Effect of B4C diffusion barriers on the thermal stability of Sc/Si periodic multilayers

The optical properties of Sc/Si periodic multilayers are analyzed at three wavelengths in the X-ray range: 0.154, 0.712 and 12.7 nm. Fitting the reflectivity curves obtained at these three wavelengths enable us to constrain the parameters, thickness, density and roughness of the various layers, of the studied multilayers. Scattering curves were also measured at 12.7 nm on some samples to obtain an estimate of the correlation length of the roughness. Two sets of multilayers are used, with and without B4C diffusion barrier at the interfaces. To see the efficiency of the B4C layers the measures are performed after annealing up to 400 °C. A dramatic change of the structure of the Sc/Si multilayer is observed between 100 and 200 °C leading to a strong loss of reflectivity. For the Sc/B4C/Si/B4C multilayer the structure is stable up to 200 °C after which a progressive evolution of the stack occurs.