Download Focused Inert Ion Beam systems for 3D rock tomography on the

Focused Inert Ion Beam systems for 3D rock tomography on the
nano-scale
Rod Boswell, Tim Senden
RSPE, ANU
Canberra, ACT, Australia
[email protected]
To study the porosity and chemical properties of many natural and man-made
materials, analysis is required across a broad range of length scales. Such materials
include, porous rock, bone and sintered materials. The ANU has developed imaging
and measuring techniques using conventional FIB/SEM instruments constructed
mathematical models of the 3D fluid flow through the materials. This analysis often
requires the imaging technique to resolve nanoscopic structures (ie <50nm resolution)
across micro- or macroscopic regions of interest, throughout a 3 dimensional body.
Tomographic sectioning is done today with a gallium FIB, removing ~20-200nm
thick slices to reveal new layers in a 50x50um cross-sectioned face. Each new layer
is iteratively imaged with ~50nm resolution with an in-situ SEM. However. with a
maximum gallium beam current of 20nA, ion beam milling time is prohibitively time
consuming for this measurement technique to become commercially viable.
Hence, it is necessary to increase the FIB milling speed. Unfortunately, above ~10nA
the gallium LMIS FIB suffers from a rapid increase in spot size. This transition
results from an increase in spherical aberration coefficient for the FIB optics, at the
large aperture angles required to transport high ion beam currents from an ion source
with a relatively low angular intensity (~20uA/sr).
On the other hand, a plasma ion source based FIB developed from original ANU
research and now commercialised as the Hyperion FIB by Oregon Physics (OP),
offers a significant advantage for high current focused ion beams since it has an
angular intensity that is approximately 3 orders of magnitude higher than the LMIS,
while having a brightness that has produced unprecedented spot sizes for a plasma
source at low beam currents.
A comparison of the gallium LMIS FIB with an OP xenon Hyperion FIB is presented
along with the 3D structure of the rock sample so derived.