FAULT LOCALIZATION
TECHNIQUES III
EMT 361
SCHOOL OF
MICROLELECTRONIC
ENGINEERING
KUKUM
Shell model
nucleus = positively charged protons and uncharged neutrons. ~ same size and
weight.
like charges repel~ "nuclear glue" that holds the nucleus together.
There must usually be more neutrons than protons for a nucleus to be stable, so it
has been thought that neutrons had something to do with this nuclear glue.
Present theories state that there is a sub-nuclear particle called a gluon that holds
the nucleus together.
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Orbits & electrons
He 1s2
Ne 1s22s22p6
Ar 1s22s22p63s23p6
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More orbits…
shell # (code)
1 (K)
2 (L)
3 (M)
4 (N)
5 (O)
6 (P)
...
set of orbitals letter
s
s,p
s,p,d
s,p,d,f
s,p,d,f,g
s,p,d,f,g,h
s,p,d,f,g,h,i...
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s, p, d, f, g, h, i...
The original designation of those orbitals was done according to their spectral
appearance, namely:
sharp, principal, diffuse, fundamental,
hence the letter code with the remaining letters being ordered alphabetically. To
cause even greater confusion, orbitals always come in groups.
There is one s-orbital, three p-orbitals, five d-orbitals, seven f-orbitals
spectroscopy
Stage 1: Ionisation
atom is ionised by knocking one or more electrons off to give a positive
ion.
Mass spectrometers always work with positive ions.
Stage 2: Acceleration
ions are accelerated - same kinetic energy.
Stage 3: Deflection
ions are deflected by a magnetic field according to their masses. The
lighter they are, the more they are deflected.
The amount of deflection also depends on the number of positive charges
on the ion - in other words, on how many electrons were knocked off in
the first stage. The more the ion is charged, the more it gets deflected.
Stage 4: Detection
beam of ions passing through is detected electrically.
Different ions are deflected by the magnetic field by different amounts. The amount of deflection
depends on: the mass of the ion. Lighter ions are deflected more than heavier ones. the charge on
the ion. Ions with 2 (or more) positive charges are deflected more than ones with only 1 positive
charge. These two factors are combined into the mass/charge ratio. Mass/charge ratio is given the
symbol m/z (or sometimes m/e). For example, if an ion had a mass of 28 and a charge of 1+, its
mass/charge ratio would be 28. An ion with a mass of 56 and a charge of 2+ would also have a
mass/charge ratio of 28. In the last diagram, ion stream A is most deflected - it will contain ions with
the smallest mass/charge ratio. Ion stream C is the least deflected - it contains ions with the
greatest mass/charge ratio.
SYLLABUS
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FTIR
NMR
AFM
STM
AES
FIB
FTIR
ftir
FTIR (Fourier Transform Infrared) Spectroscopy = FTIR
Analysis,
= failure analysis technique that provides information about the
chemical bonding or molecular structure of materials, whether
organic or inorganic.
It is used in failure analysis to identify unknown materials
present in a specimen, and is usually conducted to complement
EDX analysis.
principle
bonds and groups of bonds vibrate at characteristic
frequencies .
molecule that is exposed to infrared rays absorbs infrared
energy at frequencies which are characteristic to that molecule.
FTIR analysis- spot on specimen subjected to modulated IR
beam.
specimen's transmittance and reflectance of the infrared
rays at different frequencies is translated into an IR
absorption plot consisting of reverse peaks.
resulting FTIR spectral pattern is then analyzed and matched with
known signatures of identified materials in the FTIR library
• FTIR spectroscopy does not require a vacuum oxygen nor nitrogen absorb infrared rays.
• minute quantities of materials, whether solid, liquid ,
or gaseous - single fibers or particles are sufficient
• no library of FTIR spectral patterns - individual peaks
in the FTIR plot may be used to yield partial
information about the specimen.
