Study of copper diffusion into Ta and TaN barrier materials for MOS devices

Fick's law of diffusion was used to model the diffusion of copper into Ta and TaN barrier materials. From the matching with the experimental results, the Cu diffusion coefficients can be extracted as 2.870×10−14exp(−0.1457 eV/kT) cm2/s in Ta and 2.4×10−14exp(−0.1395 eV/kT) cm2/s in TaN. Using the calculated results, a 25-nm Ta layer was sufficient to block Cu from diffusing through it by annealing at 600 °C for half an hour and a 24-nm TaN layer was able to block the diffusion at 500 °C. Simple metal-oxide-semiconductor capacitors with dimension of 120×120 μm were fabricated with Ta and TaN barrier thickness of 25 nm and the results confirmed the thermal stability calculated according to the conditions mentioned above.