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 the 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/sec. 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 ML structure has a strong dependence on the substrate temperature and a lesser dependence on the deposition rate. ML grown at a substrate temperature of 300°K have Mo layers composed of small crystallites and exhibit significant short wavelength roughness. The lateral extent of the Mo crystallites increases and the interfacial roughness decreases with increasing substrate temperature up to 525-550°K. We attribute the larger Mo crystallites, improved texture and suppression of columnar growth observed at higher substrate temperatures to the increased surface mobility of the adatoms. The optimum conditions to obtain smooth layers by e-beam deposition were found to be a substrate temperature of ~525°K and a deposition rate of ~1 Å/sec. Thus to a great extent the smaller adatom energies of e-beam deposition can be compensated for by increasing the substrate temperature. Above TS~575°K interdiffusion is observed to significantly degrade the ML structure.