Stressed states and self-organized structuring of W/C multilayers

Characterization and quantitative analysis of stressed states of a series of W/C multilayers (10-40 periods prepared by pulsed laser deposition on Si (111) substrates of different thickness) were carried out by means of X-ray reflectometry, wide angle diffractometry and a novel laser mapping device. As the W/C multilayers were dedicated to technical applications as X-ray optics and subjected to optimization of stacking parameters (thickness and number of layers) for a long term (mechanical) stability also further investigations will be discussed. Comparison of wafer distortion as evaluated by laser scanning and strain of the W layer as deduced from X-ray diffraction let us conclude that W layers are under compressive and C layers under tensile stress. The investigation of the thermally stimulated relaxation behavior of the multilayers provided a confirmation of these results. Additional information could be obtained by comparative relaxation experiments under external mechanical constraints. Furthermore, we report on a self-organized process of structuring of the multilayers under investigation, which might be of interest also from a technical point of view. The entire surface area (diameter 2") could be converted from the smooth (as-deposited) to a structured (relaxed) state stable at room temperature. Investigations using optical and atomic force microscopy showed that the topology of the surface consists of a mountain range where the valleys are on the level of the as-deposited non-debonded surface and that long wrinkled ridges of about the same height run along arbitrary directions.