Voltage Contrast Analysis
is a failure analysis technique
performed using a Scanning
Electron Microscope (SEM) to detect
open conductor lines, open junctions, or reverse-biased junctions.
It operates on the basic principle that the emission of secondary
electrons by a sample bombarded with the primary electron beam of a SEM
is restricted or enhanced by the presence of
local electric fields
within the circuit.
Since these secondary electron emissions are the basis for forming the
SEM images, localized fields can result in
image contrast differences (darker or
brighter areas than normal, depending on the voltage polarity) that
visually indicate circuit anomalies. For instance,
applying a small positive voltage to a metal line will make it appear
darker during SEM inspection than when it is grounded. Thus, if
there's a discontinuity or a non-conducting junction along that line,
one section of the line will appear dark (the one connected to the
voltage) while the other section will appear bright.
Fluorescence (XRF) Analysis
is a failure analysis technique that employs a primary beam of x-ray to
excite a sample into emitting x-rays that are collected and analyzed to
identify the composition of the sample, similar to how
EDX and WDX analyses
are done. The advantage of XRF over EDX/WDX analysis is that it
can be used to analyze layers that would otherwise charge or decompose
with electron bombardment, since it uses x-rays for sample bombardment.
Sample charging or decomposition is a common issue with
EDX/WDX analysis, which bombard the sample with electrons. However, the
large diameter of XRF primary beam limits its spatial resolution.
Activation Analysis (NAA)
Neutron Activation Analysis
is a failure analysis technique that
is useful for detecting very
small concentrations of certain elements in a sample. Elements such as
arsenic, copper, gold, sodium and tungsten can be detected by NAA down
to concentration levels of 1011-1012 atoms per cm3.
NAA irradiate silicon samples with a flux of
of all elements in the sample. The elements present in a sample are
identified through the
the various silicon radioisotopes, particularly the longer-lived ones.
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