• Organic contaminants in solvents may also be
analyzed by first separating the mixture into its
components by GC, and then analyzing each
component by FTIR.
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NMR
• compass needle normally lines up with
the Earth's magnetic field with the northseeking end pointing north.
• twist the needle around so that it points
south - lining it up opposed to the
Earth's magnetic field.
• let it go again, it will flip back to its more
stable state.
• Hydrogen nuclei ~ little magnets
• a hydrogen nucleus can also be aligned with an external
magnetic field or opposed to it - alignment where it is opposed
to the field is less stable (at a higher energy).
• possible to flip it from the more stable to less stable by supplying
exactly the right amount of energy. - usually in the range of
energies found in radio waves - at frequencies of about 60 - 100
MHz. (FM radio 88 - 105 MHz!)
• detect this interaction between the radio waves of just the right
frequency and the proton as it flips from one orientation to the
other as a peak on a graph. This flipping of the proton from one
magnetic alignment to the other by the radio waves is known as
the resonance condition.
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Spectroscopy - interaction of electromagnetic radiation with matter.
NMR phenomenon to study physical, chemical, and biological properties of
matter - study chemical structure using simple one-dimensional techniques.
Two-dimensional techniques are used to determine the structure of more
complicated molecules.
Time domain NMR spectroscopic techniques are used to probe molecular
dynamics in solutions.
Solid state NMR spectroscopy is used to determine the molecular structure of
solids, measuring diffusion coefficients.
AFM
Atomic Force Microscopy
• AFM = form of scanning probe microscopy
(SPM)- measuring a local property of the
surface being inspected, such as its
height, optical absorption, or magnetic
properties.
• probe or tip that's positioned very close to
surface to get measurements.
• AFM operates in two modes, namely, contact
mode imaging and non-contact mode
imaging.
Contact mode imaging
• a soft cantilevered beam - sharp tip at its end - brought in
contact with the surface of the sample.
• force between tip and sample causes the cantilever to deflect in
accordance with Hooke's Law, exhibiting a spring constant that
typically ranges between 0.001 to 100 N/m - derive information
about the surface of the sample.
• amount of deflection is measured by reflecting light from a laser
diode off the back of the cantilever beam, and onto a pair or
array of position-sensitive photodetectors.
• differences between reflected light received by individual
photodetectors indicates amount of angular deflection of the
cantilever at any given point on the sample.
• cheaper (but less sensitive) alternative - using piezoresistive
AFM probes that serve as a strain gauge system.
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ability to monitor deflection allows the AFM to create an image of the
sample non-destructively even if the tip is continuously in contact with
the sample.
prevent cantilever tip from damaging the surface of the samplemaintain at a constant angular deflection so that the force applied by
the tip on the surface is also kept constant- feedback mechanism that
adjusts the distance between the tip and the surface to keep the
applied force constant .
Applied forces between the tip and the sample typically range from 10 11 to 10 -7 N.
feedback mechanism controls piezoelectric elements that hold the
sample and move it in all three axes relative to the tip. The z-movement
is used for maintaining the force at the right level, while the x- and ymovements are used for the raster-scanning the tip over the sample.
The resulting map s(x,y) of the tip's relative distance from the surface at
different x-y values of the scan is then used to form a topographical
image of the scanned area of the sample.ﾊ Thus, contact-mode
imaging is primarily used for generating images of a sample's
topography .
Non-contact imaging
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employs a small piezo element mounted under the cantilever - oscillate at
its resonance frequency.
oscillating cantilever is brought down to within 10-100 nm from the sample
surface, the oscillation gets modified by interaction forces (Van der Waals,
electrostatic, magnetic, or capillary forces) between the tip and the sample.
changes in the oscillation usually involve a decrease in resonant frequency, a
decrease in amplitude, and a phase shift.
changes in oscillation characteristics used to generate a map that characterizes
the surface of the sample - amplitude modulation = information about the
sample's topography.-Phase shifts used to distinguish different surface materials
from each other. - Frequency modulation used to get information about the
sample's properties.
