US 2020/0401045 Al  3  Dec. 24, 2020  [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.  [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.  [0061]  Software Package  1:  Advanced Chemistry Devel› opment (ACD/Labs) Software V 8.14 for Solaris (1994- 2007 A CD/Labs)  (Xl)  [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.  [0059]  <<Measurement of Acid Dissociation Constant  pKa>>  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.  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.  [0057]  In addition, the pKa of a monomer obtained by  substituting the cationic structure moiety in the salt  [0056]  The salt structure consists of an anionic structure  moiety and an actinic ray-sensitive decomposable or  radiation-sensitive decomposable cationic structure  moiety.  [0055]  The resin (AX!) includes a repeating unit (re› peating unit A) derived from a monomer having a salt  structure.  [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  [0051]  (Resin (AX!))  [0048]  <Resin (A)>  [0047]  The composition of the embodiment of the pres› ent invention is typically a chemically amplified resist  composition.  [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.  [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).  [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.  [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.  0  rnZII 