Interaction between Electromigration and Mechanical Stresses

In many micro - and nano-devices, mechanical stresses (either directly applied or generated due to the thermal cycling) and electric current induced electromigration interact with each other. The effects of these interactions on interfacial sliding at hetero-interfaces, such as metal-oxide, metal-semiconductor etc., were experimentally as well as analytically studied. Idealized systems, such as double shear-lap samples and standalone Cu filled through silicon vias (TSVs) were employed.

    

Electromigration induced sliding at Pb/Si interface (Arrows indicate discontinuity in the fiduciary lines, indicating occurrence of interface sliding)

It was shown that even electric current (or electromigration) can cause interfacial sliding. Also, It was observed that the mass flow flux due to both mechanical stresses and the electromigration can be linearly superimposed, implying that if the mass fluxes due to electromigration and the shear stress are the in the same direction, the net interfacial sliding rate will be enhanced, whereas if they are in opposite directions, the net sliding will be reduced.

    

(a) Displacement – time plots showing interfacial sliding at Si/Pb interface for different conditions. (b) Effect of thermal cycling and EM on a Cu filled TSV sample (b, a) as-fabricated, (b, b) after 3 cycles between 25^oC and 425^oC at ~0.02^oC/s, and (b, c) after 6 cycles between 25^oC and 425^oC at ~0.02^oC/s with last 3 cycles with electron flowing in upward direction (as shown by arrow).