On the influence of the stacking sequence in the nucleation of Cu3Si: Experiment and the testing of nucleation models

The nucleation of the Cu3Si phase was studied on sputter-deposited Cu/Si/Cu trilayered specimens both in curved and planar geometry. Two experimental methods, atom probe tomography and secondary neutral mass spectrometry, independently confirmed that the Cu on Si interface is significantly broader than the Si on Cu (5.3 vs. 2.4 nm from the atom probe measurements). It is demonstrated that the enhanced mixing on the top interface leads to a reduced nucleation barrier for the silicide phase. The presence of a nucleation barrier for a sharp interface, but no barrier for a broad interface, is reproduced using the polymorphic mode of nucleation. Classical nucleation theory or the transverse nucleation mode failed to explain this behavior.