Tetramethylammonium Hydroxide (TMAH) is available in solution and in the pentahydrate form as a white crystalline solid. The pentahydrate CAS# is -65-4.
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TMAH solution is widely used in the electronics industry as a developer or cleaner. TMAH is typically one of several ingredients in etching / stripping mixtures, although it may also be used as a pure chemical. It is often used in solution in water, and less frequently, in methanol. These solutions are assigned the CAS# 75-59-2. The concentration of TMAH in commercially available developers used on Penn’s campus is <3% (according to chemical inventory records 9/). The highest concentration solution of TMAH that is commonly available commercially is 25%. TMAH is a strong base; the 25% solution in water has a pH of greater than 13.
The odor of TMAH has been described as a strong, ammonia-like smell. Although pure TMAH will have virtually no odor, solutions may give off a fishy smell from triethylamine, which is a common impurity.
Refer to a specific product’s Safety Data Sheet for more hazard details. An example Safety Data Sheet from Sigma-Aldrich for a 25% solution of TMAH can be found here: Sigma-Aldrich SDS for TMAH 25%
The health hazards of TMAH pentahydrate (solid) are very similar to those of the solution, however the solid is a GHS hazard category 3 for dermal acute toxicity, whereas the solution is a GHS hazard category 2 (higher hazard) for dermal acute toxicity. This difference in hazard category is likely due to the increased risk of dermal absorption of the chemical in solution.
GHS Classification Information from the Sigma-Aldrich SDS for the TMAH 25% Solution in Water:
Acute toxicity, Oral (Category 2), H300
Acute toxicity, Dermal (Category 2), H310
Skin corrosion (Category 1), H314
Serious eye damage (Category 1), H318
Specific target organ toxicity - single exposure (Category 1), Central nervous system, H370
Specific target organ toxicity - repeated exposure, Dermal (Category 1), thymus gland, Liver, H372
Acute aquatic toxicity (Category 2), H401
Chronic aquatic toxicity (Category 2), H411
TMAH is extremely corrosive to skin, eyes, and mucous membranes and will cause serious burns to eyes, and skin on contact.
In addition to causing chemical burns, TMAH can cause systemic neurotoxicity leading to respiratory failure by ganglion block that occurs through skin absorption. No antidote has been developed yet.
The following exposure information is from the U.S. Library of Medicine Toxicology Data Network (TOXNET):
INHALATION EXPOSURE: Mild exposure may cause cough and bronchospasm. Severe inhalation may cause upper airway edema and burns, stridor, and rarely acute lung injury.
OCULAR EXPOSURE: Ocular exposure can produce severe conjunctival irritation and chemosis, corneal epithelial defects, limbal ischemia, permanent visual loss and in severe cases perforation.
DERMAL EXPOSURE: Mild exposure causes irritation and partial thickness burns. Metabolic acidosis may develop in patients with severe burns or shock. Prolonged exposure or high concentration products can cause full thickness burns.
Systemic toxicity is likely to occur with dermal exposure.
When heated to decomposition, TMAH emits toxic fumes of NOx and ammonia.
A Hazard Control Plan is recommended for procedures involving TMAH over 5%, and one may be required by EHRS under certain circumstances.
Contact EHRS for assistance with your hazard assessment.
All work with TMAH requires the approval of the P.I. The P.I. must ensure that the person or team who will be working with the chemical writes a task-specific Hazard Control Plan (HCP) if required by EHRS or the P.I.'s hazard assessment.
The HCP must be sent to EHRS for review. EHRS will upload the HCP to the “documents” section of the lab’s BioRAFT page.
The P.I. must also ensure that the person or team who will be working with the chemical understands the hazards and has received adequate training and supervision for the procedure.
All of the handling procedures detailed in SOP: Acutely Toxic Chemicals and SOP: Corrosives apply to all work involving tetramethylammonium hydroxide solutions.
Because TMAH exposures to skin and eyes will result in serious burns, and because dermal absorption may result in fatal systemic toxicity, risk assessments for work involving TMAH may determine a level of required personal protective equipment (PPE) that is beyond the minimum mandatory laboratory PPE requirements, i.e. safety glasses, lab coat, disposable nitrile gloves, closed-toed shoes, and long pants.
Additional recommended PPE includes:
*Note that Glove-manufacturer’s compatibility charts do not often include data specifically for TMAH; however, the 4-mil disposable nitrile rubber gloves commonly used in the laboratory will provide adequate protection against incidental contact with TMAH solutions. This is based on the information from the Sigma-Aldrich SDS. Testing was done on a 0.11 mm (4.33 mil) nitrile glove.
Full contact Material: Nitrile rubber Minimum layer thickness: 0.11 mm Break through time: 480 min Material tested:Dermatril® (KCL 740 / Aldrich Z, Size M)
All exposures or potential exposures to TMAH require immediate medical attention.
