The observation of stress-induced leakage current of damascene interconnects after bias temperature aging

Time-dependent dielectric breakdown (TDDB) was investigated, noting the time variation of stress-induce leakage current (SILC) between copper (Cu) lines. To clarify the TDDB mechanism, triangular voltage sweep (TVS) and bias temperature aging were alternatively performed for Cu damascene structures. The SILC was largely increased with stress time; however no Cu ion peak was detected in TVS measurements. The point-symmetric TVS hysteresis clearly indicates that the distribution of stress-induced defects is independent of electric polarity, namely it is a random or symmetric distribution. In addition, the SILC of Cu interconnect increased as slow as that of tungsten (W) in the usual bias temperature aging. Since the optimize barrier process sufficiently suppresses Cu ion drift in TDDB testing, the dielectric breakdown is only controlled by intrinsic factors. When the protection against moisture is structurally insufficient, the water-related degradation is seriously pronounced instead of Cu ion drift. The water-absorbed interconnect abruptly breaks down while the current is decreasing. Just before the breakdown, the asymmetric TVS hysteresis appears. Therefore, TVS observation enables us to distinguish whether stress-induced leakage current comes from intrinsic or extrinsic causes.