Patent ID: 6900887

Claim:
A method of measuring stray light in an exposure apparatus including an image sensor disposed at a wafer level, comprising: providing a reference pattern on a first reticle, the reference pattern including a light shielding region having first open regions for transmitting light; providing a measuring pattern on a second reticle, the measuring pattern including a light shielding region having second open regions for transmitting light; positioning the reference pattern over the image sensor such that the first open regions are over an active region of the image sensor, the first open regions corresponding to a center of the active region; positioning the measuring pattern over the image sensor such that the second open regions are over the active region of the image sensor, the second open regions corresponding to a periphery of the active region; measuring an intensity of a first light beam incident on the active region having been filtered by the reference pattern; measuring an intensity of a second light beam incident on the active region having been filtered by the measuring pattern; and evaluating an intensity of the stray light by an intensity difference between the first light beam and the second light beam.