Patent ID: 9581911
Date: 2017-02-28
CPC Classifications: G02B,G03B,G03F

Claim:
1. An illumination system for directing light along an axis from a light source to a mask, the illumination system comprising: means for directing light from the light source to a pupil plane of the illumination system; means for modulating a polarization state of the light in the pupil plane of the illumination system; and means for directing the light from the pupil plane to the mask, wherein the means for modulating the polarization state is positioned at or near the pupil plane, the means for modulating the polarization state comprises material having optical activity such that for light propagating along the axis having a linear polarization state incident on the material is rotated by an amount proportional to a thickness of the material along the axis, and, for an annular region centered on the axis, the material has a non-zero thickness along the axis that is different at different locations in the pupil, and the illumination system is an illumination system for a microlithography optical system.