In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film.
A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength (increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter (energy higher) than these excimer lasers, such as electron beam, extreme ultraviolet radiation (EUV), and X ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.
As a resist material that satisfies these conditions, a chemically amplified composition is used, which includes a base material component that exhibits a changed solubility in an alkali developing solution under the action of acid and an acid-generator component that generates acid upon exposure.
For example, a chemically amplified positive resist contains, as a base component (base resin), a resin which exhibits increased solubility in an alkali developing solution under action of acid, and an acid generator is typically used. If the resist film formed using the resist composition is selectively exposed during formation of a resist pattern, then within the exposed portions, acid is generated from the acid-generator component, and the action of this acid causes an increase in the solubility of the resin component in an alkali developing solution, making the exposed portions soluble in the alkali developing solution.
Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are now widely used as base resins for resist compositions that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 1).
Especially, in order to improve various lithography properties, a base resin having a plurality of structural units is currently used for a chemically amplified resist composition. For example, in the case of a chemically amplified positive resist composition, a resin containing a structural unit having an acid dissociable, dissolution inhibiting group that is dissociated by the action of acid generated from the acid generator, a structural unit having a polar group such as a hydroxyl group, a structural unit having a lactone structure, and the like is typically used.
Further, in order to improve various lithography properties such as resolution, exposure latitude (EL margin) and mask reproducibility, a resin having a structural unit containing an —SO2— containing cyclic group has been used (for example, see Patent Document 2).
An “—SO2— containing cyclic group” refers to a cyclic group having a ring containing —SO2— within the ring skeleton thereof, i.e., a cyclic group in which the sulfur atom (S) within —SO2— forms part of the ring skeleton of the cyclic group.
On the other hand, as acid generators usable in a chemically amplified resist composition, various types have been proposed including, for example, onium salt acid generators such as iodonium salts and sulfonium salts; oxime sulfonate acid generators; diazomethane acid generators; nitrobenzylsulfonate acid generators; iminosulfonate acid generators; and disulfone acid generators.
Among these, currently, as acid generators, onium salt acid generators having an onium ion such as triphenylsulfonium as the cation moiety are particularly used. As the anion moiety for onium salt acid generators, an alkylsulfonate ion or a fluorinated alkylsulfonate ion in which part or all of the hydrogen atoms within the aforementioned alkylsulfonate ion has been substituted with fluorine atoms is typically used (for example, see Patent Document 3).