US 9,829,796 B2  184  183  1mtrntor as a polymerization initiator (azo-based initiator,  peroxide, or the like). As the radical initiator, an azo-based  initiator is preferable, and an azo-based initiator having an  ester group, a cyano group, or a carboxyl group is preferable.  Preferable examples of the initiator include azobisisobuty› ronitrile, azobisdimethylvaleronitrile, and dimethyl 2,2’-azo› bis(2-methylpropionate ). As necessary, polymerization may  be performed in the presence of a chain transfer agent (for  example, alkyl mercaptan).  The concentration of the reaction is 5% by mass to 70%  by mass, and preferably 10% by mass to 50% by mass. The  reaction temperature is typically 10°  C. to 150°  C., prefer› ably 30°  C. to 120°  C., and more preferably 40°  C. to 100°  C.  The reaction time is typically 1 hour to 48 hours, prefer› ably 1 hour to 24 hours, and more preferably 1 hour to 12  hours.  After the reaction ends, cooling is performed to room  temperature, and purification is performed. A usual method  such as a liquid-liquid extraction method in which a residual  monomer or an oligomer component is removed by washing  with water or combining suitable solvents, a purification  method in a solution state such as ultrafiltration which  extracts and removes only substances having a specific  molecular weight or less, a reprecipitation method in which  a residual monomer or the like is removed by adding a resin  solution dropwise to a poor solvent to coagulate the resin in  the poor solvent, or a purification method in a solid state in  which filtered resin slurry is washed with a poor solvent can  be applied to the purification. For example, by bringing into  contact with a solvent (poor solvent), which does poorly  dissolve or does not dissolve the resin, corresponding to 10  times or less the volume amount of the reaction solution, or  preferably 5 times to 10 times the volume amount of the  reaction solution, the resin is solidified and precipitated.  The solvent (precipitation or reprecipitation solvent) used  in precipitation or reprecipitation operation from the poly› mer solution may be a poor solvent for the polymer, and  depending on the type of polymer, the solvent can be  suitably selected from hydrocarbon, halogenated hydrocar› bon, a nitro compound, ether, ketone, ester, carbonate,  alcohol, carboxylic acid, water, and a mixed solvent includ› ing these solvents and used. Among these, as a precipitation  or reprecipitation solvent, a solvent including at least alco› hol (in particular, methanol) or water is preferable.  Although the amount of precipitation or reprecipitation  solvent used can be suitably selected in consideration of  efficiency or yield, the amount used is generally 100 parts by  mass to 10000 parts by mass, preferably 200 parts by mass  to 2000 parts by mass, and more preferably 300 parts by  mass to 1000 parts by mass, with respect to 100 parts by  mass of the polymer solution.  Although the temperature at the time of precipitation or  reprecipitation can be suitably selected in consideration of  efficiency or operability, the temperature is typically about  0°  C. to 50°  C., and preferably around room temperature (for  example, about 20°  C. to 35°  C.). Precipitation or reprecipi› tation operation can be performed by a known method such  as a batch type or a continuous type using a generally used  mixing vessel such as a stirring vessel.  The precipitated or reprecipitated polymer is typically  subjected to generally used solid-liquid separation such as  filtration or centrifugation, dried, and then, provided for use.  The filtration is preferably performed under pressure using  a solvent-resistant filter medium. The drying is performed at  a temperature of about 30°  C. to 100°  C. at normal pressure  The content of the repeating unit represented by General  Formula (P) in the resin (A) is preferably within a range of  1 mo! % to 40 mo! %, more preferably within a range of 2  mo! % to 30 mo! %, and particularly preferably within a  range of 5 mo! % to 25 mo! %, with respect to the entirety  of repeating units in the resin (A).  In the resin (A) used in the composition of the present  invention, the content molar ratio of respective repeating  structural units is suitably set to adjust  dry  etching resistance  or standard developer suitability of a resist, adhesion to  substrate, a resist profile, and resolving power, heat resis› tance, and sensitivity which are properties generally  required for a resist.  The form of the resin (A) of the present invention may be  any form of a random form, a block form, a comb form, and  a star form.  The resin (A) can be synthesized by, for example, polym› erizing an unsaturated monomer corresponding to each  structure through radical polymerization, cationic polymer› ization, or anionic polymerization. In addition, by perform› ing a polymer reaction after polymerization is performed  using an unsaturated monomer corresponding to a precursor  of each structure, a target resin can also be obtained.  Examples of a general synthetic method include a collec› tive polymerization method of performing polymerization  by dissolving an unsaturated monomer and a polymerization  initiator in a solvent and heating the resultant product and a  dropping polymerization method of adding a solution con› taining an unsaturated monomer and an polymerization  initiator dropwise to a heated solvent over a period of 1 hour  to 10 hours, and the dropping polymerization method is  preferable.  Examples of the solvent used in the polymerization can  include solvents which can be used in preparing an active  light-sensitive or radiation-sensitive resin composition  described below, and it is more preferable that the polym› erization is performed using the same solvent as the solvent  (D) used in the composition of the present invention. Thus,  generation of particles during storage can be suppressed.  The polymerization reaction is preferably performed in an  inert gas atmosphere such as nitrogen or argon. The polym› erization is initiated using a commercially available radical  #  o~o-O-so3- oH  -continued 