EXAFS measurements on the structure of Mo/Si multilayers produced using ion bombardment and increased deposition temperature

This study focuses on explaining differences in soft X-ray reflectivity observed for Mo/Si multilayers produced by e-beam evaporation with two different additional methods: ion etching of the Si layer and optimization of the substrate temperature during deposition. A 32-period multilayer made with ion etching has a near normal incidence reflectivity of 50%, while the one made at an optimum deposition temperature shows only 41%. The values for the interface roughness or layer thickness errors obtained from the analysis of small angle reflectivity measurements cannot explain this difference, but a different morphology of the Si and Mo layers could. Extended X-ray absorption fine structure (EXAFS) experiments have been carried out at the Si-K and the Mo-K edge to obtain information on the multilayer structure and chemical composition. The results of these EXAFS measurements on the two types of multilayers indicate that both the Si and the Mo have an amorphous structure and that no Mo-Si compounds are formed at the interfaces. However, it is found that multilayers made with ion etching have a reduced fraction of oxygen (less than or equal to 0.5%) in the Si layer compared to layers produced without etching (4.7%). The latter fraction of oxygen, originating from the background gas in the deposition system, results in higher absorption of soft X-ray radiation and therefore affects the near normal incidence reflectivity. Although both the Si and Mo layers produced with the three different deposition methods are amorphous, some structural differences have been found using the EXAFS analysis.