One challenge in non-contact imaging is being able to keep the correct tip-tosample distance while preventing the tip from touching the surface - since there
is a maximum distance for the inter-atomic forces to become detectable.
Furthermore, the tendency of most samples to develop a liquid meniscus
layer in ambient conditions complicates this task.
advantages & disadvantages
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1) it generates true 3-dimensional surface images;
2) it does not require special sample treatments that can result in the
sample's destruction or alteration;
3) it does not require a vacuum environment in order to operate (it
can operate in both air and liquid).ﾊ
1) the image size that it provides is much smaller than what
electron microscopes can create; and
2) it is slow in scanning an image, unlike an electron microscope which
does it in almost real-time.
In the semiconductor industry, AFM is primarily used for the imaging of
VLSI cross-sections. Materials that can be imaged by AFM include
metals, polymers, photoresists, etc.
STM
Scanning Tunneling Microscopy
• STM = non-optical, very high-resolution microscopy for obtaining
images of conductive surfaces at atomic scale level (~2
angstroms, i.e., 0.2 nanometer).ﾊ
• Just like AFM ~ scanning probe microscopy - employing an
atomically sharp probe tip that is scanned over the sample
surface in order to accomplish its imaging function.
• Aside from atomic level imaging, STM can also be used to alter
the sample by manipulating individual atoms, initiating chemical
reactions, and creating ions.
operation
• 'quantum mechanical tunneling.’
• fact = very small current will flow between a sharp
metal probe tip and the surface of an
electrically
conductive material if:
1) a voltage is applied between the
tip and the conductive material;
2) the tip is positioned just a few
nanometers away from the sample surface, i.e.,
no contact is made between the tip and the
sample.
ooppeerraattiioonn
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current produced = 'tunneling current' , ~ 1nA for an applied voltage of 1 V.
amount of tunneling current = exponentially dependent on distance between the tip and the
sample surface.
sensitivity of tunneling current to the tip's distance from the sample is utilized by the STM in
its operation.
in constant current mode - the distance between the tip and the sample surface is kept
constant in order to keep the tunneling current constant.- topography of the sample surface
changes = microscope must move probe tip according to how the sample topography varies
in order to keep the tip-to-sample distance constant.
tip mounted on a piezoelectric tube which controls the position of the tip in three dimensions
relative to the sample. The piezo element that moves the tip towards or away from the
sample surface is controlled by a feedback circuit that monitors the tunneling current in
order to determine whether the tip is too close or too far from the surface- feedback circuit
supplies the electrode of the piezo element with a control voltage that moves the tip in the
right direction to keep the distance of the tip from the sample constant.
tip is scanned line by line over a small area of the sample surface in the x-y plane,
topographic data based on the z-axis position of the tip - is collected by the computer
image of topography of sample reconstructed from the collected data - Under the right
conditions, high-quality STM's can produce images with sufficient resolution to show
individual atoms.STM images are commonly presented in greyscale, with protrusions shown
in white and depressions in black.
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important tool for surface physics and chemistry studies.
ability to show the structure of the uppermost layer of atoms or molecules, can
reveal surface defects, display the morphology of various depositions, or
measure the surface roughness of a wafer in the angstrom-range.
may also be used in the study of conduction or charge transport mechanisms.
can be used to move single atoms accurately, by pushing or dragging them with
the tip at low temperatures. Electrons emitted by the tip can also be used to alter
the sample. The ability of STM to serve as a tool for 'rearranging' atoms
has made it an important tool in nanosciences .
STM does not need a vacuum in order to operate, although it is usually operated
in an ultrahigh vacuum environment to avoid contamination or oxidation of
sample surfaces when high-resolution imaging of metals or semiconductors is
required.
