Polymer solution for nanoimprint lithography to reduce imprint temperature and pressure

Abstract

An improved method of forming features on substrates by imprinting is provided. In the method, a polymer solution that contains at least one polymer dissolved in at least one polymerizable monomer and the polymer solution is deposited on the substrate to form a liquid film thereon. Further, the liquid film is cured by causing the at least one monomer to polymerize and optionally cross-linking the at least one polymer to thereby form a polymer film, the polymer film having a glass transition temperature of less than 100° C., and the polymer film is imprinted with a mold having a desired pattern to form a corresponding negative pattern in the polymer film. Alternatively, the liquid film is imprinted with the mold and the liquid film is cured in the presence of the mold to form the polymer film with the negative pattern.

1 . An improved method of forming features on substrates by imprinting, said improved method comprising:
 (a) forming a polymer solution comprising at least one polymer dissolved in at least one polymerizable monomer; and   (b) depositing said polymer solution on said substrate to form a liquid film thereon; and then either:   (c) curing said liquid film by causing said at least one monomer to polymerize and optionally cross-linking said at least one polymer to thereby form a polymer film, said polymer film having a glass transition temperature of less than 100° C., and imprinting said polymer film with a mold having a desired pattern to form a corresponding negative pattern in said polymer film; or   (d) imprinting said liquid film with said mold and curing said liquid film in the presence of said mold to form said polymer film with said negative pattern.   
     
     
         2 . The method of  claim 1  wherein said features have critical dimensions less than 100 nm. 
     
     
         3 . The method of  claim 1  wherein said liquid film is cured by a polymerization process selected from the group consisting of heating or exposure to UV radiation or both. 
     
     
         4 . The method of  claim 1  wherein said polymer solution further comprises at least one component selected from the group consisting of at least one initiator, at least one cross-linker, and at least one viscosity modifier. 
     
     
         5 . The method of  claim 4  wherein said at least one initiator is selected from the group consisting of hydrogen peroxide, benzoyl peroxide, azo compounds selected from the group consisting of (a) thermal curing initiators selected from the group consisting of 2,2′-azobisiso-butyronitrile, 4,4′-azobis(cyclohexane-carbonitrile), 4,4′-azobis(4-cyanovaleric acid) and 2,2′-azobis(2-methylpropane), t-butyl peroxy-2ethylhexanoate di(t-butylcyclohexyl)peroxydicarbonate, dicumyl peroxide, dioctanoyl peroxide, dimyristyl peroxide, dilauroyl peroxide, 1,1-di(t-butylperoxycyclohexane), t-butyl peroxydiethylacetate, and cumyl hydroperoxide, and (b) photoinitiators selected from the group consisting of α-hydroxy-ketones, α-amino-ketones, and benzophenones. 
     
     
         6 . The method of  claim 4  wherein said at least one cross-linker is selected from molecules that have difunctional or polyfunctional polymerizable groups. 
     
     
         7 . The method of  claim 6  wherein said at least one cross-linker is selected from the group consisting of ethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, triethylene glycol dimethacrylate, tetraethyleneglycol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, polyethylene glycol (PEG) dimethacrylate wherein the polyethylene glycol has a molecular weight from 400 to 6000, tetraethylene glycol dimethacrylate, ethoxylated Bisphenol A dimethacrylate with up to 50 ethoxy units, cyclohexane dimethanol dimethacrylate, tripropylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, dipentaerythritol pentamethacrylate, alkoxylated glyceryl with up to 30 carbon atoms, trimethylolpropane triacrylate, tris(2-hydroxyethyl) isocyanurate trimethacrylate, 3-(acryloyloxy)-2-hydroxypropyl methacrylate, mono-2-(methacryloyloxyethyl) maleate, divinyl benzene, methacrylic anhydride, pentaerythritol triallyl ether, di(ethylene glycol) dimethacrylate, di(ethylene glycol) divinyl ether, tetraethylene glycol divinyl ether, di(ethylene glycol) diacrylate, 3-(acryloyloxy)-2-hydroxypropyl methacrylate and mono-2-(methacryloyloxy)ethyl maleate, wherein any methacrylate group can be replaced with an acrylate group or an acrylamide group or a methacrylamide group and wherein the foregoing compounds are either unsubstituted or substituted with at least one group selected from the group consisting of halogen, alkyl, or aryl groups. 
     
