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EP-3887878-B1 - MIRROR FOR AN ILLUMINATION OPTICAL UNIT OF A PROJECTION EXPOSURE APPARATUS COMPRISING A SPECTRAL FILTER IN THE FORM OF A GRATING STRUCTURE AND METHOD FOR PRODUCING A SPECTRAL FILTER IN THE FORM OF A GRATING STRUCTURE ON A MIRROR

EP3887878B1EP 3887878 B1EP3887878 B1EP 3887878B1EP-3887878-B1

Inventors

  • JALICS, CHRISTOF
  • SCHUSTER, Fabian
  • KIEREY, HOLGER
  • SANDNER, ANDREAS
  • MEISCH, Tobias

Dates

Publication Date
20260506
Application Date
20191125

Claims (6)

  1. Method of producing a spectral filter in the form of a grating structure (30) on a mirror for an illumination optical unit (4) of a projection exposure apparatus (1) comprising the following steps: 1.1. providing a substrate (37) for a mirror body, 1.2. applying a structuring layer (40) on the substrate (37), 1.3. structuring the structuring layer (40), 1.4. structuring the substrate (37), 1.5. wherein the following method is used for structuring the substrate (37): an inert dry etching method, wherein structuring layer (40) and substrate (37) have different etching rates, 1.6. applying a closed protective layer (38) on the substrate (37).
  2. Method according to Claim 1, characterized in that one or more of the following method features or combinations thereof is/are used for structuring the substrate (37): 2.1. an inert dry etching method with an etching angle in the range of 0° to 60°, 2.2. an inert dry etching method, wherein the structuring layer (40) was provided with a sidewall steepness (b) in the range of 0° to 60° during the structuring,
  3. Method according to either of Claims 1 and 2, characterized in that a combination of an inert etching method and a reactive etching method is used for structuring the substrate (37).
  4. Method according to any of Claims 1 to 3, characterized in that an etching method with a predefined longitudinal etching angle in the range of 0° to 60° is used for structuring the substrate (37).
  5. Method according to any of Claims 1 to 4, characterized in that an etching method with a predefined transverse etching angle in the range of 0° to 60° is used for structuring the substrate (37).
  6. Method according to any of Claims 1 to 5, characterized in that at least one of the following parameters is controlled in a targeted manner for setting the sidewall steepness of the structuring layer (40): focusing of a laser beam for structuring the structuring layer (40), intensity of the exposure in a lithography process for structuring the structuring layer (40), duration of the development of a lithography process for structuring the structuring layer (40), hard bake and/or reflow, temperature of the structuring layer (40) after a structuring thereof.

Description

The present patent application claims the priority of the German patent application DE 10 2018 220 629 5. The invention relates to a mirror for an illumination optical unit of a projection exposure apparatus. The invention furthermore relates to a method for producing a spectral filter in the form of a grating structure on a mirror for an illumination optical unit. Moreover, the invention relates to an illumination optical unit and an illumination system for a projection exposure apparatus, and a projection exposure apparatus. Finally, the invention relates to a method for producing a microstructured or nanostructured component and to a component produced according to the method. WO 2017/036 717 A2 discloses a beam splitting apparatus. US 6,524,756 B1 discloses gray scale all-glass photo masks. Jaeyoun Kim et al. discloses the Design and fabrication of low-loss hydrogenated amorphous silicon overlay DBR for glass waveguide devices (IEEE. Journal of Selected Topics in Quantum Electronics, volume 8, No. 6, November 1, 2002). Lockhart R. et al. discloses high efficiency MEMS tunable gratings for external cavity lasers and micro spectrometers (Optical MEMS and nano-optics, 2008, IEEE/LEOs International Conference on IEEE, August 11, 2008). TW 201106032 A discloses ultra-high multiplex analytical systems and methods. Knop K. et al. discloses microfabrication and evaluation of diffractive optical filters prepared by reactive sputter etching (Journal of applied physics, American Institute of Physics, volume 50, No. 6, June 1, 1979). Svakhin A. S. et al. discloses the investigation of the formation of diffraction gratings on the surface of optical wave guides (Soviet Journal of Quantum Electronics, American Institute of Physics, volume 9, No. 5, May 1, 1979). The use of a grating structure as spectral filter is known for example from DE 10 2012 010 093 A1. There is a need to improve such a grating structure, in particular a mirror for an illumination optical unit comprising such a grating structure. This object is achieved by means of the features of Claim 1. The heart of the invention consists in forming the grating structure with a defined edge steepness. The edge steepness, in particular the maximum edge steepness, of the grating structure, is in particular in the range of 15° to 60°, in particular in the range of 30° to 45°. In this case, the edge steepness is measured relative to a surface of the mirror, in particular to a tangent to the respective local surface of the mirror in the region between two grating ridges. The edges of the grating structure are formed in particular without undercuts. The grating structure has no etched undercut, in particular. According to the invention, it has been recognized that the grating structure can be better protected as a result. It is possible, in particular, in this way to form a mirror comprising a spectral filter in the form of a grating structure having a better durability. For performance reasons, grating structures on a mirror for an illumination optical unit of a projection exposure apparatus are usually formed as steeply as possible, in particular as far as possible perpendicularly, with respect to the mirror surface. Surprisingly, it has been found that for the issue of the durability of the grating structures, in particular with regard to the hydrogen stability thereof, it can be advantageous to form the grating structures with a reduced edge steepness. In accordance with a further aspect of the invention, the grating structure is covered by a closed protective layer. The grating structure is in particular completely covered by a closed protective layer. Penetration of harmful hydrogen into the grating structure can be prevented by means of the protective layer. It is thereby possible to prevent stresses in the material that may result in undesired layer detachments. In the case of a mirror substrate composed of a material which is attacked in a harmful hydrogen atmosphere, this material can be protected. Such materials can be for example tin, silicon or the compounds thereof. In accordance with a further aspect of the invention, the protective layer is composed of one or more plies comprising a constituent of molybdenum and/or silicon. The protective layer can also comprise constituents of copper, silver, platinum, gold, rhodium, a metal, an oxide or a combination of such substances or consist of corresponding substances. The protective layer is composed, in particular, of a hydrogen-stable material. In particular, a plurality of molybdenum-silicon double plies can serve as the protective layer. In particular, a layer stack composed of a plurality of such plies, in particular a plurality of such molybdenum-silicon double plies, can serve as the protective layer. The number of double plies can be in the range of 10 to 100, in particular in the range of 30 to 80, in particular in the range of 40 to 60. Molybdenum-silicon double plies are suitable in particular fo