Bipolar Schottky logic device failure modes due to contact metallurgical degradation

Failure modes of bipolar Schottky logic devices due to metallurgical degradation of PtSi/Ti-W/Al contacts were studied. Both to the purpose prepared wafers and commercial 74LSOO TTL Low-Power Schottky devices were used. Metallurgical failures are primarily due to Al diffusion through the Ti-W barrier layer. As a consequence, thermal treatments induce electrical failures which begin with a loss of fan-out followed by longer rise and fall switching times. Finally complete device failure is observed when the output stays always at the high logic level. Emitter-base leakages and short-circuits, due to Si dissolution in the overlaying metal system, can explain the observed electrical degradations which are markedly delayed by a thin oxygen layer present at the Al/Ti-W interface.