     
         8 . The method of  claim 4  wherein said at least one viscosity modifier is selected from the group consisting of polyethyl oxazoline, polynorbornene, poly alpha-pinenes and poly beta-pinenes, poly(styrene-co-methylstyrene), poly(tetrahydrofuran), poly(vinyl alcohol-co-ethylene), poly(vinyl chloride-co-isobutyl vinyl ether), poly(vinyl chloride-co-vinyl acetate), poly(vinyl phenyl ketone), poly(vinyl phenol-co-methyl methacrylate), hydroxy ethyl cellulose, grafted polymeric polysaccharide, and styrene-diene polymers. 
     
     
         9 . The method of  claim 1  wherein said at least one polymer has a concentration in said polymer solution of about 0.1 to 50 wt %. 
     
     
         10 . The method of  claim 1  wherein said polymer solution comprises one monomer and one polymer. 
     
     
         11 . The method of  claim 10  wherein said monomer is either the same as monomer units comprising said polymer or is different from monomer units comprising said polymer. 
     
     
         12 . The method of  claim 11  wherein either said monomer is the same as monomer units comprising said polymer and said polymer film is a relatively pure polymer that is substantially uniform in composition or wherein said monomer is different from monomer units comprising said polymer and wherein said polymer film comprises a polymer blend, an interpenetrating network of two polymers, a co-polymer, or a block co-polymer. 
     
     
         13 . The method of  claim 1  wherein said at least one polymer is dissolved into any monomer that said polymer is soluble in. 
     
     
         14 . The method of  claim 1  wherein said at least one polymer has a structure selected from the group consisting of: 
       Type A: 
       
         
           
           
               
               
           
         
       
       where:
 R 1 ═H, CH 3 , Cl, F, aryl group, 
 R 2 =bond, C(O), O, C(O)O, OC(O), 
 R 3 ═CH 2 , CH 2 CH 2  or branched or linear alkyl chain with 2 to 10 carbons, 
 R 4 ═H, CH 3 , F, Cl, Br, branched or linear alkyl chain with 2 to 20 carbons, aryl or substituted aryl, OR 5 , C(O)OR 5  and C(O)R 5 , 
 R 5 ═H, CH 3 , branched or linear alkyl chain of 2 to 20 carbons with or without substitution, aryl or substituted aryl groups; 
 
       Type B
 Type B comprise the same monomer structure as that of Type A, but using polymerization of more than one monomer species to form copolymers, block co-polymers or polymer blends; 
 
       Type C: 
       
         
           
           
               
               
           
         
       
       where:
 R 1 ═H, CH 3 , alkyl or aryl group with and without substitution; and 
 
       Type D: 
       
         
           
           
               
               
           
         
       
       where:
 R 1 ═H, Cl, Br, Fl, alkyl or aryl and substituted alkyl or aryl with 1 to 20 carbon atoms; and 
 R 2 =alkylene or substituted alkylene with 1 to 20 carbon atoms. 
 
     
     
         15 . The method of  claim 14  wherein said at least one polymer has a weight average molecular weight within a range of about 5,000 to 3,000,000. 
     
     
         16 . The method of  claim 14  wherein said at least one polymer has a polydispersity within a range of about 1 to 20. 
     
     
         17 . The method of  claim 14  wherein at least one said polymer has polymerizable end-groups that can be substituted for any of said structures and optionally in combination with or without cross-linkers. 
     
     
         18 . The method of  claim 17  wherein said polymer is selected from the group consisting of polystyrene with methacrylate terminated, poly(tetrahydrofuran) divinyl ether, poly(ethylene glycol) diacrylate, poly(ethylene glycol) dimethacrylate, poly(propylene glycol) diacrylate, poly(propylene glycol) dimethacrylate, and poly(dimethyl siloxane) with divinyl terminated. 
     
     
         19 . The method of  claim 1  wherein said polymerizable monomer is selected from the group consisting of methyl methacrylate, butyl methacrylate, hexyl methacrylate, hexyl acrylate, ethylhexyl methacrylate, ethylhexyl acrylate, octyl acrylate, octyl methacrylate, benzyl methacrylate, benzyl acrylate, trifluoroethyl acrylate, trifluoroethyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, styrene, α-methylstyrene, vinyltoluene, chloromethyl styrene, butadiene, vinyl pyrrolidone, vinyl imidazole, allyl alcohol, and vinyl acetate, acrylonitrile, glycidyl methacrylate, ethyl acrylate, ethyl methacrylate, and mixtures thereof. 
     
     
         20 . The method of  claim 1  wherein said solution further includes at least one macro monomer with polymerizable end-groups, each containing a polymer. 
     
     
         21 . The method of  claim 1  wherein said imprinting comprises compression molding, followed by a pattern transfer process. 
     
     
         22 . The method of  claim 21  wherein following said imprinting, said mold is removed and an anisotropic etching process is used to transfer said pattern into the entire polymer film thickness by removing polymer film remaining in the compressed areas.