Hyperion Ion Probe
cross-sectioning.
in beam current density and sample throughput.
Other applications such as prototyping MEMS and
In the semiconductor industry, it is necessary to
embedded circuit components have been demonstrated with
quantitatively measure the “in-depth” distribution of dopants
this high-current FIB. Figure 5 shows a micro-scale spiral RF
used for ultra-shallow junctions and ultra-thin gate dielectrics.
antenna, oft en used in RF ICs, that has been fabricated here
For SIMS to be able to accurately measure the distribution
in <60 minutes. A 5 μm thick layer of copper has been locally
of these structures, it has become necessary to bombard the
sputter deposited over a ~250x250 μm area of silicon oxide
surface under analysis with ultra-low energy oxygen ions
with a 3 μA Xe
+
beam hitting a copper target and creating a
in order to minimize the depth of the amorphized surface.
conformal deposit in ~25 minutes. A bitmap has been uploaded
Oxygen-focused ion beams with kinetic energies of <250 eV
to the FIB pattern generator, directing a 250 nA, 25 keV Xe
+
are oft en used today for this type of analysis, whereas next
beam to mill away the excess copper. Th e deposited copper has
generation devices will require ion energies as low as 100 eV [7].
a measured electrical conductivity that is within a factor of 3 of
Unfortunately, the low sputter yield at these ion energies, along
bulk copper, such that this 2.5 nH (calculated) inductor would
with the challenges of forming high-current density-focused
have a quality factor (Q) of ~20 at 5 GHz, ignoring substrate
ion beams at such low energies, has made this type of analysis
losses and parasitic capacitive eff ects that can aff ect these
very time consuming. For example, at the 32 nm node there are
parameters at higher frequencies.
implanted junctions at depths of only 10 nm with post-anneal
Oft en spiral RF inductors are developed with a combination
concentration gradients of the 1-2 nm/decade. A 150 eV profi le
of electromagnetic simulations and characterizing a number
of these structures today can take 8 hours with duoplasmatron-
of prototype spirals on test wafers. However, the simulation
based SIMS tools. However, Hyperion can bring this analysis
process is far from trivial [6] at the dimensional scales used for
time down to ~30 minutes to make this type of analysis routine.
today’s compact RF ICs. Th e performance of a geometrically
Figure 6 shows the potential gain in current density with
simple spiral antenna is complicated by eff ects, such as substrate
the addition the Hyperion source to a so-called Floating
interactions, mutual capacitance between antenna spirals, and
Low Energy Ion Gun (FLIG
TM
—trademark of Ionoptika Ltd)
conductor losses as the metal lines approach the dimensions of
employed by many quadrupole SIMS instruments.
the RF skin depth.
Here, we compare spot size (16-84 percent edge resolution)
Coupled with 3D EM simulation tools, Hyperion
versus beam current for the prototype FLIG of Dowsett et al.
provides a rapid and relatively low-cost method for prototype
[8] for a sample impact energy of 500 eV and an ion column
studies of spiral inductors, along with other embedded circuit
transport energy of 5.5 keV. An optical model has been
components and MEMS structures.
constructed for this ion beam system with the duoplasmatron
curve (black line in Figure 6) closely matching experimental
Secondary Ion Mass Spectrometry (SIMS) data collected by this author.
Th e 50-year reign of the duoplasmatron, as the highest Th e Oregon Physics Hyperion ion source comfortably
performance oxygen plasma ion source used for SIMS, is provides a brightness of 2500 Am
-2
sr
-1
V
-1
for O
+
2
ions (4500
thoroughly over. Hyperion not only provides over 10 times Am
-2
sr
-1
V
-1
when O
+
is included) with an axial energy spread
higher brightness but also <50% of the axial energy spread of 5 eV. Calculations show that replacing the duoplasmatron
when compared to a duoplasmatron. Th is step-function in with the Hyperion source and an additional lens positioned
ion-source performance can translate to a 20-50 times increase
200µm
200µm
12µm
7µm
Figure 5: Prototyped copper-on-silicon oxide spiral antenna. 2.5 nH inductance Figure 6: Comparison of the duoplasmatron ion source (black line) with Hyperion
for wireless RF IC.
(red line) for low-energy SIMS.
2009 September •
www.microscopy-today.com 21
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