Thermal stability of a Ti-Si-N diffusion barrier in contact with a Ti adhesion layer for Au metallization

Depth profiling by backscattering spectrometry, x-ray photoelectron spectroscopy and diffractometry, scanning electron microscopy, and sheet resistance measurements were used to study the thermal stability of ternary Ti27Si20N53 films as diffusion barriers between a gold overlayer and substrates of aluminum nitride, silicon oxide, and β-silicon carbide when thin titanium films are added on either side of the barrier to enhance adhesion. It is shown that titanium and gold interdiffuse upon 30 min annealing in vacuum at 400 °C and above, which raises the sheet resistance of the gold layer by factors that increase with the amount of titanium present. For the same annealing ambient and duration, nitrogen begins to diffuse at 600 °C from the Ti27Si20N53 layer into the titanium layer, releasing silicon. This silicon reacts eutectoidally with the gold, leading to breakup of the barrier.