Focused ion beam technology, capabilities and ... - FEI Company

10
Deposition
As FIB technology is frequently used for milling an
additional technique can convert the ion beam system
into a deposition system allowing the addition of material
instead of removing material. This is realized by
adding a so-called gas delivery system, that locally
supplies a chemical compound close to the surface
impact point. The chemical gas compound often
consists of a organic-metallic molecule such as methyl
cyclo pentadienyl Pt (IV) tri methyl. When this compound
is exposed to the ion beam it will decompose
locally and deposit Pt onto the surface. In general the
cracking of the molecule is not 100% so there are
always some additional matrix molecules such as organic
residues that are also deposited. The purity of the
deposit is therefore generally lower compared to, for
example, CVD deposits. The main advantage in comparison
to CVD or PVD is the highly local deposition,
and the capability to create different heights of the
deposit in one exposure. In addition the direct deposition
capability is flexible and does not require complex
mask structures.
Molecules are absorbed on the irradiated area, and by
using the patterning capability of the system three
dimensional structures can be grown at selected positions,
with full control of size, position and height.
So this capability is a very welcome addendum to the
FIB’s milling power. The material deposited depends on
the gas chemistry used and various options are possible.
Readily available gas chemistry allows the deposition of
Pt, W, SiO2, C.
Figure 17: Light microscope image of the sample deposited ex-situ
on a TEM grid. Ex-situ foil extraction using electro-static probes
works even for materials with low structural integrity.
Important characteristics for the depositions are the
minimum size (typically around 50 nm), the purity of
the material, and its conductivity which is usually lower
than the pure metal.
Creation of TEM lamella
An important capability, derived from the system’s
milling capacity, is the creation of thin lamella that are
transparent to an electron beam and hence can serve as
a TEM sample. As the position of the ion beam can be
controlled to a high degree, the TEM lamella can be
created at any location that is of interest to the user.
Focused ion beam machining for the creation of TEM
samples is now firmly established as the most versatile
and accurate method currently available. There are
several ways to extract the FIB machined foil from the
bulk sample without having to use mechanical preparation
at all, so for the first time it is not necessary to
sacrifice the sample when performing TEM analysis
with the highest accuracy.
Site specific
The fact that the location of the foil site can be defined
inside the FIB makes this the only true site-specific
technique available. The momentary feed-back of what
and where FIB milling takes place is essential to
generate the best samples from the region of interest.
Lateral placement of foils is quite simple, and the aimed
thickness is in the range of 100 nm and can be controlled
to a high degree.
Material independent
As the ion beam removes atoms from the sample in an
atomic collision process rather than with a mechanical
bulk cut or mechanical polish, the amount of ions
needed to remove different materials with varying hardness
is not related to the structure or the composition
of the sample. This means that milling any material or
a combination of materials is as straightforward as a
simple single crystal sample for ion beam machining.
Even voided, brittle or soft/hard combinations of materials
are easy for the FIB process. Many TEM samples
that were difficult or impossible to make until now (soft
polymer coating on metal, hard metal on soft metal)
are now easy to make using FIB technology.