Limitation of Ti/TiN diffusion barrier layers in silicon technology

Abstract

The usefulness of Ti/TiN and TiSi 2/TiN bilayers as low resistive contacts and diffusion barriers between doped silicon and aluminium has been examined. The Ti layer was magnetron sputtered and the TiN layers were deposited by reactive magnetron sputtering in an argon/nitrogen mixture. After Ti/TiN deposition part of the samples were annealed in a vacuum furnace to form a TiSi 2/TiN structure. The films were characterized by Rutherford backscattering spectrometry (RBS), X-ray diffractometry (XRD) and resistivity measurements. The integrity of the final metallization systems, with aluminium as top level, for annealing temperatures in the range 400–600°C was evaluated by RBS and electrical measurements on fully processed test vehicles containing structures for contact resistivity measurements and shallow implanted gated diodes. A significant discrepancy has been observed between recorded RBS data and electrical measurements. No reaction was detected by RBS at temperatures below 525°C although a significant degradation of the electrical performance was readily observed at lower annealing temperatures, e.g. an increase in contact resistance and large reverse leakage currents. It is concluded that RBS, commonly used in the study of diffusion barrier properties, gives optimistic information on the upper limit of the metallurgical stability of the barrier layers, whereas other factors such as step coverage, compositional variation and mechanical stress are of predominant significance when actual device metallization is concerned.