The photo-acid generator (b) used in the invention can be  selected appropriately from photo-initiators for cationic  photo-polymerization, photo-initiators for radical photo-po› lymerization, photo-decoloring agents for dyes, photo-dis- coloring agents, compounds which are used in microresist  and can generate acids when irradiated with known light  (including 400-200 nm ultraviolet rays and far ultraviolet  rays, particularly preferably g-ray, h-ray, i-ray and KrF  excimer laser light), ArF excimer laser light (193 nm), F$_{2 }$ excimer laser (157 nm), EUV (13 nm), electron beams,  X-rays, molecular beams or ion beams, or mixtures of two  or more thereof.  Examples of another photo-acid generator usable in the  invention as a compound capable of generating an acid upon  irradiation with an actinic ray or radiation include onium  salts, such as diazonium salts, ammonium salts, phospho› nium salts, iodonium salts, sulfonium salts, selenonium salts  and arsonium salts; organic halogen compounds; organome› tallic/halogenated organic compounds; photo-acid genera› tors having protective groups of o-nitrobenzyl type; com› pounds generating sulfonic acid by photolysis, typically  iminosulfonate; disulfone compounds, diazoketosulfone and  diazodisulfone compounds.  In addition, it is also possible to use polymers having  main or side chains in which are introduced the groups or  compounds capable of generating acids when irradiated with  the foregoing light.  Further, the compounds capable of generating acids upon  exposure to light as described in  V.  N. R. Pillai,  Synthesis,  (1), 1 (1980), A. Abad et al.,  Tetrahedron Lett.,  (47), 4555  (1971), D. H. R. Barton et al.,  J. Chem. Soc.,  (C), 329  (1970), U.S. Pat. No. 3,779,778 and European Patent No.  126,712 can be employed, too.  Of the compounds capable of generating acids upon  irradiation with the foregoing actinic rays or radiation, the  compounds illustrated below can be used to particular  advantage.  (1) Trihalomethyl-substituted oxazole derivatives repre› sented by the following formula (PAGl) or trihalomethyl› substituted s-triazine derivatives represented by the follow- ing formula (PAG2):  In the above formulae, R 201  represents a substituted  unsubstituted aryl or alkenyl group, R$^{202 }$represents a sub› stituted or unsubstituted aryl, alkenyl or alkyl group, or  ----C(Y)$_{3}$ ,  and Y represents a chlorine or bromine atom.  Examples of those derivatives include the following com› pounds, but these examples should not be construed as  limiting such derivatives.  The content of acid-decomposable polymer (a) in the  present resist composition is generally from 70 to 80% by  weight, preferably from 75 to 96% by weight, far preferably  from 80 to 96% by weight, based on the total solids in the  composition.  (b) Compound Capable of Generating Acid by Irradiation of 65  Actinic Ray or Radiation (Hereinafter Referred to as "Photo› Acid Generator (b )", too)  (PAGl)  (PAG2)  26  US 7,232,640 Bl  25  OH  -continued 