Thermally induced interface chemistry in Mo/B4C/Si/B4C multilayered films

B4C diffusion barrier layers are often introduced into Mo/Si multilayered films for enhancement of thermal stability. We observe that such multilayered films exhibit both period expansion and period compaction upon annealing at temperatures below 300 degrees C, depending on the annealing temperature and time. Using in-situ grazing incidence x-ray reflection measurements during sequential annealing, we resolved picometer periodicity changes in Mo/B4C/Si/B4C, Si/B4C, and Mo/B4C multilayer films, and show that the two opposite period-change effects are a result of interaction of Si with B4C layers, leading to expansion, and MoxSiy formation, leading to compaction. The study of Si/B and Si/C multilayer sub-systems suggests that the cause of expansion is the formation of relatively low density SixBy compounds at the Si-B4C interface. Although the Mo-B4C interface seems to be stable based on reflectometry data, other techniques such as depth profiling x-ray photoelectron spectroscopy and wide angle x-ray diffraction measurements show that Mo and B4C actually intermix. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4751029]