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Edwards
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the byproducts and their potential
hazards, designing the foreline
piping system to minimize problems
– by optimizing joints, seals, valves
and elbows, for example, plus temperature management – as well as
monitoring and, ultimately, gas
abatement.
Hazardous process byproducts
can build up in the pump if
precautions aren’t taken.
“When we’re considering what’s
coming down the foreline — or what
may be forming in the foreline as a
result of a particular process — then
we have to be conscious about what
form that material may take,” Mann
said. “Sometimes it’s a gas, a solid, a
powder or a liquid.” The first course
of action is to stop byproducts from
forming in the first place. “It’s not
always possible to do that so then it’s
a case of can you keep the hazardous
material moving through the system
to a point where you can manage
it safely and effectively like in the
abatement system, for example.”
It’s good practice to try and minimize the number of joints in the
system, particularly if the possibility
of leaks is a concern, which ca be
either hazardous gases leaking out of
the system or it can mean air leaking
into the system, both of which can
present their own hazards. “These
are fairly common sense things, but
there are other things that people
may not think about or be aware of,
in as much as we try to avoid horizontal runs of pipe or minimize them
as much as possible. In some cases
it might be appropriate to have 45
degree lengths of pipe, rather than
a 90 degree bend in a pipe because
— particularly with powders — it’s
more inclined to keep them moving
through the system,” Mann said.
It may be appropriate to have
certain isolation points in the system.
Mann said it’s good practice to have
gate valves above dry pumps, for
example, in order to keep the pumps
running. ”That’s generally good
practice from a reliability point of
view, as far as the pump is concerned, but also it has some safety
aspects as well. Every time you stop
a pump, there’s a risk that you could
have backflow of gasses through the
exhaust system and into the foreline,”
he said. Isolation points will also help
with routine pump maintenance.
But then, as I say it’s good to have
isolation points in the system so that if
you do have to stop the pump, say for
maintenance, or if it needs changing
out for any reason, then you can
isolate the foreline. You can bring the
foreline up to atmospheric pressure
slowly and under purged conditions,
so that you’re isolating that part of the
system from atmosphere when you do
remove the pump.”
Temperature management can
also be important, particularly with
condensable by-products passing
through the system. “You can often
keep things moving if you can understand the temperature requirements
of the material and if you can keep
it in a gaseous form or even a fluid
form to keep it moving rather than
condensing as a solid. That’s a good
Modular integrated sub-fab
solutions ensure safe system
operation, including mitigation
of process exhaust hazards, and
reduce exposure of service staff
to hazardous materials.
thing to do,” Mann said.
The integrated solution approach
developed by Edwards is designed to
closely couple the dry pumps and the
abatement system. “The temperature
between the two is carefully managed
so that we are minimizing the risk
wherever possible,” he added.
An integrated solution can also be
shipped from the factory pre-leak
tested. “When it’s installed in the
fab, the customer can have confidence that the pipe work has been
properly joined up. We’re using the
correct seals, which sometimes those
could be Viton, Kalrez, PTFE or
even metal, depending on the application and the risk,” Mann said.
The Edwards abatement system is
an inward-fired combustor to reduce
the likelihood of material settling
and depositing inside the combustion
chamber. It also enables the temperatures to be carefully controlled
to reduce the likelihood of NOx and
carbon monoxide forming.
“These are all things that we
can do with our knowledge of the
application and with best-known
methods,” Mass said. “By managing
that, we take the risk and worry
away from the customer.”
6 | Wednesday, July 22www.semiconductordigest.com
