Microlithography projection exposure apparatuses serve for producing microstructured components via a photolithographic method. In this case, a structure-bearing mask, the so-called reticle, is illuminated with the aid of a light source unit and an illumination optical unit and is imaged with the aid of a projection optical unit onto a photosensitive layer. In this case, the light source unit provides radiation that is directed into the illumination optical unit. The illumination optical unit serves to provide a uniform illumination with a predetermined angle-dependent intensity distribution at the location of the structure-bearing mask. For this purpose, various suitable optical elements are provided within the illumination optical unit. The structure-bearing mask illuminated in this way is imaged with the aid of the projection optical unit onto a photosensitive layer. In this case, the minimum structure width that can be imaged with the aid of such a projection optical unit is determined, among other things, by the wavelength of the radiation used. The smaller the wavelength of the radiation, the smaller the structures that can be imaged with the aid of the projection optical unit. Imaging radiation having a wavelength in the range of 193 nm or imaging radiation in the range of extreme ultraviolet (EUV), i.e. in the range of 5 nm to 15 nm, is principally used in this case. When radiation having a wavelength in the range of 193 nm is used, both refractive optical elements and reflective optical elements are used within the illumination optical unit and the projection optical unit. By contrast, when imaging radiation having a wavelength in the range of 5 nm to 15 nm is used, exclusively reflective optical elements (mirrors) are used.
In a microlithography projection exposure apparatus it is desirable for uniform irradiation conditions to be present throughout operation at the photosensitive layer. It is only in this way that, in general, microstructured components having uniform quality can be produced. Therefore, the irradiation conditions at the structure-bearing mask are desirably as uniform as possible. In this case, at the structure-bearing mask, both the intensity distribution of the incident radiation over the location on the mask and the angle-dependent intensity distribution at each location of the mask should satisfy predetermined conditions. However, various influences can alter the intensity distribution and the angle-dependent intensity distributions at the structure-bearing mask during operation. This can be e.g. heating of reflective optical elements, which thereupon change their position or form slightly. Furthermore, it is possible for the light source unit to experience alterations. By way of example, positional alterations of the source plasma that generates the radiation with respect to a collector come into consideration. Furthermore, by way of example, contaminations can also have the effect that the reflectivity of individual or all optical elements of the light source unit or of the illumination optical unit is altered. All these influences lead to an alteration of the radiation distributions at the structure-bearing mask. For this reason, it is desirable for the illumination optical unit to be embodied in such a way that it can be reconfigured in a simple manner in order to react to such system alterations described.