US Patent 7833694 Lactone-containing compound, polymer, resist composition, and patterning process

Lactone-containing compounds having formula (1) are novel wherein R1 is H, F, methyl or trifluoromethyl, R2 and R3 are H or monovalent hydrocarbon groups, or R2 and R3 may together form an aliphatic hydrocarbon ring, R4 is H or CO2R5, R5 is a monovalent hydrocarbon group, W is CH2, O or S, and k1 is 3, 4 or 5. They are useful as monomers to produce polymers which are transparent to radiation ≦500 nm. Radiation-sensitive resist compositions comprising the polymers as base resin exhibit excellent properties including resolution, LER, pattern density dependency and exposure margin.