Synchrotron x-ray diffraction and transmission electron microscopy studies of interfacial reaction paths and kinetics during annealing of fully-002-textured Al/TiN bilayers

Abstract

Dense fully-002-textured polycrystalline TiN layers, 110 nm thick with a N/Ti ratio of 1.02±0.03, were grown on SiO2 by ultrahigh vacuum magnetically unbalanced magnetron sputter deposition at Ts=450 °C in pure N2 utilizing high N2+/Ti flux ratios and low energy (EN2+=20 eV) ion irradiation of the growing film. Al overlayers, 160 nm thick and possessing a strong 002 texture inherited from the underlying TiN, were then deposited at Ts=100 °C without breaking vacuum. Synchrotron x-ray diffraction was used to follow interfacial reaction paths and kinetics during postdeposition annealing as a function of time (ta=200–1200 s) and temperature (Ta=500–580 °C). Changes in bilayer microstructure and microchemistry were investigated using transmission electron microscopy (TEM) and scanning TEM to obtain compositional maps of cross-sectional and plan-view specimens by energy dispersive x-ray analysis. The initial bilayer reaction step during annealing involves the formation of a continuous AlN interfacial layer which, due to local epitaxy with the TiN underlayer, grows with the metastable zinc-blende structure up to a thickness x≃3–5 nm, and with the wurtzite structure thereafter. Ti atoms released during AlN formation diffuse into the Al layer leading to supersaturation followed by the nucleation of dispersed regions of tetragonal Al3Ti with inherited 002 preferred orientation. The aluminide domains grow rapidly until they reach the free surface; thereafter growth is two dimensional as Al3Ti grains spread radially. The overall activation energy for Al3Ti formation and growth is 1.8±0.1 eV. In situ synchrotron x-ray diffraction analyses during thermal ramping show that the onset temperature for interfacial reactions was increased by more than 100 °C for fully dense completely 002-textured bilayers compared to 111-textured bilayers deposited by conventional reactive sputter deposition.