On the interplay of internal/external stress and thermal stability of Mo/Si multilayers

Mo/Si multilayer (ML) systems were deposited on Si(100) substrate by DC magnetron sputtering. The MLs were annealed at temperatures up to 440 °C under high-vacuum conditions, both with and without the influence of external mechanical stress, and characterized before and after thermal treatment by means of X-ray reflectometry, wide-angle X-ray scattering and optical microscopy. Two ML configurations were compared, one composed of pure Mo and Si layers and another with additional B4C and C interlayers at the Mo/Si interfaces, respectively. The external mechanical stress applied caused bending of the substrate and adherent ML, with an accompanied internal stress of approximately 60 GPa. An important outcome of the investigation was that dedicated release bending of MLs can reduce/compensate the influences of the internal stressed states. Thermal stability could be increased for both ML systems during sample annealing. For ML samples with additional B4C and C layers at the Mo/Si interfaces, the influence of external stress was more significant compared to that for pure Mo/Si MLs. This indicates that the additional layers mainly act as diffusion barriers and additionally as stress-relaxing buffers.