Thermal fatigue as a possible failure mechanism in copper interconnects

Microelectronic devices experience thermal cycles with amplitudes as large as 100 K during normal use. Differences in the thermal expansion coefficients of the different materials comprising the device lead to strain changes during thermal cycling. We demonstrate here that cyclic thermal strains lead to surface damage formation and failure in copper lines during the application of an alternating electrical current. The presence of soft coatings like photoresist on the Cu lines does nothing to inhibit damage formation in the copper lines. Thus, thermal fatigue of Cu interconnects may be a serious reliability threat to devices containing soft interlevel dielectric materials.