[labnetwork] Argon in a BCl3 cylinder

[Fouad Karouta]

Hi Sean,

I rather agree with Steven Paolini and you should replace the BCl3 cylinder.
As the BCl3 is liquid an exposure to another gas like Ar at a pressure > 15 psi would lead to Ar going into the cylinder. 
We did have a similar issue in the past with a different gas and after solving the leak issue the BCl3 never behaved as before and especially etching results with BCl3 were no longer satisfactory as before the leak. 
We ended up replacing the cylinder.

Kind regards,
Fouad

*************************************
Manager ANFF ACT Node
Australian National Fabrication Facility
Research School of Physics and Engineering
L. Huxley Building (#56), Mills Road, Room 4.02
Australian National University
ACT 2601, Canberra, Australia
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Email: fouad.karouta at anu.edu.au
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-----Original Message-----
From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Dwayne Chrusch
Sent: Thursday, 20 June 2019 7:17 AM
To: Rinehart, Sean <sean.rinehart at yale.edu>
Cc: labnetwork at mtl.mit.edu
Subject: Re: [labnetwork] Argon in a BCl3 cylinder

Hello,

If you’re using a 2 stage (or multi-stage) regulator, only the second stage (regulator output) and intermediate stage chambers are contaminated.

Here’s a link to how a 2 stage regulator works; https://www.youtube.com/watch?v=UfaucxS5rIc

In order to flow gas from the intermediate chamber to the secondary chamber, the secondary pressure must be lower than the intermediate pressure. If the pressure in the secondary is greater than the intermediate, the orifice between the intermediate chamber and the gas cylinder would remain closed. 

You should be able to purge the contaminated gas out. First, close off the cylinder. Next, use your vacuum system to evacuate the gas from the system. Let the MFC drop to zero flow. Set the gas flow rate to as high as safely possible. This will pull the contaminated gas out of the low side and intermediate chamber of the regulator (assuming it’s dual stage). In theory, there will always be some stubborn Ar gas, but it may be practical to purge “enough”. You could always recharge the gas line, and then re-purge it. 


Regards,

Dwayne D. Chrusch, MSc.
Operations Manager, Training & Safety Coordinator Nanosystem Fabrication Lab (NSFL)
E3-487 Engineering
75A Chancellor's Circle
University of Manitoba
Winnipeg, Manitoba
Canada, R3T 5V6
Tel: +1 (204) 474-8246
Fax +1 (204) 261-4639
http://home.cc.umanitoba.ca/~shafaic/NSFL_site/NSFL_Home.html


> On Jun 19, 2019, at 12:15 PM, Rinehart, Sean <sean.rinehart at yale.edu> wrote:
> 
> Hello all,
>  
> Recently our facility’s BCl3 cylinder had been charged with argon, increasing the delivery pressure to 25 psi. The cause has been corrected, but now I’m evaluating whether or not the cylinder needs to be replaced, and would appreciate some advice.
>  
> Since the root issue was fixed, the pressure has slowly dropped from 25 psi to 15 psi with use. Based on this, it seems like with more use the argon should completely deplete from the cylinder, but maybe someone can tell me if that’s actually true, and if there’s a way to evaluate gas concentrations. Additionally, the plasma glow is whitish instead of pink, so there’s definitely BCl3 content in the delivered gas.
>  
> Thank you,
>  
> Sean Rinehart
> Assistant Director, Cleanroom Operations Yale University
> 203 432 4303
>  
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> labnetwork at mtl.mit.edu
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