Feb.4,2021  3  US 2021/0033971 Al  (d3)  R26  I  +s-R 27  I  R2s  (a)  -continued  Herein  RA  is each independently hydrogen or methyl. Z$^{1 }$is  a single bond, phenylene group, -O-Z 11 , ----C(=O)› O-Z11- or ----C(=O)-NH-Z 11 -, wherein Z 11  is a  C$_{1 }$-C$_{6 }$ aliphatic hydrocarbylene group or phenylene group,  which may contain a carbonyl moiety, ester bond, ether bond  or hydroxyl moiety. Z 2  is a single bond or ester bond. Z 3  is  a single bond, -Z$^{31}$----C(=O)-O-, -Z $^{31}$---0- or  -Z$^{31}$-O----C(=O)-, wherein Z 31  is a C$_{1}$-C$_{12 }$ saturated  hydrocarbylene group which may contain a carbonyl moiety,  ester bond, ether bond, iodine or bromine. Z 4  is methylene,  2,2,2-trifluoro-l,1-ethanediyl or carbonyl. Z 5  is a single  bond, methylene, ethylene, phenylene, fluorinated phe› nylene,  ---O-Z 51 -,  -C(=O)-O-Z 51 -,  or  -C(=O)-NH-Z 51 -, wherein Z 51  is a C$_{1}$-C$_{6 }$ aliphatic  hydrocarbylene group, phenylene group, fluorinated phe› nylene group, or trifluoromethyl-substituted phenylene  group, which may contain a carbonyl moiety, ester bond,  ether bond or hydroxyl moiety. R 21  to R$^{28 }$are each inde› pendently a C$_{1 }$-C$_{20 }$hydrocarbyl group which may contain a  heteroatom, any two ofR 23 , R $^{24 }$and R$^{25 }$or any two ofR26 ,  R $^{27 }$and R $^{28 }$may bond together to form a ring with the sulfur  atom to which they are attached. M- is a non-nucleophilic  counter ion.  [0030]  The resist composition may further comprise an  acid generator, organic solvent, quencher, and/or surfactant.  [0031]  In another aspect, the invention provides a process  for forming a pattern comprising the steps of applying the  positive resist composition defined above onto a substrate to  form a resist film thereon, exposing the resist film to  high-energy radiation, and developing the exposed resist  film in a developer.  [0032]  Preferably, the high-energy radiation is i-line, KrF  excimer laser, ArF excimer laser, EB, or EUV of wavelength  3 to 15 nm.  [0033]  The positive resist composition can enhance the  decomposition efficiency of an acid generator, has a remark› able acid diffusion-suppressing effect, a high sensitivity, and  a high resolution, and forms a pattern of good profile with  improved edge roughness and size variation after exposure  and development. By virtue of these properties, the resist  composition is fully useful in commercial application and  best suited as a micropatterning material for photomasks by  EB lithography or for VLSis by EB or EUV lithography. The  resist composition may be used not only in the lithography  for forming semiconductor circuits, but also in the formation  of mask circuit patterns, micromachines, and thin-film mag› netic head circuits.  [0034]  As used herein, the singular forms "a," "an" and  "the" include plural referents unless the context clearly  [0049]  In formula (a),  RA  is hydrogen or methyl. X 1 A  is a  single bond, ester bond or amide bond. X 1 B  is a single bond  or a C$_{1 }$-C$_{20 }$ di- or trivalent hydrocarbon group which may  contain an ether bond, carbonyl moiety, ester bond, amide  bond, sultone ring, lactam ring, carbonate moiety, halogen,  hydroxyl moiety or carboxyl moiety.  [0050]  The C$_{1 }$-C$_{20 }$ di- or trivalent hydrocarbon group  represented by X 1 B  may be straight, branched or cyclic and  may be either aliphatic or aromatic. Examples thereof  include C$_{1 }$-C$_{20 }$ alkanediyl groups, C$_{3}$ -C$_{10 }$ cyclic saturated  hydrocarbylene groups, C$_{1 }$-C$_{20 }$ alkanetriyl groups, C$_{3}$ -C$_{10 }$ [0048]  Preferably, the recurring units (a) have the formula  (a).  [0047]  One embodiment of the invention is a positive  resist composition comprising a base polymer comprising  recurring units (a) having the structure of an ammonium salt  of a carboxylic acid having an iodized or brominated hydro› carbyl group, with the proviso that the hydrocarbyl group  does not contain an iodized or brominated aromatic ring, and  recurring units of at least one type selected from recurring  units (bl) having a carboxyl group in which the hydrogen  atom is substituted by an acid labile group and recurring  units (b2) having a phenolic hydroxyl group in which the  hydrogen atom is substituted by an acid labile group.  It is  noted that the carboxylic acid having an iodized or bromi› nated hydrocarbyl group is sometimes referred to as  "iodized or brominated carboxylic acid."  [0046]  CDU: critical dimension uniformity  [0045]  LWR: line width roughness  [0044]  LER: line edge roughness  [0043]  PAG: photoacid generator  [0042]  PEB: post-exposure bake  [0041]  GPC: gel permeation chromatography  [0040]  Mw/Mn: molecular weight dispersity  [0039]  Mn: number average molecular weight  [0038]  Mw: weight average molecular weight  [0037]  EUV: extreme ultraviolet  [0036]  EB: electron beam  [0035]  The abbreviations and acronyms have the follow› ing meaning.  dictates otherwise. "Optional" or "optionally" means that  the subsequently described event or circumstances may or  may not occur, and that description includes instances where  the event or circumstance occurs and instances where it does  not. The notation (Cn-Cm) means a group containing from  n to m carbon atoms per group. As used herein, the term  "iodized" or "brominated" compound indicates a compound  containing iodine or bromine or a compound substituted  with iodine or bromine. In chemical formulae, Me stands for  methyl, and Ac for acetyl.  DESCRIPTION OF EMBODIMENTS  Advantageous Effects of Invention  Positive Resist Composition 