[labnetwork] Decommissioning Silane and Phosphene Stainless Gas Delivery Lines

[Bill Flounders]

All,
I welcome the pump purge recommendations and support we all use
our best discretion regarding number of cycles, length of time etc.
Document what you did for your own records.

I disagree with using the term "hazardous waste" for the phosphine tubing.
This sets a precedent in our community that I do not see as justified.
It carries an increased disposal cost and handling concerns.
If you believe the material is potentially contaminated then I encourage
you to propose reasonable and appropriate decontamination procedure.
You have everything you need in house to make this safe for pick up.

In General:
I would pump/purge as recommended to insure safe for disassembly.
Disassemble with appropriate PPE if you consider potentially
contaminated. Treat with water, solvent, acid or base as appropriate
for decontamination and dispose as non hazardous waste.

Due to the high volatility of PH3, I would not consider the pumped/purged
tubing hazardous. If you wanted additional assurance, rinse with water
or alcohol. To verify non hazardous, rinse with water and pH test the 
liquid.
Even for a low volatility acid gas such as BCl3, I wouldn't consider the
tubing hazardous waste. But I would document that I gave it a rinse with
mild sodium hydroxide solution, rinsed and pH tested prior to disposal.

Bill Flounders
UC Berkeley




Paolini, Steven wrote:
>
> Excellent question.
>
> I cannot quote industry standards nor am I aware any exist, but the 
> bottom line is many pump and purge cycles are in order. I would use 
> the system for the pumping part of the procedure since it will pump 
> well below what the venturi can provide at the cabinet. I would say 
> that the exact # of cycles is up to you and your available time. If I 
> were challenged with this, I would pump the lines down to the lowest 
> level of vacuum achievable through your system and still allow it to 
> remain there for at least a half hour (or more if your delivery lines 
> are longer than 50 feet) since there are always some stubborn 
> molecules of gas that have to crash into bends and ultimately enter 
> the chamber. I would then run pure N2 through the MFC’s at full scale 
> for another half hour before repeating the cycle. I would do this at a 
> minimum of 20 cycles.
>
> In regards to disposal, I would treat the Phosphine lines as hazardous 
> waste but the Silane lines should be relatively non-toxic aside from 
> possible deposits of SiO2 (dusting). I hope that other subscribers can 
> correct me if I am wrong about this but my methods have been  
> successful over the years.
>
> Best of luck and be careful,
>
> Steve Paolini
>
> Equipment dood
>
> Harvard Center for Nanoscale Systems.
>
> *From:*labnetwork-bounces at mtl.mit.edu 
> [mailto:labnetwork-bounces at mtl.mit.edu] *On Behalf Of *Hmelo, Anthony B
> *Sent:* Friday, September 09, 2016 9:42 AM
> *To:* labnetwork at mtl.mit.edu
> *Cc:* Hmelo, Anthony B
> *Subject:* [labnetwork] Decommissioning Silane and Phosphene Stainless 
> Gas Delivery Lines
>
> All:
>
> VINSE is in the process of relocating a PECVD reactor to a new 
> cleanroom facility and I am seeking advice on the industry standards 
> for decommissiong Silane and Phosphene stainless gas delivery lines 
> that run from the respective gas cabinets to the tool in its current 
> location. Beyond thoroughly purging the lines with nitrogen flow 
> through the tool and exhausting the purge gas  through the tool 
> exhaust, are there other considerations involved in abandoning the gas 
> delivery lines? For example, are the lines considered to be 
> permanently contaminated and will they require special disposal?
>
> Any advice on decommissioning these lines will be deeply appreciated.
>
> With thanks,
>
> Anthony B Hmelo, PhD
>
> Associate Director, VINSE
>
> Research Associate Professor of Physics and Astronomy
>
> Research Associate Professor of Materials Science and Engineering
>
> Vanderbilt University
>
> Nashville TN 37235
>
> 615-343-7212
>
>
>
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