84  US 7,344,821 B2  83  R$_{1 }$ to R$_{6 }$ each independently represents a hydrogen atom  or a fluorine atom, provided that at least one ofR$_{1 }$to R$_{6 }$ represents a fluorine atom;  Z represents an alkylene group, an oxygen atom or a  sulfur atom;  m represents an integer of O to 2; and  Re represents a hydrogen atom or an unsubstituted methyl  group;  (B3)  (B2)  wherein B$_{1 }$ and B$_{2 }$ each represents a group capable of  decomposing by an action of an acid, or a group  including a group capable of decomposing by an action  of an acid to generate a carboxyl group or a hydroxyl  group; and  B$_{3 }$ represents a hydrogen atom, a methyl group, a halogen  atom or a cyano group.  4.  The positive resist composition according to claim  3,  wherein B$_{1 }$ and B$_{2 }$ each includes a cyclic structure.  5.  A pattern formation method comprising:  forming a resist film from a positive resist composition  according to claim  1;  exposing the resist film with an electron beam, an EUV  light or an X ray, so as to form an exposed resist film;  and  developing the exposed resist film.  6.  The positive resist composition according to claim  1,  which contains said at least one compound (A) in an amount  of from 6 to 20% by weight based on a total solid content of  the positive resist composition.  7.  The positive resist composition according to claim  1,  wherein said at least one compound (A) comprises: a  compound that generates a sulfonic acid upon treatment  with one of an actinic ray and radiation; and a com› pound that generates a carboxylic acid upon treatment  with one of an actinic ray and radiation.  *  *  *  *  *  (Bl)  2.  The positive resist composition according to claim  1,  wherein R$_{1 }$ to R$_{6 }$ each represents a fluorine atom.  3.  The positive resist composition according to claim  1,  wherein the resin (B) further comprises at least one of a  repeating unit represented by formula (Bl) and a  repeating unit represented by formula (B2): 