[labnetwork] Nitrogen Purity for Sputtering

[John D Shott]

Mark:

In general, I believe that boiled off gas from a cryogenic source is always going to be higher quality in terms of background moisture and oxygen than just about any bottled source.

We also have a single tank that supplies both a copper-piped house N2 system and SS-piped UHP nitrogen system. Other than piping differences, the UHP system also has a purifier at the vaporizer end of the system.

As I recall ... I don't have my data at hand ... our house system in pretty good: on the order of 0.5-0.6 ppm moisture and oxygen both at the source and well downstream. As I recall, our UHP nitrogen is on the order of 5X lower in both moisture and oxygen. Those are based on occasional spot checks ... meaning only once in several years.

We are in the process of adding hygrometers on both nitrogen systems, as well as on our argon and CDA. Too early to say much, but we don't see much in the way of wild swings in moisture including immediately after a tank fill.

A couple of other comments:

1. Do you mean POU filters or purifiers?

2. Someone probably knows better than I, but is diffusion of moisture and oxygen through Teflon that much slower than through polyflo or other plastic tubing?  Maybe Teflon is OK, but plastic tubing is a no-no if you want to deliver high purity gas. I'd suggest going to SS with, if you have to, a short length of SS flex line. We have some polyflo and Teflon tubing in use ... but I am not proud of myself to have to confess that in this public forum.

3. I'd consider brining in a reputable analytical lab to look at oxygen and moisture levels, particularly if you can compare your bottled gas to you process gas.

4. In my experience, house gases are an easy scapegoat for process problems, but I have never found them to be the real culprit .... Also, moisture is easy to get into a system, but takes forever to get out unless you can bake it out, trap it with titanium sublimation, etc.

Let me know if you have further questions or would like me to sent that actual data that I mentioned.

I vote for using your bulk system and eliminating the bottles ...

John

Sent from my iPhone

On Jul 30, 2015, at 4:43 PM, "Mark Heiden" <mheiden at engr.ucr.edu<mailto:mheiden at engr.ucr.edu>> wrote:

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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