Jan.  28,  2021  1  US 2021/0026244 Al  Solution to Problem  POSITIVE RESIST COMPOSITION FOR EUV  LITHOGRAPHY AND METHOD OF  FORMING RESIST PATTERN  TECHNICAL FIELD  BACKGROUND  CITATION LIST  Patent Literature  Non-Patent Literature  SUMMARY  Technical Problem  [0001]  The present disclosure relates to a positive resist  composition for EUV (extreme ultraviolet) lithography and  a method of forming a resist pattern using EUV.  [0002]  Polymers that display increased solubility in a  developer after undergoing main chain scission through  irradiation with ionizing radiation, such as an electron beam,  or short-wavelength light, such as ultraviolet light, are  conventionally used as main chain scission-type positive  resists in fields such as semiconductor production.  [0003]  Specifically,  Patent  Literature  (PTL)  1,  for  example, discloses a positive resist formed of an a-methyl› styrene-methyl a-chloroacrylate copolymer as a main chain  scission-type positive resist, whereas PTL 2, for example,  discloses a positive resist formed of an a-methylstyrene-2,  2,2-trifluoroethyl a-chloroacrylate copolymer as a main  chain scission-type positive resist. In PTL 1 and 2, resist  patterns are formed by irradiating resist films formed of  these positive resists with electron beams.  [0004]  Moreover, in recent years, EUV lithography using  extreme ultraviolet light (EUV) has been attracting attention  as a technique that enables formation of fine patterns and has  a small proximity effect during exposure compared to when  an electron beam or the like is used. Non-Patent Literature  (NPL) 1, for example, evaluates patterning performance  during exposure using extreme ultraviolet light for a resist  film formed using a positive resist composition that contains  an a-methylstyrene-methyl a-chloroacrylate copolymer.  [0005]  PTL 1: JP-HS-3636B  [0006]  PTL 2: WO2017/130872Al  [0007]  NPL  1:  Roberto Fallica (and 6 others), "Litho› graphic performance of ZEP520A and mr-PosEBR resists  exposed by electron beam and extreme ultraviolet lithogra› phy", Journal of Vacuum Science & Technology B, October  2017  [0008]  However, resist films formed using the conven› tional positive resists described above have low sensitivity  to extreme ultraviolet light and leave room for improvement  in terms of enabling efficient formation of a resist pattern.  [0009]  Accordingly, an object of the present disclosure is  to provide a positive resist composition for EUV lithography  that can form a resist film having high sensitivity to extreme  ultraviolet light and to also provide a method that enables  efficient formation of a resist pattern using extreme ultra› violet light.  [0010]  The inventor conducted diligent studies with the  aim of achieving the object set forth above. The inventor  reached a new finding that a resist film formed using a  positive resist composition that contains a specific copoly› mer including 5 or more fluorine atoms has high sensitivity  to extreme ultraviolet light and that a resist pattern can be  efficiently obtained by exposing the resist film using extreme  ultraviolet light. In this manner, the inventor completed the  present disclosure.  [0011]  Specifically, the present disclosure aims to advan› tageously solve the problem set forth above, and a presently  disclosed positive resist composition for EUV lithography  comprises: a copolymer including a monomer unit (A)  represented by general formula  (I), shown below,  where, in general formula (I), R  1  is an organic group  including 5 or more fluorine atoms, and a monomer unit (B)  represented by general formula (II), shown below,  where, in general formula (II), R 2  is a hydrogen atom, a  fluorine atom, an unsubstituted alkyl group, or a fluorine  atom-substituted alkyl group, R 3  is a hydrogen atom, an  unsubstituted alkyl group, or a fluorine atom-substituted  alkyl group, p and q are each an integer of not less than  O  and  not more than 5, and p+q=5; and  [0012]  a solvent.  [0013]  Through inclusion of a copolymer including the  specific monomer unit (A) and monomer unit (B) set forth  above as a positive resist in this manner, it is possible to form  a resist film having high sensitivity to extreme ultraviolet  light.  [0014]  Note that in a case in which p in general formula  (II) is 2 or more, the plurality ofR $^{2 }$groups may be the same  or different. Moreover, in a case in which q in general  formula (II) is 2 or more, the plurality of R 3  groups may be  the same or different.  [0015]  In the presently disclosed positive resist composi› tion for EUV lithography, R 1  is preferably a fluoroalkyl  group. When R$^{1 }$is a fluoroalkyl group, it is possible to form  a resist film having further improved sensitivity to extreme  ultraviolet light.  [0016]  In the presently disclosed positive resist composi› tion for EUV lithography, a total number of fluorine atoms  included in the monomer unit (A) and the monomer unit (B)  (II)  (I)  Cl  H  +i-t+- R100C  H 