Stress, microstructure, and stability of Mo/Si, W/Si, and Mo/C multilayer films

The stresses in periodic Mo/Si, W/Si, and Mo/C multilayer films were determ ined from wafer-curvature measurements. The layer thickness of each materia l was varied systematically, and parametric stress contours were generated, showing contours of constant stress in the two-dimensional layer thickness parameter space. These results illustrate that the net stress in a periodi c multilayer is not an intrinsic property of the film (for specific deposit ion conditions) but, rather, depends strongly on the individual layer thick nesses. X-ray diffraction measurements show (a) how the lattice spacing in the W and Mo crystallites varies with layer thickness, and (b) in the case of the W/Si films, how the phase composition of the polycrystalline W layer s vary with W layer thickness. In the case of the W/Si and Mo/Si multilayer s, irreversible stress changes were observed after the samples were stored in air at room temperature for a period of several months. Stress-temperatu re measurements made on the as-deposited W/Si and Mo/Si samples also reveal irreversible stress changes (both positive and negative, depending on the layer thicknesses) after thermal cycling to 300 degrees C; x-ray diffractio n measurements were used to identify any associated changes in the W and Mo microstructure. We describe mechanisms that can explain the observed stres s behavior, and also discuss the significance of these results, particularl y with regard to the use of these films for high-performance multilayer x-r ay optics. (C) 2000 American Vacuum Society. [S0734-2101(00)01703-6].