Oct. 21, 2010  37  US 2010/0266955 Al  In the formula, R is the same as defined above, and the  plurality of R may be either the same or different from each  other; R$^{14 }$represents an alkyl group; and a represents an  integer of 1 to 10.  [Chemical Formula 38]  (Al-31)  [0233]  In formula (Al-11 ), the alkyl group for R $^{14 }$is pref› erably a linear or branched alkyl group, more preferably a  linear alkyl group, and most preferably a methyl group or an  ethyl group.  [0234]  g is preferably an integer of0 to 3, more preferably  1 to 3, and still more preferably 1 or 2.  [0235]  In formula (Al-21), the alkyl group for R$^{14 }$is pref› erably a linear or branched alkyl group, more preferably a  linear alkyl group, still more preferably a methyl group or an  ethyl group, and most preferably a methyl group.  [0236]  In formula (Al-31), the alkyl group for R 11  is the  same as defined for the alkyl group represented by R, prefer› ably a methyl group or an ethyl group, and most preferably an  ethyl group.  [0237]  The alkyl group for R$^{14 }$is preferably a linear or  branched alkyl group, more preferably a linear alkyl group,  and most preferably a methyl group or an ethyl group.  [0238]  g is preferably an integer of0 to 3, more preferably  1 to 3, and still more preferably 1 or 2.  [0239]  The component (Al) can be obtained, for example,  by a conventional radical polymerization or the like of the  monomers corresponding with each of the structural units,  using a radical polymerization initiator such as azobisisobu› tyronitrile (AIBN).  [0240]  Furthermore, in the component (Al), by using a  chain transfer agent such as HS----CH$_{2}$----CH$_{2}$----CH$_{2}$----C  (CF$_{3}$ ) $_{2}$---0H, a ----C(CF$_{3}$ ) $_{2}$---0H group can be introduced at  the terminals of the component (Al). Such a copolymer hav› ing introduced a hydroxyalkyl group in which some of the  hydrogen atoms of the alkyl group are substituted with fluo› rine atoms is effective in reducing developing defects and  LER (line edge roughness: unevenness of the side walls of a  line pattern).  [0241]  The weight average molecular weight (Mw) (the  polystyrene equivalent value determined by gel permeation  chromatography) of the component (Al) is not particularly  limited, but is preferably 1,000 to 50,000, more preferably  1,500 to 30,000, and most preferably 2,500 to 20,000. When  the weight average molecular weight is no more than the  upper limit of the above-mentioned range, the resist compo› sition exhibits a satisfactory solubility in a resist solvent. On  the other band, when the weight average molecular weight is  at least as large as the lower limit of the above-mentioned  range, dry etching resistance and the cross-sectional shape of  the resist pattern becomes satisfactory.  [0242]  Further, the dispersity (Mw/Mn) is preferably 1.0 to  5.0, more preferably I .Oto 3.0, and most preferably 1.2 to 2.5.  Here, Mn is the number average molecular weight.  [0243]  In the component (A), as the component (Al), one  type may be used alone, or two or more types may be used in  combination.  [0244]  In the component (A), the amount of the component  (Al) based on the total weight of the component (A) is pref› erably 25% by weight or more, more preferably 50% by  weight or more, still more preferably 7 5% by weight or more,  and may be even 100% by weight. When the amount of the  component (Al) is 25% by weight or more, a resist pattern  exhibiting a high resolution and a high rectangularity can be  formed.  [0245]  In the positive resist composition of the present  invention, the component (A) may contain "a base component  which exhibits increased solubility in an alkali developing  solution under action of acid" other than the component (Al)  (hereafter, referred to as "component (A2)").  In the formula, R is the same as defined above, and the  plurality of R may be either the same or different from each  other; R$^{11 }$represents an alkyl group of 1 to 5 carbon atoms;  R $^{14 }$represents an alkyl group; a represents an integer of  1.  to  10; and g represents an integer of0 to 8.  [0231]  In general formulas (Al-11), (Al-21) and (Al-31),  R, R 11 , R 14 , a and g are the same as defined above.  [0232]  a is preferably an integer of 1 to 8, more preferably  1 to 5, still more preferably 1 or 2, and most preferably 1. 