Tetramethylammonium hydroxide (TMAH): Toxicity and Methods to Reduce Risk in the Workplace
DiZio, Kathleen; Melville, Richard ; Timlin, Ernest
(IBM, San Ramon, CA and IBM, Hopewell Junction, NY)
Tetramethylammonium hydroxide (TMAH), CAS #75-59-2, is employed in an increasing number of semiconductor manufacturing processes. Newer applications may use TMAH concentrations as high as 25% at elevated temperatures. Contact with concentrated TMAH solutions may cause serious intoxication. Several fatalities have been reported by the Asia Pacific semiconductor and photoelectric industries. Factors that may be important in determining the degree of intoxication include the concentration of TMAH, the % body surface area affected, the period before decontamination, and the possibility of concurrent inhalation exposure and dermal contact. Early toxicity studies in rats and guinea pigs identified TMAH as highly toxic with an oral LD50 in rats between 34 and 50 mg/kg and a dermal LD50 in guinea pigs of 25 to 50 mg/kg. Later studies in rats sponsored by IBM found that contact with less than 1 milliliter of a 12% or 25% TMAH solution was lethal within 3 hours. IBM investigated possible underlying mechanisms of acute systemic toxicity including the direct effects on neurotransmission and on blood gases. IBM took prompt action to assess and, where necessary, enhance the health and safety procedures associated with TMAH based on the results of these animal studies. IBM notified the US EPA under the significant new information provisions of the Toxic Substances Control Act, Section 8e. Furthermore, IBM modified internal chemical labels for formulations containing TMAH, sponsored chemical-resistant glove and coverall permeation testing on TMAH solutions, performed process reviews on specific TMAH-using operations, and notified employees and contractors of the potential hazard. IBM implemented vigorous controls on the introduction of new processes employing concentrated TMAH solutions. Senior management is briefed on the potential hazards of the process, the tool and engineering requirements, and the availability of potential alternatives to TMAH. IBM develops work plans to reduce or eliminate potential TMAH hazards. In addition, IBM is working in cooperation with several development partners and suppliers to identify less hazardous alternatives to TMAH.