Mirror, optical system and method for operating an optical system
AssigneeCarl Zeiss SMT GmbH
InventorsHartmut Enkisch, Toralf Gruner, Bernhard Gellrich
Life of this patent
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Abstract
A mirror, such as for a microlithographic projection exposure apparatus, comprises an optical effective surface. The mirror comprises a mirror substrate and a plurality of cavities in the mirror substrate. Fluid can be applied to each cavity. A deformation is transferable to the optical effective surface by varying the fluid pressure in the cavities. Related optical systems methods are provided.
Claims15
A mirror, comprising:
- an optical effective surface;
- a mirror substrate comprising a substrate material, the substrate material having a plurality of cavities therein, each cavity being separated from the other cavities by the substrate material;
- and
- a plurality of fluid inlets and a plurality of fluid outlets,
- wherein:
- each of the plurality of cavities comprises a fluid conduit;
- each of the plurality of cavities is configured to have a fluid applied thereto;
- a deformation is transferable to the optical effective surface by varying a fluid pressure in the plurality of cavities;
- each of the plurality of cavities has a corresponding fluid inlet and a corresponding fluid outlet;
- and
- each of the fluid inlets and the fluid outlets is present in an outer perimeter of the substrate.
A method for operating an optical system comprising a mirror, the mirror comprising an optical effective surface and a mirror substrate, the mirror substrate having a cooling channel arranged therein, the method comprising:
- flowing through the cooling channel to absorb heat generated in the mirror substrate due to electromagnetic radiation impinging on the optical effective surface, the cooling fluid having a variable cooling fluid temperature and a variable cooling fluid pressure;
- varying the cooling fluid temperature and the cooling fluid pressure depending on a power of a light source that generates the electromagnetic radiation so that first and second parasitic contributions to a deformation of the optical effective surface at least partly compensate one another,
- wherein the first parasitic contribution is caused by a temperature gradient generated by the cooling fluid in the cooling channel, and the second parasitic contribution is caused by a mechanical pressure transferred from the cooling fluid to the mirror substrate, and
- wherein the optical system is projection lens of a microlithographic projection exposure apparatus, and
- wherein varying the cooling fluid temperature and the cooling fluid pressure is at least partly based on a preliminary calibration, and ascertaining the preliminary calibration comprises generating a look up table comprising combinations of values of the power of the light source, the cooling fluid temperature and the cooling fluid pressure that are suitable for the at least partial compensation of the first and second parasitic contributions.
Dependencies are inferred from the claim text.