Surface oxidation reduces the conductivity of the sample's surface and affects
the tunneling current, resulting in imaging problems.
operates on the flow of the tunneling current, it cannot be used on nonconductive samples - possible to coat a non-conductive sample with a
conductive layer such as gold to make it observable under an STM, but this
coating step can mask hide certain
features or degrade imaging resolution.
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AES
Auger Emission
Spectroscopy
• AES = Auger Analysis= FA technique
used in the identification of elements
present on the surface of the sample.
• AES involves the bombardment of the
sample with an energetic primary beam
of electrons - generates, among other
things, a certain class of electrons
known as Auger electrons
operation
• an electron ejected by the primary electron beam from its shell,
say, the K-shell.
• Another electron from an outer shell (say, the L1-level) of the
same atom emits energy in the form of a photon in order to go
down to the K-shell position vacated by the ejected electron
• photon released by the second electron will either get lost or
eject yet another electron from a different level, say, L2.
• Auger electrons are electrons ejected in this manner, such as
the third electron from L2 in the example - generation of an
Auger electron requires at least three electrons, which in the
example above are the K, L1, and L2 electrons.
• In this example, the emitted Auger electron is referred to as a
KLL Auger electron.
• Hydrogen and Helium atoms have less than three electrons,
and are therefore undetectable by AES.
• energy content of emitted Auger electron is unique to the atom
where it came from.
• AES works by quantifying the energy content of each of the
Auger electrons collected and matching it with the right
element.
• energy of Auger electrons is usually between 20 and 2000 eV.
• depths from which Auger electrons are able to escape from the
sample without losing too much energy are low, usually less
than 50 angstroms - come from the surface or just beneath the
surface.
• AES can only provide compositional information about the
surface of the sample -to use AES for compositional analysis of
matter deep into the sample, a crater must first be milled onto
the sample at the correct depth by ion-sputtering.
• excellent lateral resolution, allowing reliable analysis
of very small areas (less than 1 micron).
• offers satisfactory sensitivity, detecting elements that
are less than 1% of the atomic composition of the
sample.
• Coupled with ion-sputter milling capability and raster
scanning, AES can even be used to generate 3-D
maps of elemental distributions of a volume of the
sample = scanning auger
microscopy (SAM).
• Auger spectrum. - peaks at Auger electron energy
levels corresponding to the atoms from which the
auger electrons were released
in the semiconductor industry include but are not limited to the
following:
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1) identification of surface contaminants;
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2) detection of very thin SiO2 and other oxide layers on
surfaces;
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3) determination of contamination levels in barrier metals;
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4) analysis of corrosion failures; and
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5) detection of P, B, and As concentrations in SiO2 layers.
following limitations:
1) charging up of insulative surfaces when struck by the primary
electron beam;
2) damage to certain materials, especially organic ones, when
struck by the electron beam;
3) occurrance of matrix effects, i.e., signal alterations when some
elements are present in particular matrices.
FIB
Focused Ion Beam
• FIB for failure analysis high magnification microscopy
, die surface milling or cross-sectioning ,
and
even material deposition .
• uses a finely focused beam of gallium (Ga+) ions
rastered on the surface of the material to be
analyzed.
• As it hits the surface, a small amount of material is
sputtered or dislodged, from the surface.
• dislodged material - form of secondary ions ,atoms ,
and secondary electrons - collected and analyzed as
signals to form an image on a screen as the primary
beams scans the surface = high magnification
microscopy
• The higher the primary beam current, the more
material is sputtered from the surface.
• If only high-mag microscopy is intended, only a lowbeam operation must be employed.
• High-beam operation is used to sputter or remove
material from
the surface, such as during highprecision milling or cross-sectioning of an area on the
die.
• FIB system can also bombard an area
on the die with various gases as it
performs primary beam sputtering.
Depending on the gases used, these
gases can react with the primary beam
to either etch material from or deposit
material onto the surface.
Cross-section
of a
DRAM cell produced by FIB
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