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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>Great information, Mac, thanks for sharing it. Glad to see people actually looking into this.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Just to follow up, in our facility there is a lot of beaker development done. This is in ventilated clean wet benches, with eye protection and face shields, with nitrile gloves. There is MF312 available, which is >5% TMAH, but <u>rarely</u> used except in dilution. Everything in general is 2.38% or lower.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal style='text-align:justify'>We <u>DO NOT ALLOW</u> HSQ development in 25% TMAH <u>AT ALL</u>. We see that as too high a risk. It is only used for Si etching in fume hoods using full PPE, and there are strong warnings regarding its use.<o:p></o:p></p><p class=MsoNormal style='text-align:justify'><o:p> </o:p></p><p class=MsoNormal style='text-align:justify'>Replacement of TMAH will need to be made cost-comparative for acceptance, and more testing, including contamination/defects/device performance, needs to be done. This means that the HVM folks need to be on-board, and I have seen little evidence so far. Hopefully soon.<o:p></o:p></p><p class=MsoNormal style='text-align:justify'><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>Garry J. Bordonaro<o:p></o:p></p><p class=MsoNormal>Microlithographic Engineer<o:p></o:p></p><p class=MsoNormal>Cornell NanoScale Facility<o:p></o:p></p><p class=MsoNormal>250 Duffield Hall<o:p></o:p></p><p class=MsoNormal>343 Campus Road<o:p></o:p></p><p class=MsoNormal>Ithaca NY 14853-2700<o:p></o:p></p><p class=MsoNormal>(607) 254-4936<o:p></o:p></p><p class=MsoNormal><a href="mailto:bordonaro@cnf.cornell.edu">bordonaro@cnf.cornell.edu</a><o:p></o:p></p><p class=MsoNormal><a href="http://www.cnf.cornell.edu/">http://www.cnf.cornell.edu/</a><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Please acknowledge CNF in your publications:<o:p></o:p></p><p class=MsoNormal>"This work was performed in part at the Cornell NanoScale Science & Technology Facility (CNF), a member of the National Nanotechnology Coordinated Infrastructure (NNCI), which is supported by the National Science Foundation (Grant NNCI-2025233)."<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p></div><p class=MsoNormal><o:p> </o:p></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b>From:</b> labnetwork <labnetwork-bounces@mtl.mit.edu> <b>On Behalf Of </b>Mac Hathaway<br><b>Sent:</b> Tuesday, April 28, 2026 3:34 PM<br><b>To:</b> Lab Network (labnetwork@mtl.mit.edu) <labnetwork@mtl.mit.edu><br><b>Subject:</b> [labnetwork] TMAH Working Group - TMAH Alternatives - Summary of Findings<o:p></o:p></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto'><span style='font-family:"Times New Roman",serif;color:black'>Hello Labnetwork:</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto'><span style='font-family:"Times New Roman",serif;color:black'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto'><span style='font-family:"Times New Roman",serif;color:black'>The recent discussion about PPE for lithography work seems an appropriate moment to present the findings of the TMAH Working Group.</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto'><span style='font-family:"Times New Roman",serif;color:black'><br>The TMAH Working Group is an informal ad-hoc group formed a couple of years ago amongst primarily academic nanofabrication facility folks concerned about students handling TMAH and the relatively poor awareness of its special hazards. As some of you will be aware, its primary hazard is associated not with its extremely corrosive nature, but rather with the fact that it is a potent neurotoxin, on par with HF but without any known antidote. The goal of the TMAH Working Group was to find viable and less toxic alternatives to TMAH. What follows is a summary of our findings. </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto'><o:p> </o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-family:"Times New Roman",serif;color:black'>TMAH is used in our labs primarily in 3 ways: </span><o:p></o:p></p><ol start=1 type=1><li class=MsoNormal style='color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l2 