Patent ID: 8059266
Filing Date: 2011-11-15
Classification: G01J,G03B,G03F

Abstract:
1. A lithographic apparatus, comprising: an illumination system configured to produce a beam of radiation; a test pattern configured to facilitate measuring stray light, wherein the test pattern comprises a dark area surrounded by a bright area, and wherein the bright area is substantially larger than the dark area; a detector having an aperture in an image plane where a projected image of the test pattern is created, wherein a shape of the aperture corresponds to a shape of the dark area; a positioning mechanism configured to position the aperture of the detector at a first and a second location, the first location being aligned to an image of the dark area, and the second location being aligned to an image of the bright area; a moving mechanism configured to move the aperture of the detector in the image plane and to move the projected image of the test pattern substantially synchronously with the aperture of the detector, the aperture being positioned initially in the first location during a dark area measurement, and the aperture being positioned initially in the second location during a subsequent bright area measurement; a transducer coupled to the detector that measures radiation intensity during the dark area measurement and the bright area measurement; a processor coupled to the transducers that compares a first integrated signal representing a result of the dark area measurement, and a second integrated signal representing a result of the bright area measurement to yield a final result that indicates effects of stray light in the lithographic apparatus; and an output indicator coupled to the processor that communicates an output to facilitate monitoring and evaluation of performance of the lithographic apparatus, wherein the output is generated based on the final result.