General emergency response information can be found at Emergency Info
General procedures for chemicals spill response can be found in Section X: Chemical Spills in this CHP.
Do not hesitate to call EHRS for assistance with spill cleanup for Acutely Toxic and Corrosive Materials
24 hours: 215-898-
Contact Penn Police (511) only if the spill involves a fire, imminent risk of fire, an injury requiring an ambulance, or if there is a hazard that may affect others in the building.
From: On Behalf Of Matthieu Nannini, Dr.
Sent: May-19-11 8:29 AM
To:
Subject: Re: [labnetwork] TMAH
Here's an article relating the tragic event.
http://joh.med.uoeh-u.ac.jp/pdf/E50/E50_2_01.pdf
From: On Behalf Of Robert M. Hamilton
Sent: May-18-11 4:43 PM
To: Matthieu Nannini, Dr.
Want more information on TMAH Developer? Feel free to contact us.
Cc:
Subject: Re: [labnetwork] TMAH vs KOH
Matthieu Nannini,
At the Berkeley NanoLab we support both KOH and TMAH use at a dedicated work process station. We have not had issues with these processes. Having said this, we have added the following caution statement about TMAH exposure to our lab and safety manuals after our Office of Environmental Health & Safety shared data about fatal TMAH exposures in Taiwan:
"TMAH (Tetramethylammonium hydroxide) is widely used as a photoresist developer (2-3%) and for the anisotropic etching of silicon (10-15%). TMAH is a strong base and hazardous by ingestion, inhalation, skin (dermal) exposure and eye contact. In addition to alkalinity-related chemical burn, dermal exposure to TMAH may also result in respiratory failure and/or cardiac arrest. A study of case reports of Taiwan semiconductor factory injuries linked exposure of 25% TMAH to three cases of heart failure. It is important to treat TMAH skin exposure by flooding the effected area with water for at least 15 minutes and to report all exposures."
More generally, caustic burns (KOH or TMAH) can be worse than acid burns. It is difficult to cleanse the orbit of an eye when exposure occurs and caustic quickly penetrate tissue. While 15 minutes may seem an inordinate amount of time for a topical exposure to a chemical, trauma specialists who we've consulted tell us such long rinses have definite value.
Sincerely,
Bob Hamilton
Robert M. Hamilton
Marvel NanoLab
University of CA at Berkeley
Rm 520 Sutardja Dai Hall
Berkeley, CA -
Hello Mattieu,
IMHO, from a health perspective, TMAH appears far more dangerous than KOH. We recently prepared a lab-wide notification concerning TMAH and its known but often overlooked dangers based on skin adsorption as opposed to ingestion as an identified route of exposure.
"Materials Safety Bulletin
September 24,
TMAH: New Hazard Awareness Concerning an Old Chemical Tetramethylammonium hydroxide (TMAH) is widely used in micro- or nanofabrication as an etchant and developer. In MSD, TMAH is typically one of several ingredients in commercial etching/stripping mixtures, although it may also be used as a pure chemical.
While it has long been known to be very toxic if ingested, recent industrial experience indicates that skin exposure may result in serious injury/illness or even death. Since , there have been 3 recorded fatalities from skin exposure to TMAH solutions as dilute as 25%. Two of the recorded fatalities occurred due to heart attack despite immediate decontamination and prompt medical care. Thus skin, exposure to >1% TMAH over a few percent of the body must be treated as a life-threatening event. MSDSs may be out of date and not properly describe this high dermal toxicity.
When handling this material, the minimum set of personal protective equipment includes:
safety goggles (not glasses), disposable nitrile gloves, a buttoned lab coat, leg covering and closed-toe shoes. The disposable gloves may only provide brief protection and must be replaced if they become wetted. More protective gloves are the Stansolv or Tri-Ionic glove models sold by MAPA.
In the event of a splash, contaminated clothing must be removed and the wetted area thoroughly washed with soap and water, using the emergency shower if necessary.
Call 911 and summon emergency medical help.
You should not handle TMAH containing materials when working alone.
Tri-Ionic clean room gloves provide excellent protection from TMAH exposure."
David A. Bunzow
User Facilities Program Manager
The Molecular Foundry
Materials Science Division
Lawrence Berkeley National Laboratory
1 Cyclotron Road MS 67-
Berkeley, CA
On 5/18/ 9:20 AM, Matthieu Nannini, Dr. wrote:
Dear all,
Having only one base dedicated bench running TMAH @ 85C I have now to make a choice between TMAH and KOH since new researcher are asking for KOH. Maintaining the 2 chemicals requires resources that I don't have.
Process wise, TMAH is better with oxide masks but KOH is better with SiN masks. KOH also etches faster and nicer.
My questions are in terms of safety: could you share your experiences with KOH vs TMAH in terms of ease of use, safety, etc...
Thanks
-----------------------------------
Matthieu Nannini
McGill Nanotools Microfab
Manager
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