Characteristics and thermal behavior of W/Si multilayers with well-defined interfaces

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Abstract
Multilayers consisting of alternating thin bilayers of W and Si (period: 1.5<d<9 nm) have been analyzed by x-ray scattering (absolute reflectivity, period, mosaicity, interface roughness, crystallinity, and density) and by cross-sectional transmission electron microscopy observations (periodicity, crystalline phase, and damaged area). Our purpose was to determine the thermal properties of the multilayers with respect to the period value under pulsed laser heating (with a nanosecond Nd-YAG laser at different energy densities up to 1 J/cm2 and at a wavelength λ=0.53 μm) and by furnace annealing (250<T<1000 °C under 10−7 Torr pressure). We propose that two distinct diffusion mechanisms are involved in annealings: first, interdiffusion in the amorphous phase and then crystallization into WSi2, the latter related to a period contraction of about 5–10%. The diffusion coefficients and the crystallization temperature depend drastically on the period value. Simulations of small-angle x-ray scattering curves take well into account this thermal evolution. Extinctions and modulations of the intensities of the Bragg peaks are well fitted by thickness and roughness variations.