Jun.  18,2020  104  US 2020/0192221 Al  [0219]  The resist composition is shown in Table  1  together  with the sensitivity and CDU of EUV lithography.  TABLE  1  Polymer  Acid generator  Quencher Organic solvent PEB temp. Sensitivity CDU  (pbw)  (pbw)  (pbw)  (pbw)  Example  Polymer 1  PAG 1  PGMEA (2,000)  (100)  (25.0)  DAA (500)  2  Polymer 2  PGMEA (2,000)  (100)  DAA (500)  3  Polymer 3  PGMEA (2,000)  (100)  DAA (500)  4  Polymer 4  PGMEA (2,000)  (100)  DAA (500)  5  Polymer 5  PGMEA (2,000)  (100)  DAA (500)  6  Polymer 5  Q-1  PGMEA (2,000)  (100)  (1.00)  DAA (500)  7  Polymer 5  PAG 1  Q-1  PGMEA (2,000)  (100)  (10.0)  (1.00)  DAA (500)  8  Polymer 6  PAG 1  PGMEA (2,000)  (100)  (25.0)  DAA (500)  9  Polymer 7  PGMEA (2,000)  (100)  DAA (500)  10  Polymer 7  Q-3  PGMEA (2,000)  (100)  (1.50)  DAA (500)  11  Polymer 7  Q-4  PGMEA (2,000)  (100)  (1.20)  DAA (500)  12  Polymer 7  Q-4  PGMEA (2,000)  (70)  (1.20)  DAA (500)  Comparative  Polymer 3  (30)  Comparative  Comparative  PAG 1  Q-2  PGMEA (2,000)  Example  Polymer 1  (25.0)  (3.00)  DAA (500)  (100)  2  Comparative  PAG 1  PGMEA (2,000)  Polymer 2  (25.0)  DAA (500)  (100)  3  Comparative  Q-1  PGMEA (2,000)  Polymer 3  (3.00)  DAA (500)  (100)  (" c.)  (mJ/cm 2 )  (nm)  95  29  3.0  95  26  2.7  95  27  2.6  95  28  2.3  95  28  2.6  95  35  2.0  95  22  2.3  95  29  3.0  95  29  2.4  95  31  2.0  95  36  2.1  95  38  2.2  95  30  5.6  95  38  4.7  95  35  3.9  [0220]  It  is demonstrated in Table  1  that positive resist  compositions comprising a base polymer comprising recur› ring units having a nitrogen-containing tertiary ester struc› ture offer a  high sensitivity and improved CDU.  [0221]  Japanese Patent Application No. 2018-234513 1s  incorporated herein by reference.  [0222]  Although some preferred embodiments have been  described, many modifications and variations may be made  thereto in light of the above teachings.  It  is therefore to be  understood that the invention may be practiced otherwise  than as specifically described without departing from the  scope of the appended claims.  1.  A positive resist composition comprising a base poly› mer comprising recurring units having a carboxyl group in  which the hydrogen is substituted by a nitrogen-containing  tertiary hydrocarbon group.  2.  The positive resist composition of claim  1  wherein the  nitrogen-containing tertiary hydrocarbon group is a nitro› gen-containing tertiary cyclic hydrocarbon group.  3.  The positive resist composition of claim  1  wherein the  recurring units have the formula (a):  wherein  RA  is hydrogen or methyl, X 1  is each indepen› dently a single bond, phenylene, naphthylene, or a  C$_{1 }$-C$_{12 }$ linking group containing an ester bond, ether  bond or lactone ring, and R is a nitrogen-containing  tertiary hydrocarbon group having the formula (al) or  (a2):  ~  o~o  I  R  (a)  (al) 