Polymer compound, positive resist composition and process for forming resist pattern

A polymer compound comprising:

• a constituent unit (a1) represented by the following general formula (1)′:
• wherein R represents a hydrogen atom, a fluorine atom, a lower alkyl group having 20 or less carbon atoms, or a fluorinated lower alkyl group having 20 or less carbon atoms, R1 represents at most 20-membered cyclic group which may have a substituent, n represents 0 or an integer of 1 to 5, and m represents 0 or 1,
• a constituent unit (a2) derived from an (α-alkyl of 1 to 5 carbon atoms) acrylate ester having a lactone-containing monocycle or a polycyclic group, and
• a constituent unit (a3) which is a constituent unit other than the constituent unit (a1) and the constituent unit (a2) and is derived from an (α-alkyl of 1 to 5 carbon atoms) acrylate ester which has an aliphatic cyclic group-containing non-acid dissociable dissolution inhibiting group and does not have a polar group.

A polymer compound comprising:

• a constituent unit (a1) represented by the following general formula (1):
• wherein R represents a hydrogen atom, a fluorine atom, a lower alkyl group having 20 or less carbon atoms, or a fluorinated lower alkyl group having 20 or less carbon atoms, R1 represents at most 20-membered cyclic group which may have a substituent, and n represents 0 or an integer of 1 to 5,
• a constituent unit (a2) derived from an (α-alkyl of 1 to 5 carbon atoms)acrylate ester having a lactone-containing monocycle or a polycyclic group, and
• a constituent unit (a3) which is a constituent unit other than the constituent unit (a1) and the constituent unit (a2) and is derived from an (α-alkyl of 1 to 5 carbon atoms)acrylate ester which has an aliphatic cyclic group-containing non-acid dissociable dissolution inhibiting group and does not have a polar group;
• wherein the constituent unit (a1) is a constituent unit represented by the following general formula (2):
• wherein R and n are as defined above, X represents a polar group, and 1 represents 0 or an integer of 1 to 3.