Part per billion determination of oxygen containing impurities in ammonia-nitrogen mixtures

Abstract

Ammonia-nitrogen feedstock streams, free of oxygen containing impurities, are essential reagents for fabricating low oxygen contaminated nitride films. An analytical method is described for determining part per billion levels of oxygen containing impurities, which are converted to nitric oxide (NO) through reaction with microwave discharge produced active nitrogen. Quantitative determinations are then based on detecting the resulting chemiluminescence of NO at characteristic wavelengths. This metastable transfer spectrometric method (MTES) provides direct measurements of oxygen impurities over the 14 to 500 ppb region and has dynamic range extending to 200 ppm. The method, unparalleled in its measurement sensitivity for oxygen impurities in flowing nitrogen gas streams, is calibrated with an NBS standard and applied to the determination of the purification efficiency of an on-line resin system for removal of O₂, CO and NO from ammonia-nitrogen mixtures. Gaseous streams, doped deliberately in the 0.2 to 100 ppm level with either O₂, CO or NO following purification were found to contain less than 10 ppb of the residual impurity. A commercially available 1% ammonia in nitrogen semiconductor grade reagent (99.999%) is shown by MTES to be contaminated with 470 ppb of oxygen impurities.