Non-destructive X-ray study of the interphases in Mo/Si and Mo/B₄C/Si/B₄C multilayers

We have tested and validated a non-destructive analysis method of multilayer structure, which combine X-ray emission spectroscopy and X-ray reflectometry at 0.154 and 1.33 nm. In this purpose, a series of Mo/Si and Mo/B₄C/Si/B₄C multilayers, deposited by magnetron sputtering, have been designed. The thickness of the Mo layer is 2 nm and that of the Si layers varies between 1 and 4 nm. The B₄C layer thickness introduced at the Mo/Si and Si/Mo interfaces is 0.3 or 1 nm. It is shown that the reflectivity of the multilayers lowers with the decreasing silicon thickness. This is correlated to the diffuse character on the nanometer scale of the Mo/Si and Si/Mo interfaces as shown by secondary ion mass spectrometry, and the formation of silicides (MoSi₂ and Mo₅Si₃) at these interfaces as evidenced by X-ray emission spectroscopy. As expected, the introduction of B₄C diffusion barriers considerably improves the reflectivity coefficient in the soft X-ray range, due to thinner and more abrupt interfaces.