Optimization of growth conditions of vapor deposited Mo/Si multilayers

Abstract

The dependence of the layer structure and interfaces of e-beam deposited Mo/Si multilayers (ML) on growth conditions has been studied. The substrate temperature was varied over a range of 300–600 K at deposition rates of 1 and 3 Å/s. The structure of the ML was determined using small-angle x-ray scattering, large-angle x-ray scattering, and cross-sectional high-resolution electron microscopy. The variation of the normal incidence reflectivity was measured as a function of soft x-ray wavelength using synchrotron radiation. We found that the lateral extent of the Mo crystallites and the thickness and roughness of interlayers are a sensitive function of the substrate temperature. The morphology shows a lesser dependence on the deposition rate. The formation of the Mo-on-Si interlayer is partially thermally activated with an activation energy of ∼0.2 eV. We propose that the rate limiting mechanism is surface diffusion during growth. At the optimal deposition conditions, of a substrate temperature of ∼525 K and a deposition rate of 1 Å/s, the ML structure was found to have a smoothness and maximum normal incidence reflectivity comparable to the best sputtered Mo/Si films.