Tetramethylammonium hydroxide
| Tetramethylammonium hydroxide | |
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tetramethylammonium hydroxide |
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| Identifiers | |
| CAS number | 75-59-2  |
| PubChem | 60966 |
| ChemSpider | 54928 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | C4H13NO |
| Molar mass | 91.15 g mol−1 |
| Related compounds | |
| Other anions | tetramethylammonium chloride |
| Other cations | tetraethylammonium hydroxide |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Tetramethylammonium hydroxide (TMAH or TMAOH) is a quaternary ammonium salt with the molecular formula (CH3)4NOH. It is used as an anisotropic etchant of silicon. It is also used as a basic solvent in the development of acidic photoresist in the photolithography process. Since it is a phase transfer catalyst, it is highly effective in stripping photoresist. It is also used as a surfactant in the synthesis of ferrofluid, to prevent agglomeration.
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[edit] Toxicity
TMAH solution is a strong base. The tetramethylammonium ion can damage nerves and muscles, causing difficulties in breathing and possibly death in a short period of time after exposure by contact, even with only a small amount. It is structurally similar to acetylcholine, an important peripheral neurotransmitter at both the neuromuscular junction and autonomic ganglia. This structural similarity is reflected in its mechanism of toxicity - it binds to and activates the nicotinic acetylcholine receptors, although the response may subsequently densentize in the continued presence of this agonist. The action of tetramethylammonium is most pronounced in autonomic ganglia, and so tetramethylammonium is traditionally classed as a ganglion-stimulant drug.[1] The ganglionic effects may contribute the deaths that the have followed accidental industrial exposure, although the "chemical burns" induced by this strong base are also severe.[2]
It also smells like dead fish if it is not pure, from trimethylamine impurity. TMAH has virtually no odor when pure.
[edit] Wet anisotropic Etching
TMAH belongs to the family of quaternary ammonium hydroxide (QAH) solutions and is commonly used to anisotropically etch silicon. Typical etching temperatures are between 70°-90°C and typical concentrations are 5-25 wt% TMAH in water. (100) silicon etch rates generally increase with temperature and decrease with increasing TMAH concentration. Etched silicon (100) surface roughness decreases with increasing TMAH concentration, and smooth surfaces can be obtained with 20% TMAH solutions. Etch rates are typically in the 0.1-1 micron per minute range.[3]
Common masking materials for long etches in TMAH include silicon dioxide (LPCVD and thermal) and silicon nitride. Silicon nitride has a negligible etch rate in TMAH; the etch rate for silicon dioxide in TMAH varies with the quality of the film, but is generally on the order of 0.1 nm/minute.
[edit] See also
[edit] References
- ^ Bowman, W.C. and Rand, M.J. (1980), "Peripheral Autonomic Cholinergic Mechanisms", in Textbook of Pharmacology 2nd Ed., Blackwell Scientific, Oxford 10.21
- ^ Lin, C.C. et al. (2010). Tetramethylammonium hydroxide poisoning. Clin Toxicol (Phila) 48: 213-217.
- ^ J. T. L. Thong, W. K. Choi, C. W. Chong, TMAH etching of silicon and the interaction of etching parameters, Sensors and Actuators A: Physical, Volume 63, Issue 3, December 1997, Pages 243-249, ISSN 0924-4247, DOI: 10.1016/S0924-4247(97)80511-0. (http://www.sciencedirect.com/science/article/B6THG-3S9D11W-3V/2/46a49827456cb9320e8b0173ba32b1bf)
