Reflective Optical Element for EUV Lithography and Method of Manufacturing a Reflective Optical Element

A method of manufacturing a reflective optical element of an optical system for extreme ultraviolet (EUV) lithography, wherein the reflective optical element comprises a multilayer system configured to reflect an incident electromagnetic wave having an operating wavelength in the EUV range, and a capping layer made from a capping layer material, wherein the method comprises:

• determining, for the capping layer material, a dependency according to which the reflectivity of the reflective optical element varies with the thickness of the capping layer;
• determining a plateau-region in the dependency in which the reflectivity of the reflective optical element is substantially constant;
• and
• creating a thickness profile in the capping layer such that both the maximum thickness and the minimum thickness in the thickness profile are located in the plateau-region.

Reflective optical element for extreme ultraviolet (EUV) lithography, comprising:

• a multilayer system configured to reflect an incident electromagnetic wave having an operating wavelength in the EUV range, the reflected wave having a phase φ;
• and
• a capping layer made from a capping layer material and having a thickness d;
• wherein the capping layer has a variation in the capping layer thickness d such that the variation in the phase φ relative to the variation in the capping layer thickness is greater than 25%.