[labnetwork] TMAH alternatives

Wed Jun 28 14:11:40 EDT 2023

With some sick time I had to endure, I went down the rabbit hole of TMAH and similar compounds toxicity. Scientific archeology is fun!

First, TMAH isn't a good thing to study - corrosive effect of being a base doesn't allow good study of TMA ion, so salts like TMA chloride are better test materials.
With that, even those papers are not very abundant. Some of latest TMAH work is purely TMA, no comparisons. I actually happened to briefly talk to Ernst Timlin from IBM about things they did - that was a while ago though.  I assume their briefs are a big part of current motivation:
https://sesha.org/abstract/tetramethylammonium-hydroxide-tmah-toxicity-and-methods-to-reduce-risk-in-the-workplace/

Second, TMAH oral LD50 by weight is something like a cup of CD26 developer for my weight. So I am not surprised when they say rats given half of that dose look strange - if you know the taste of TMAH, you would certainly understand those poor animals!

Most relevant papers - and looks like any relative safety claims are based on that  - are

Hunt, Reid. "Some effects of quaternary ammonium compounds on the autonomic nervous system." Journal of Pharmacology and Experimental Therapeutics 28.3 (1926): 367-388.
https://jpet.aspetjournals.org/content/28/3/367.short

Burn, J. H., and Henry Hallett Dale. "The action of certain quarternary ammonium bases." Journal of Pharmacology and Experimental Therapeutics 6.4 (1915): 417-438.
https://jpet.aspetjournals.org/content/6/4/417

If anyone has an access, it would be great to look at full texts.

Other relevant  papers:
Gebber, Gerard L., and Robert L. Volle. "Mechanisms involved in ganglionic blockade induced by tetramethylammonium." Journal of Pharmacology and Experimental Therapeutics 152.1 (1966): 18-28.
https://jpet.aspetjournals.org/content/152/1/18.short

Another interesting one is
Wien, R., et al. "The ganglion blocking properties of homologous compounds in the methonium series." British Journal of Pharmacology and Chemotherapy 7.4 (1952): 534.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1509303/?page=2

While not a TMA, but a more complex molecule - they see increased neural effect with gradual methyl to ethyl replacement.

Sorry for the long one!

Mike

_______________________________________________

Michael Yakimov

Research scientist

College of Nanoscale Science and Engineering

SUNY Polytechnic Institute

253 Fuller rd.

Albany NY 12203

Phone: 518-437-8609 lab

e-mail: yakimom at sunypoly.edu

________________________________
From: labnetwork <labnetwork-bounces at mtl.mit.edu> on behalf of Hathaway, Malcolm R <hathaway at cns.fas.harvard.edu>
Sent: Friday, June 23, 2023 11:48 AM
To: Labnetwork Mailing List <labnetwork at mtl.mit.edu>
Subject: Re: [labnetwork] TMAH alternatives

Hello All,

Thanks for all your responses regarding potential replacements for TMAH.

It appears that some folks have been making their own investigations along these lines, and others are interested in doing so.  Since some of this work is on-going, the idea was suggested that we create an email list where we can coordinate these efforts.  This will be called the TMAH Working Group, so that it can encompass a wide membership, including NNCI member institutions as well as others, including perhaps some industry folks as well.

As we find out more, we'll keep the main Labnetwork apprised of our progress.

So, if you have an interest in furthering this work, or would like to share your findings or recommendations, email me at hathaway at cns.fas.harvard.edu, and I'll put you on the mailing list.

The first notable finding is that Sachem Envure 3330 and Transene SE-33 appear to be the same stuff, i.e. Envure is repackaged in smaller lots for smaller companies and labs by Transene. As Graham at Queens pointed out, Huntsman seems to develop novolac photoresists reasonably well, with some variation in develop time.

As mentioned previously, the active ingredient in Envure/Transene is TEMAH (triethyl methyl ammonium hydroxide), while Huntsman uses (hydroxyethyl) methyl ammonium hydroxide.  With regard to safety, we only have, as yet, whatever the manufacturers say.  The marketing info suggests one of the Transene products (SE-33) is around 8x less toxic, while the others may be 15x less toxic.  Huntsman just says their stuff is "safer".  Clearly, a bit more digging in is called for!

The initial email for the TMAH Group will go out shortly,

Thanks,

Mac Hathaway
Harvard CNS
________________________________
From: Graham Gibson <gibsong at queensu.ca>
Sent: Saturday, June 17, 2023 2:42 PM
To: Hathaway, Malcolm R <hathaway at cns.fas.harvard.edu>; Labnetwork Mailing List <labnetwork at mtl.mit.edu>
Subject: RE: TMAH alternatives

   Hi Mac,

   I have tried Huntsman’s E-Grade THEMAH as well as another of their products, E-Grade CHOLINE OH, as a developer for standard Novolac photoresists, though not for HSQ (yet). I was pretty happy with their performance in general, though THEMAH was a bit slow compared to standard TMAH developer.

  Cheers,

Graham Gibson

Operations Manager, NanoFabrication Kingston

Queen’s University

945 Princess Street

Kingston, Ontario, Canada

K7L 0E9

gibsong at queensu.ca<mailto:gibsong at queensu.ca>

www.nanofabkingston.ca<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.nanofabkingston.ca_&d=DwMFAg&c=WO-RGvefibhHBZq3fL85hQ&r=TEMLD8-VsxCGtcVzmvpT5GFNSczskEKHzW6aYlttmIY&m=OsyPDb0Ur6EvRRta3mwKsTIMksoH8kgvJF4CjMEccxyIPWc8KlY75EEy4r7Mkh_e&s=C1IJR82INSIBlZMD65yCnLorWFHWjaFNg1gJ81DnzVI&e=>

From: labnetwork <labnetwork-bounces at mtl.mit.edu> On Behalf Of Hathaway, Malcolm R
Sent: Thursday, June 15, 2023 2:20 PM
To: Labnetwork Mailing List <labnetwork at mtl.mit.edu>
Subject: [labnetwork] TMAH alternatives

Hello Labnetworkers,

Has anyone tried one of the TMAH substitutes that have become available?

How do they work?  Are your users satisfied with their results?

For background, TMAH (tetramethylammonium hydroxide) is widely used in commercial resist developers (3%) and for HSQ developing (25%).  In its 25% concentration, TMAH is a potent contact neurotoxin, which is fatal roughly 75% of the time, for exposures greater than 7.5% of body area.  Nasty stuff.

Several companies now have safer alternatives available, which we'd like to try out, such as:

 Envure 3330 (Sachem Chemical),

E-Grade THEMAH SLM ((hydroxyethyl) methylammonium hydroxide, from Huntsman Chemical), and

Novo-safe SE-33 (ethyl tri-methy ammonium hydroxide from Transene).

We are particularly interested in using one of these as an HSQ developer, so we can do away with 25% TMAH.

Any experiences, good or bad, will be most welcome.

Thanks,

Mac Hathaway

Senior Process and Systems Engineer

Harvard Center for Nanoscale Systems
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