Abstract: A method for removing at least one reflective layer (4a, 4b) from an optical element (1) for EUV lithography, wherein the optical element (1) has a substrate (2) and an interlayer (6) between the substrate (2) and the at least one reflective layer (4a, 4b). The method includes etching away the at least one reflective layer (4a, 4b) as far as the interlayer (6) with an etching gas (7), wherein the material of the interlayer (6) does not react with the etching gas (7), and wherein, after the etching away, the interlayer (6) has a surface roughness of less than 0.5 nm rms, preferably of less than 0.2 nm rms, and more preferably of less than 0.1 nm rms. Also, an optical element (1) for reflecting radiation in the EUV wavelength range includes a substrate (2), at least one reflective layer (4a, 4b), and an interlayer (6) arranged between the substrate (2) and the at least one reflective layer (4a, 4b).

Abstract: A method for removing at least one reflective layer (4a, 4b) from an optical element (1) for EUV lithography, wherein the optical element (1) has a substrate (2) and an interlayer (6) between the substrate (2) and the at least one reflective layer (4a, 4b). The method includes etching away the at least one reflective layer (4a, 4b) as far as the interlayer (6) with an etching gas (7), wherein the material of the interlayer (6) does not react with the etching gas (7), and wherein, after the etching away, the interlayer (6) has a surface roughness of less than 0.5 nm rms, preferably of less than 0.2 nm rms, and more preferably of less than 0.1 nm rms. Also, an optical element (1) for reflecting radiation in the EUV wavelength range includes a substrate (2), at least one reflective layer (4a, 4b), and an interlayer (6) arranged between the substrate (2) and the at least one reflective layer (4a, 4b).

Abstract: A method of manufacturing an optical element having an optical surface of a non-rotationally symmetric shape is described. Measuring light is generated using an interferometer optics, wherein the interferometer optics has at least one diffractive component having a grating. The optical surface is positioned at a first position relative to the diffractive component, wherein first measuring light diffracted at the diffractive component is incident on the optical surface at plural locations thereof, and at least one first interference pattern generated from first measuring light reflected from the optical surface is detected. The optical surface is positioned at a second position relative to the at least one diffractive component, wherein second measuring light diffracted at the diffractive component is incident on the optical surface at plural locations thereof, and at least one second interference pattern generated from second measuring light reflected from the optical surface is detected.

Abstract: A method of manufacturing an optical element having an optical surface of a non-rotationally symmetric shape is described. Measuring light is generated using an interferometer optics, wherein the interferometer optics has at least one diffractive component having a grating. The optical surface is positioned at a first position relative to the diffractive component, wherein first measuring light diffracted at the diffractive component is incident on the optical surface at plural locations thereof, and at least one first interference pattern generated from first measuring light reflected from the optical surface is detected. The optical surface is positioned at a second position relative to the at least one diffractive component, wherein second measuring light diffracted at the diffractive component is incident on the optical surface at plural locations thereof, and at least one second interference pattern generated from second measuring light reflected from the optical surface is detected.

Abstract: A method of qualifying a diffraction grating comprises performing plural measurements by illuminating a region of the grating with a beam of measuring light and detecting an intensity of measuring light diffracted by the grating into a 0th diffraction order. A wavelength of the measuring light or a polarization of the measuring light or an angle of incidence of the measuring light onto the diffraction grating is varied between subsequent measurements. A shape parameter of diffracting elements forming the grating comprises a pitch, height or width of structural features of the diffracting elements. The shape parameter is advantageously used in analyzing interferometric measurements performed on optical surfaces during manufacture of optical elements of a high accuracy.