Thermally induced decomposition of B4C barrier layers in Mo/Si multilayer structures

We investigate the influence of the Mo crystalline state (quasi-amorphous or crystalline) on the thermal stability of Mo/Si thin film multilayers with B4C diffusion barrier layers at either of the two interfaces. We find that multilayers containing amorphous Mo layers are more stable than those containing crystalline layers. This observation is in contrast to the case where Si3N4 diffusion barriers are used. Using X-ray diffraction, X-ray reflection and X-ray photo-electron spectroscopy we show that this difference can be attributed to the dissociation of B4C followed by diffusion of B in Mo. Due to the favorable thermodynamic properties of MoxBy compounds, the boron atoms react with the Mo layer, forming a MoxBy layer that effectively improves the multilayer thermal resistance.