Rapid Thermal Annealed Cr Barrier Against Cu Diffusion

Abstract

Rapid thermal annealing (RTA) of Cr films in an ambient was found to be effective in improving the barrier capability of Cr films in a Cu metallization system. The junction diodes whose Cr barrier was RTA treated at a temperature of 400°C were able to sustain a 30 min thermal annealing at temperatures up to 700°C without causing degradation to the electrical characteristics of the diodes. This is a 200°C improvement over the junction diodes using a Cr barrier without RTA treatment. Nitrogen degradation in the grain boundaries of the Cr layer was presumably responsible for the improvement in the barrier capability. However, the efficiency of improvement in the barrier capability was reduced for RTA treatment at temperatures above 600°C. With RTA treatment at 800°C, the material analysis indicated that was formed in addition to oxygen segregation at the Cr/Si interface. The thus formed resulted in a poor Cr/Si interface that caused larger leakage currents for the junction diodes under reverse bias. Moreover, outward diffusion of Si was found in the 800°C RTA‐treated Cr layer, which facilitated formation of within the Cr layer for the 800°C annealed Cu/Cr/Si samples. In summary, the improvement in the barrier capability of the Cr layers is closely related to the RTA temperature, and the optimum temperatures were determined to be between 400 and 600°C. © 1999 The Electrochemical Society. All rights reserved.