Abstract

One important type of structural imperfection that can affect the properties of multilayer (ML) structures is interfacial roughness. In x-ray optical ML, roughness both decreases the reflectivity and introduces a background halo that can degrade the resolution of imaging optics. A promising technique for characterizing the roughness of surfaces and interfaces in ML structures is x-ray scattering. The use of x-ray scattering as a structural probe has several important advantages. It is inherently a non-invasive technique, well-suited for dynamic measurements including in situ growth studies. The penetration of x-rays allows both surfaces and buried interfaces to be directly probed. Furthermore, due to the short wavelength of x-rays, x-ray scattering can provide structural information on spatial scales ranging down to atomic dimensions. There is increasing interest to use nonspecular x-ray scattering to study the roughness of interfaces in x-ray ML structures. The first experimental results indicate that the x-ray scattering can exhibit a rich variety of behavior associated with the structural correlations between interfaces^1-4. We present a simple theory that, within the limitations imposed by certain simplifying approximations, can provide a straightforward means of relating realistic interface structures to measurements of nonspecular scattering.

© 1992 Optical Society of America