Photomask for measuring lens aberration, method of manufacturing the same, and method of measuring lens aberration

In combination with an exposure apparatus having a light source, and an optical lens, a photomask for use in measuring the aberration of the optical lens, said photomask comprising:

• a transparent substrate having a first surface facing towards said light source of the exposure apparatus along the optical axis of the exposure apparatus, and a second surface facing towards the optical lens along the optical axis of the exposure apparatus;
• a first opaque pattern on the first surface of the transparent substrate, and defining at least one aperture that exposes the first surface of said transparent substrate and thereby delimits a region of the photomask through which light from the light source can pass such that only a predetermined portion of light from the light source can pass through said photomask to the optical lens;
• and
• a second opaque pattern on the second surface of the transparent substrate, portions of opaque material of said second opaque pattern being aligned with said apertures, respectively, whereby light passing through said apertures will form images corresponding to that of said second opaque pattern.

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

• forming a first layer of opaque material and a second layer of opaque material on a first surface of a transparent substrate and a second surface opposite to the first surface, respectively;
• patterning the first layer to form a first opaque pattern having a plurality of apertures that expose the first surface, wherein said apertures limit the amount of exposure light that can pass through the photomask via said transparent substrate;
• and
• patterning the second opaque layer to form a second opaque pattern on the second surface, portions of the opaque material of said second opaque pattern being aligned with said apertures, respectively, whereby exposure light passing through said apertures will form an image corresponding to that of said second opaque pattern.

A method of measuring the aberration of an optical lens, said method comprising:

• providing a photomask including a transparent substrate having a first surface and a second surface on opposite sides from each other, a first opaque pattern on the first surface and defining a plurality of apertures that expose the first surface, and a second opaque pattern on the second surface and opaque portions of which are aligned with said apertures, respectively;
• positioning the photomask in an exposure apparatus so that the first opaque pattern of the photomask faces a light source of the exposure apparatus along the optical axis of the exposure apparatus, and the second opaque pattern of the photomask faces the optical lens along the optical axis of the exposure apparatus, with the apertures aligned along the optical axis of the exposure apparatus with the plane of the pupil of the optical lens;
• mounting a wafer having a photoresist layer thereon in the exposure apparatus;
• forming a first pattern on the wafer by exposing the photoresist layer to light form the light source passed through the photomask such that the light passes through the apertures of the first opaque pattern and forms an image on the photoresist layer corresponding to the second opaque pattern;
• and
• determining the location of the first pattern formed on the wafer, relative to a reference position, and estimating an aberration of the optical lens based on the location of the first pattern formed on the wafer.