[Fwd: Re: Chemical exposure]

Mahnaz Mansourpour mahnaz at snf.stanford.edu
Tue Aug 17 13:08:04 PDT 2004


Mary

Sounds good, although sounds horrible.

mahnaz

Dick Crane wrote:

> Mary,
>
> Concerning the signs, are these the words (Avoid Exposure to Fumes:  Open Slowly)
> you want? If so, I have them ready in a day or so.
>
> Dick
>
> Mary Tang wrote:
>
> > Hi all --
> >
> > Here's some more detail from Scott Andrews about how he got a good whiff
> > of SPR-220.  I'm just about to ask Maureen to make up some colored,
> > laminated signs which say "Avoid Exposure to Fumes:  Open Slowly" which
> > I'd like to post on the 90 C and 110 C ovens (maybe the little blue M
> > too?), the flammables cabinets and the flammables refrigerator.
> >
> > Mary
> >
> > -------- Original Message --------
> > Subject: Re: Chemical exposure
> > Date: Mon, 16 Aug 2004 21:17:38 -0700 (PDT)
> > From: "Scott D. Andrews" <sandrew at stanford.edu>
> > Reply-To: Scott Andrews <scott.andrews at stanford.edu>
> > To: Mary Tang <mtang at snf.stanford.edu>
> >
> > Hi Mary,
> >
> > > When transferring wafers straight from spin (when the resist is still wet) to
> > > either hot plates or the post-spin-bake oven, wafers should be placed inside
> > > an enclosed box.
> >
> > When transferring the wafers, I was using a single wafer box to carry
> > then
> > over. I still smelled a little, but I assume that was contamination on
> > my
> > tweezers or gloves.  As I said, this was really minor, and I wouldn't be
> > too concerned about any exposure here.  Perhaps you can answer one more
> > question, though.  I have wondered about the best procedure when
> > trasfering full wafers.  Can they be put back in the vertical holders
> > (the
> > main boxes that hold 25 wafers) after spinning?  I was always concerned
> > about screwing up the spin at the edge where it touches the box and also
> > contaminating my box which would then spread vapors for days.  I have a
> > few reservations too about using the single holders -- although that is
> > usually what I do.  Since occassionally, small amounts of resist go onto
> > the backside of the wafer either due to contaminated tweezers or a bad
> > spin, putting it in a box can cause it to become sticky and again vent
> > for
> > days.  Do you have any good suggestions on how to handle this?
> >
> > > Was your exposure during the post-spin-bake?  If so, which stations were you
> > > using and what was your procedure?
> >
> > All the exposure I had was during post-spin baking.  I was spinning very
> > thick resist (SPR-220, 1 krpm, 30 sec) as a protection layer.  I was
> > only
> > using the headway, hot plates, and the white ovens next to it.
> > Initially, I
> > was using 90 degrees and then transferred to the 115 degree oven for the
> > final bake.  My exact procedure was:
> >
> > 1) Put blue tape on back of my wafer (needed because it had free
> > standing
> > membranes that would have been destroyed by the vacuum)
> > 2) Spin SPR-220, 1 krpm, 30 sec
> > 3) Remove tape
> > 4) Move to hot plate, bake for 100 seconds at 90 degrees
> > 5) Spin SPR-220, 1 krpm, 30 sec on backside
> > 6) Move to 90 degree oven for ~30-45 minutes (Since this was a
> > protection
> > layer, I didn't care if I had the proper time, I just needed it dry)
> > 7) Move to 115 degree oven for another 30 minutes or so
> >
> > > Another observations I've had is how many of us open the doors on the
> > > flammables cabinets (and may apply here as well)...  The exhaust is static and
> > > when a door is opened quickly, it counters the exhaust, potentially drawing
> > > fumes across the person opening the door...
> >
> > I TOTALLY agree about the flammables cabinets.  I've have always been
> > concerned about that.  I didn't realize that the speed of opening the
> > cabinets makes a difference.  I always assumed the exhaust simply wasn't
> > enough.
> >
> > > I'll try this out in the litho area a few times, and if this helps, I'll
> > > put some signs up ("open the door slooowwwwllly") and add it to our
> > > safety training info.
> >
> > Please let me know what you find.  One recommendation on the sign is to
> > indicate why one should open it slowly too.  Since the processes people
> > use in the cleanroom are complex often information seems to get lost as
> > to
> > why certain thing need to be done.  For example sometimes I thought the
> > order of certain operations such as opening certain valves were critical
> > to get a machine to operate safely/properly.  Only later when I
> > understood
> > the process more, did I realize it was just the order the trainer had
> > happened to use during training.  I think knowing why helps us all
> > protect
> > the equipment and ourselves if we know why certain things need to be
> > done.
> > For example, if the sign only said "open the door slowly," I would
> > assume
> > that the door was fragile and watch for something wrong near the hinge.
> > Thus, if I still smelled fumes, I would not realize I had opened it too
> > fast.  Also, with regards to the furnaces, this may very well be part of
> > the problem.  After getting several whiffs of the fumes, I tended to
> > open
> > the door as quickly as possible, insert the wafers, and close it quickly
> > with the thought that the less time the door was open, the less time for
> > fumes to escape.
> >
> > > I'm really sorry this happened, and truly appreciate you letting us
> > > know...
> >
> > I realize thing like this happen.  I just appreciate you taking this so
> > seriously and helping make the lab a safe place for us to work.
> >
> > > Knowing that you are a conscientious person in the lab, I'm concerned that
> > > there is something wrong in our procedures and/or our equipment setup.  Again,
> > > if you could provide a little more detail (which stations, etc.) and insight
> > > as to what you feel might help, it would be much appreciated...
> >
> > I really think I was doing everything generally right.  Especially after
> > breathing the fumes the first time, I tried to be very careful because I
> > knew it wasn't healthy.  As I mentioned, the only stations were the
> > headway, the nearest hot plates, and the two white furnaces.
> >
> > Thanks for your help.  Let me know if there is any other info I can
> > provide.
> >
> > -Scott




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