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Impurities in hydride gases part 1: Investigation of trace moisture in the liquid and vapor phase of ultra-pure ammonia by FTIR spectroscopy
Authors:Hans H. Funke  Mark W. Raynor  Belgin Yücelen  Virginia H. Houlding
Affiliation:(1) Advanced Technology Center, Matheson Tri-Gas, 1861 Lefthand Circle, 80501 Longmont, CO
Abstract:Trace moisture in ammonia is a critical impurity in the growth of epitaxial nitride films. Because moisture is very soluble in the liquid phase of ammonia, moisture in the vapor phase increases dramatically with cylinder use, and is often far higher than the nominal purity specification. A reliable method was developed for sampling and analyzing trace moisture in both liquid-and vaporphase ammonia using FTIR. Analysis of liquid-phase ammonia gives a stable and representative moisture value whereas gas-phase moisture levels strongly depend on sampling time, flow rate, temperature, mixing, and extent of cylinder use. The variation of vapor-phase moisture is discussed in terms of a variable vaporization model with applications to high flow.
Keywords:Moisture  impurities  ammonia  partition coefficient  FTIR spectroscopy  liquid phase delivery  gas phase  thermodynamic equilibrium
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