Yield Management
Finding the void in the dark
Yield management is as much about finding the unexpected
problems as well as the expected potential issues. Planning for
potential defects that can impact yield can allow a
manufacturer to respond in a timely and less disruptive
fashion. Chang Hwan Lee, Woo Yong Hwang,
Chul Hong Kim and Hyung Won Yoo of Hynix
Issue III 2009
Semiconductor and Yong Gao and Seong Ho Yoo
square4
of KLA-Tencor Corporation discuss .com
how introducing Darkfield inspection enables
early detection of potentially disruptive
metal line sidewall void defects.
oasiasemiconductor
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www
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efect monitoring strategies
are used to identify and
track excursions that cause
both yield and reliability
issues. A particular defect
type can affect yield, reliability or both.
Eliminating yield killer defects does not
necessarily ensure high reliability. Latent defects
may exist on high yielding wafers that eventually
affect device reliability. Such defects can be
particularly expensive to a fab, as the reliability
issues may not be identified until the device is in
use in a customer environment. Successful
defect monitoring methodologies provide
engineers with the excursion information
required to take the corrective action necessary
to eliminate both yield and reliability problems.
As part of the volume production of DRAM,
NAND flash and CMOS image sensor devices,
Hynix Semiconductor has implemented defect issue. This allowed Hynix to optimise Figure 1. Images of
innovative monitoring strategies for identifying process timing and flow in order to prevent sidewall voids before
defect issues that affect device reliability. One defect formation, resulting in improved device and after FIB cross-
such issue involved a metal sidewall void defect reliability and quality. sectioning. More
seen on 66nm DRAM devices that did not affect severe sidewall voids
yield, but did affect device reliability. This article Device Reliability lead to device
describes the correlation of sidewall voids to In addition to testing device performance, Hynix reliability issues
device reliability and the metal sidewall void performs extensive reliability testing on the
defect mechanism. In addition, an overview is devices. At one point, standard reliability
provided of the excursion monitoring strategy analysis, including extended burn in testing
that was implemented to identify and track the under severe environmental conditions,
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