Illumination system for illuminating a mask in a microlithographic exposure apparatus

A method, comprising:

• determining an angular distribution to be produced by a diffractive optical element configured to be inserted in an illumination system of a microlithographic projection exposure apparatus so that, during use of the illumination system, the diffractive optical element produces together with a pupil shaping system, which is between the diffractive optical element and a pupil surface of the illumination system, an intensity distribution in the pupil surface of the illumination system that approximates a desired intensity distribution,
• wherein:
• the diffractive optical element comprises a plurality of gratings;
• the gratings are configured so that, during use of the diffractive optical element, each ray of light incident on the gratings is deflected so that rays of the light emerging from the gratings diverge from each other;
• a Fourier transform of an angular distribution produced by the diffractive optical element differs from the desired intensity distribution;
• and
• the determination comprises taking into account at least one of the following:
• an aberration produced by illuminator optics which are configured to illuminate the diffractive optical element;
• and
• an aberration produced by the pupil shaping optical subsystem.

An illumination system, comprising:

• a diffractive optical element configured to be inserted into a light beam path of the illumination system so that, during use of the illumination system, the diffractive optical element produces an intensity distribution in a pupil surface of the illumination system;
• a zoom lens group having a front focal plane;
• and
• an optical raster element between the zoom lens group and the pupil surface of the illumination system,
• wherein:
• the diffractive optical element is disposed in the front focal plane of the zoom lens group;
• a Fourier transform of an angular distribution produced by the diffractive optical element differs from the intensity distribution;
• and
• the illumination system is a microlithographic illumination system.