Photo mask, focus measuring method using the mask, and method of manufacturing semiconductor device

A method of manufacturing a photo mask having an alternating type phase shift mask (PSM) provided in a light-transmitting substrate, said PSM having a light-transmitting portion, and a focus test mask provided in said light-transmitting substrate, said focus test mask including an asymmetrical diffraction grating pattern in which diffraction efficiencies of plus primary diffracted light and minus primary diffracted light are different, the asymmetrical diffraction grating pattern including a shielding portion which shields light;

• a first transmitting portion which transmits light;
• and a second transmitting portion which transmits light, a ratio of widths of the shielding portion, the first transmitting portion, and the second transmitting portion being n:1:1, where n is a positive real number except 2, the asymmetrical diffraction grating pattern approximately satisfying 163°≦360°/(n+2)+θ≦197° where θ (≠90°) indicates an absolute value of a difference between a phase of the light transmitted through the first transmitting portion and that of the light transmitted through the second transmitting portion;
• and a reference pattern configured to obtain an image as a reference for measuring a shift of an image of the asymmetrical diffraction grating pattern, the method comprising:
• dry-etching the light-transmitting substrate to simultaneously form the second transmitting portion of the asymmetrical diffraction grating pattern and a groove of the PSM region;
• and
• wet-etching the groove of the PSM region to form the light-transmitting portion of the PSM.