Comparative study of Al metallization degradation in power diodes under passive and active thermal cycling

Degradation of Al metallization on Si-based semiconductor
chips under operation is a reliability problem known
for many years but the mechanisms of this phenomenon are not
fully understood. To quantify contributions of different possible
effects, a passive thermal cycling setup has been developed
allowing for accelerated tests by varying the device temperature
on a short time scale without applying electrical power. The
setup is also capable of testing devices in different atmospheres.
The results obtained by the thermal tests of diode chips are
compared to those from power cycled diodes with focus on
degradation of the top metallization layer. The data on structural
and electrical characterization of the samples show that the
passive thermal cycling induces metallization degradation very
similar to that found for the power cycled devices. Thus, it can be
concluded that the thermal-induced stresses are the dominating
mechanisms for the metallization fatigue and following failure.
The role of oxidation and corrosion effects is also studied
in the experiments on passive thermal cycling using different
environmental conditions. It is suggested that the formation
of self-passivating aluminum oxide under ordinary atmospheric
conditions can play a positive role in limiting the structural, and
electrical degradation of the metallization layers. The obtained
results represent a considerable contribution into understanding
of major failure mechanisms related to metallization fatigue and
reconstruction.