56  US 8,614,033 B2  55  The organic anion of the above  x- corresponds to sulfonic  acid, imide acid and methide acid, and the like, which are an  acid generating upon irradiation with the actinic rays or radia› tion such as an electron beam or extreme ultraviolet ray.  As the acid generator used in the present invention, in  addition to a low molecular compound, a compound wherein  a group generating an acid upon irradiation with the actinic  rays or radiation has been introduced into the main chain or a  side chain of the high molecular compound can also be used.  As further described above, in a case where a group generat› ing an acid upon irradiation with the actinic rays or radiation  is present in the repeating units of the high molecular com› pound (A) used in the present invention, apart from the high  molecular compound (A) of the present invention, it does not  matter if the acid generator (B) is not present therein.  It is preferable that the acid generator be a compound  generating an acid upon irradiation with an electron beam or  extreme ultraviolet ray.  In the present invention, the examples of the preferable  onium compounds can include a sulfonium compound repre› sented by the following general formula (1 ), or an iodonium  compound represented by the general formula (2).  In the general formulae (1) and (2), each of  Rau Ra$_{2}$ ,  Ra$_{3}$ ,  Ra$_{4 }$ and  Ras  represents an organic group.  x- represents an organic anion.  Next, the sulfonium compound represented by the general  formula (1) and the iodonium compound represented by the  general formula (2) will be further described.  While each ofRa$_{1 }$to  Ra$_{3 }$ of the general formula (1) and  Ra$_{4 }$ and  Ras  of the general formula (2) represent an organic group,  preferably at least one ofRa$_{1 }$ to  Ra$_{3}$ ,  and at least one ofRa$_{4 }$ and  Ras  be an aryl group, respectively. As an aryl group, a  phenyl group, and a naphthyl group are preferable, and fur› ther preferred is a phenyl group.  The examples of the organic anion of  x- in the general  formulae (1) and (2) include sulfonic acid anion, carboxylic  acid anion, bis(alkylsulfonyl)amid anion, and tris(alkylsulfo› nyl)methide anion, and the like, and preferably an organic  anion represented by the following general formulae (3 ), ( 4)  or (5), more preferably an organic anion represented by the  following general formula (3).  The examples of the organic groups of the above Rc1 to Rc4  can include an alkyl group, an aryl group, or a group in which  a plurality thereof are connected to one another. Among these  organic groups, more preferred is an alkyl group of which  I-position is substituted with a fluorine atom or with a fluo› roalkyl group, and a phenyl group of which the position is  substituted with a fluorine atom or with a fluoroalkyl group.  By having a fluorine atom or a fluoroalkyl group, the acidity  of the acid generated by the light irradiation increases, and the  sensitivity rises. However, it is preferable that the terminal  group do not have a fluorine atom as a substituent.  In the present invention, in view of suppressing the diffu› sion of the acid generated by the exposure toward the unex› posed area and improving resolution or pattern profile, the  aforementioned acid generator (B) is preferably a compound  generating an acid having a size of 130  A $^{3 }$or more in volume  (more preferably sulfonic acid), more preferably a compound  generating an acid having a size of 190  A $^{3 }$or more in volume  (more preferably sulfonic acid), still more preferably a com› pound generating an acid having a size of 270  A $^{3 }$or more in  volume (more preferably sulfonic acid), and particularly pref› erably a compound generating an acid having a size of 400  A 3  or more in volume (more preferably sulfonic acid). However,  in view of the sensitivity or the solubility in the coating  solvent, the above-described volume is preferably 2000  A $^{3 }$or  less, further preferably 1500  A $^{3 }$or less. This volume value is  determined by using "WinMOPAC" available from FUJITSU  LIMITED. That is to say, first, the chemical structure of the  acid according to each example was input, and then, using this  structure as an initial structure, the most stable conformation  of each acid was determined by molecular force field calcu› lation using the MM3 method, and thereafter, with respect to  these most stable conformation, molecular orbital calculation  using the PM3 method was performed, which enables to  compute the "accessible volume" of each acid.  The particular preferable acid generators for use in the  present invention are illustrated below. Incidentally, the com› puted volume value is affixed to a part of these examples (unit  A 3 ).  In addition, the computed value obtained here is the  volume value of an acid wherein a proton is attached to an  anion part.  In the formulae (3), ( 4) and (5), Rei, Rc$_{2}$ ,  Rc$_{3 }$ and Rc$_{4 }$ represents independently an organic group, respectively.  (2)  R,4-r+-R,s  x- (1)  Ra1  I  Ra2-r  x- R,3  (zl)  (3)  (4) ( 5 (z2)  113A 3  (z3)  220A 3 