1. Field of the Invention
This invention relates to a positive sensitive resin composition comprising a novel copolymer of 4-(1-methylethenyl)phenol, a (meth)acrylate and a (meth)acrylic acid (PIPE copolymer), an ether-bond-containing olefinic unsaturated compound and an acid-generating agent, as well as a process for forming a resist pattern therewith. In particular, it relates to a positive sensitive resin composition comprising a copolymer of 4-(1-methylethenyl)phenol, a (meth)acrylate and a (meth)acrylic acid useful as a base polymer, an ether-bond-containing olefinic unsaturated compound and an acid-generating agent, as well as a process for forming a resist pattern by applying or adhering the composition to a substrate and then irradiating it with an active energy beam such as ultraviolet rays, visible light and heat rays for developing it.
2. Description of the Related Art
A resist material in combination with an exposure technique has been utilized in lithography such as patterned circuit formation in an electron device and printing.
An application of such patterned circuit formation in an electron device may be, for example, a process for manufacturing a color filter for a variety of multicolored liquid-crystal color displays such as a liquid-crystal color television.
Such a color filter has been conventionally manufactured by, for example, screen printing and electrodeposition. However, as a color display has been improved for its resolution, it has been more important to refine a pattern. Thus, a variety of patterning processes utilizing photolithography has been investigated.
For example, JP-A 8-94827 has disclosed a process for manufacturing a color filter comprising the steps of [1] forming a transparent conductive layer on a transparent substrate; [2] forming a positive photosensitive coating layer; [3] exposing a part of the transparent conductive layer; [4] forming a colored area by electrodeposition; and [5] repeating the steps [3] and [4] as required. Of these steps, a pattern refinement level depends on the steps [2] and [3], in which photolithography is used. In particular, it significantly depends on a positive photosensitive composition applied on the transparent conductive layer. The above invention employs a positive photosensitive composition essentially comprising (a) a polymer containing both carboxyl and hydroxyphenyl groups in one molecule, (b) a compound containing two or more vinyl ether groups in one molecule, and (c) a compound generating an acid by irradiating an active energy beam.
This photosensitive composition is developed as follows; by heating the film on which the positive photosensitive composition has been applied, an addition reaction of the carboxyl group and/or hydroxyphenyl group with the vinyl ether group forms a crosslink, which is insoluble to a solvent or an alkali developing solution, and then, after irradiating with an active energy beam and then, as necessary, heating the film, an acid generated in the irradiated area acts as a catalyst to cleave the crosslink structure and thus to again make the irradiated area soluble to a solvent or an alkali developing solution. For further improving a resolution, a preferable polymer (base polymer) in a positive photosensitive composition is one containing both carboxyl and hydroxyphenyl groups in one molecule which meets all the following five requirements as much as possible;    (a) a higher solubility to a solution which solves a crosslinking agent, an acid-generating agent and others (solvent solubility);    (b) a certain dissolution rate of the cloven crosslink moieties in an alkali developing solution after exposure (dissolution rate in an alkali developing solution);    (c) good diffusivity of an acid generated by irradiation with an active energy beam (acid diffusivity);    (d) transparency of a photosensitive coating at an exposure wavelength (transparency); and    (e) thermal stability during the heating step after application of the film and exposure (thermal stability).
As an example of a polymer meeting these requirements somewhat, a copolymer from p-hydroxystyrene, n-butyl acrylate and acrylic acid has been disclosed in, for example, JP-As 8-94827 and 8-94829. We have, however, investigated the copolymer for its performance and have concluded that it is insufficiently soluble in a solvent or thermally stable.
JP-A 61-293249 has disclosed a binary copolymer of 4-(1-methylethenyl)phenol and n-butyl acrylate as an example of a copolymer for a resin composition exhibiting damping property. The copolymer has an extremely lower dissolution rate in an alkali developing solution and is poorly compatible with a vinyl ether compound. It cannot be, therefore, used as it is.