Patterning process and resist composition

A process for forming a pattern, comprising the steps of:

• applying a positive resist composition onto a substrate to form a resist film, the resist composition comprising a polymer and an acid generator,
• heat treating the resist film and exposing it to high-energy radiation,
• heat treating the exposed resist film and developing it with a developer,
• then causing the resist film to crosslink and cure with the aid of acid and/or heat to form a first pattern,
• applying another positive resist composition on the first pattern and the substrate to form another resist film,
• heat treating and exposing the other resist film to high-energy radiation, and
• heat treating and developing the other resist film with a developer to form a second pattern,
• said polymer comprising recurring units (a-1) or (a-2) or both and recurring units which become soluble in an alkaline developer under the action of an acid, the recurring units (a-1) and (a-2) being represented by the general formula (1):
• wherein R1 and R6 are each independently hydrogen, methyl or hydroxymethyl,
• R2 and R7 are each independently a single bond or a straight, branched or cyclic alkylene group of 1 to 6 carbon atoms, which may have an ether or ester group, with the proviso that when R2 and R7 each are a straight, branched or cyclic alkylene group of 1 to 6 carbon atoms, it has a carbon atom attached to the ester moiety in the formula, which is primary or secondary,
• R3, R4, R5, R8, R9, R10, and R11 are each independently hydrogen or a straight, branched or cyclic alkyl group of 1 to 6 carbon atoms, a1 and a2 are numbers in the range:
• 0≦a1<1.0, 0≦a2<1.0, and 0<a1+a2<1.0.