Abstract :
Abstract — In semiconductor perspective reliability is the
ability of a device to conform to its electrical and
visual/mechanical specifications over a specified period of
time under specified conditions at a specified confidence
level. Since the beginning reliability has been remained an
important part of semiconductor industry. For the last six
decades device reliability have improved with each scaled
generation of technology. Manufacturers of devices with
critical applications like military, automotive and medical
mainly contributed to initiate and develop semiconductor
reliability field.
The reliability of semiconductor products as a function of
time is commonly described by a bathtub curve .This is
because the plot of the product failure rate as a function of
time has the shape of a cross sectioned bathtub as shown in
fig. 1. Three failure regimes can be distinguished in the
bathtub curve. In the ‘infant mortality’ or ‘early failure’
period, the products show a high, but decreasing failure rate
as a function of time until the failure rate stabilizes. This
period is referred to as the ‘random failure’ period. Finally,
in the ‘wear-out’ period, the failure rate increases again
when end-of-life of the products is reached. The nature of the
failures in the three periods is generally very different. The
majority of the failures in the ‘early failure’ period are
caused by manufacturing defects like e.g. particles, near
opens and shorts in metal lines, weak spots in isolating
dielectrics or poorly bonded bond wires in the package. In
the ‘random failure’ period many different root causes occur
but failures related to specific events like lightning, load
dump spikes occurring during disconnection of car batteries
or other overstress situations are most notable. Failures in
the ‘wear out’ period are related to intrinsic properties of the
materials and devices used in the product in combination
with the product use conditions like temperature, voltage and
currents including their time dependence.
The major long-term reliability concerns include the
wear-out mechanisms of time dependent dielectric
breakdown (TDDB) of gate dielectrics, hot carrier injection
(HCI), negative bias temperature instability (NBTI), electro
migration (EM), and stress induced voiding (SIV). Among
the wear-out mechanisms, TDDB and NBTI seem to be the
major reliability concerns as devices scale. The gate oxide has
been scaled down to only a few atomic layers thick with
significant tunneling leakage. While the gate leakage current
may be at a negligible level compared with the on-state
current of a device, it will first have an effect on the overall
standby power. For a total active gate area of 0.1 cm2, chip
standby power limits the maximum tolerable gate leakage
current to approximately 1-10 A/cm2, which occurs for gate
oxides in the range of 15-18A
