Download Thermal Analysis Infrared Microscopy During device functioning, the

Thermal Analysis
1. Infrared Microscopy
During device functioning, the zones affected by defects have
a higher local temperature than the defect-free ones. The
infrared microscope can be used at wafer level, for thermal
analysis, displaying the temperature distribution. Thermal
images based on the infrared radiance emitted from the
structures are constructed, and hot spots (regions with high
temperatures) can be found as areas were defects are present.
Then, the defects can be studied by other methods(SEM, etc.),
and methods for diminishing their action are elaborated. The
IR microscope is particularly useful for visualizing interface or
structural defects, beyond the layers that are transparent to
IR.
2. Equipment for Dynamic Mechanical-Thermal Analysis
The equipment can be used for analyszing the behavior of the
device at wafer level. Suitable especially for microelectromechanical systems (MEMS), the method is aimed at
characterizing the behavior of the mechanical moving part of
MEMS, the actuating system.
3. Mechanical Properties
Characterizing mechanical properties of the materials used for
manufacturing semiconductors could be a consititutive part of
the failure analysis. This is true mainly for semiconductor
devices with moving mechanical parts, for example MEMS. The
mechanical properties are valuable inputs for the design, and
then are monitored during manufacturing, as significant
parameters for describing failure risks. Some examples are
given in the following. The residual stress is a key parameter
for MEMS, which might significantly decrease the performance
and reliability of the device. It is important to accurately
measure the residual stresses at various manufacturing steps,
by XRD test of vibration method of by in situ measurements
aimed to identify local residual stresses of MEMS thin films.
Other methods for obraining mechanical parameters could be
mentioned: nanoindentation, bulge methods, bending tests,
tensile tests, and others.
4. Other Methods
If the failure mechanism is not discovered with the
aforementioned means, some other tools must be used.
Ecamples of such tools for discovering more about the failure
couse are:
 Methods using secondary electrons, back-scattered and
Auger electrons: Auger electron spectroscopy, scanning
Auger microprobe, transmission electron microscope,
transmission electron energy-loss microscopy, lowenergy electron diffraction.
 Methods using electron-induced photon emission:
electron probe microanalysis with x-ray, appearance
potential spectroscopy.
 Methods using photo- and Auger electron emission:
electron spectroscopy for chemical analysis, x-ray
induced Auger electron spectroscopy, ultraviolet
photoelectron spectrometry.
 Methods using sampling by laser-induced emission:
atomic absorption spectroscopy, optical emission
spectroscopy.
 Methods using fluorescence and reflection: x-ray
fluorescence spectrometric analysis, light microscopy IR,
UV and Raman scattering, laser optical spectrometry.
 Methods using ion beam and scattering: ion scattering
spectrometry, Rutherford back-scattering spectrometry,
neutron activation analysis, focused ion beam-FIB (which
uses a 30-keV beam of positive gallium ions to irradiate
the surface of the sample in a defined area; this
irradiation causes surface charging, which can be
neutralized by a flow a low energy electrons, around 30
eV, from a flood gun; images can be made using a signal
consisting of either secondary ions or secondary electrons
with or without charge neutralization by the electron
flood gun; the FIB has been used to image structures, to
cross-section elements of concern and to cut elements
free for subsequent examination).
 Methods using acoustic waves, for example acoustic
scanning microscope (ASM), used for the near surface
zone of the semiconductor structures, able to detect the
modifications of material properties-on surface and near
the surface (structure modifications, regions with weak
adherence, micro-cracks, micro-exfoliations).
It is important to note that all these special means (and others)
must be used only to identify the failure mechanism. In other
words, the special means must be needed by the logic of the
failure analysis. A tendency to embellish the failure reports by
adding “beautiful” results (impressive pictures or diagrams
obtained with sophisticated tools) is encountered all over the
world. Often, such a technique is used only for making a
scientific paper more convincing, but it is also the most
powerful argument for increasing the price required for a
failure report. The customer must be aware that sometimes
expensive reports are not the best ones.