Pattern forming method

A pattern forming method comprising:

• forming a first photoresist layer on an underlying region;
• forming a transparent film on the first photoresist layer;
• forming a second photoresist layer on the transparent layer, the second photoresist layer having an exposure sensitivity which is different from an exposure sensitivity of the first photoresist layer;
• radiating exposure light on the first photoresist layer, the transparent film and the second photoresist layer via a photomask including a first transmissive region and a second transmissive region which cause a phase difference of 180° between transmissive light components passing therethrough, the first transmissive region and the second transmissive region being provided in a manner to neighbor in an irradiation region;
• developing the second photoresist layer which has been irradiated with the exposure light, thereby exposing the transparent film;
• etching the transparent film by using, as a mask, the second photoresist which has been left after the development, thereby exposing the first photoresist layer;
• and
• developing the exposed first photoresist layer, thereby forming a structure comprising a first region where the underlying region is exposed, a second region where an upper surface of the first photoresist layer is exposed and a third region where a stacked structure comprising the first photoresist layer, the transparent film and the second photoresist layer are left.