REFLECTIVE OPTICAL ELEMENT, AND OPTICAL SYSTEM OF A MICROLITHOGRAPHIC PROJECTION EXPOSURE APPARATUS

摘要

A reflective optical element (50) having a substrate (52) and a multilayer system (51) that has a plurality of partial stacks (53), each with a first layer (54) of a first material and a second layer (55) of a second material. The first material and the second material differ from one another in refractive index at an operating wavelength of the optical element. Each of the partial stacks has a thickness (Di) and a layer thickness ratio (Γi), wherein the layer thickness ratio is the quotient of the thickness of the respective first layer and the partial stack thickness (Di). In a first section of the multilayer system, for at least one of the two variables of partial stack thickness (Di) and layer thickness ratio (Γi), the mean square deviation from the respective mean values therefor is at least 10% less than in a second section of the multilayer system.

主权项

1. A reflective optical element, comprising a substrate and a multilayer system arranged on the substrate,
wherein the multilayer system has a plurality of partial stacks each comprising a first layer of a first material having a first thickness and at least one second layer of a second material having a second thickness, wherein the first material and the second material differ from one another in respective values of the real part of the refractive index at an operating wavelength of the reflective optical element, wherein each of the partial stacks has a respective partial stack thickness (Di) and a respective layer thickness ratio (Γi), wherein the respective layer thickness ratio (Γi) is defined as a quotient of the thickness of the respective first layer and the respective partial stack thickness (Di); wherein in a first section of the multilayer system, for at least one of: the respective partial stack thickness (Di) and the respective layer thickness ratio (Γi), a mean square deviation rom respective mean values therefor is at least 10% less than in a second section of the multilayer system; wherein for the second section of the multilayer system, the respective partial stack thickness (Di) and the respective layer thickness ratio (Γi) are such that the reflective optical element has a reflectivity R, a wavelength dependence of which in a wavelength interval of Δλ=0.5 nm has a PV value of less than 0.25, wherein the PV value is defined as PV=(Rmax_rel—Rmin_rel)/Rmax_abs, wherein Rmax_rel denotes a maximum reflectivity value in the wavelength interval Δλ, Rmin_rel denotes a minimum reflectivity value in the wavelength interval Δλ, and Rmax_abs denotes an absolute maximum reflectivity value; and wherein the respective partial stack thickness (Di) and the respective layer thickness ratio (Γi) in the multilayer system are such that a wavelength dependence of the reflectivity R of the reflective optical element in a wavelength interval of Δλ=0.5 nm has at least two local reflectivity extrema which differ from one another in reflectivity by at least 0.1%, relative to a larger value of the two local reflectivity extrema.