is used for inspecting topographies of specimens at very
magnifications using a piece of equipment called the
SEM magnifications can go to more than 300,000 X but most semiconductor
manufacturing applications require magnifications of less than 3,000 X
only. SEM inspection is often used in the analysis of die/package cracks
and fracture surfaces, bond failures, and physical defects on the die or
inspection, a beam of electrons is focused on a spot volume of the
specimen, resulting in the transfer of energy to the spot. These
bombarding electrons, also referred to as
dislodge electrons from the specimen itself. The dislodged electrons, also
are attracted and collected by a positively biased grid or detector, and
then translated into a signal.
To produce the
SEM image, the electron beam is
the area being inspected, producing many such signals. These signals are
then amplified, analyzed, and translated into images of the topography
being inspected. Finally, the image is shown on a CRT.
of the primary electrons determines the quantity of
electrons collected during inspection. The emission of secondary electrons
from the specimen increases as the energy of the primary electron beam
increases, until a certain limit is reached. Beyond this limit, the
collected secondary electrons diminish as the energy of the primary beam
is increased, because the primary beam is already activating electrons
deep below the surface of the specimen. Electrons coming from such depths
usually recombine before reaching the surface for emission.
secondary electrons, the primary electron beam results in the emission of
(or reflected) electrons from the specimen. Backscattered electrons
possess more energy than secondary electrons, and have a definite
direction. As such, they can not be collected by a secondary electron
detector, unless the detector is directly in their path of travel. All
emissions above 50 eV are considered to be backscattered electrons.
Example of a SEM photo of a contaminated area on a leadframe; EDX analysis
is usually performed to identify such contaminants
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is useful in distinguishing one material from another, since the yield of
the collected backscattered electrons increases monotonically with the
specimen's atomic number. Backscatter imaging can distinguish elements
with atomic number differences of at least 3, i.e., materials with atomic
number differences of at least 3 would appear with good contrast on the
image. For example, inspecting the remaining Au on an Al bond pad after
its Au ball bond has lifted off would be easier using backscatter imaging,
since the Au islets would stand out from the Al background.
A SEM may be
equipped with an EDX analysis system to enable it
to perform compositional analysis on specimens. EDX analysis is
useful in identifying materials and contaminants, as well as estimating
their relative concentrations on the surface of the specimen.
SEM inspection, the following must be observed:
must be high enough to provide a good image but low enough to prevent
2) To maximize
due to material differences, use as low an EHT as possible.
3) If possible,
the specimen to prevent
Sputter-coating is considered destructive. Never sputter-coat units that
still need to undergo electrical testing, curve tracing, EDX analysis,
must be set to
its default value, unless a higher probe current is needed to focus the
point of interest properly.
Two examples of Scanning Electron Microscopes
Mechanisms/Attributes Used For:
Die/Package Cracks, Die Attach Failures/Defects, Bonding Failures/Defects,
Wire Defects/Fractures, Lead Defects/Failures, Foreign Materials on
Die/Package, Die Surface Defects, Seal Cracks/Defects, etc.
Electron Microscopy (TEM)
is a technique used for analyzing the morphology, crystallographic
structure, and even composition of a specimen. TEM provides a much
spatial resolution than SEM, and can facilitate the analysis of features
at atomic scale (in the range of a few nanometers) using electron beam
energies in the range of 60 to 350 keV.
Unlike the SEM
which relies on dislodged or reflected electrons from the specimen to form
an image, the TEM collects the electrons that are
through the specimen. Like the SEM, a TEM uses an electron gun to
produce the primary beam of electrons that will be focused by lenses and
apertures into a very thin, coherent beam.
This beam is
then controlled to strike the specimen. A portion of this beam gets
transmitted to the
of the specimen, is collected, and processed to form the image.
materials, the specimen diffracts the incident electron beam, producing
that can be translated into contrast to form an image. For amorphous
materials, contrast is achieved by variations in electron scattering as
the electrons traverse the chemical and physical differences within the
consideration when performing TEM analysis is
The quality of sample preparation contributes greatly to whether the
micrograph will be good or not, so analysts are required to exercise the
necessary diligence in preparing the sample for TEM analysis.
Inspection; EDX/WDX Analysis
EBIC; FA Lab
Equipment; Basic FA
Package Failures; Die
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