Impurities in hydride gases part 1:: Investigation of trace moisture in the liquid and vapor phase of ultra-pure ammonia by FTIR spectroscopy

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 vapor-phase 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.