May 12, 2005  11  US 2005/0100814 Al  fluoroalcohol functional group having the struc› ture:  -C(Rf)(Ri)OH  [0113]  wherein Rf and Rf’ areas described  above; and  [0115]  wherein R$^{45 }$is a hydrogen atom or CN  group; R 46  is C$_{1}$-C$_{8 }$ alkyl group, hydrogen  atom, or CO$_{2}$R 47  group, where R 47  is C$_{1}$-C$_{8 }$ alkyl group or hydrogen atom.  (H)(R $^{45}$)C~C(R$^{46}$)(CN)  [0116]  The fluoropolymer or copolymer comprises a  repeat unit ( discussed infra) derived from at least one  ethylenically unsaturated compound containing a fluoroal› cohol functional group that can have fluoroalkyl groups  present as part of the fluoroalcohol group and are described  earlier with regard to copolymer (b). These fluoroalkyl  groups are designated  Rf and Rr as described above.  [0117]  As is well known to those skilled in the polymer  art, an ethylenically unsaturated compound undergoes free  radical polymerization to afford a polymer having a repeat  unit that is derived from the ethylenically unsaturated com› pound. Specifically, an ethylenically unsaturated compound  having structure:  [0118]  is described above with regard to copolymer (al).  [0119]  Each fluorine-containing copolymer according to  this invention has an absorption coefficient of less than 4.0  µm- $^{1 }$at a wavelength of 157 nm, preferably of less than 3.5  µm- 1  at this wavelength, more preferably, of less than 3.0  µm- 1  at this wavelength, and, still more preferably, of less  than 2.5  µm- 1  at this wavelength.  [0120]  The fluorinated polymers, photoresists, and pro› cesses of this invention that include a fluoroalcohol func› tional group may have the structure:  [0121]  wherein Rf and R/ are as described above; Z is as  described above.  [0122]  Some illustrative, but nonlimiting, examples of  representative comonomers containing a fluoroalcohol func› tional group and within the scope of the invention are  presented below:  -ZCH$_{2}$C(R,)(Ri)OH  (H)(R $^{48}$)C~C(R$^{4}$9)(CN)  \  c=c  I  \  S  T  ev-0’,C(O’,hOH  ev-cu,ocu,qa,,Jpn  00-0’,C(O’,hOH  oo-cu,ocu;c(a,,)p  CH2-CHOCH2CH20CH2C(CF3)20H  CH2-CHO(CH2)40CH2C(CF3)20H  ev-o-cu;c(ce,Jpn  oo-O-CU,C(O’,),PH  -continued  [0123]  Various bifunctional compounds which can ini› tially afford crosslinking and subsequently be cleaved (e.g.,  upon exposure to strong acid) are also useful as comonomers  in the copolymers of this invention. As an illustrative, but  non-limiting  example,  the  bifunctional  comonomer  NB-F-OMOMO-F-NB  is  desirable as a comonomer  in the copolymers of this invention. This and similar bifunc› tional comonomers, when present in the copolymer compo› nent(s) of photoresist compositions of this invention, can  afford copolymers that are of higher molecular weight and  are lightly crosslinked materials. Photoresist compositions,  incorporating these copolymers comprised of bifunctional  monomers, can have improved development and imaging  characteristics, since, upon exposure (which photochemi› cally generates strong acid as explained infra), there results  cleavage of the bifunctional group and consequently a very  significant drop in molecular weight, which factors can  afford greatly improved development and imaging charac› teristics ( e.g., improved contrast). These fluoroalcohol  groups and their embodiments are described in more detail  as above and in PCT/US00/11539 filed Apr. 28, 2000.  [0124]  At least a portion of the nitrile functionality that is  present in the nitrile/fluoroalcohol polymers results from  incorporation of repeat unit(s) derived from at least one  ethylenically unsaturated compound having at least one  nitrile group and having the structure:  [0125]  wherein R 48  is a hydrogen atom or cyano group  (CN); R$^{49 }$is an alkyl group ranging from 1 to about 8 carbon  atoms, CO$_{2}$R$^{50 }$group wherein R$^{50 }$is an alkyl group ranging  from 1 to about 8 carbon atoms, or hydrogen atom. Acry› lonitrile, methacrylonitrile, fumaronitrile (trans-1,2-dicya› noethylene ), and maleonitrile ( cis-1,2-dicyanoethylene) are  preferred. Acrylonitrile is most preferred.  [0126]  The nitrile/fluoroalcohol polymers typically are  characterized in having a repeat unit derived from at least  one ethylenically unsaturated compound containing the  fluoroalcohol functional group that is present in the nitrile/  [0114]  (ii) a repeat unit derived from at least one  ethylenically unsaturated compound having the  structure: 