Fine pattern forming method

A fine pattern forming method for patterning a film formed on a substrate, the fine pattern forming method comprising steps of:

• forming patterns made of a first photoresist film, arranged at a first pitch on the film;
• trimming the patterns made of the first photoresist film;
• depositing a protection film on trimmed patterns made of the first photoresist film, the protection film being made of reaction products of an etching gas, thereby obtaining first patterns;
• forming other patterns made of a second photoresist film, arranged at a second pitch, on the protection film, the other patterns made of the second photoresist film being shifted by half of the first pitch from the corresponding patterns made of the first photoresist film;
• trimming the other patterns made of the second photoresist film into second patterns;
• and
• etching the film using the first patterns and the second patterns,
• wherein the step of trimming the patterns made of the first photoresist film and the step of trimming the other patterns made of the second photoresist film are carried out using at least one of oxygen radicals and ozone gas, and
• wherein the protection film made of the reaction products of the etching gas is tolerant of the oxygen radicals and the ozone gas.