Structure and stressed state of molybdenum layers in Mo/Si multilayers

Structure and stressed state of molybdenum layers in Mo/Si multilayer periodical compositions prepared by direct current magnetron sputtering have been investigated by methods of X-ray tensometry in grazing-incidence asymmetrical geometry, cross-sectional transmission electron microscopy and small-angle X-ray reflectometry. The level of symmetrical biaxial stresses depends non-monotonously on the thickness of Mo layers. Value and sign of stresses are defined by the following processes: bombardment of the growing surface of metallic layers by particles with enhanced energy, recrystallization of Mo grains and the formation of silicon-substitutional solid solution in molybdenum. The bombardment is accompanied by a formation of self-interstitial Mo atoms that sink at internal dislocation defects, an increase in quantity of lattice points in the film plane and a generation of biaxial compressive stresses. The recrystallization reduces the density of grain boundaries, at the same time decreases the average specific volume of condensed atoms and generates tensile stresses in Mo layers. Compared to those for pure bulk molybdenum, notably lower average lattice spacing was measured in unstressed sections for Mo layer thicknesses less than 20 nm. This indicates the formation of a solid solution of Si in molybdenum presumably in vicinity of Mo-on-Si interface.