Abstract
During moisture-and-bias reliability stress tests of THBT (temperature and humidity biased test) and HAST (highly accelerated stress test) extensive electrochemical oxidation of a TiN ARC layer is seen to occur. This oxidation proceeds at the nominal temperatures and humidity levels associated with such THBT and HAST tests; excessive heating due to EOS (electrical overstress) or other anomalous electrical conditions was not involved. The oxidation rate increases with applied voltage. Metal line width also affects the spread of oxidation. Oxidation requires the presence of adequate humidity to act as an electrolyte, and therefore is seen to propagate wherever moisture penetration can occur in the passivation dielectrics. The presence of a silicone gel die coating is found to render the die more susceptible to TiN oxidation. Electrical failures – typically open circuits or increased resistance due to corrosion – are found to occur as a consequence of this oxidation and its effect on the surrounding structures. This mechanism is a concern for integrated circuits with TiN in the upper metal layers, operating at voltages >5V in humid conditions. Two approaches at reducing this electrochemical reaction are offered.
