Silicon-containing polymer, resist composition and patterning process

Silicon-containing polymers comprising recurring units of formula (1) are novel wherein R¹ is a single bond or alkylene, R² is hydrogen or alkyl, R³, R⁴ and R⁵ are alkyl, haloalkyl, aryl or silicon-containing group, R⁶ is hydrogen, methyl, cyano or -C(O)OR⁸ wherein R⁸ is hydrogen, alkyl or acid labile group, R⁷ is alkyl, -NR⁹R¹⁰ or -OR¹¹ wherein R⁹, R¹⁰ and R¹¹ are hydrogen or alkyl, a and b are positive numbers satisfying 0