US 8,298,748 B2  92  91  -continued  n represents an integer of0 to 3, preferably an integer of0  to 2, more preferably 0 or 1, and most preferably 1.  When the structural unit is included in the component (Al’)  the amount of the structural unit (al) based on the combined  total of all structural units constituting the component (Al’) is  preferably 10 to 80 mo! %, more preferably 20 to 70 mo! %,  and still more preferably 25 to 60 mo!%. When the amount of  the structural unit (al) is at least as large as the lower limit of  the above-mentioned range, a pattern can be easily formed  using a resist composition prepared from the component  (Al). On the other hand, when the amount of the structural  unit (al) is no more than the upper limit of the above-men› tioned range, a good balance can be achieved with the other  structural units.  (Structural Unit (a2))  The component (Al’) may also have a structural unit (a2)  derived from an acrylate ester containing a lactone-contain› ing cyclic group, as long as the effects of the present invention  are not impaired.  The term "lactone-containing cyclic group" refers to a  cyclic group including one ring containing a -O----C(O)› structure (lactone ring). The term "lactone ring" refers to a  single ring containing a---0-C(O)-structure, and this ring  is counted as the first ring. A lactone-containing cyclic group  in which the only ring structure is the lactone ring is referred  to as a monocyclic group, and groups containing other ring  structures are described as polycyclic groups regardless of the  structure of the other rings.  When the component (Al’) is used for forming a resist film,  the lactone-containing cyclic group of the structural unit (a2)  is effective in improving the adhesion between the resist film  and the substrate, and increasing the compatibility with the  developing solution containing water.  As the structural unit (a2), there is no particular limitation,  and an arbitrary structural unit may be used.  Specific examples of lactone-containing monocyclic  groups include a group in which one hydrogen atom has been  removed from a 4- to 6-membered lactone ring, such as a  group in which one hydrogen atom has been removed from  ~-propiolatone, a group in which one hydrogen atom has been  removed from y-butyrolactone, and a group in which one  hydrogen atom has been removed from 1\-valerolactone. Fur› ther, specific examples of lactone-containing polycyclic  groups include groups in which one hydrogen atom has been  removed from a lactone ring-containing bicycloalkane, tricy› cloalkane or tetracycloalkane.  More specifically, examples of the structural unit (a2)  include structural units represented by general formulas (a2- 1) to (a2-5) shown below.  [Chemical Formula 50]  (a2-1)  (a2-5)  (a2-4)  (a2-3)  (a2-2)  ~o  $^{0 }$\ $_{R29 }$ R’_{__(RA"  R’)(  0  0  $^{0 }$\  R ,  I  -- A"  0  0  In the formulas, R represents a hydrogen atom, an alkyl group  of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5  carbon atoms; each R’ independently represents a hydrogen  atom, an alkyl group of 1 to 5 carbon atoms, an alkoxy group  of 1 to 5 carbon atoms or----COOR", wherein R" represents a  hydrogen atom or an alky I group; R $^{29 }$represents a single bond  or a divalent linking group; s" represents an integer of0 to 2;  A" represents an oxygen atom, a sulfur atom or an alkylene  group of 1 to 5 carbon atoms which may contain an oxygen  atom or a sulfur atom; and m represents 0 or 1.  In general formulas (a2-1) to (a2-5),  R  is the same as  defined for R in the structural unit (al).  Examples of the alkyl group of 1 to 5 carbon atoms for R’  include a methyl group, an ethyl group, a propyl group, an  n-butyl group and a tent-butyl group. 