Being the manner amendment the degree of ellipse of the light decay filter null lighting beam for degree of ellipse

摘要

Ellipticity in an illumination beam may be corrected by measuring an ellipticity of the illumination beam and substantially eliminating the ellipticity using a light attenuating filter at a defocus position of the illumination beam, wherein the light attenuating filter has a two-dimensional pattern that compensates for ellipticity variations in the illumination beam. The light attenuating filter may stand alone, or the filter may be combined with a uniformity correction system, such that it corrects both uniformity and ellipticity. In one embodiment, the light attenuating filter is printed with an assembly of microscopic dots according to the two-dimensional pattern.