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 reflectivit y observed for Mo/Si multilayers produced by e-beam evaporation with t wo different additional methods: ion etching of the Si layer and optim ization of the substrate temperature during deposition. A 32-period mu ltilayer made with ion etching has a near normal incidence reflectivit y of 50%, while the one made at an optimum deposition temperature show s only 41%. The values for the interface roughness or layer thickness errors obtained from the analysis of small angle reflectivity measurem ents cannot explain this difference, but a different morphology of the Si and Mo layers could. Extended X-ray absorption fine structure (EXA FS) experiments have been carried out at the Si-K and the Mo-K edge to obtain information on the multilayer structure and chemical compositi on. The results of these EXAFS measurements on the two types of multil ayers 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 fracti on 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 th e near normal incidence reflectivity. Although both the Si and Mo laye rs produced with the three different deposition methods are amorphous, some structural differences have been found using the EXAFS analysis.