Application of three-dimensional SIMS in material
analysis: Potential and limitations
Stadermann F. J., Reger N., and Ortner H. M. (1996). Abstract
for International Symposium on Material Science Applications of Ion
Beam Techniques, Seeheim, Germany.
Secondary ion mass spectrometry (SIMS) can be used both for
chemical imaging of a sample's surface and for depth profiling. A
combination of these applications is employed to generate series of
element distribution images from increasingly deeper layers of the
sample, which can then be used to visualize the three-dimensional
composition of the analyzed volume. This 3-D SIMS technique is
labor-intensive during measurement preparation and data processing, but
is potentially very powerful since it gives insights into a sample's
internal structure which may not be easily accessible otherwise.
In a number of examples we will show how 3-D SIMS can be
applied to a variety of samples including particles and matrices with
heterogeneously distributed impurities. With the help of
three-dimensional image processing even large amounts of acquired data
(typically 400 MB for a single measurement) can be presented in a way
that allows rapid visual inspection of the analyzed sample volume.
Although 3-D SIMS is very powerful in certain applications,
there are several problems that limit its widespread use. Some of these
problems are sample-related, while others are due to intrinsic
limitations of the SIMS technique. An ideal sample should have a flat
surface and a relatively homogeneous matrix to ensure constant sputter
rates. If these conditions are not fulfilled, the information gained
from a 3-D SIMS analysis may be limited. Intrinsic limitations of the
technique arise from the fact that the SIMS instrument cannot easily be
optimized simultaneously for different parameters. Of course it is
possible in a SIMS analysis to achieve a lateral resolution of 300 nm,
a depth resolution of 20 nm, a high mass resolution (m/delta m) of
10.000, detection limits in the ppb-range for many elements, a large
sputter rate, a scanned area of up to 500 x 500 µm2, and apply
electron charge-compensation for the analysis of non-conductive
samples, but only one at a time. In 3-D SIMS analysis several
of these parameters have to be optimized simultaneously, requiring a
careful evaluation of their individual importance in a given analysis.
We will present an overview of realistically achievable conditions in
3-D SIMS measurements.