Patterning process, resist composition, polymer, and polymerizable ester compound

A pattern forming process comprising the steps of applying a resist composition comprising a polymer adapted to undergo deprotection reaction under the action of an acid, to form a hydroxyl group, which in turn, reacts with any neighboring ester or acid anhydride to form a lactone ring so that the polymer may reduce its solubility in an organic solvent developer, an acid generator, and an organic solvent onto a substrate, prebaking the composition to form a resist film, exposing the resist film to high-energy radiation, baking, and developing the exposed film in an organic solvent-based developer to form a negative pattern wherein the unexposed region of film is dissolved away and the exposed region of film is not dissolved.

A negative pattern-forming resist composition comprising a polymer, an acid generator, and an organic solvent,

• said polymer being dissolvable in a developer selected from the group consisting of 2-octanone, 2-nonanone, 2-heptanone, 3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone, methylcyclohexanone, acetophenone, methylacetophenone, propyl acetate, butyl acetate, isobutyl acetate, amyl acetate, isoamyl acetate, butenyl acetate, phenyl acetate, propyl formate, butyl formate, isobutyl formate, amyl formate, isoamyl formate, methyl valerate, methyl pentenoate, methyl crotonate, ethyl crotonate, methyl propionate, ethyl propionate, ethyl 3-ethoxypropionate, methyl lactate, ethyl lactate, propyl lactate, butyl lactate, isobutyl lactate, amyl lactate, isoamyl lactate, methyl 2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methyl benzoate, ethyl benzoate, benzyl acetate, methyl phenylacetate, benzyl formate, phenylethyl formate, methyl 3-phenylpropionate, benzyl propionate, ethyl phenylacetate, and 2-phenylethyl acetate, and
• said polymer being adapted to form a lactone ring under the action of an acid so that the polymer may reduce its solubility in the developer.

A polymer comprising recurring units having the general formula (1) or (2):

• wherein R1 is hydrogen or methyl, R2 is a C1-C20 alkyl group which may contain an oxygen functional group, R3 is a C2-C20 acid labile group which may contain an oxygen functional group, A1 is a trivalent C3-C20 organic group which may contain an oxygen functional group, and A2 is a tetravalent C3-C20 organic group which may contain an oxygen functional group,
• said polymer being adapted to undergo deprotection reaction under the action of an acid, to form a hydroxyl group, which in turn, reacts with any neighboring ester or acid anhydride to form a lactone ring so that the polymer may reduce its solubility in an organic solvent developer.

A polymerizable ester compound having the general formula (1a):

• wherein R1 is hydrogen or methyl, R2 is a C1-C20 alkyl group which may contain an oxygen functional group, R3 is a C2-C20 acid labile group which may contain an oxygen functional group, and A1 is a trivalent C3-C20 organic group which may contain an oxygen functional group.