Patent ID: 7277165

Claim:
A method of measuring flare in an optical lithographic system having a source that emits actinic radiation, comprising: a. providing an exposure mask that comprises at least first and second discrete features of a first opacity characteristic in a field of a second opacity characteristic, wherein the first and second features each have rotational symmetry of order greater than four and are of different respective areas, the first opacity characteristic is substantially complete opacity and the second opacity characteristic is substantially complete transparency, b. providing an exposure target having a surface that is sensitive to actinic radiation, c. positioning the exposure mask and the exposure target in the lithographic system such that actinic radiation emitted by the lithographic system illuminates the sensitive surface of the exposure target through the exposure mask, whereby each feature of the exposure mask projects a geometric image on the sensitive surface of the exposure target, d. employing the optical lithographic system to emit a dose of actinic radiation, and e. measuring the extent to which regions of the sensitive surface that are within the geometric image of a feature of the exposure mask are exposed to actinic radiation during step d due to flare.