US 9,869,931 B2  12  11  2,4,5-trifluorophenyl,  2,3,4-trifluorophenyl,  2,3,4,5-tetra› fluorophenyl, 2,3,5,6-tetrafluorophenyl, 2,3,4,5,6-pentafluo› rophenyl, 2-trifluoromethylphenyl, 3-trifluoromethylphenyl,  4-trifluoromethylphenyl,  2,4-di(trifluoromethyl)phenyl,  4-hydroxy-2,3,5,6-tetrafluorophenyl, 4-methoxy-2,3,5,6-tet› rafluorophenyl, 4-acetoxy-2,3,5,6-tetrafluorophenyl, 4-piv› aloyloxy-2,3 ,5, 6-tetrafluoropheny 1,  4-cyclohexy lcarbony› loxy-2,3 ,5 ,6-tetrafluoropheny l, 4-adamantylcarbonyloxy-2,  3,5,6-tetrafluorophenyl,  4-phenylcarbonyloxy-2,3,5,6- tetrafluorophenyl,  4-cyclohexylsulfonyl-2,3,5,6- tetrafluorophenyl,  and  4-phenylsulfonyl-2,3,5,6- tetrafluorophenyl; R 15 , R 16 , R 17 , R 18 , and R 19  are each  independently fluorine, trifluoromethyl, pentafluoroethyl,  trifluoroethyl, octafluorobutyl, or nonafluorobutyl, R 15  and  R$^{16 }$may bond together to form a ring; R 20 , R 21 , R 22 , and R 23  are each independently fluorine or trifluoromethyl, each of p,  q, r and s is an integer of 1 to 5.  Typically, the resist composition is a chemically amplified  positive resist composition.  The resist composition may further comprise at least one  component selected from among an organic solvent, a  dissolution inhibitor, an acid generator, a basic compound,  and a surfactant.  In another aspect, the invention provides a pattern form- ing process comprising the steps of coating the resist com› position defined above onto a substrate, baking, exposing the  resulting resist film to high-energy radiation, and developing  with a developer.  Preferably, the high-energy radiation is EUV radiation  having a wavelength of 3 to 15 nm or an EB at an  accelerating voltage of 1 to 150 keV.  In the step of exposing the resist film to high-energy  radiation, preferably the surface of the substrate underneath  the resist film is electrically charged positive.  The resist composition has many advantages including a  significantly high contrast of alkaline dissolution rate before  and after exposure, a high sensitivity, a high resolution, a  satisfactory pattern profile after exposure, a controlled rate  of acid diffusion, and a minimal line edge roughness. The  resist composition, typically chemically amplified positive  resist composition is suited as the micropatterning material  for VLSis and photomasks, and the patterning material in  the EB and EUV lithography.  Advantageous Effects of Invention  DESCRIPTION OF EMBODIMENTS  The singular forms "a," "an" and "the" include plural  referents unless the context clearly dictates otherwise.  "Optional" or "optionally" means that the subsequently  described event or circumstance may or may not occur, and  that the description includes instances where the event  occurs and instances where it does not. As used herein, the  notation  (Cn-Cm)  means a group containing from n to m  carbon atoms per group.  The abbreviations and acronyms have the following  meaning.  UV: ultraviolet radiation  DUY: deep ultraviolet  EUV: extreme ultraviolet  EB: electron beam  Mw: weight average molecular weight  Mn: number average molecular weight  Mw/Mn: molecular weight distribution or dispersity  GPC: gel permeation chromatography  Herein R  $^{11 }$is fluorine or an organic group selected from the  group consisting of trifluoromethyl, pentafluoroethyl, trif› luoroethyl, octafluorobutyl, nonafluorobutyl, 2-fluorophe- nyl,  3-fluorophenyl, 4-fluorophenyl,  2,4-difluorophenyl,  2,3-difluorophenyl, 3,4-difluorophenyl, 3,5-difluorophenyl,  Dy3+  Gd $^{3}$+  sr2+  R20  I  ’…,  p  ’  -:::::7  ~)  R22, 