Analysis of Mo/Si multilayers by means of RBS

The potential of Rutherford Backscattering Spectrometry (RBS) for analyzing a multilayer sample consisting of 50 ultrathin Mo/Si double layers on Si was investigated. The thickness of each double layer was about 7 nm, whereby the thickness of each Mo-layer is of the order of 2 nm. For this analysis, a beam of 250 keV d+ ions was directed at an angle of incidence α = 74° with respect to the surface normal, to resolve at least the first four Mo layers individually. From measurements at higher energies (400–650 keV) and perpendicular incidence, the absolute amount of Mo and Si in the multilayers was determined. Under these conditions the individual layers cannot be resolved, but from the slopes of the plateaus corresponding to Mo and Si, it can be quantitatively deduced that the mean thickness ratio 〈dMo/dSi〉 per double layer increases. We were able to determine a systematic change in the mean thickness of successive double layers by ∼20 pm. Information on the individual layer thicknesses can be deduced from a comparison to computer simulations.