[labnetwork] Nitrogen Purity for Sputtering

[Tom Britton]

Hi Mark,

A couple of items to point out.

1. Using Teflon tubing in a high purity gas system can lead to contamination of your nitrogen as Teflon is permeable to gases, including oxygen, hydrogen and moisture. (See attachments) For high purity liquids, Teflon tubing is an excellent material, but is not a good choice for high purity gas. I would recommend replacing the Teflon tubing with electropolished 10Ra stainless steel tubing. The two reasons for this are 1. stainless steel is not permeable to gas/moisture, and 2. the electropolished surface provides a very smooth surface so as not to aid moisture in its ability to stick to the surface of the metal.

2. If the professor's process is moisture sensitive, I would suggest a point of use purifier like the one attached. Depending on required flow rates, the cost is going to be around $1000 - $1,500, and should last for years if sized correctly. Depending on the media chosen in the purifier, you can eliminate moisture to less than 1 ppb, or a host of other contaminants to the same level of removal.

If you want to discuss this deeper, just give me a call and I'd be happy to help.

Good luck sir!

Tom

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: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Mark Heiden
Sent: Thursday, July 30, 2015 4:13 PM
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] Nitrogen Purity for Sputtering

We are moving a sputtering system from a remote installation into our cleanroom and the intent has been to take it "off the bottle" and use the building process nitrogen system for process gas as well as venting. The bottles on the old install were 99.999% but the building process nitrogen is not certified to any exact number. The piping comes out of the 9000 gal. tank and through a vaporizer, then it goes through filters then splits into "house" nitrogen which is copper piping and "process" nitrogen which is all stainless steel with 10ra polished inside.

>From the stainless building process nitrogen line regulator, we ran high purity Teflon PFA tubing to the point of use filter on the MFC. Since I can't provide a precise purity for the evaporated nitrogen gas coming from the bulk tank and the tubing from the regulator to the filters is not stainless, a PI that was using the system is terrified that the nitrogen won't be pure enough. Could I get your opinions on what the purity may be expected to be and if it is less than 99.999% would the filters correct this anyway?

I'm sure most operations that spent the money for a "process" nitrogen system are not then running everything on bottles anyway so how do you ensure that the nitrogen being delivered to the systems is pure enough?

Thanks in advance,


Mark Heiden
NanoFab Cleanroom Manager
Center for Nanoscale Science and Engineering
University of California, Riverside
951-827-2551


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