Ion-Bombardment of Thin-Layers - the Effect on the Interface Roughness and Its X-Ray Reflectivity

In this paper we report on experiments which indicate the necessity of the use of ion-beam bombardment for e-beam deposited multilayer x-ray coatings. Measurements are described in which ion bombardment (200-300 eV Ar+) is used to ion etch metal layers after initial deposition and during deposition (ion-assisted deposition). In both cases a considerable smoothing of the metal surface occurs, resulting in enhanced x-ray reflectivities of metal-carbon multilayer coatings. As examples we show reflection measurements of Ni-C and W-C with nine and ten layer pairs, respectively, and d almost-equal-to 2.8 nm. Finally we discuss a special case: ion etching of Mo layers in Mo-Si coatings. On the one hand, we demonstrate the occurrence of smoothing of Mo, thereby enhancing the reflectivity of the layer and, on the other hand, the occurrence of ion bombardment induced intermixing at the Mo-Si interface, responsible for a decrease of the reflectivity.