level1 lfo1'><b><span style='font-family:"Times New Roman",serif'>Developer for novolac photoresist</span></b><span style='font-family:"Times New Roman",serif'>. The concentration is low (2.38% typically) and so the toxicity is lower than it is for full strength (25%). There has been one fatality ascribed to an extensive exposure to 2.3% TMAH as well as other cases with less catastrophic outcomes. </span><o:p></o:p></li></ol><ol start=2 type=1><li class=MsoNormal style='color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo2'><b><span style='font-family:"Times New Roman",serif'>Developer for HSQ-type e-beam resist</span></b><span style='font-family:"Times New Roman",serif'>. The concentration for this application is higher (25%) and the motivation to find an alternative is therefore greater. While relatively few substantial (greater than 5-7% of body area) exposures to 25% TMAH have occurred, the current fatality rate seems to be around 75%. These findings are part of what inspired the IBM study mentioned in a recent labnetwork post.</span><o:p></o:p></li></ol><ol start=3 type=1><li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3'><b><span style='font-family:"Times New Roman",serif;color:black'>Etchant for Si</span></b><span style='font-family:"Times New Roman",serif;color:black'>. The traditional etchant for this application is KOH, but for cases where metal ions are problematic, TMAH is the default. This application is the most hazardous as it typically requires larger volumes, longer times, and higher temperatures </span><o:p></o:p></li></ol><p class=MsoNormal><span style='font-family:"Times New Roman",serif;color:black'>The TMAH Working Group has identified two primary chemical suppliers who have made an effort to develop and market TMAH-alternative quaternary ammonium salts<b>. SACHEM Chemical</b> is selling some more obvious alternatives like tetraethyl-, ethyltrimethyl-, and tetrabutyl-ammonium hydroxide under the brand NOVO-SAFE, distributed by Transene (</span><span style='font-size:12.0pt;font-family:"Times New Roman",serif'><a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__transene.com_tmah-2Dsubstitutes_&d=DwMF-g&c=WO-RGvefibhHBZq3fL85hQ&r=TEMLD8-VsxCGtcVzmvpT5GFNSczskEKHzW6aYlttmIY&m=byprFfYOOKk_Ho4LCBXGTSIneDLMb-MumT0G2i4B9pwQnqlo6887VnIvGL9YMrnu&s=fBK-owS68YfMmHfTua1jlFdSyGUYpOp1RsNNUHmtpwo&e="><span style='font-size:11.0pt'>https://transene.com/tmah-substitutes/</span></a></span><span style='font-family:"Times New Roman",serif;color:black'>). <b>Huntsman Chemical</b> produces some more unconventional quaternary ammonium hydroxides like choline-OH and THEMAH (</span><span style='font-size:12.0pt;font-family:"Times New Roman",serif'><a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__www.huntsman.com_products_detail_550_tmah-2Dalternatives&d=DwMF-g&c=WO-RGvefibhHBZq3fL85hQ&r=TEMLD8-VsxCGtcVzmvpT5GFNSczskEKHzW6aYlttmIY&m=byprFfYOOKk_Ho4LCBXGTSIneDLMb-MumT0G2i4B9pwQnqlo6887VnIvGL9YMrnu&s=jOCJCGKlfcQRtfZS83iCQ_uiogAH7ceQkA_LFAZbBkM&e="><span style='font-size:11.0pt'>https://www.huntsman.com/products/detail/550/tmah-alternatives</span></a></span><span style='font-family:"Times New Roman",serif;color:black'>). Several labs, including Queens Univeristy in Canada, Ohio State and Purdue, have tested products from both companies in standard tests for at least one of the applications above. There is quite a bit of data collected at this point, but the general observation is that all of the products tested are safer (in many cases dramatically safer) than TMAH and either equivalent or slightly slower than TMAH for etching and developing applications. Further testing is required to determine the suitability of any given product for any given application, but we do have some general recommendations and confidence that something will work as long as you are willing to sacrifice some aspect of performance.