Copper grain boundary diffusion in electroless deposited cobalt based films and its influence on diffusion barrier integrity for copper metallization

Electroless deposited Co-based alloys have been proposed as diffusion barriers for ultralarge-scale integrated microelectronic devices. In this study, Cu grain boundary diffusion in electroless deposited Co0.9W0.02P0.08 and Co0.9P0.1 in the temperature range between 300 and 450 °C was quantitatively studied and compared to physical vapor deposited (PVD) pure Co films. The transport of Cu atoms through these films is predominately via the grain boundaries, namely type-C diffusion kinetics. The diffusivity values were extracted from Cu depth profiles measured by secondary ion mass spectrometry. Copper diffusion through the various Co films obeys an Arrhenius relationship. Copper diffusivity in the electroless films is 2–3 orders of magnitude smaller than in PVD Co films. The diffusivity of Cu through electroless deposited Co0.9W0.02P0.08 is 5–10 times smaller than in electroless deposited Co0.9P0.1. The reduced diffusivity in the electroless films is a result of the significantly lower value of the pre-exponential factor. A qualitative explanation for the reduction of this factor is suggested based on a former study, which demonstrated that the Cu concentration in grain boundaries of electroless deposited Co-based films is considerably smaller than in pure Co. The obtained diffusivity values are compared with a functional electrical evaluation of barrier integrity in metal–oxide–semiconductor capacitors. We show that Cu diffusivity values combined with a failure criterion are in agreement with the electrical evaluation results and are of practical relevance in predicting barrier integrity.