Company Information

 
Chemically Speaking LLC is a specialty gas consulting company that can provide safety, environmental and emergency response support to users, transporters, distributors, waste disposers or manufacturers of specialty and industrial gases used in the chemical, medical, electronics and automotive industries. Chemically Speaking can also provide safety and emergency response training. Expert witness or incident investigation.

News

Sept 2018

Accidental Reaction of Metal Alkyls (Organometallic compounds) with Moisture or Air Causing a Cylinder to Rupture

Metal Alkyls (Organometallic) are finding increasing use in the Silicon Semiconductor Fabrication Industries. The most commonly used are:

Trimethylgallium (TMG)

Trimethylaluminum (TMA)

Trimethylindium (TMI)

Diethylzinc (DEZ)

The III-V device manufacturers typically dispense these from a cylinder configured to function as a bubbler (A carrier gas is bubbled through the liquid/solid to be saturated with the vapor). To maintain a precise concentration the cylinders are immersed in a heated or chilled water bath (glycol). These are located within the tool (MOCVD) and are maintained under positive pressure. A leak if it were to occur would be outward causing a fire.

The silicon device manufacturers on the other hand dispense Trimethylaluminum by pulling a vacuum on the vapor space of the canister in the ALD process (Atomic Layer Deposition). Due to the larger volumes used, a small host container is located close to the tool in the cleanroom. This is constantly filled by bulk and supply containers located in the subfab, these are pressurized to fill the canister. Diethylzinc is used to grow a transparent conductive layer for a thin film photovoltaic cell. The use of Metal Alkyls is forecasted to increase dramatically for all uses.

Pyrophoricity (spontaneous ignition) and fire is probably the most well-known hazard characteristic of these key organometallic compounds. A fire is commonly encountered during accidental release of Metal Alkyls into air. Most current safety precautions for handling these materials are associated with the pyrophoricity.

Violent reaction with liquid water is also a well-known problem. The hydrolysis reaction may generate sufficient heat to trigger a self sustained decomposition reaction.

Can the ingress of air or water in the ALD process trigger a self sustaining decomposition reaction that ruptures the container? These Metal Alkyls are also thermally unstable. Heat can trigger a decomposition reaction. Imagine a spill that ignites around a container, water cannot be used to cool the container or put out the fire.

There have been 5 known fatalities plus numerous injuries

Known incidents

TMG container explosion after glycol is sucked in (date unknown)

TMI container explosion after air sucked in, Dec 11,1998

TMI container explosion after it was heated to decomposition temperature, 2012

TMI container explosion from moisture from valve, Oct 9, 2013

TMA container explosion after air is sucked in, Jan 7, 2016

TMI container explosion after air is sucked in, May 2018

 

A test program is to better understand what can happen with Trimethylaluminum in a typical ampoule (1 liter) in a worst case incident has been proposed for 2019.

Open valve to suck in air.

Drip 5 cc of water into container.

If any of the tests do not trigger a decomposition reaction, heat container to decomposition temperature

 

The test program will

Video from 4 angles

High speed video of container rupture

Canister pressure measurement

Temperature measurement

Overpressure sensors in a x-y grid

 

Test Directors:

Prof. Jenq-Renn Chen, Department of Safety, Health and Environmental Engineering, National First University of Science and Technology, Kaohsiung, Taiwan. jrc@nfust.edu.tw

Eugene Ngai, Chemically Speaking LLC, Whitehouse Station, NJ 08889, eugene_ngai@comcast.net




 

 

Recent publications


  1.  Ngai, E., Chen, J.R. , et al, “CGA G-13 Large-Scale Silane Release Tests – Part I. Silane Jet Flame Impingement Tests and Thermal Radiation Measurement”, Tenth International Symposium on Hazards, Prevention, and Mitigation of Industrial Explosions, Bergen, Norway, 10-14 June 2014
  2. Ngai, E., Chen, J.R. , et al,  “CGA G-13 Large-Scale Silane Release Test –Part II. Unconfined Silane-Air Explosions”, Tenth International Symposium on Hazards, Prevention, and Mitigation of Industrial Explosions, Bergen, Norway, 10-14 June 2014
  3. Ngai, E., “Dangerous Gas Mixtures: Avoiding Cylinder Accidents” Specialty Gas Reporter, 2nd Qtr 2014

    http://www.cryogas.com/pdf/SGRLink_Ngai_Cylinders.pdf

  4. Ngai, E. “Phosphine, From Swamp Gas to Applications in the Clean Room”, Cryogas International, 2nd Qtr 2014 www.cryogas.com/pdf/Link_Phospine_Ngai.pdf
  5. Ngai, E. Y., Fuhrhop, R., Chen, J. R.*, Chao, J., Bauwens, C. R., Mjelde, C., Miller, G., Sameth, J., Borzio, J., Telgenhoff, M.. Wilson, B., CGA G-13 Large-Scale Silane Release Tests – Part I. Silane Jet Flame Impingement Tests and Thermal Radiation Measurement, Journal of Loss Prevention in the Process Industries, http://dx.doi.org/10.1016/j.jlp.2014.12.010
  6. Ngai, E.Y., Fuhrhop, R., Chen, J. R.*, Chao, J., Bauwens, C. R., Mjelde, C., Miller, G., Sameth, J., Borzio, J., Telgenhoff, M. Wilson, B., CGA G-13 Large-Scale Silane Release Tests – Part II. Unconfined Silane-Air Explosion, Journal of Loss Prevention in the Process Industries (2014), http://dx.doi.org/10.1016/j.jlp.2014.12.011.