Proposed for cleaning optical elements for the ultraviolet wavelength range having at least one metal-containing layer on a surface is a process that includes: —supplying activated hydrogen to the surface having the metal-containing layer; subsequently supplying inert gas having an H2O volume fraction of below 5 ppm, preferably below 1 ppm, particularly preferably below 0.2 ppm. To this end, an optical system (1) includes a housing (122), a supply line (161) of activated hydrogen, a supply line (162) of inert gas having an H.sub.2O volume fraction of below 5 ppm and a discharge line (163) for pumping gas out of the housing.

An assembly for a projection exposure apparatus for EUV projection lithography has an illumination optical unit for guiding illumination light to an illumination field, in which a lithography mask can be arranged. The illumination optical unit comprises a first facet mirror, which comprises a plurality of mirror arrays with respectively a plurality of individual mirrors. The individual mirrors provide individual mirror illumination channels for guiding illumination light partial beams to the illumination field. The mirror arrays of the first facet mirror are arranged in an array superstructure. Gaps extend along at least one main direction (HRα) between neighboring ones of the mirror arrays. Furthermore, the illumination optical unit comprises a second facet mirror, which comprises a plurality of facets, which respectively contribute to imaging a group of the individual mirrors of the field facet mirror into the illumination field via a group mirror illumination channel.

A diffusive ultraviolet illuminator is provided. The illuminator can include a reflective mirror and a set of ultraviolet radiation sources located within a proximity of the focus point of the reflective mirror. The ultraviolet radiation from the set of ultraviolet radiation sources is directed towards a reflective surface located adjacent to the illuminator. The reflective surface can diffusively reflect at least 30% the ultraviolet radiation and the diffusive ultraviolet radiation can be within at least 40% of Lambertian distribution. A set of optical elements can be located between the illuminator and the reflective surface in order to direct the ultraviolet radiation towards at least 50% of the reflective surface.

A mirror, in particular for a microlithographic projection exposure apparatus has an optically effective surface (11), a mirror substrate (12), a reflection layer stack (21) for reflecting electromagnetic radiation that is incident on the optical effective surface, and at least two piezoelectric layers (16a, 16b, 16c), which are arranged successively between the mirror substrate and the reflection layer stack in the stack direction of the reflection layer stack and to which an electric field can be applied to produce a locally variable deformation, wherein at least one intermediate layer (22a, 22b) made of crystalline material is arranged between the piezoelectric layers (16a, 16b, 16c), wherein the intermediate layer is designed to leave an electric field, which is present in the region of the piezoelectric layers (16a, 16b, 16c) that adjoin the intermediate layer (22a, 22b) in the stack direction of the reflection layer stack (21), substantially uninfluenced.

A projection lens of an EUV-lithographic projection exposure system with at least two reflective optical elements each comprising a body and a reflective surface for projecting an object field on a reticle onto an image field on a substrate if the projection lens is exposed with an exposure power of EUV light, wherein the bodies of at least two reflective optical elements comprise a material with a temperature dependent coefficient of thermal expansion which is zero at respective zero cross temperatures, and wherein the absolute value of the difference between the zero cross temperatures is more than 6K.

A method of manufacture of an extreme ultraviolet reflective element includes: providing a substrate; forming a multilayer stack on the substrate, the multilayer stack includes a plurality of reflective layer pairs having a first reflective layer and a second reflective layer for forming a Bragg reflector; and forming a capping layer on and over the multilayer stack, the capping layer formed from titanium oxide, ruthenium oxide, niobium oxide, ruthenium tungsten, ruthenium molybdenum, or ruthenium niobium, and the capping layer for protecting the multilayer stack by reducing oxidation and mechanical erosion.

Provided are a mask inspection apparatus and a mask inspection method that can prevent a reduction in a reflectance of a drop-in mirror, which is caused by carbon contaminants. A mask inspection apparatus according to the present invention includes a drop-in mirror including multi-layer film and a reflective surface. The drop-in mirror is configured to reflect illumination light incident on the reflective surface and illuminate the mask. An area of the reflective surface is configured to be greater than an area of an illuminated spot irradiated with the illumination light on the reflective surface. The drop-in mirror is configured to be movable. A position of the illuminated spot on the reflective surface is configured to be moved when the drop-in mirror is moved.

A method aleviating blistering, cracking and chipping in topmost layers of a multilayer system exposed to reactive hydrogen, when producing a reflective optical element (50) having a maximum reflectivity at an operating wavelength of 5 nm to 20 nm. A multilayer system (51) composed of 30-60 stacks (53) is applied to a substrate (52). Each stack has a layer (54) of thickness d.sub.MLs composed of a high refractive index material and a layer (55) of thickness d.sub.MLa composed of a low refractive index material. The thickness ratio is d.sub.MLa/(d.sub.MLa+d.sub.MLs)=Γ.sub.ML. Two to five further stacks (56) are applied to the multilayer system. at least one further stack having a layer (54) of thickness d.sub.s composed of a high refractive index material and a layer (55) of thickness d.sub.a composed of a low refractive index material, wherein the thickness ratio is d.sub.a/(d.sub.a+d.sub.s)=Γ and wherein Γ≠Γ.sub.ML.

An extreme ultraviolet (EUV) collector inspection apparatus and method capable of precisely inspecting a contamination state of an EUV collector and EUV reflectance in accordance with the contamination state are provided. The EUV collector inspection apparatus includes a light source arranged in front of an EUV collector to be inspected and configured to output light in a visible light (VIS) band from UV rays, an optical device configured to output narrowband light from the light, and a camera configured to perform imaging from an UV band to a VIS band. An image by wavelength of the EUV collector is obtained by using the optical device and the camera and a contamination state of the EUV collector is inspected.

An optical element (1) for reflecting EUV radiation (4) includes: a substrate (2); a coating (3) applied to the substrate (2), which coating reflects the EUV radiation (4); a top layer (5) protecting the reflective coating (3), which top layer is applied to the reflective coating (3); and an intermediate layer (6) having at least one reactive material (7) which, together with an activating gas (O2) penetrating through a gap (5a) in the top layer 95), forms at least one reaction product (8) sealing the gap (5a). A related EUV lithography system has at least one such reflective optical element (1), and a related method for sealing a gap (5a) in the top layer (5) of such an optical element (1) are also disclosed.