## RESIST COMPOSITION, METHOD OF FORMING RESIST PATTERN, POLYMERIC COMPOUND, AND COPOLYMER 

[0001] The present invention relates to a resist composi› tion, a method of forming a resist pattern, a polymeric compound, and a copolymer. 

[0002] Priority is claimed on Japanese Patent Application No. 2016-197492, filed Oct. 5, 2016, and Japanese Patent Application No. 2017-176005, filed Sep. 13, 2017, the contents of which are incorporated herein by reference. 

## DESCRIPTION OF RELATED ART 

[0003] 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, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. A resist material in which the exposed portions of the resist film become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions of the resist film become insoluble in a developing solution is called a nega› tive-type. 

[0004] In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have led 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 used 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 (EB), extreme ultraviolet radiation (EUV), and X ray. 

[0005] Resist materials for use with these types of expo› sure 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. 

[0006] 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 a developing solution under the action of acid and an acid-generator component that generates acid upon expo› sure. 

[0007] For example, in the case where the developing solution is an alkali developing solution (alkali developing process), a chemically amplified positive resist which con› tains, 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 a resist film formed using such a resist composition is selectively exposed at the time of forming a resist pattern, in exposed areas, acid is generated from the acid generator component, and the polarity of the base resin increases by the action of the generated acid, thereby making the exposed areas of the resist film soluble in the alkali developing solution. Thus, by alkali developing, the exposed portions of the resist film are dissolved and removed, whereas the 

## TECHNICAL FIELD 

unexposed portions of the resist film remain as patterns, thereby forming a positive resist pattern. 

[0008] On the other hand, when such a base resin is applied to a solvent developing process using a developing solution containing an organic solvent ( organic developing solution), the solubility of the exposed portions in an organic developing solution is decreased. As a result, the unexposed portions of the resist film are dissolved and removed by the organic developing solution, and a negative resist pattern in which the exposed portions of the resist film are remaining is formed. Such a solvent developing process for forming a negative-tone resist composition is sometimes referred to as "negative-tone developing process". 

[0009] In general, the base resin used for a chemically amplified resist composition contains a plurality of structural units for improving lithography properties and the like. 

[0010] For example, in the case of a resin composition which exhibits increased solubility in an alkali developing solution by the action of acid, a structural unit containing an acid decomposable group which is decomposed by the action of acid generated from an acid generator component and exhibits increased polarity. Further, a structural unit containing a lactone-containing cyclic group or a structural unit containing a polar group such as a hydroxy group is used in combination. 

[0011] As the acid-generator component used in a chemi› cally amplified resist composition, various kinds have been proposed. For example, onium salt acid generators such as iodonium salts and sulfonium salts; oxime sulfonate acid generators; diazomethane acid generators; nitrobenzylsul› fonate acid generators; iminosulfonate acid generators; and disulfone acid generators are known. 

[0012] As onium salt acid generators, those which have an onium ion such as triphenylsulfonium in the cation moiety are mainly used. Generally, 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 sub› stituted with fluorine atoms is typically used. 

[0013] In the formation of a resist pattern, the behavior of acid generated from the acid-generator component upon exposure is one of the factors which has large influence on the lithography properties. 

[0014] In particular, when a resist film is exposed with EUV (extreme ultraviolet) or EB (electron beam), in the resist material, control of acid diffusion becomes a problem. Conventionally, for controlling acid diffusion, various meth› ods of changing the design of the base resin has been proposed. 

[0015] For example, there has been disclosed a resist composition in which a polymeric compound having a specific acid dissociable, functional group has been used to enhance the reactivity to acid, and improve solubility in a developing solution (see, for example, Patent Literatures 1 and 2). 

[0016] Further, for improving lithography properties, for example, there has been proposed a chemically amplified resist composition which uses, as a base component, a polymeric compound containing a structural unit having an acid decomposable group with a specific structure (an acid decomposable group containing a tertiary carbon atom hav› ing bonded thereto an aliphatic hydrocarbon group contain› ing an ether bond) (see, for example, Patent Literature 3). 

