Positive-working photosensitive composition and pattern forming method using the same

A positive-working photosensitive composition comprising:

• (A) a resin that comprises a repeating unit having a diamantane structure and can decompose under action of an acid to increase solubility in an alkali developer, and wherein the resin (A) has a weight-average molecular weight of 3,000 to 30,000 and a dispersion degree of 1.4 to 2.1;
• (B) a compound that can generate an organic acid represented by formula (2), (3), (3′), (4) or (5) upon irradiation with an actinic ray or radiation;
• and
• (C) a solvent,
• in formula (2), Rf represents an organic group having a fluorine atom, R represents a hydroxyl group or an organic group, Ar represents an aromatic group, 1 represents an integer of 1 to 6, m represents an integer of 0 to 4, and n represents an integer of 0 to 4, provided that m+n is an integer of 1 or above,
• in formulae (3) and (3′), A1 represents a divalent linkage group, A2 and A3 each independently represents a single bond, an oxygen atom or —N(Rx)—, Rx represents a hydrogen atom, an aryl group, an alkyl group or a cycloalkyl group, A4 represents a single bond or —C(═O)—, Ra represents a hydrogen atom or an organic group, p represents 2 or 3, Rb represents a p-valent linkage group, and when A3 is —N(Rx)—, Ra and Rx, or Rb and Rx may combine with each other to form a ring,
• in formulae (4) and (5), Y represents an alkylene group substituted with at least one fluorine atom, and Rc represents an alkyl group or a cycloalkyl group.