Leakage and breakdown reliability issues associated with low-k dielectrics in a dual-damascene Cu process

Leakage and breakdown characteristics of low-k dielectrics are becoming increasingly important reliability issues for interconnects as they are scaled to 0.18 um and below. Several of the low-k dielectrics, integrated into a dual-damascene Cu process flow, are quite leaky and have difficulty in meeting a leakage spec of 1E-8 A/cm² at 25°C. Time-dependent dielectric breakdown (TDDB) for some of the low-k candidate films is also an issue because of generally low breakdown strengths <2 MV/cm. Furthermore, Cu out-diffusion through poor barrier confinement can result in increased electronic leakage and premature TDDB. Also, moisture absorption by these low-k materials serves to: increase the dielectric constant, increase the leakage and reduce the breakdown strength. These findings can have important reliability implications for Cu/low-k and care must be exercised in dual-damascene integration schemes