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INSPECTION
Figure 1) Conceptual
diagram of GD-OES
emission source and
the subsequent “glow”
that generates excited
atoms for analysis (1).
Issue V 2009
No charge found to be the detrimental to film properties and
One specific advantage with both techniques, could not be determined with other techniques.
especially over charged beam techniques
including SIMS, is the absence of any surface The GD-OES sampling process also allows non-
equilibrium or charging issues at the near surface traditional materials to be characterized. Soda
nor variations in signal intensity at interface lime glass, used as a backing material with some
-pv-management.com regions. Such artifacts obscure the detection of PV technologies, provides an example where some
elements in the first nanometers of a thin film, and traditional surface techniques are not effective, but
.solar
limit the information available to an engineer. With GD-OES shines (no pun intended). A straight-
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GD-OES and LA ICP-MS, these elements at the forward example is an analysis of both old and
near surface can be characterized without new thin films to help determine a reason for
28
extensive, and sometimes expensive, surface reduction in photovoltaic efficiency over time.
alteration techniques, and contamination at Shown in Figure 4, the application of GD-OES to
interface regions can also be detected. The end films on soda lime glass allowed the oxygen in the
result is a faster, more efficient path to problem old film to be clearly observed. This oxygen
solving for thin film engineers. formation at the near surface was found to
increase contact resistance and shown as
A GD-OES example shown in Figure 2 illustrates important for photovoltaic efficiency in this film.
where these advantages are observed in the
analysis data. First, all elements were detected in Tracing elements
simultaneous fashion which allowed a comparison In addition to qualitative analysis, both GD-OES
of major and minor constituents in the thin film. and LA ICP-MS can utilize NIST traceable
This simultaneous collection of data comes without standards and perform quantitative determination
Figure 2) Cartoon changing of ion sources or other alterations in the of metallic elements. Such applications can be
diagram for LA ICP-MS excitation source and the inherent added cost. used to determine compositional amounts of
indicates front-end The deposition of proprietary metals “X” and “Y” elements as shown in Figures 3 and 4 as well as
sampling on right with should have been consistent for 250 nm, but the determination of trace levels of contaminants in
laser and ionization initial 10 nm data indicates Metal Y starts at a very thin films. Laser ablation utilizes a more sensitive
and detection with the high concentration and that consistency is really mass spectrometer technique for detection, and
ICP and mass not gained for either metal prior to reaching the can measure accurately at low part-per-billion
spectromete substrate. The inconsistent film deposition was concentrations for some elements. Note that
although GD-OES is not as sensitive as the laser
technique (ppm concentrations), GD-OES is still
much more sensitive than EDS techniques with
percent level type detection limits.
An example of quantitative analysis and problem
solving for an indium thin film is shown in Figure 5.
In this case two different indium films displayed
different performance characteristics post-process
and metallic contamination was probed as the
potential root cause. Using LA ICP-MS an old
“good” film was shown to have less contamination
then a new “bad” film with the offending elements,
Cr, Fe, Ni, and Mo, indicative of stainless steel.
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