The linear or branched, saturated hydrocarbon group pref› erably has  1  to 25 carbon atoms, more preferably  1  to 15, and  still more preferably  4  to  10.  Examples of the linear, saturated hydrocarbon group  include a methyl group, an ethyl group, a propyl group, a 5  butyl group, a pentyl group, a hexyl group, a heptyl group, an  octyl group, a nonyl group and a decyl group.  Examples of the branched, saturated hydrocarbon group  include a 1-methylethyl group, a 1-methylpropyl group, a  2-methylpropyl group, a 1-methylbutyl group, a 2-methylbu- tyl group, a 3-methylbutyl group, a 1-ethylbutyl group, a  2-ethylbutyl group, a 1-methylpentyl group, a 2-methylpen- tyl group, a 3-methylpentyl group and a 4-methylpentyl  group, but excluding tertiary alkyl groups.  The linear or branched, saturated hydrocarbon group may  have a substituent. Examples of the substituent include an  alkoxy group, a halogen atom, a halogenated alkyl group, a  hydroxyl group, an oxygen atom (=0), a cyano group and a  carboxy group.  The alkoxy group as a substituent for the linear or branched  saturated hydrocarbon group is preferably an alkoxy group  having  1  to 5 carbon atoms, more preferably a methoxy  group, an ethoxy group, an n-propoxy group, an iso-propoxy  group, an n-butoxy group or a tert-butoxy group, and most 25  preferably a methoxy group or an ethoxy group.  Examples of the halogen atom as a substituent for the linear  or branched, saturated alkyl group include a fluorine atom, a  chlorine atom, a bromine atom and an iodine atom, and a  fluorine atom is preferable.  Example of the halogenated alkyl group as a substituent for  the linear or branched, saturated hydrocarbon group includes  a group in which part or all of the hydrogen atoms within the  aforementioned linear or branched, saturated hydrocarbon  group have been substituted with the aforementioned halogen  atoms.  The cyclic saturated hydrocarbon group of 3 to 20 carbon  atoms for R  6 ’, R  7 ’ and R  8 ’ may be either a polycyclic group or  a monocyclic group, and examples thereof include groups in  which one hydrogen atom has been removed from a mono- cycloalkane, and groups in which one hydrogen atom has  been removed from a polycycloalkane ( e.g., a bicycloalkane,  a tricycloalkane or a tetracycloalkane ).  More specific  examples include groups in which one hydrogen atom has  been removed from a monocycloalkane such as cyclopen› tane, cyclohexane, cycloheptane or cyclooctane; and groups  in which one or more hydrogen atoms have been removed  from a polycycloalkane such as adamantane, norbornane,  isobornane, tricyclodecane or tetracyclododecane.  The cyclic, saturated hydrocarbon group may have a sub- stituent. For example, part of the carbon atoms constituting  the ring within the cyclic alkyl group may be substituted with  a hetero atom, or a hydrogen atom bonded to the ring within  the cyclic alkyl group may be substituted with a substituent.  In the former example, a heterocycloalkane in which part  of the carbon atoms constituting the ring within the afore› mentioned monocycloalkane or polycycloalkane has been  substituted with a hetero atom such as an oxygen atom, a  sulfur atom or a nitrogen atom, and one hydrogen atom has  been removed therefrom, can be used. Further, the ring may  contain an ester bond (----C( =0  )---0-) in the ring structure  thereof. More specific examples include a lactone-containing  monocyclic group, such as a group in which one hydrogen  atom has been removed from y-butyrolactone; and a lactone› containing polycyclic group, such as a group in which one  hydrogen atom has been removed from a bicycloalkane, tri› cycloalkane or tetracycloalkane containing a lactone ring.  Specific examples of the substituent for substituting part of  the hydrogen atom constituting the aliphatic hydrocarbon  group, include an alkoxy group, a halogen atom, a haloge› nated alkyl group, a hydroxy group, an oxo group (=0), a  cyano group, an aryl group, an alkoxyalkyloxy group, an  alkoxycarbonylalkyloxy group, a carboxy group,  ----eoo-z+  (wherein  z+  is the same as defined above), ----C(=O)-O- R 6 ’, -O----C(=O)-R 7 ’ and-O-R 8 ’. EachofR 6 ’, R 7 ’ and  R  8 ’  independently represents a linear or branched saturated  hydrocarbon group of  1  to 25 atoms, a cyclic saturated hydro- Specific examples of the substituent group for substituting  part of the carbon atoms include -0-, -C(=O)---0-,  ----C(=O)-,  ---0----C(=O)---O-,  -C(=O)-NH-,  -NH-(wherein the H may be substituted with a substituent  such as an alkyl group or an acyl group), -S-,  -S(=O)$_{2}$ - and -S(=O)$_{2}$---0-. When the aliphatic hydrocarbon  group is cyclic, the aliphatic hydrocarbon group may contain  any of these substituent groups in the ring structure.  The substituent group containing a hetero atom may be a  group consisting of a hetero atom, or may be a group contain› ing a group or atom other than a hetero atom.  With respect to the substituent containing a hetero atom for  substituting part of the carbon atom constituting the aliphatic  hydrocarbon group, a hetero atom is an atom other than  carbon and hydrogen, and examples thereof include an oxy› gen atom, a nitrogen atom, a sulfur atom and a halogen atom.  Examples of the halogen atom include a fluorine atom, a  chlorine atom, an iodine atom and a bromine atom.  In the aliphatic hydrocarbon group, part of the carbon  atoms constituting the aliphatic hydrocarbon group may be  substituted with a substituent group containing a hetero atom,  or part or all of the hydrogen atoms constituting the aliphatic  hydrocarbon group may be substituted with a substituent.  The aliphatic hydrocarbon group for R  1  may be either a  saturated hydrocarbon group (that is, alkyl group), or an  unsaturated aliphatic hydrocarbon group. Further, the ali› phatic hydrocarbon group may be chain-like or cyclic. The  chain-like aliphatic hydrocarbon group may be linear or  branched. The cyclic aliphatic hydrocarbon group may be  either a polycyclic group or a monocyclic group.  Among the aforementioned examples, as R 7 ’ and R 8 ’, in  terms of improvement in lithography properties and shape of  the resist pattern, a linear or branched, saturated hydrocarbon  group of  1  to 15 carbon atoms or a cyclic saturated hydrocar- bon group of 3 to 20 carbon atoms is preferable.  The aforementioned linear or branched, aliphatic unsatur- ated hydrocarbon group may have a substituent. Examples of  substituents include the same substituents as those which the  aforementioned linear or branched alkyl group may have.  Examples of the branched aliphatic unsaturated hydrocar› bon group for  R 6 ’, R 7 ’  and R 8 ’  include a 1-methylpropenyl  group and a 2-methylpropenyl group.  Examples of the linear aliphatic unsaturated hydrocarbon  group for R 6 ’, R 7 ’ and R 8 ’ include a vinyl group, a propenyl  group ( an ally  1  group) and a butyny  1  group.  Examples of the combination of a linear or branched alkyl  group with a cyclic alkyl group include groups in which a  cyclic alkyl group as a substituent is bonded to a linear or  branched alkyl group, and groups in which a linear or  branched alkyl group as a substituent is bonded to a cyclic  alkyl group.  Alternatively, R  6 ’, R  7 ’ and R  8 ’ may be a combination of a  linear or branched alkyl group and a cyclic group.  In the latter example, as the substituent, the same substitu› ent groups as those for the aforementioned linear or branched  alkyl group, or an alkyl group of  1  to 5 carbon atoms can be  used.  US 9,063,416 B2  107  108 