</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><o:p> </o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-family:"Times New Roman",serif;color:black'>Here is summary of the work performed at Queens University by Graham Gibson:</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span style='font-size:12.0pt;font-family:"Garamond",serif'>A systematic study was done at Queen’s University to characterize photoresist developing normally done by 2.38 wt% TMAH. A typical positive and negative Novolac-based photoresist were developed with TMAH and 8 other potential alternative quaternary ammonium hydroxide solutions, after screening out more than 10 others. Each UV-patterned sample was developed for a specific time, with the amount of resist dissolved measured by profilometry. At least 3 development times gives a linear plot, where the slope is the developing rate.</span></b><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span style='font-size:12.0pt;font-family:"Garamond",serif'>Among the candidate quats were ETMAH and TEAH from SACHEM and Choline-OH and XHE-125 from Huntsman. The SACHEM products were purchased from Transene and the Huntsman products were obtained as samples from the manufacturer (note that XHE-125 is an experimental product not yet commercially available). Each candidate was prepared at 5 different concentrations, each having a developing rate as described above.</span></b><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span style='font-size:12.0pt;font-family:"Garamond",serif'>During screening, it was evident that some quats were not suitable developers, either because they were a poor solvent for the soluble part of the resist or too good a solvent for the insoluble part of the resist.</span></b><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span style='font-size:12.0pt;font-family:"Garamond",serif'>In all cases, the standard TMAH developer was the fastest developer at a given wt% concentration. Based on the results, all the candidate developers in the full concentration study were able to develop the photoresist satisfactorily at some concentration. Focusing on the four highest performing candidates listed above, the concentration at which each had equivalent developing rate to 2.38% TMAH for the positive photoresist was:</span></b><o:p></o:p></p><p class=MsoListParagraph style='text-indent:-.25in'><b><span lang=EN-CA style='font-size:12.0pt;font-family:Aptos'>-</span></b><b><span lang=EN-CA style='font-size:7.0pt;font-family:"Times New Roman",serif'> </span></b><b><span lang=EN-CA style='font-size:12.0pt;font-family:"Garamond",serif'>TMAH: 2.38%</span></b><o:p></o:p></p><p class=MsoListParagraph style='text-indent:-.25in'><b><span lang=EN-CA style='font-size:12.0pt;font-family:Aptos'>-</span></b><b><span lang=EN-CA style='font-size:7.0pt;font-family:"Times New Roman",serif'> </span></b><b><span lang=EN-CA style='font-size:12.0pt;font-family:"Garamond",serif'>ETMAH: 3.25%</span></b><o:p></o:p></p><p class=MsoListParagraph style='text-indent:-.25in'><b><span lang=EN-CA style='font-size:12.0pt;font-family:Aptos'>-</span></b><b><span lang=EN-CA style='font-size:7.0pt;font-family:"Times New Roman",serif'> </span></b><b><span lang=EN-CA style='font-size:12.0pt;font-family:"Garamond",serif'>Choline-OH: 4.30%</span></b><o:p></o:p></p><p class=MsoListParagraph style='text-indent:-.25in'><b><span lang=EN-CA style='font-size:12.0pt;font-family:Aptos'>-</span></b><b><span lang=EN-CA style='font-size:7.0pt;font-family:"Times New Roman",serif'> </span></b><b><span lang=EN-CA style='font-size:12.0pt;font-family:"Garamond",serif'>XHE-125: 5.70%</span></b><o:p></o:p></p><p class=MsoListParagraph style='text-indent:-.25in'><b><span lang=EN-CA style='font-size:12.0pt;font-family:Aptos'>-</span></b><b><span lang=EN-CA style='font-size:7.0pt;font-family:"Times New Roman",serif'> </span></b><b><span lang=EN-CA style='font-size:12.0pt;font-family:"Garamond",serif'>TEAH: 7.50%</span></b><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span style='font-size:12.0pt;font-family:"Garamond",serif'>The selectivity of TMAH was also better than any of the candidates, although all the above 4 candidates still had good selectivity. The relative erosion rate (rate of loss of insoluble resist divided by developing rate) for these candidates for the positive resist at the concentration of equivalence were as follows (all selectivities were better for the negative resist):</span></b><o:p></o:p></p><p class=MsoListParagraph style='text-indent:-.25in'><b><span lang=EN-CA style='font-size:12.0pt;font-family:Aptos'>-</span></b><b><span