+20% bias. The resist film was baked (PEB) on a hot plate  at the temperature shown in Table 1 for 60 seconds and  developed in a 2.38 wt % TMAH aqueous solution for 30  seconds to form a hole pattern having a size of 23 nm.  The resist pattern was evaluated. The size of 50 holes was 5  measured under CD-SEM (CG-5000, Hitachi, Ltd.), from  which a size variation  (3a)  was computed and reported as  CDU. The exposure dose that provides a hole pattern having  a size of 23 nm is reported as sensitivity.  The resist composition is shown in Table 1 together with 10  the sensitivity and CDU of EUV lithography.  wherein the high-energy radiation is EB or EUV,  wherein the positive resist composition comprises a base  resin containing a polymer comprising recurring units  (a) having the formula (a), and recurring units (bl)  having a carboxyl group whose hydrogen is substituted  by an acid labile group and/or recurring units (b2)  having a phenolic hydroxyl group whose hydrogen is  substituted by an acid labile group, an organic solvent  and an acid generator, and an organic solvent, the  polymer having a weight average molecular weight, of  1,000 to 500,000,  US 10,303,056 B2  74  73  TABLE 1  Acid  Polymer  generator  Basic compound Organic solvent  (pbw)  (pbw)  (pbw)  (pbw)  Example 1  Polymer 1  PAGl  Quencher 1  PGMEA(400)  (100)  (25.0)  (3.00)  CyH(2,000)  PGME(l00)  Example 2  Polymer 2  Quencher 1  PGMEA(400)  (100)  (3.00)  CyH(2,000)  PGME(l00)  Example 3  Polymer 3  Quencher 1  PGMEA(2,000)  (100)  (3.00)  DAA(500)  Example 4  Polymer 4  Quencher 1  PGMEA(2,000)  (100)  (3.00)  DAA(500)  Example 5  Polymer 5  PAGl  Quencher 1  PGMEA(2,000)  (100)  (6.0)  (3.00)  DAA(500)  Example 6  Polymer 5  PAG2  Quencher 1  PGMEA(2,000)  (100)  (6.0)  (3.00)  DAA(500)  Example 7  Polymer 5  PAG3  Quencher 1  PGMEA(2,000)  (100)  (5.0)  (3.80)  DAA(500)  Example 8  Polymer 5  PAG4  Quencher 1  PGMEA(2,000)  (100)  (5.0)  (3.80)  DAA(500)  Comparative  Comparative  PAGl  Quencher 1  PGMEA(400)  Example 1  Polymer 1  (25.0)  (3.00)  CyH(2,000)  (100)  PGME(l00)  Comparative  Comparative  Quencher 1  PGMEA(2,000)  Example 2  Polymer 2  (3.00)  DAA(500)  (100)  PEB  temp. Sensitivity CDU  (" C.)  (mJ/cm 2 )  (nm)  80  20  4.0  80  22  3.7  80  20  3.1  85  18  2.8  80  19  2.7  80  17  2.4  80  22  2.2  80  24  2.1  80  33  5.2  90  23  4.7  It  is evident from Table 1 that the positive resist compo› sitions within the scope of the invention exhibit satisfactory  resolution and sensitivity and reduced CDU. When poly› mers containing recurring units (dl) to (d3) are used as the  base resin, CDU is further reduced.  Japanese Patent Application No. 2016-128886 is incor- porated herein by reference.  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.  The invention claimed is:  1.  A pattern forming process comprising the steps of  coating a positive resist composition onto a substrate, baking  to form a resist film, exposing the resist film to high-energy  radiation, and developing the exposed resist film in a devel› oper,  wherein the high-energy radiation is EB or EUV,  wherein the positive resist composition comprises a base  resin containing a polymer comprising recurring units  (a) having the formula (a), recurring units (b 1) having  a carboxyl group whose hydrogen is substituted by an  acid labile group andior recurring, units (b2) having a  phenolic hydroxyl group whose hydrogen is substituted  by an acid labile group and recurring units of at least  2.  A pattern forming process comprising the steps of  coating a positive resist composition onto a substrate, baking  to form a resist film, exposing the resist film to high-energy  radiation, and developing the exposed resist film in a devel› oper,  wherein  RA  is hydrogen or methyl, R $^{1 }$is hydrogen or C$_{1 }$-C$_{4 }$ straight or branched alkyl, and R 2  is a single bond or  methylene.  (a) 