US 10,921,710 B2  93  94  wash away particles. After exposure, a step of rinsing  (post-soaking) may be introduced to remove any water  remaining on the film after exposure.  In the pattern forming process, an alkaline aqueous solu- tion, typically an aqueous solution of 0.1 to 5 wt %, more  preferably 2 to 3 wt% TMAH is often used as the developer.  The negative tone development technique using an organic  solvent instead is also applicable wherein the unexposed  region is developed and dissolved in the organic solvent.  In the organic solvent development, the organic solvent  used as the developer is preferably selected from 2-oc› tanone, 2-nonanone, 2-heptanone, 3-heptanone, 4-hep› tanone, 2-hexanone, 3-hexanone, diisobutyl ketone, meth- ylcyclohexanone,  acetophenone,  methylacetophenone,  propyl acetate, butyl acetate, isobutyl acetate, pentyl acetate,  isopentyl acetate, butenyl acetate, phenyl acetate, propyl  formate, butyl formate, isobutyl formate, pentyl formate,  isopentyl formate, methyl valerate, methyl pentenoate,  methyl crotonate, ethyl crotonate, methyl lactate, ethyl lac› tate, propyl lactate, butyl lactate, isobutyl lactate, pentyl  lactate, isopentyl lactate, methyl 2-hydroxyisobutyrate,  ethyl 2-hydroxyisobutyrate, methyl benzoate, ethyl benzo› ate, benzyl acetate, methyl phenylacetate, benzyl formate,  phenylethyl formate, methyl 3-phenylpropionate, benzyl  propionate, ethyl phenylacetate, and 2-phenylethyl acetate.  These organic solvents may be used alone or in admixture of  two or more.  Examples and Comparative Examples are given below by  way of illustration and not by way of limitation. The 40  abbreviation "pbw" is parts by weight. For all polymers, Mw  and  Mn are determined by GPC versus polystyrene stan› dards using THF solvent. Monomer 1 used herein is iden› tified below.  Under nitrogen atmosphere, a solution was prepared by  dissolving 25.2 g of Monomer 1, 4.80 g of 3-hydroxyada› mantyl methacrylate, 20.0 g of 1-isopropylcyclopentyl  methacrylate, and 3.29 g of dimethyl 2,2’-azobisisobutyrate  in 70 g of PGMEA. Under nitrogen atmosphere, the solution  was added dropwise over 4 hours to 23 g of PGMEA while  stirring at 80°  C. After the completion of dropwise addition,  stirring was continued at 80°  C. for 2 hours. The reaction  solution was cooled to room temperature and added drop› wise to 800 g of methanol. The thus precipitated solid was  collected by filtration and vacuum dried at 50°  C. for 20  hours, obtaining Polymer 1 in white powder solid form.  Amount 38.8 g, yield 78%.  Polymers 2 to 8 and Comparative Polymers 1 to 8 were  synthesized by the same procedure as in Synthesis Example  1 aside from changing the type and amount of monomers.  Synthesis Examples 2 to 8 and Comparative  Synthesis Examples 1 to 8  EXAMPLE  Synthesis Example 1  Synthesis of Polymers 2 to 8 and Comparative Polymers  1 to 8  Synthesis of Polymer 1  Polymer 1  Monomer 1  a~ 0.40, b  ~  0.10, c  ~  0.50  Mw~ 8,500  Mw/Mn~ 1.55  1) Synthesis of Polymers 