US Patent 7189481 Characterizing flare of a projection lens

Flare of an imaging system is measured using resist by employing the imaging system to directly expose a first part of the resist at an image plane of the imaging system to a first dose of radiation and to indirectly expose a second part of the resist as a result of flare. The imaging system exposes the second part of the resist to a second dose of radiation. Flare of the imaging system is determined from a pattern that is formed in the second part of the resist.