Image Quality Prediction Of Normal-Incidence X-Ray/EUV Muitilayers In The Presence Of Substrate And Interface Fabrication Errors

Abstract

It is well known that the presence of optical fabrication errors on the optical surfaces of an imaging system will degrade image quality. Theoretical treatments of these effects covering any wavelength domain can be found in the literature, and include the conventional grazing incidence X-ray/EUV optical systems. However, very little work has been done toward extending image quality analysis into the new and promising field of normal-incidence X-ray/EUV multilayer optical imaging systems. In this paper, a detailed physical optics (interference and diffraction) treatment of surface scatter phenomena due to optical fabrication errors in X-ray/EUV multilayers over the entire relevant range of spatial frequencies will be described. The effects on the scattered radiation field of a variety of assumptions concerning the statistical correlation of interface roughness will be explored. It is well known that, at soft X-ray wavelengths, substrate figure errors blur the image. In this paper, it will be shown that uncorrelated interface microroughness reduces the reflectance of multilayers in addition to causing wide angle scatter, and that small-angle scatter from mid spatial frequency optical fabrication errors limits the achievable image quality (fractional encircled energy.)