It  is an object of the present invention to provide an actinic› ray- or radiation-sensitive resin composition exhibiting  enhanced resolution, roughness characteristic, pattern con› figuration and outgassing performance without detriment to  sensitivity.  It  is another object of the present invention to  provide a method of forming a pattern using the composition.  The above objects are attained by employing as a photoacid  generator a novel compound characterized in that an electron  donating group is introduced in the sulfonium cation thereof  and that the acid generated thereby exhibits a low diffusion.  Namely, the above problem can be solved by the present  invention identified by the following features.  (1 )An actinic-ray- or radiation-sensitive resin composition  comprising an arylsulfonium salt that when exposed to  actinic rays or radiation, generates an acid, the arylsulfonium  salt containing at least one aryl ring on which there are a total  In this connection, when use is made of, for example, a  radiation source capable of emitting an electron beam, X-rays  or EUV, the exposure is carried out in vacuum. This might  cause any low-boiling-point compounds, such as solvents,  Consequently, resists for ArF excimer laser containing a  resin with an alicyclic hydrocarbon structure have been devel› oped.  However, in using a radiation source of a further shorter  wavelength, for example, an exposure radiation source of an  ArF excimer laser (193 nm), as the compounds containing  aromatic groups inherently exhibit a sharp absorption in the  region of 193 nm, the above-mentioned chemical amplifica- tion system has not been satisfactory.  [Non-patent reference 1] "Fundamentals of nanoimprint  and its technology development/application deployment› technology of nanoimprint substrate and its latest technology  deployment" edited by Yoshihiko Hirai, published by Fron› tier Publishing (issued in June, 2006).  When a KrF excimer laser is used as an exposure radiation  source, a resin whose fundamental skeleton is formed of a  poly(hydroxystyrene) exhibiting a low absorption mainly in  the region of 248 nm is employed as a major component of a  resist composition. Accordingly, there can be attained a high  sensitivity, high resolution and favorable pattern formation.  Thus, a system superior to the conventional naphthoquinone  diazide/novolak resin system is realized.  A resist composition of chemical amplification type is a  pattern forming material that is capable of, upon exposure to  far ultraviolet or other radiation, generating an acid in  exposed areas and, by a reaction catalyzed by the acid, chang› ing the solubility in a developer between the areas having  been exposed to actinic radiation and the nonexposed areas to  thereby attain pattern formation on a substrate.  2. Description of the Related Art  Patent reference  1:  U.S. Pat. No. 6,548,221,  Patent reference 2: European Patent No. 1480078,  Patent reference 3: Jpn. Pat. Appln. KOKAI Publication  No. (hereinafter referred to as JP-A-) 2007-94356,  Patent reference 4: JP-A-Hl 1-30856,  Patent reference 5: JP-A-2004-158287, and  Patent reference 6: JP-A-2008-162101.  In the present invention, the terms "actinic rays" and  "radiation" mean, for example, brightline spectra from a mer- cury lamp, far ultraviolet represented by an excimer laser,  extreme ultraviolet, X-rays, soft X-rays, an electron beam and  the like. In the present invention, the term "light" means  actinic rays or radiation.  The present invention relates to an actinic-ray- or radia› tion-sensitive resin composition that when exposed to actinic  rays or radiation, makes a reaction to thereby change its  properties and a method of forming a pattern using the com› position. More particularly, the present invention relates to an  actinic-ray- or radiation-sensitive resin composition for use in  a semiconductor production process for an IC and the like, a  circuit board production for a liquid crystal, a thermal head  and the like, the fabrication of an imprint mold structure,  other photofabrication processes, a lithographic printing  plate and an acid-hardenable composition and also relates to  a method of forming a pattern with the use of the composition.  1. Field of the Invention  This application is based upon and claims the benefit of  priority from prior Japanese Patent Application No. 2010- 019284, filed Jan. 29, 2010, the entire contents of which are  incorporated herein by reference.  and resist materials decomposed by high energy to evaporate  to thereby dirty the exposure apparatus. This outgassing prob› lem is becoming serious. In recent years, various researches  have been conducted toward the reduction of the outgassing,  and various improvements have been proposed for photoacid  generators (see, for example, patent reference 2).  There is a demand in the art for the development of a  photosensitive composition that not only can reduce outgas› sing but also is enhanced in sensitivity, resolution, pattern  configuration, roughness characteristic, etc. through the  improvement of a photoacid generator (see, for example,  patent references 3 and 4).  In particular, the roughness characteristic and resolution  become important in accordance with the reduction of pattern  dimension. In the field of lithography using X-rays, an elec› tron beam or EUV, as the formation of a fine pattern of several  tens of nanometers is targeted, it is required to realize, in  particular, excellent resolution and roughness characteristic.  Further, the microfabrication using a resist composition is  not only directly used in the manufacturing of integrated  circuits but also, in recent years, finds application in the  fabrication of so-called imprint mold structures, etc. ( see, for  example, patent references 5 and 6 and non-patent reference  1). Therefore, in the use ofX-rays, soft X-rays or an electron  beam as an exposure radiation source as well, it is an impor› tant task to simultaneously realize high sensitivity, high reso› lution, favorable pattern configuration and favorable rough› ness characteristic, and it is now needed to resolve the task.  PRIOR ART REFERENCE  Patent Reference  BACKGROUND OF THE INVENTION  CROSS-REFERENCE TO RELATED  APPLICATIONS  ACTINIC-RAY-OR RADIATION-SENSITIVE  RESIN COMPOSITION AND METHOD OF  FORMING PATTERN USING THE  COMPOSITION  BRIEF SUMMARY OF THE INVENTION  Non-Patent Reference  2  US 8,962,233 B2  1 