[labnetwork] Piranha processing vessels

[Mary Tang]

Thanks Bob!

A wonderful example of how "contamination" can be managed by means other 
than the paranoia -- something we struggle with as we try to serve a 
broader community while trying to keep our electronics and detector 
researchers happy.  I would hazard a guess that this works in industry 
because distillation is vacuum rather than heated and that an additional 
RCA-equivalent clean is used before high temperature processing steps, 
thus minimizing the risk of driving in mobile ions.

That said, at Stanford, we do promote paranoia when it comes to 
dedicated teflon cassettes in MOS stations because of their propensity 
to absorb whatever chemical they are exposed to.  I've not seen any data 
that shows cross-contamination due to this, but have seen the results of 
off-gassing on wafers stored or heated in chemical bath cassettes.  The 
risk of significant carryover of HF into piranha may be very low, but 
might be worth considering dedicated cassettes when using pyrex.

Mary


-- 
Mary X. Tang, Ph.D.
Stanford Nanofabrication Facility
Paul G. Allen Bldg 141, Mail Code 4070
Stanford, CA  94305
(650)723-9980
mtang at stanford.edu
http://snf.stanford.edu



On 4/28/2016 1:21 PM, Robert M. HAMILTON wrote:
> Keith,
>
> I'll stick my neck out!
>
> The UC Berkeley NanoLab uses fused silica tanks with encased heaters 
> and ground-fault detection for our piranha baths. I am guessing your 
> suggestion of Pyrex or an alternative borosilicate glass will raise 
> the hackles of some Labnetwork readers. And, I cannot claim experience 
> with the impact of borosilicate glasses, used for piranha cleans, for 
> MOS devices.
>
> However, I can point to a patent issued to Alameda Instruments that 
> made H2SO4 reclaim/reprocessing systems for a number of major 
> semiconductor manufacturers. I also have known, since boyhood the 
> research glassblower who made their vacuum stills. The glass used was 
> Pyrex or an alternative Duran, which is Schott's equivalent. This 
> leads me to the conclusion H2SO4 from a pyrex still was good enough 
> for Intel, Pyrex is probably good enough for you.
>
> Having said this if there is accidental contamination via HF your 
> Pyrex will contribute alkali and your devices will be DOA. We have 
> seen HF contamination in our baths on a few occasions.
>
> For reference see: https://www.google.com/patents/US4980032
>
> Bob Hamilton
>
> PS Caveat emptor! Corning now uses the term Pyrex for a broader number 
> of glasses than their traditional 7740.
>
>
> Robert Hamilton
> University of CA, Berkeley
> Marvell NanoLab Equipment Manager
> Rm 520 Sutardja Dai Hall, MC 1754
> Berkeley, CA 94720
> Phone 510-809-8618 (desk - preferred)
> Mobile 510-325-7557 (my personal mobile)
> E-mail preferred: bob at eecs.berkeley.edu <mailto:bob at eecs.berkeley.edu>
> http://nanolab.berkeley.edu/
>
>
>
> On Thu, Apr 28, 2016 at 10:59 AM, Keith Franklin <keithf at ualberta.ca 
> <mailto:keithf at ualberta.ca>> wrote:
>
>     Good day all,
>
>     We're currently revisiting what vessels or tanks we use for
>     processing with hot piranha.  Our most common application is for
>     cleaning a partially filled cassette of 4" Si wafers.  We
>     typically purchase Pyrex 6944 vessel and have our glass shop cut
>     them down to a more reasonable height.  In our last purchase
>     cycle, we noticed that the ID has changed ever so slightly and
>     it's now challenging to squeeze our standard Entegris cassette
>     into this vessel.  We're currently looking into custom machined
>     PVC, PP,  Teflon & Quartzware, as well as off the shelf small
>     volume tanks, etc.
>
>     I'm hoping to better understand what other similar labs are using
>     for this application (& potentially 6" wafers as well).  Any
>     advice or feedback would be greatly appreciated.
>
>     Kind Regards,
>     Keith
>     __
>
>     Keith Franklin
>
>     Operations Manager
>
>     University of Alberta - nanoFAB
>
>     W1-060 ECERF Building
>
>     9107 - 116 Street
>
>     Edmonton, Alberta
>
>     Canada T6G 2V4 Ph: 780-492-0170 <tel:780-492-0170>
>
>     www.nanofab.ualberta.ca <http://www.nanofab.ualberta.ca>
>
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