Stewart:
The smell of sulphur byproducts brings back old memories from early plasma
etching operations.
Hydrocarbon oil is OK for running SF6 but it will change viscosity with use
which can affect your pumping speed and change your process results thru time.
Adding an Al2O3 filter unit will help to neutralize the Lewis Acids that are
generated. Care must be taken when changing oil and disposal for obvious
reasons. Fomblin would be a better alternative but it is expensive. It will
allow you to run Oxygen without fear of blowing up a pump also. One way to
minimize the smell is to do pump purges about three where you backfill the
chamber with nitrogen and allow it to pump to base pressure which should be
around 20 mtorr
Exhausting your pump to an acid exhaust is sufficient as long as you have enough
draw but not so much to suck oil out of the pump. Having a damper to adjust the
amount of exhaust might help if possible. Make sure the hose is tight on both
ends and is at least 2" diameter.
Good luck Bob Henderson
-----Original Message-----
From: [email protected]
To: [email protected]
Sent: Thu, 14 Sep 2006 1:00 PM
Subject: [mems-talk] Setting up a small plasma etch system
Hi all: We found an old Technics PEII plasma system and, after some tinkering,
got it to work. I'm mostly interested in knowing whether our current setup is
safe, and how to improve it if not.
We're currently running SF6. The mechanical pump has regular hydrocarbon oil,
and it is vented through a hose to a fume hood. Here are my concerns at the
moment:
1) When we open the chamber after etching, there is a distinct sharp smell. This
dissipates after a while. Any ideas of what this is, and whether it's really bad
for you? I have an idea that it's some product of the reaction of fluorine or
sulfur with H20, but I'm not sure. If we pumped for a long time after reacting
but before opening the chamber, would this help?
2) After many (~10) runs, a white residue builds up on the aluminum plates of
the chamber. It can be removed with water. Any ideas of what this is?
3) I've heard that sulfurous acid and HF can build up in the pump oil, which is
both bad for the pump and for those who change the oil. I have thought about
changing the oil over to an insert oil such as Fomblin (which would also allow
me to run O2 in the etcher). Will this prevent the buildup of these acids?
4) Is simply venting the pump exhaust to a fume hood good enough?
5) Anything else we should know? We're trying to keep this simple, so we don't
want to spend a lot of money on scrubbers etc. if possible.
