For lithographic pattern formation in semiconductor manufacturing processes, there has been a demand to provide resist compositions with harder resist performance requirements such as, in response to a reduction in wavelength of high energy exposure radiation for fine patterning, a wider depth of focus tolerance (abbreviated as “DOF”) than that required under exposure to long wavelength radiation, a small pattern line edge roughness (abbreviated as “LED”) and high resolution, in addition to general performance requirements such as high sensitivity, good substrate adhesion and high etching resistance.  Chemically amplified resist compositions are being used as resist materials suitable for exposure to such short wavelength radiation.  Herein, the chemically amplified resist composition refers to a pattern forming material that contains a photoacid generating agent (referred to as “photoacid generator”) capable of generating an acid by irradiation with high energy radiation (referred to as “exposure”) and forms a resist pattern by causing a difference in developer solubility between exposed and unexposed portions through a reaction using the acid generated by exposure as a catalyst. 
The uniformity of the resist materials is becoming a problem as these pattern forming materials come to practical use in the extreme ultraviolet (EUV) range for finer patterning.  More specifically, the resist material is in general conventionally prepared from a resist resin capable of changing its developer solubility by the action of an acid, a solvent and a photoacid generator (as an additive) capable of generating an acid.  In such a composition, however, the uniformity of dispersion of the resist resin and the photoacid generator is not sufficient for still finer patterning.  It has thus recently been reported to produce a resist resin by copolymerization of a conventional resist raw material monomer with a monomer having a photoacid generating function and thereby impart the photoacid generating function to the resist resin (see Patent Documents 1 to 7).  For example, Patent Documents 6 and 7 each disclose a resist composition using a resist resin obtained by polymerization or copolymerization of a methacrylic acid ester whose side chain contains a triphenylsulfonium salt of sulfonic acid having a fluorine atom at α-position thereof.