TiN diffusion barrier failure by the formation of Cu3Si investigated by electron microscopy and atom probe tomography

Abstract

The authors investigate the interdiffusion damage of Cu/TiN stacks deposited on Si(001) substrates by low-temperature unbalanced direct current magnetron sputtering. Pristine and diffusion-annealed samples are examined by x-ray diffraction, four-point-probe resistivity measurements, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and atom probe tomography. Two relevant diffusion processes are identified. The local diffusion of Cu through defects and grain boundaries in the TiN layer leads to the formation of the η″-Cu3Si phase at the barrier/substrate interface. Three-dimensional reconstructions obtained by atom probe tomography additionally reveal the outward diffusion of Si atoms from the substrate through the TiN bulk toward the Cu top layer, eventually also resulting in the formation of a discontinuous Cu3Si surface layer.