Patent ID: 7477365
Filing Date: 2009-01-13
Classification: G03F

Abstract:
1. A method for determining a geometric parameter of an optical spot of a light beam, the method comprising: providing a calibration target, the calibration target including a systematic variation in a parameter; measuring the calibration target with respect to the systematic variation using the light beam to obtain a plurality of measurements; and analyzing the measurements and the systematic variation to determine the geometric parameter of the optical spot; wherein in the case that the geometric parameter includes a size of the optical spot, the calibration target includes a first portion, a second portion and a third portion, a dimension of the first portion in a first axis systematically decreasing along a second axis, the second portion and the third portion extending along opposite sides of the first portion and being separated by the first portion in the first axis and including a material of different optical response than that of the first portion, and the measuring including scanning the light beam along the calibration target in the second axis to make measurements of the calibration target, and the analyzing including: wherein in the case that the geometric parameter includes a level of symmetry of the optical spot, the calibration target including a gradient in a parameter along an axis, the gradient being a function of the axis, and the analyzing including analyzing differences in the measurements to determine the level of symmetry, the measuring including: and the calibration target including one of: