Microstructural evolution of cu interconnect under AC, pulsed DC and DC current stress

Abstract

Damascene Cu interconnects are increasingly used as electrical connections in integrated circuits. During fabrication and operation these interconnects are subjected to temperature variations. These thermal effects cause the different layers of a microelectronic device to undergo mechanical stresses due to differences in thermal coefficients. The same thermal effects can be generated by applying a sinusoidal alternating current (AC) to a sputtered interconnect. Thermal cycling due to joule heating of the interconnect will cause thermal fatigue damage. Our goal is to study this phenomenon on dual damascene Cu interconnects and to compare these results with direct current (DC) and bipolar pulsed DC stressed samples. The outcome of these experiments demonstrate that failure under DC, bipolar pulsed DC and sinusoidal AC arise in the same way and is not a result of thermal cycling, but diffusive mechanisms. These diffusive mechanisms can be slowed down by using a passivation layer on top of the interconnect and air gaps instead of a dielectric beside the line as showed during a test.