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byproducts. “One of the biggest challenges with turbo pumps is ensuring
no byproduct deposition. When you
have a very high speed machine
spinning close to the wafer, the
last thing you want is for the gas to
solidify on the rotor and start peeling
off and contaminating the wafer.
Now with some of these exotic materials, vapor pressures are becoming
more of a challenge, so temperature
management systems (TMS) on
turbopumps, is becoming more important. Increasing temperature in a
mechanical system is always difficult
because it does have an impact on
performance limits and how far you
can push it,” Tollner said.
Cryos and turbos
A turbopump relies on the ability to
capture molecules through rotating
a surface faster than the molecules
moves, and basically knocks the
molecule out of the chamber. This
works well for most gases, but it’s
difficult with hydrogen which has a
high velocity. Where a cryopump,
by comparison, absorbs the material
on charcoal, essentially capturing
it. The main disadvantage is that it
needs to be periodically warmed up
or “regenerated.” Tollner said there
are some technology barriers related
to how long the charcoal last when
pumping hydrogen, service intervals
and predictive maintenance, but
those are being addressed within the
new Chamber Solutions Division.
“Edwards has always thrived on
driving innovation, and we will see
that filter across to the CTI products
very soon.” He added that they will
be looking at how to optimize the
use of both types of pumps in combination for pumping heavier gases in
combination with light gases. “We’ve
got both products and both technologies to look at the different options
and bring them together,” he said.
“The technologies are very, different,
but there’s also a lot of synergies and
things we can leverage from each
other.”
A case study
In an article published in the March
2020 issue of Semiconductor Digest,
titled “Understanding Cooling and
Particulate Contamination Challenges for Next Generation ALE
Technologies,” author Raj Meklote,
VP engineering for Semiconductor Chamber Solutions, Edward
Vacuum, notes that for atomic layer
processes, controlling particles is
a key requirement in managing
defectivity and yield. In-chamber
cryo-trapping can reduce water
vapor partial pressure, which directly
impacts the generation of particles.
The number of particles is also
affected by the design of the turbomolecular pump used to evacuate the
chamber. Particle transport models
have shown that particles can recoil
back into the chamber from rapidly
spinning turbomolecular pump
rotors. Refinements in pump design
can reduce the number of recoiling
particles. “Combining enhanced
cryo-trapping and turbomolecular
pumping technologies has the potential to significantly reduce particulate contamination and associated
yield losses,” he writes.
Meklote shows how a mixed-refrigerant Joule-Thomson refrigeration
can provide the necessary wafer
temperatures and cooling power with
smaller footprint, better reliability
and lower power consumption than
alternative cooling technologies,
while improvements in turbomolecular pump design can reduce the
number of particles deflected back
into the chamber by the pump’s rotor
blades. Cryo-trapping can reduce
particle generation by removing
the water that mediates the particle
formation process. Together, these
technologies will be critical enablers
of next generation processes and
devices.
Tollner heralds this work as a great
example of how Edwards and CTI/
Polycold engineers came together
in a short time to develop solutions
with similar mindsets and values.
“CTI’s entire business has always
been on-tool, so they have a real
sharp focus when it comes to what
the customer’s requirements and the
technical challenges,” he said. “Edwards comes from is a very strong
semiconductor background, but more
sub-fab. You bring those two together, and it’s really exciting to see
what can come out of it.”
A customized approach
The days of picking a vacuum
product out of a catalog for advanced
semiconductor manufacturing
processes are long gone. Instead,
Tollner said almost every pump
is customized to a particular application. “Typically, it’s a single
product, single customer, single
application. And the challenge is that
the development cycle is very quick,
and the development challenges
keep changing. As the equipment
manufacturers are developing, things
change very quickly,” he said. The
creates unique challenges for the new
Division. “We definitely see that the
focus on R&D, innovation, and speed
and agility will all be very different
for this division. This is exciting
for the customers because we will
be shaping ourselves to match their
requirements.”
6 | Tuesday, July 21www.semiconductordigest.com
