Actinic-ray- or radiation-sensitive resin composition, actinic-ray- or radiation-sensitive film, photomask blank and method of forming pattern

An actinic-ray- or radiation-sensitive resin composition comprising:

• (A) a resin that when acted on by an acid, is decomposed to thereby increase its alkali solubility, which resin comprises at least either any of repeating units (I) of general formula (I) below or any of repeating units (II) of general formula (II) below,
• (B) an onium salt acid generator that when exposed to actinic rays or radiation, generates a sulfonic acid whose volume ranges from 250 Å3 to less than 350 Å3, and
• (C) an onium salt acid generator that when exposed to actinic rays or radiation, generates a sulfonic acid whose volume is 400 Å3 or greater,
• in which
• in general formula (I), R1 represents a hydrogen atom or a methyl group;
• L1 represents a single bond or a bivalent connecting group;
• Ar1 represents an aromatic connecting group;
• X1 represents a group leaving when acted on by an acid;
• and m is an integer of 1 to 3, and
• in general formula (II), R2 represents a hydrogen atom, a methyl group, a hydroxymethyl group, an alkoxymethyl group or a halogen atom;
• and X2 represents a group leaving when acted on by an acid.