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above-mentioned resin (A) in the exposed portion, whereby the salt structure is converted into an acid structure. In a case where the salt structure in the repeating unit A is converted into the acid structure, the basicity to an acid generated from the photoacid gen› erator upon irradiation with actinic rays or radiation is reduced. As a result, in the exposed portion, a depro› tection reaction of the acid-decomposable group gen› erated from the photoacid generator proceeds smoothly. 

[0045] As described above, in the resist film formed with the composition of the embodiment of the present invention, the resin (A) includes the repeating unit A having an acid diffusion control function. With this configuration, a prob› lem of uneven concentration distribution caused by the aggregation of acid diffusion control agents and the like, which occurs with a resist film formed from a resist com› position including an acid diffusion control agent alone in addition to the resin (related art), can be solved. That is, with the composition of the embodiment of the present invention, the suppression (neutralization) of diffusion of an acid generated from a photoacid generator proceeds uniformly, and the LWR performance of a pattern thus formed is excellent. 

[0046] Hereinafter, the components included in the com› position of the embodiment of the present invention will be described in detail. Furthermore, the composition of the embodiment of the present invention is a so-called resist composition, and may be either a positive tone resist com› position or a negative tone resist composition. In addition, the composition of the embodiment of the present invention may be either a resist composition for alkali development or a resist composition for organic solvent development. 

[0047] The composition of the embodiment of the pres› ent invention is typically a chemically amplified resist composition. 

[0048] <Resin (A)> 

[0049] The composition of the embodiment of the pres› ent invention includes a resin (hereinafter also referred to as a "resin (A)"). 

[0050] As the resin (A), for example, the resin (AX!) which will be described later and the resin (AX2) which will be described later can be used, and among these, the resin (AX!) is preferable. 

[0051] (Resin (AX!)) 

[0052] The resin (AX!) includes a resin including a repeating unit derived from a monomer having a salt structure (repeating unit A) and a repeating unit having an acid-decomposable group (repeating unit B). 

[0053] In a case where the composition of the embodi› ment of the present invention includes the resin (AX!), usually, a pattern thus formed is a positive tone pattern with a use of an alkali developer as a developer, and the pattern thus formed is a negative tone pattern with a use of an organic developer as the developer. 

[0054] • Repeating Unit A 

[0055] The resin (AX!) includes a repeating unit (re› peating unit A) derived from a monomer having a salt structure. 

[0056] The salt structure consists of an anionic structure moiety and an actinic ray-sensitive decomposable or radiation-sensitive decomposable cationic structure moiety. 

[0057] In addition, the pKa of a monomer obtained by substituting the cationic structure moiety in the salt 

structure with a hydrogen atom is -0.80 or more. The pKa is preferably -0.50 or more, and more preferably 0 or more. In addition, an upper limit value thereof is not particularly limited, but is, for example, 30 or less. 

[0058] Moreover, a value of the pKa is preferably larger than the pKa of an acid generated from a photoacid generator (a photoacid generator which contributes to the deprotection reaction of an acid-decomposable group upon irradiation with actinic rays or radiation, such as a photoacid generator (B) which will be described later). Further, the pKa can be measured by the following method. 

[0059] <<Measurement of Acid Dissociation Constant pKa>> 

[0060] In the present specification, the acid dissociation constant pKa refers to an acid dissociation constant pKa in an aqueous solution, and is defined, for example, in Chemical Handbook (II) (Revised 4th Edition, 1993, compiled by the Chemical Society of Japan, Maruzen Company, Ltd.), and a lower value thereof indicates higher acid strength. Specifically, the acid dissociation constant pKa in an aqueous solution can be actually measured by using an infinite-dilution aqueous solution and measuring the acid dissociation constant at 25° C., and the acid dissociation constant pKa can also be determined using the following soft› ware package 1 by computation from a value based on a Hammett substituent constant and the database of publicly known literature values. Any of the values of pKa described in the present specification represent values determined by calculation using the software package. 

[0061] Software Package 1: Advanced Chemistry Devel› opment (ACD/Labs) Software V 8.14 for Solaris (1994- 2007 A CD/Labs) 

[0062] The monomer having a salt structure is preferably a monomer represented by General Formula (Xl) from the viewpoint that the L WR of a pattern thus formed is more excellent. With regard to the monomer represented by Gen› eral Formula (Xl), a monomer obtained by substituting the cationic structure moiety in the salt structure with a hydro› gen atom satisfies a pKa of -0.80 or more. 

<img src='content_image/936204.jpg'>

[0063] P 11 represents a polymerizable group. The type of the polymerizable group is not particularly limited, examples thereof include known polymerizable groups, and from the viewpoint of reactivity, a functional group capable of performing an addition polymerization reaction is pref› erable, and an ethylenically unsaturated polymerizable group is more preferable. Examples of the polymerizable group include substituents represented by (Ql) to (Q7) shown below. In addition, a hydrogen atom in the substituent represented by each of (Ql) to (Q7) shown below may be substituted with other substituents such as a halogen atom. 

(Xl) 

