110  US 9,557,643 B2  109  -continued  ~o  j:  ~CN  Ll{  0  0  -continued  It is also one of particularly preferred embodiments that  the polar group which can be contained in the repeating unit  (b) is an acidic group. Preferred acidic groups include a  phenolic hydroxyl group, a carboxylic acid group, a sulfonic  acid group, a fluorinated alcohol group (such as hexafluor- oisopropanol group), a sulfonamide group, a sulfonylimide  group, an (alkylsulfonyl)(alkylcarbonyl)methylene group,  an (alkylsulfonyl)(alkylcarbonyl)imide group, a bis(alkyl› carbonyl)methylene  group,  a  bis(alkylcarbonyl)imide  group, a bis(alkyl sulfonyl)methyl ene group, a bis(alkyl- sulfonyl)imide group, tris(alkylcarbonyl)methylene group  and a tris(alkylsulfonyl)methylene group. Among others, the  repeating unit (b) is preferably a repeating unit having a  carboxyl group. By virtue of containing a repeating unit  having an acidic group, the resolution increases in usage of  forming contact holes. As the repeating unit having an acidic  group, all of a repeating unit where an acidic group is  directly bonded to the main chain of the resin, such as  repeating unit by an acrylic acid or a methacrylic acid, a  repeating unit where an acidic group is bonded to the main  chain of the resin through a linking group, and a repeating  unit where an acidic group is introduced into the polymer  chain terminal by using an acidic group-containing polym- erization initiator or chain transfer agent at the polymeriza› tion, are preferred. In particular, a repeating unit by an  acrylic acid or a methacrylic acid is preferred.  The acidic group which can be contained in the repeating  unit (b) may or may not contain an aromatic ring, but in the  case of containing an aromatic ring, the acidic group is  preferably selected from acidic groups except for a phenolic  hydroxyl group. In the case where the repeating unit (b) has  an acidic group, the content of the repeating unit having an  acidic group is preferably 30 mo! % or less, more preferably  20 mo!  % or less, based on all repeating units in the resin  (A). In the case where the resin (A) contains a repeating unit  having an acidic group, the content of the repeating unit  having an acidic group in the resin (A) is usually 1 mo! %  or more.  Specific examples of the repeating unit having an acidic  group are illustrated below, but the present invention is not  limited thereto.  In specific examples, Rx represents  H, CH$_{3}$ ,  CH$_{2}$0H  or  CF$_{3}$ • 