Photomask for measuring lens aberration, method of its manufacture, and method of its use

A photomask for measuring lens aberration, comprising:

• a transparent substrate having a first surface facing a light source and a second surface facing optical lenses of which the lens aberration will be measured;
• a reference pattern group formed on the second surface of the transparent substrate;
• an encoded pattern group formed on the second surface of the transparent substrate and spaced apart from the reference pattern group;
• and
• an aperture to face the second surface of the transparent substrate and including a square shape opening and a Fresnel zone opening,
• wherein the aperture is spaced apart from the second surface of the transparent substrate.

A method of manufacturing a photomask for measuring lens aberration, the method comprising:

• providing a transparent substrate having first and second surfaces;
• forming a shielding film on the second surface of the transparent substrate;
• forming a reference pattern group and an encoded pattern group on the second surface of the transparent substrate by patterning the shielding film;
• and
• forming an aperture that faces the second surface of the transparent substrate.

A method of measuring lens aberration, comprising:

• providing a photomask that includes a transparent substrate having a first surface and a second surface, a reference pattern group and an encoded pattern group spaced apart from each other on the second surface of the transparent substrate, and Fresnel lens shaped openings that face the second surface of the transparent substrate;
• locating the photomask in an exposure apparatus so that the first surface of the transparent substrate faces a light source of the exposure apparatus and an aperture faces an optical lens of which the lens aberration will be measured;
• placing the reference pattern group of the photomask in a first position;
• forming a reference photoresist pattern by exposing a photoresist film on a wafer loaded in the exposure apparatus using the photomask;
• shifting the photomask to locate the encoded pattern group at the first position;
• forming an encoded photoresist pattern by exposing the photoresist film on the wafer using the shifted photomask;
• and
• measuring the lens aberration on a pupil plane of the optical lens based on the distance between the reference photoresist pattern and the encoded photoresist pattern.