[labnetwork] Query on safety concern

[Mac Hathaway]

Hi V,

So, I'm sure others here have more direct experience with diborane and 
phosphine systems than I have, but just to clarify a couple of points:

Do you /have/ a load-lock on this system?  When you say indigenous, you 
mean more or less "home-built", yes?

If you have a load-lock, why do you prefer not to use it?  If this unit 
is home-built, perhaps it does not have some of the more advanced 
features of a commercial unit, such as gas-flow interlocks, to prevent 
flow of gases into the chamber when the chamber is open.  If it does not 
have such interlocks, you have a very dangerous system on your hands, 
which perhaps could be retrofitted with these features.

To re-emphasize what Len said, I would venture to say diborane and 
phosphine are among the most deadly gases in most cleanrooms.  You 
really want to consider this when coming up with your operating 
procedures.  Opening phospine/diborane process chambers, for whatever 
reason, is typically a very involved procedure, which very carefully 
defined steps to maximize safety and minimize exposure to the gases 
involved (including lingering chamber fumes).

I haven't found any particular ones in discussions here, but there may 
be some plasma post treatment that would de-activate the 
phosphine/diborane before opening the reactor each time.  Otherwise, 
just lots of pump/purge cycles.  For regular sample loading, a load-lock 
would be best.

If you can forward more details about this system, I think it will be 
easier to give you some better suggestions.


Mac Hathaway
Process Engineer and Safety Officer
Center for Nanoscale Systems
Harvard University



On 3/24/2014 7:43 PM, vanaparthy at ee.iitb.ac.in wrote:
>   Hi Leonard ,
>   Thanks,We installed Gas detection system in loading
> area to take care  of any issue with toxic gas is detected,appropriate
> alarms and evacuations will be initiated.
>
>
V,

Diborane and Phosphine gases are very toxic and deadly...

I'm not sure why you are not using the ll's for sample transfer.  It would
appear that an SOP would employ the use of load locks to create a barrier
between the reaction chamber and the outside world.  I would be concerned
about a failure in your gas delivery system or even outgassing during the
opening of the process chamber.

5X N2 pump purges in my opinion is not nearly enough.  A typical pump
purge for toxic gas cylinder changes is at least 25x.  Are you using a
Nederman style snorkel exhaust or any fume exhaust abatement whilst
unloading your samples?  Are you using any PPE or supplied air masks?

You may want to consider keeping your process chamber under vacuum to keep
its integrity. Ambient moisture from atmosphere upon opening the chamber
will surely create unwanted fumes and contaminates.

How large is chamber?

Thank you,

-Len

Leonard E. Olona
University Cleanroom Manager
University of Oklahoma
110 West Boyd Street Rm 550
Norman, Oklahoma  73019
D: +1- 405 325-4374
C: +1- 405 630-9068
F: +1- 405 325-7066










On 3/24/14 10:40 AM,"vanaparthy at ee.iitb.ac.in"  <vanaparthy at ee.iitb.ac.in>
wrote:


Hello,


We have a indigenous Plasma Immersion Ion Implantation system in our lab
which is capable to P(B2H6) and n(PH3) type of implantation. We are not
using the load lock for loading/Unloading the sample, Execute this by
venting the process chamber to atmosphere. Before unloading the sample we
do the pump purge with N2 gas  for five times.

Is the above procedure followed by us is a standard procedure or do we
need to follow some more safety precautions before opening the chamber.

Please advise.



--
Thanks&  Regards,
V.RAJENDRA PRASAD
  Lab Manager,
  CEN,IITBNF, Electrical Engg Dept, Annexe,
  IIT Bombay, Mumbai, Powai- 400076
  Tel No.+91 9930621667






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