unsubstituted maleimide, either.