Exposure method and apparatus, and method for fabricating device with light amount distribution having light larger in four areas

An illumination system for illuminating an object with illumination light, the illumination system comprising:

• a distribution setting member arranged to deflect the illumination light, thereby to generate a plurality of light beams corresponding to a light amount distribution on a pupil plane of the illumination system;
• and
• a polarization setting member for changing polarization of at least part of the plurality of light beams generated by the distribution setting member,
• wherein said light amount distribution comprises a plurality of areas being away from an optical axis of the illumination system and an area which substantially includes the optical axis, the area which substantially includes the optical axis is connected to the plurality of areas which are away from the optical axis,
• and wherein the polarization setting member is adapted to change polarization of the illumination light so that polarization direction in the plurality of areas away from the optical axis are tangential to a circumference about the optical axis.