[Fwd: Re: Chemical exposure]

Dick Crane rcrane at snf.stanford.edu
Tue Aug 17 08:50:34 PDT 2004


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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