QUANTITATIVE X-RAY-ANALYSIS OF INTERDIFFUSING TA/SI MULTILAYER STRUCTURES

Multilayers of amorphous tantalum and silicon form a synthetic one-dimensional lattice which can be observed by a sequence of intense low angle X-ray diffraction peaks. Annealing a Ta/Si multilayer structure of 20 layer pairs, each layer pair consisting of nominally 4 nm thick tantalum and 7 nm thick silicon layers, leads to rapid diffusion of silicon into the tantalum layers forming a homogeneous TaSi(x) solution. The thickness of the pure silicon layers decreases linearly with increasing annealing temperature. The width DELTA-t of the transition layers between the silicon and the TaSi(x) layers is analysed by comparing the measured absolute reflectivity of the multilayer structure with calculated data up to the 10th diffraction order. The computational approach is based on the Fresnel equations and assumes a linear composition profile at the interfaces leading to a trapezoidal lattice structure. An upper limit value of 0.7 nm for the interface width is estimated. The interdiffusion is complete at T = 540-degrees-C, indicated by the breakdown of the multilayer structure.