[labnetwork] Anhydrous HCl after it escapes ...

Sun Jun 8 16:35:28 EDT 2014

Hi John,

Based on what you wrote below, we would recommend changing the pre and post purge cycles to 60 from a safety standpoint; 30 is not enough. 50 is recommended on all HPM's for safety reasons, and from a quality standpoint on post cylinder change purge cycles you want to make sure any residual atmosphere is gone, therefore 60 is the standard Troy used at ON Semi for the post purge on all corrosives. He also recommend you look at the heel weights (what's left in the cylinder) as sometimes running the bottles too low can cause issues. If you're unsure of what the heel weight should be, ask the gas supplier. Typically 10% is a good number, so on a 60 lb cylinder most manufacturers would recommend changing the cylinder at 6 lbs remaining in the cylinder, but it's common to increase the heel if contamination occurs at the pigtail connection. For HCl, HBR and DCS it is not uncommon to increase the heel from 10% to 15% just to alleviate contamination issues.

Hope this helps. Feel free to call us if you want to discuss this further in depth.

Enjoy the day.

Thank you!

Tom Britton
Director of Sales
Critical Systems, Inc.
Direct: 208-890-1417
Office: 877-572-5515
www.CriticalSystemsInc.com<http://www.criticalsystemsinc.com/>

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From: John Shott [mailto:shott at stanford.edu]
Sent: Friday, June 06, 2014 2:55 PM
To: Tom Britton; labnetwork at mtl.mit.edu
Subject: Re: [labnetwork] Anhydrous HCl after it escapes ...

Tom, Craig, and Dennis:

Thanks for each of your comments.  I should have thought to mention more about the details of our gases:

We are using electronic grade HCl specified to be 99.995% pure.  While I think that there is one grade higher, at $1200 a cylinder it should be pretty good ...
Note: this is also set up with a DISS fitting (CGA 634 for HCl).

For our purge gas we use 10% He in a balance of nitrogen, again with a DISS fitting.  Each of the component gases is of UH grade that, I believe translates in to:

Nitrogen:

02           < 1ppm
H20       < 3ppm
THC      < 0.5ppm

Helium:

02           < 1ppm
H20       < 2ppm
THC      < 0.5ppm

After a cylinder change, we do a He leak check of the purge gas following each cylinder change.  I think that we are currently using 30 purge cycles both pre- and post-purge ... it sounds as if that should be bumped up.  While I believe that we have hastelloy running between cabinet and tool, I believe that the components in the panel are all SS ... but I believe are electopolished to

We have a manifolded two-cylinder (plus purge) cabinet that supplies an epi reactor.  It is not uncommon to use a 60 pound cylinder of HCl in a period of 1-2 weeks ... so, we unfortunately, have a number of chances for problems each year.

Thanks again for all of your input,

John

On 6/6/2014 1:07 PM, Tom Britton wrote:

Hi John,

Sorry to hear about your HCl issue. As we all know, HCl is very difficult to manage once it escapes. Neutralizing is seldom effective in a clean room environment, and replacement of metal components that have come in contact with the HCL is the proper way to keep it from spreading.  If the proper leak test procedures are in place, one thing that could be causing the leaks is residual moisture that may be present due to either  low quality purge gas or inadequate purging.

To solve the problem of how to prevent leaks with HCl and other corrosives these are the questions I would start with.

*         What is the quality of the purge gas?

*         Are you using a purifier on the purge gas?

*         Is H2O or O2  analysis done on the gas system prior to gas introduction?

*         How many purge cycles on gas line prior to gas introduction?

*         How many purge cycles post cylinder change are being done?

If you want, I can set up a conference call with Troy Reese, who was the gas systems manager at ON Semi before he came to us, and we can go over these questions. Troy is very knowledgeable in these situations and we would be happy to help wherever possible. He is also presenting with you at the Bootie Camp coming up at the UGIM conference, so we can talk about it there as well if necessary.

See you at Harvard.

Thank you!

Tom Britton
Director of Sales
Critical Systems, Inc.
Direct: 208-890-1417
Office: 877-572-5515
www.CriticalSystemsInc.com<http://www.criticalsystemsinc.com/>

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-----Original Message-----
From: labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu> [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of John Shott
Sent: Thursday, June 05, 2014 1:09 PM
To: labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>
Subject: [labnetwork] Anhydrous HCl after it escapes ...

Labnetwork Community:

Sooner or later, it seems, anhydrous hydrogen chloride (or a number of equally corrosive materials) is going to escape.  At least that is our experience at the Stanford Nanofabrication Facility.  Despite our best efforts to use quality components, do proper leak checking, etc., it seems as if we end up with a leak either in a gas cabinet or in a tool near a mass flow controller.  At that point, anything near the site of the original leak has been covered with now moisture-laden hydrogen chloride ... which, I believe, is far more corrosive than the original anhydrous material.

For those of you who have encountered similar situations, how do you recover or what to you replace?  Do you have effective means of neutralizing those metal surfaces?  Do your replace VCR gaskets with thicker-than-normal or grooved "super gaskets"?  Do you replace the entire assembly?  Do you leak check, put back in service, and pray?

Thanks for sharing your experience and insights,

John

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