Effect of sputtering bias voltage on the structure and properties of Zr-Ge-N diffusion barrier films

The diffusion barrier properties of Zr-Ge-N thin films are reported, focusing on issues relevant to their application as diffusion barriers for Cu interconnections in Si devices. The Zr-Ge-N films were prepared by reactive r.f. magnetron sputtering with different bias voltage. The analyses of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) indicate that the final structure and composition of Zr-Ge-N film are very sensitive to the sputtering bias voltage. The N content in Zr-Ge-N film changes very little, and only decreases from 51.6 to 48.4 at.% when sputtering bias voltage increases from DV to 150 V. However, the correlation between bias voltage change and the atomic ratio of Zr and Ge is very remarkable. These results clearly show that the Ge atoms are preferentially resputtered with increasing substrate bias voltage. The high sputtering bias appears to be in favor of the growth of ZrN grains. The copper diffusion barrier properties of Zr-Ge-N on Si have been examined and compared to ZrN. XRD and four-point probe method (FPP) both showed the onset of formation of copper suicide crystallites for ZrN barriers annealed at 650 degrees C. In contrast, TEM on a Zr-Ge-N barriers annealed even at high annealing temperatures of 800 degrees C revealed sharp interfaces and the energy dispersive X-ray spectroscopy (EDS) line scan showed no Cu diffusion through the barrier into Si substrate. The results suggest that Zr-Ge-N is superior to ZrN as a copper diffusion barrier on Si. (C) 2012 Elsevier B.V. All rights reserved.