A
polymer comprising recurring units of formula (1) is provided wherein some
hydrogen atoms of phenolic hydroxyl groups and / or alcoholic hydroxyl groups and / or carboxyl groups are replaced by
acid labile groups. The
polymer is crosslinked with a crosslinking group having a C-O-C linkage resulting from reaction of some of the remaining alcoholic hydroxyl groups and / or carboxyl groups with an alkenyl
ether compound or halogenated
alkyl ether compound. The amount of the
acid labile group and the crosslinking group combined is on the average from more than 0 mol % to 80 mol % of the entirety of the phenolic hydroxyl group, alcoholic hydroxyl group and carboxyl group. The
polymer has Mw of 1,000-500,000. R1 is H or methyl, R2 is C1-C8
alkyl, R3 is a
divalent C1-C18
hydrocarbon group which may have a hetero atom, R4 and R5 are H or monovalent C1-C18
hydrocarbon groups which may have a hetero atom, x and y are integers satisfying x+y< / =5, x', y' and z' are integers satisfying x'+y'+z'< / =5, p, q and r are numbers satisfying 0< / =p< / =0.4, 0< / =q< / =0.4, 0.01< / =p+q< / =0.8, and p+q+r=1. A chemically amplified positive
resist composition comprising the polymer as a base resin has high sensitivity,
high resolution, a wide
latitude of
exposure, and process adaptability and forms
resist patterns having
plasma etching resistance and
heat resistance.