Pattern forming method and phase shift mask manufacturing method

A phase shift mask manufacturing method for processing a light-shielding layer over a transparent substrate into a predetermined pattern by partly removing said light-shielding layer and then forming recesses, that serve as phase shift portions, in an underlying layer below said light-shielding layer at least a part of where said light-shielding layer is removed, said phase shift mask manufacturing method comprising the steps of:

• processing said light-shielding layer into a light-shielding pattern having said predetermined pattern;
• forming a resist film on said light-shielding pattern;
• performing writing on said resist film based on writing data and developing said resist film, thereby forming a resist pattern;
• and
• etching said underlying layer using said light-shielding pattern and said resist pattern as a mask, thereby forming said recesses in said underlying layer,
• wherein said writing data includes a portion where pattern data corresponding to at least the two recesses adjacent to each other through a light-shielding portion of said light-shielding pattern are combined into one pattern data.