US Patent 7125641 Polymers, resist compositions and patterning process

A polymer comprising recurring units of (1a) or (1b) wherein R1 is an acid labile group, adhesive group or fluoroalkyl, R2 is H, F, alkyl or fluoroalkyl, R3 and R4 each are a single bond, alkylene or fluoroalkylene, R5 is H or an acid labile group, “a” is 1 or 2, 0<U11<1 and 0<U12<1 and having a Mw of 1,000–500,000 is used as a base resin to formulate a resist composition which is sensitive to high-energy radiation, maintains high transparency at a wavelength of up to 200 nm, and has improved alkali dissolution contrast and plasma etching resistance.