High-performance devices, such as microprocessors and memory chips, are typically composed of structures with strict dimensional tolerances and geometries and are made up of various materials, all in close proximity in a three-dimensional system. Material interactions lead to reliability issues such as fracture, delamination, fatigue cracking, and void formation. To measure material response in such complicated systems, we have developed electrical methods to determine the properties of these materials without the need for special specimens. Our fatigue test applies controlled joule heating via a 4-point probe system under conditions where electromigration does not take place. Cyclic thermal strain is induced, allowing for determinations of fatigue lifetime and estimates of strength. Whereas tests that directly measure force-displacement response are restricted to certain specimen geometries or limited to surfaces, the electrical approach can evaluate extremely narrow lines, including those buried beneath other materials. We have validated our method using aluminum, gold, and state-of-the-art damascene copper lines and vias.
Interfaces between conducting carbon nanotube networks and metal contacts are evaluated by direct current methods. Whereas stand-alone nanotubes are known to withstand extremely high currents, their integration into real devices requires connection to other materials such as metal bond pads. Testing has shown material degradation as a function of applied current and can be used to assess overall robustness.