Apr. 18,  2019  85  US 2019/0113844 Al  ing, exposure, post-exposure baking (PEB), and develop› ment.  If  necessary, any additional steps may be added.  [0154]  For example, the positive resist composition is first  applied onto a substrate on which an integrated circuit is to  be formed (e.g., Si, SiO$_{2}$ ,  SiN, SiON, TiN, WSi, BPSG,  SOG, or organic antireflective coating) or a substrate on  which a mask circuit is to be formed (e.g., Cr, CrO, CrON,  MoSi$_{2}$ ,  or SiO$_{2}$ )  by a suitable coating technique such as spin  coating, roll coating, flow coating, dipping, spraying or  doctor coating. The coating is prebaked on a hotplate at a  temperature of 60 to 150°  C. for 10 seconds to 30 minutes,  preferably at 80 to 120°  C. for 30 seconds to 20 minutes. The  resulting resist film is generally 0.01 to 2.0 µm  thick.  [0155]  The resist film is then exposed to a desired pattern  of high-energy radiation such as UV, deep-UV, EB, EUV,  x-ray, soft x-ray, excimer laser light, y-ray or synchrotron  radiation, directly or through a mask. The exposure dose is  preferably about 1 to 200 mJ/cm 2 ,  more preferably about 10  to 100 mJ/cm 2 ,  or about 0.1 to 100 µC/cm 2 ,  more preferably  about 0.5 to 50 µC/cm 2 .  The resist film is further baked  (PEB) on a hotplate at 60 to 150°  C. for 10 seconds to 30  minutes, preferably at 80 to 120°  C. for 30 seconds to 20  minutes.  [0156]  Thereafter the resist film is developed with a devel› oper in the form of an aqueous base solution for 3 seconds  to 3 minutes, preferably 5 seconds to 2 minutes by conven› tional techniques such as dip, puddle and spray techniques.  A typical developer is a 0.1 to 10 wt%, preferably 2 to 5 wt  % aqueous solution of tetramethylammonium hydroxide  (TMAH), tetraethylammonium hydroxide (TEAH), tet› rapropylammonium hydroxide (TPAH), or tetrabutylammo› nium hydroxide (TBAH). The resist film in the exposed area  is dissolved in the developer whereas the resist film in the  unexposed area is not dissolved. In this way, the desired  positive pattern is formed on the substrate. Inversely in the  case of negative resist, the exposed area of resist film is  insolubilized and the unexposed area is dissolved in the  developer.  It is appreciated that the resist composition of the  invention is best suited for micro-patterning using such  high-energy radiation as KrF and ArF excimer laser, EB,  EUV, x-ray, soft x-ray, y-ray and synchrotron radiation.  [0157]  In an alternative embodiment, a negative pattern  may be formed via organic solvent development using a  positive resist composition comprising a base polymer hav› ing an acid labile group. The developer used herein is  preferably selected from among 2-octanone, 2-nonanone,  2-heptanone,  3-heptanone,  4-heptanone,  2-hexanone,  3-hexanone,  diisobutyl  ketone,  methylcyclohexanone,  acetophenone, methylacetophenone, propyl acetate, butyl  acetate, isobutyl acetate, pentyl acetate, butenyl acetate,  isopentyl acetate, propyl formate, butyl formate, isobutyl  formate, pentyl formate, isopentyl formate, methyl valerate,  methyl pentenoate, methyl crotonate, ethyl crotonate,  methyl propionate, ethyl propionate, ethyl 3-ethoxypropi› onate, methyl lactate, ethyl lactate, propyl lactate, butyl  lactate, isobutyl lactate, pentyl lactate, isopentyl lactate,  methyl 2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate,  methyl benzoate, ethyl benzoate, phenyl acetate, benzyl  [0162]  Thiophenecarboxylic acid sulfonium salts 1 to 20  used in resist compositions are identified below. Sulfonium  salts 1 to 20 were synthesized by ion exchange between an  ammonium salt of thiophenecarboxylic acid or derivative  thereof providing the anion shown below and a sulfonium  chloride providing the cation shown below.  [0161]  Examples of the invention are given below by way  of illustration and not by way of limitation. The abbreviation  "pbw" is parts by weight.  Example  [0160]  A hole or trench pattern after development may be  shrunk by the thermal flow, RELACSfi or DSA process. A  hole pattern is shrunk by coating a shrink agent thereto, and  baking such that the shrink agent may undergo crosslinking  at the resist surface as a result of the acid catalyst diffusing  from the resist layer during bake, and the shrink agent may  attach to the sidewall of the hole pattern. The bake is  preferably at a temperature of 70 to 180°  C., more preferably  80 to 170°  C., for a time of 10 to 300 seconds. The extra  shrink agent is stripped and the hole pattern is shrunk.  [0159]  Rinsing is effective for minimizing the risks of  resist pattern collapse and defect formation. However, rins› ing is not essential.  If  rinsing is omitted, the amount of  solvent used may be reduced.  [0158]  At the end of development, the resist film is rinsed.  As the rinsing liquid, a solvent which is miscible with the  developer and does not dissolve the resist film is preferred.  Suitable solvents include alcohols of 3 to 10 carbon atoms,  ether compounds of 8 to 12 carbon atoms, alkanes, alkenes,  and alkynes of 6 to 12 carbon atoms, and aromatic solvents.  Specifically, suitable alcohols of 3 to 10 carbon atoms  include n-propyl alcohol, isopropyl alcohol, I-butyl alcohol,  2-butyl alcohol, isobutyl alcohol, t-butyl alcohol, 1-penta› nol, 2-pentanol, 3-pentanol, t-pentyl alcohol, neopentyl  alcohol, 2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl- 3-pentanol, cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol,  2,3-dimethyl-2-butanol, 3,3-dimethyl-1-butanol, 3,3-dim› ethyl-2-butanol,  2-ethyl-1-butanol,  2-methyl-1-pentanol,  2-methyl-2-pentanol, 2-methyl-3-pentanol, 3-methyl-1-pen› tanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol, 4-methyl- 1-pentanol,  4-methyl-2-pentanol,  4-methyl-3-pentanol,  cyclohexanol, and 1-octanol. Suitable ether compounds of 8  to 12 carbon atoms include di-n-butyl ether, diisobutyl ether,  di-s-butyl ether, di-n-pentyl ether, diisopentyl ether, di-s› pentyl ether, di-t-pentyl ether, and di-n-hexyl ether. Suitable  alkanes of 6 to 12 carbon atoms include hexane, heptane,  octane, nonane, decane, undecane, dodecane, methylcyclo› pentane, dimethylcyclopentane, cyclohexane, methylcyclo› hexane, dimethylcyclohexane, cycloheptane, cyclooctane,  and cyclononane. Suitable alkenes of 6 to 12 carbon atoms  include hexene, heptene, octene, cyclohexene, methylcyclo› hexene,  dimethylcyclohexene,  cycloheptene,  and  cyclooctene. Suitable alkynes of 6 to 12 carbon atoms  include hexyne, heptyne, and octyne. Suitable aromatic  solvents include toluene, xylene, ethylbenzene, isopropyl› benzene, t-butylbenzene and mesitylene. The solvents may  be used alone or in admixture.  acetate, methyl phenylacetate, benzyl formate, phenylethyl  formate, methyl 3-phenylpropionate, benzyl propionate,  ethyl phenylacetate, and 2-phenylethyl acetate, and mixtures  thereof. 