lang=EN-CA style='font-size:7.0pt;font-family:"Times New Roman",serif'> </span></b><b><span lang=EN-CA style='font-size:12.0pt;font-family:"Garamond",serif'>TMAH: 0.003</span></b><o:p></o:p></p><p class=MsoListParagraph style='text-indent:-.25in'><b><span lang=EN-CA style='font-size:12.0pt;font-family:Aptos'>-</span></b><b><span lang=EN-CA style='font-size:7.0pt;font-family:"Times New Roman",serif'> </span></b><b><span lang=EN-CA style='font-size:12.0pt;font-family:"Garamond",serif'>XHE-125: 0.007</span></b><o:p></o:p></p><p class=MsoListParagraph style='text-indent:-.25in'><b><span lang=EN-CA style='font-size:12.0pt;font-family:Aptos'>-</span></b><b><span lang=EN-CA style='font-size:7.0pt;font-family:"Times New Roman",serif'> </span></b><b><span lang=EN-CA style='font-size:12.0pt;font-family:"Garamond",serif'>ETMAH: 0.007</span></b><o:p></o:p></p><p class=MsoListParagraph style='text-indent:-.25in'><b><span lang=EN-CA style='font-size:12.0pt;font-family:Aptos'>-</span></b><b><span lang=EN-CA style='font-size:7.0pt;font-family:"Times New Roman",serif'> </span></b><b><span lang=EN-CA style='font-size:12.0pt;font-family:"Garamond",serif'>TEAH: 0.017</span></b><o:p></o:p></p><p class=MsoListParagraph style='text-indent:-.25in'><b><span lang=EN-CA style='font-size:12.0pt;font-family:Aptos'>-</span></b><b><span lang=EN-CA style='font-size:7.0pt;font-family:"Times New Roman",serif'> </span></b><b><span lang=EN-CA style='font-size:12.0pt;font-family:"Garamond",serif'>Choline-OH: 0.022</span></b><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span style='font-size:12.0pt;font-family:"Garamond",serif'>Effectively, then, a lab could use any one of these quats at the concentration indicated as a replacement for 2.38% TMAH with some success. The exact equivalent concentration depends on the resist, so some experimentation is required.</span></b><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-family:"Times New Roman",serif;color:black'>Here is a link to an abstract regarding work done at Ohio State and Purdue on Novosafe Developer SE-44-26 and Novosafe SE-44 from Transene: <a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__eipbn.org_abstracts_2024_papers_9A-2D3.pdf&d=DwMFAw&c=WO-RGvefibhHBZq3fL85hQ&r=TEMLD8-VsxCGtcVzmvpT5GFNSczskEKHzW6aYlttmIY&m=1_54H_dFFYNv-wcmLpnX3rpvsgl5GrSCHKKSuBptlAD_JLPboiw9os5SiHW9-I43&s=rRzF1J0kBIyVqCC3oyl_AYzFIyaOJfOqiGCKaIUwarA&e=">https://urldefense.proofpoint.com/v2/url?u=https-3A__eipbn.org_abstracts_2024_papers_9A-2D3.pdf&d=DwMFAw&c=WO-RGvefibhHBZq3fL85hQ&r=TEMLD8-VsxCGtcVzmvpT5GFNSczskEKHzW6aYlttmIY&m=1_54H_dFFYNv-wcmLpnX3rpvsgl5GrSCHKKSuBptlAD_JLPboiw9os5SiHW9-I43&s=rRzF1J0kBIyVqCC3oyl_AYzFIyaOJfOqiGCKaIUwarA&e=</a></span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><o:p> </o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-family:"Times New Roman",serif'>We welcome your thoughts and comments. Thanks to all 20 members of the TMAH Working Group, who have offered lots of hard work and thoughtful discussion to the rendering of these findings. </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-family:"Times New Roman",serif'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto'><span style='font-family:"Times New Roman",serif'>Mac Hathaway Center for Nanoscale System - Harvard University</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto'><span style='font-family:"Times New Roman",serif'>Aimee Price Institute for Materials and Manufacturing Research - The Ohio State University</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto'><span style='font-family:"Times New Roman",serif'>Dave Hollingshead Institute for Materials and Manufacturing Research - The Ohio State University</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto'><span style='font-family:"Times New Roman",serif'>Graham Gibson NanoFabrication Kingston - Queens University</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto'><span style='font-family:"Times New Roman",serif'>Justin Wirth Birck Nanotechnology Center - Purdue University</span><o:p></o:p></p><div><div><p class=MsoNormal style='mso-margin-top-alt:auto'><span style='font-size:12.0pt;font-family:"Times New Roman",serif'> </span><o:p></o:p></p></div></div></div></body></html>