US 8,298,748 B2  9  10  aliphatic hydrocarbon group containing a ring in the structure  thereof, and a combination thereof.  The linear or branched aliphatic hydrocarbon group pref› erably has 10 to 20 carbon atoms, and more preferably 10 to  15 carbon atoms.  As the linear aliphatic hydrocarbon group, a linear alkyl  group is preferable. Specific examples thereofinclude a decyl  group, an undecyl group, a dodecyl group, a tridecyl group, an  isotridecyl group, a tetradecyl group, a pentadecyl group, a  hexadecyl group, an isohexadecyl group, a heptadecyl group,  an octadecyl group, a nonadecyl group, an icosyl group, a  henicosyl group and a docosyl group.  The branched aliphatic hydrocarbon group preferably has  10 to 20 carbon atoms, and more preferably 10 to 15 carbon  atoms.  As the branched aliphatic hydrocarbon group, a branched  alkyl group is preferable. Specific examples thereof include  an isodecyl group and an isoundecyl group.  The linear or branched aliphatic hydrocarbon group  (chain-like aliphatic hydrocarbon group) may or may not  have a substituent. Examples of the substituent include a  fluorine atom, a fluorinated alkyl group of 1 to 5 carbon  atoms, and an oxygen atom  (=0).  As examples of the hydrocarbon group containing a ring in  the structure thereof, a cyclic aliphatic hydrocarbon group (a  group in which one hydrogen atom has been removed from an  aliphatic hydrocarbon ring), and a group in which the cyclic  aliphatic hydrocarbon group is bonded to the terminal of the  aforementioned chain-like aliphatic hydrocarbon group or  interposed within the aforementioned chain-like aliphatic  hydrocarbon group, can be given.  The cyclic aliphatic hydrocarbon group preferably has 10  to 20 carbon atoms, and more preferably 10 to 15 carbon  atoms.  The cyclic aliphatic hydrocarbon group may be either a  polycyclic group or a monocyclic group.  Examples of the monocyclic group include cyclodecane  and cyclododecane.  As the polycyclic group, a group in which one hydrogen  atom has been removed from a polycycloalkane of 10 to 20  carbon atoms is preferable. Specific examples of the polycy- cloalkane include adamantane, diadamantane, dicyclohex› ane, tricyclodecane and tetracyclododecane.  The cyclic aliphatic hydrocarbon group may or may not  have a substituent. Examples of the substituent include an  alkyl group of 1 to 5 carbon atoms, a fluorine atom, a fluori- nated alkyl group of 1 to 5 carbon atoms, and an oxygen atom  (=0).  Examples of the aromatic hydrocarbon group include an  aryl group in which one hydrogen atom has been removed  from an aromatic hydrocarbon ring, such as a bipheny 1 group,  a fluorenyl group, a naphthyl group, an anthryl group or a  phenanthryl group;  an aromatic hydrocarbon group in which part of the carbon  atoms constituting the ring of the aforementioned monova- lent aromatic hydrocarbon group has been substituted with a  hetero atom such as an oxygen atom, a sulfur atom or a  nitrogen atom; and  an arylalkyl group, such as a benzyl group, a phenethyl  group, a 1-naphthylmethyl group, a 2-naphthylmethyl group,  a 1-naphthylethyl group or a 2-naphthylethyl group.  Specific examples of the structural unit (a0-1) are shown  below.  [Chemical Formula 5]  The alkyl chain within the arylalkyl group preferably has 1  to 4 carbon atom, more preferably 1 or 2, and most preferably  1.  The aromatic hydrocarbon group may or may not have a  substituent. Examples of the substituent include an alkyl  group of 1 to 5 carbon atoms, a fluorine atom, a fluorinated  alkyl group of 1 to 5 carbon atoms, and an oxygen atom  (=0).  In the present invention, as R 1, an aliphatic hydrocarbon  group is preferable, and an aliphatic polycyclic group is more  preferable in terms of improvement in etching resistance,  suppression of thickness loss of a resist pattern, shape of the  resist pattern and suppression of outgas.  R  R  R 