110  US  9,104,101 B2  109  The organic group for P preferably contains 1 to 20 carbon  atoms, more preferably 2 to 15 carbon atoms, and still more  preferably 3 to 12 carbon atoms.  side chains (hereinafter referred to as "component (Cl)") and  main  chain-degradable  resin  components  (hereinafter  referred to as "component (C2)").  Examples of the component (Cl) include resins containing  at least one structural unit among the aforementioned struc- tural units (all) to (a13), and optionally containing an afore› mentioned structural unit (a2) to (a6) or the like. More spe› cific examples of the component (Cl) include resins  containing the structural units ( a 12) and ( a3 2), resins contain› ing the structural units (a12), (a32) and(a5), resins containing  the structural units (a13) and (a33), resins containing the  structural units (a13), (a33) and (a6), resins containing the  structural units ( a 11) and ( a2 ), resins containing the structural  units (all), (a2) and (a31), resins containing the structural  units (al 1), (a2), (a31) and (a4), resins containing the struc› tural units (all) and (a32), resins containing the structural  units (all), (a32) and (a5), resins containing the structural  units (all) and (a33), and resins containing the structural  units (all), (a33) and (a6).  Examples of the organic group include aliphatic hydrocar› bon groups and aromatic hydrocarbon groups.  The aliphatic hydrocarbon group may be a chain-like  group, a cyclic group, or a combination thereof, and may be  either saturated or unsaturated.  Examples of the aromatic hydrocarbon group include  hydrocarbon groups containing an aromatic hydrocarbon  ring, and the group may be composed solely of the aromatic  hydrocarbon ring, or may be a combination of the aromatic  hydrocarbon ring and an aliphatic hydrocarbon group.  The organic group may also include a linking group such as  an ether group, polyether group, ester group [----C(=O)› O-], carbonyl group [-C(=O)-], -NH-, -N=,  -NH-C(=O)- or -NR 25  (wherein R 25  represents an  alkyl group), or a silicon atom within the group structure.  Examples of the component (C2) include polymers in  which n arm portions each composed of a polymer chain are  bonded to an organic group having a valency of n (wherein n  represents an integer of 2 or greater) via linking groups that  include a joining group which can be cleaved under the action  of acid.  This expression that the joining group "can be cleaved  under the action of acid" means that the action of the acid  generated from the structural unit (a0) or an optional compo› nent (B) upon exposure can cause the bonding within the  main chain of the component (C2) to break at the position of  the joining group.  Examples of the alkyl group for R$^{25 }$include lower alkyl  groups of 1 to 5 carbon atoms.  Further, a part or all of the hydrogen atoms within the  organic group may or may not each be substituted with a  substituent such as an alkyl group, alkoxy group, halogen  atom or hydroxyl group.  As the alkyl group with which a hydrogen atom of the  organic group may be substituted, an alkyl group of 1 to 5  carbon atoms is preferred, and a methyl group, ethyl group,  propyl group, n-butyl group ortert-butyl group is particularly  desirable.  In these types of polymers, when acid is generated from the  structural unit (a0) or an optional component (B) upon expo› sure, the action of the acid causes cleavage of the joining  group. As a result, the molecular weight decreases signifi› cantly, and a polar group is formed at the position of the  joining group, resulting in an increase in the solubility within  an alkali developing solution and a decrease in the solubility  within an organic developing solution.  As the alkoxy group with which a hydrogen atom of the  organic group may be substituted, an alkoxy group of 1 to 5  carbon atoms is preferred, a methoxy group, ethoxy group,  n-propoxy group, iso-propoxy group, n-butoxy group ortert› butoxy group is more preferred, and a methoxy group or  ethoxy group is particularly desirable.  Examples of the halogen atom with which a hydrogen atom  of the organic group may be substituted include a fluorine  atom, chlorine atom, bromine atom and iodine atom, and a  fluorine atom is particularly desirable.  Specific examples of the organic group for P include  groups having the structures represented by formulas shown  below.  More specific examples of the component (C2) include  polymers having a core portion represented by a general  formula (1) shown below and arm portions composed of  polymer chains bonded to the core portion (hereinafter  referred to as the "polymer (C21)").  [Chemical Formula 48]  In formula ( 1 ), P represents an organic group having a valency  of a, a represents an integer of 2 to 20, X 21  represents an  arylene group or an alkylene group of 1 to 12 carbon atoms,  and X$^{22 }$represents a joining group that can be cleaved under  the action of acid.  (Core Portion)  The core portion of the polymer ( C21) is represented by the  general formula (1) shown above.  In the general formula (1 ), a represents an integerof2 to 20,  preferably an integer of 2 to 15, and more preferably an  integer of3 to 10. Provided a satisfies this range, the resolu› tion improves and an excellent pattern shape can be obtained.  P represents an organic group having a valency of a. In  other words, when Pis divalent (a=2), the core portion of the  polymer (C21) is a structure in which two groups represented  by are bonded to P. When Pis trivalent (a=3), three groups  represented by-X$^{22}$-X 21 - are bonded to P. In this man› ner, as the valency a of P increases, the number of groups  -X 22  -X 21  - bonded to P increases, and the polymer (C21)  becomes a more dense radial-shaped structure. 