Interfacial reactions in epitaxial Al/Ti1−<i>x</i>Al<i>x</i>N (0≤<i>x</i>≤0.2) model diffusion-barrier structures

Abstract

Transmission electron microscopy (TEM), cross-sectional TEM, scanning TEM with energy dispersive x-ray analysis, and Auger electron spectroscopy were used to investigate the nature of rate-controlling interfacial reactions in epitaxial Al/Ti1−xAlxN thin-film couples. TiN and NaCl-structure Ti1−xAlxN layers, 120 nm thick, with compositions x=0.1 and 0.2 were grown on MgO(001) substrates by ultrahigh vacuum reactive magnetron cosputter deposition in N2 discharges. Epitaxial Al films, 200-nm-thick, were then grown in Ar on top of the nitride layers during the same vacuum cycle. The reaction paths for Al/TiN and Al/(Ti,Al)N interactions during anneals at Ta=600 °C for ta up to 150 min was similar, but the extent of reaction was dramatically decreased by the substitution of (Ti,Al)N barrier layers for TiN. The primary mobile species during annealing was Ti which penetrated into the Al layers and reacted to form the ordered tetragonal intermetallic phase Al3Ti while Al segregation resulted in the formation of a narrow metastable zincblende structure AlN layer at the Al/nitride interface. The room-temperature resistivity of 1-μm-thick nitride layers varied from 15 μΩ cm for TiN to 60 μΩ cm for Ti0.8Al0.2N.