Interface characteristics of Mo/Si and B4C/Mo/Si multilayers using non-destructive X-ray techniques

A methodology combining non-destructive X-ray techniques is proposed to study the interfacial zones of periodic multilayers. The used X-ray techniques are X-ray emission spectroscopy induced by electrons and X-ray reflectivity in the hard and soft X-ray ranges. The first technique evidences the presence of compounds at the interfaces and gives an estimation of the thickness of the interfacial zone. These informations are used to constrain the fit of the X-ray reflectivity curves that enables to determine the thickness and roughness of the various layers of the stacks. The results are validated in the soft X-ray range where the reflectivity curves are very sensitive to the chemical state of the elements present in the stack. The methodology is applied to characterize Mo/Si (1-4 nm/2 nm) and B₄C/Mo/Si (1 nm/2 nm/2 nm) multilayers. It is shown that the two interfacial zones of the Mo/Si multilayers are composed of the silicides MoSi₂ and Mo₅Si₃. It is found that the interface thickness is about to be 0.4-0.8 nm depending on the samples. The molybdenum silicides are also evidenced at the interfaces of the B₄C/Mo/Si multilayers. However, their interface thickness is 0.2 nm thinner than that of the same stack without the B₄C layers, these layers being at the Mo-on-Si side or at the Si-on-Mo side. Thus, the B₄C layers do not stop but only reduce the interdiffusion between the Mo and Si layers.