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The study on improving the electrical integrity of Cu-CoSi2 contacted-junction diodes by using the reactively sputtered TaNx as a diffusion barrier is presented in this paper. In this study, the Cu (300 nm)-CoSi2 (50 nm)/n+p junction diodes were intact with respect to metallurgical reaction up to a 350°C thermal annealing while the electrical characteristics started to degrade after annealing at 300°C in N2 ambient for 30 min. With the addition of a 50-nm-thick TaNx diffusion barrier between Cu and CoSi2, the junction diodes were able to sustain annealing up to 600°C without losing the basic integrity of the device characteristics, and no metallurgical reaction could be observed even after a 750°C annealing in a furnace. In addition, the structure of TaNx layers deposited on CoSi2 at various nitrogen flow rates has been investigated. The TaNx film with small grain sizes deposited at nitrogen flow ratios exceeding 10% shows better barrier capability against Cu diffusion than the others.