82  US 9,152,050 B2  81  ane, methylcyclohexane, dimethylcyclohexane, cyclohep› tane, cyclooctane, and cyclononane. Suitable alkenes of 6 to  12 carbon atoms include hexene, heptene, octene, cyclohex› ene, methylcyclohexene, dimethylcyclohexene, cyclohep- tene, and cyclooctene. Suitable alkynes of 6 to 12 carbon  atoms include hexyne, heptyne, and octyne. Suitable alcohols  of3 to 10 carbon atoms include n-propyl alcohol, isopropyl  alcohol, I-butyl alcohol, 2-butyl alcohol, isobutyl alcohol,  tert-butyl alcohol, 1-pentanol, 2-pentanol, 3-pentanol, tert- amyl alcohol, neopentyl alcohol, 2-methyl-1-butanol, 3-me› thyl-1-butanol, 3-methyl-3-pentanol, cyclopentanol, 1-hex› anol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol, 3,3- dimethyl-1-butanol,  3,3-dimethyl-2-butanol,  2-ethyl-1- butanol,  2-methyl-1-pentanol,  2-methyl-2-pentanol,  2-methyl-3-pentanol, 3-methyl-1-pentanol, 3-methyl-2-pen› tanol, 3-methyl-3-pentanol, 4-methyl-1-pentanol, 4-methyl- 2-pentanol, 4-methyl-3-pentanol, cyclohexanol, and 1-oc› tanol. Suitable ether compounds of 8 to 12 carbon atoms  include di-n-butyl ether, diisobutyl ether, di-sec-butyl ether,  di-n-pentyl ether, diisopentyl ether, di-sec-pentyl ether, di› tert-amyl ether, and di-n-hexyl ether. The solvents may be  used alone or in admixture. Besides the foregoing solvents,  aromatic solvents may be used, for example, toluene, xylene,  ethylbenzene,  isopropylbenzene,  tert-butylbenzene  and  mesitylene.  such as dip, puddle or spray techniques. Suitable developers  are 0.1 to 10 wt %, preferably 2 to 10 wt %, more preferably  2 to 8 wt % aqueous solutions of tetramethylammonium  hydroxide  (TMAH),  tetraethylammonium  hydroxide  (TEAH), tetrapropylammonium hydroxide (TPAH) and tet› rabutylammonium 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.  It  is appre› ciated that the resist composition of the invention is best  suited for micro-patterning using such high-energy radiation  as EB, EUV (soft x-ray), x-ray, y-ray and synchrotron radia› tion among others.  Although TMAH aqueous solution is generally used as the  developer, TEAH, TPAH and TBAH having a longer alkyl  chain are effective in inhibiting the resist film from being  swollen during development and thus preventing pattern col› lapse. JP 3429592 describes an example using an aqueous  TBAH solution for the development of a polymer comprising  recurring units having an alicyclic structure such as adaman› tane methacrylate and recurring units having an acid labile  group such as t-butyl methacrylate, the polymer being water  repellent due to the absence of hydrophilic groups.  The TMAH developer is most often used as 2.38 wt %  aqueous solution, which corresponds to 0.26N. The TEAH,  TPAH, and TBAH aqueous solutions should preferably have  an equivalent normality. The concentration ofTEAH, TPAH,  and TBAH that corresponds to 0.26N is 3.84 wt%, 5.31 wt%,  and 6.78 wt%, respectively.  When a pattern with a line size of32 nm or less is resolved  by the EB and EUV lithography, there arises a phenomenon  that lines become wavy, lines merge together, and merged  lines collapse.  It  is believed that this phenomenon occurs  because lines are swollen in the developer and the thus  expanded lines merge together. Since the swollen lines con- taining liquid developer are as soft as sponge, they readily  collapse under the stress ofrinsing. For this reason, the devel› oper using a long-chain alkyl developing agent is effective for  preventing film swell and hence, pattern collapse.  Alternatively, a negative tone pattern may be formed by  organic solvent development. The organic solvent used as the  developer  is  preferably  selected  from  2-octanone,  2-nonanone,2-heptanone,3-heptanone,4-heptanone,2-hex› anone, 3-hexanone, diisobutyl ketone, methylcyclohex› anone, acetophenone, methylacetophenone, propyl acetate,  butyl acetate, isobutyl acetate, amyl acetate, isoamyl acetate,  butenyl acetate, phenyl acetate, propyl formate, butyl for› mate, isobutyl formate, amyl formate, isoamyl formate,  methyl valerate, methyl pentenoate, methyl crotonate, ethyl  crotonate,  methyl propionate,  ethyl  propionate,  ethyl  3-ethoxypropionate, methyl lactate, ethyl lactate, propyl lac› tate, butyl lactate, isobutyl lactate, amyl lactate, isoamyl lac› tate, methyl 2-hydroxyisobutyrate, ethyl 2-hydroxyisobu› tyrate, methyl benzoate, ethyl benzoate, benzyl acetate,  methyl phenylacetate, benzyl formate, phenylethyl formate,  methyl 3-phenylpropionate, benzyl propionate, ethyl pheny› lacetate, and 2-phenylethyl acetate. These organic solvents  may be used alone or in admixture of two or more.  Various polymers (Polymers 1 to 7) to be added to resist  compositions were prepared by combining suitable mono› mers, effecting copolymerization reaction in methyl ethyl  ketone solvent, pouring into hexane for crystallization,  repeatedly washing with hexane, isolation, and drying. The  polymers were analyzed by $^{1 }$H-NMR to determine their com› position and by GPC to determine Mw and dispersity  Mw/Mn.  Examples and Comparative Examples are given below for  further illustrating the invention, but they should not be con› strued as limiting the invention thereto. Mw is a weight aver› age molecular weight as measured by GPC versus polysty› rene standards, and Mw/Mn designates molecular weight  distribution or dispersity. All parts (pbw) are by weight.  Example  Preparation of Polymers  Polymer 1  OH  Polymer 1  Mw=8,300  Mw/Mn=l.85  At the end of organic solvent development, the resist film is  rinsed. As the rinsing liquid, a solvent which is miscible with 60  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 alkanes of 6 to 12 carbon atoms include 65  hexane, heptane, octane, nonane, decane, undecane, dode› cane, methylcyclopentane, dimethylcyclopentane, cyclohex-