Microlithography is used for producing microstructured components such as, for example, integrated circuits or LCDs. The microlithography process is carried out in a so-called projection exposure apparatus having an illumination device and a projection objective. The image of a mask (=reticle) illuminated via the illumination device is projected via the projection objective onto a substrate (e.g. a silicon wafer, that is coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection objective, in order to transfer the mask structure to the light-sensitive coating of the substrate.
During the operation of optical systems such as, for instance, the projection exposure apparatus described above, particularly in the case of globally or locally high thermal loads, absorption of high thermal loads can increase the temperature of temperature-sensitive components (such as e.g. mirrors, lenses or mount elements) or other (sub)systems, which can impair the imaging properties of the optical system.
One example of this is the impairment of temperature-sensitive elements present in the optical system, such as e.g. position sensors, or of temperature-sensitive subsystems in the imaging beam path of the projection exposure apparatus described above.
Thus, for instance, in projection objectives designed for the EUV range (that is to say at wavelengths of less than 15 nm, e.g. approximately 13.5 nm), wherein, owing to a general lack of availability of suitable light-transmissive refractive materials, mirrors are used as optical components for the imaging process, it is known to provide, in addition to a carrying structure that carries mirrors and mirror actuators, a measuring structure, which is typically arranged outside the carrying structure and which is intended to ensure a thermally as well as mechanically stable fixing of position sensors or other measuring systems for determining the mirror positions. Undesired heating of the measuring structure is serious due to the relatively small (e.g., approximately 1 mm to 100 mm) distance between the position sensors and the mirrors that heat up during the operation of the projection exposure apparatus.
US 2005/0018154 A1 discloses a microlithographic projection exposure apparatus which includes at least one heat shield intended to absorb the heat emitted by the mirrors and/or the carrying structure thereof such that the heat is dissipated by a heat transfer circuit that is in mechanical contact with the heat shield.