Electrical and Metallurgical Characterization of Niobium as a Diffusion Barrier Between Aluminum and Silicon for Integrated Circuit Devices

Abstract

Electrical, metallurgical, electromigration, and functional characterizations of an (Al‐0.5% Cu)/Nb interconnect metallization for use in 1.2 μm SRAM integrated circuit devices have been performed. The results indicate that niobium is an excellent diffusion barrier to aluminum and silicon. It is shown that the presence of niobium has significantly improved the electromigration strength (at ) and the thermal and electrical stability of metal to silicon and metal to metal contacts. The barrier characteristics of the niobium were studied electrically (via junction leakage current and contact resistance measurements) and analytically (via TEM examination of aluminum‐niobium‐silicon interfaces). TEM and electron diffraction analyses show the formation of the phase. It is found that the phase has a much slower rate of growth than in the temperature range studied. Results do not indicate any significant increase in junction leakage current of contact resistance after 540 min of heat‐treatment at 425°C. The results further indicate that the niobium does not have any negative effects on the performance of 1.2 μm CMOS SRAM devices. It appears, however, that the presence of niobium has an effect on the speed distribution of the devices.