Impurities in hydride gases. Part 2: Investigation of trace CO2 in the liquid and vapor phases of ultra-pure ammonia

• Published in: Journal of electronic materials 2004-08, Vol.33 (8), p.873-880
• Main Authors: FUNKE, Hans H, WELCHHANS, Jon, WATANABE, Tadaharu, TORRES, Robert, MOULDING, Virginia H, RAYNOR, Mark W
• Format: Article
• Language: English
• Subjects: Ammonia; Analytical chemistry; Carbon dioxide; Chemical vapor deposition; Chemistry; Chromatographic methods and physical methods associated with chromatography; Chromatography; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Physics; Temperature; Thermodynamics; Vapor phase epitaxy; growth from vapor phase
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-004-0214-7

Ammonia (NH^sub 3^) as a precursor for epitaxial nitride films is required to be free of trace oxygenated impurities, such as CO2, that have been shown to negatively affect growth processes and device performance. Carbon dioxide can react reversibly with the NH^sub 3^ gas to form ammonium carbamate, NH^sub 4^COONH^sub 2^ (a solid with low solubility in liquid NH^sub 3^) and, therefore, can be present in cylinder sources both in the free and chemically bound form. A gas Chromatograph (GC)-based method has been developed to accurately quantify the total CO2 content in both vapor- and liquid-phase NH^sub 3^ streams. A heated GC-sampling manifold is used to thermally decompose any NH^sub 4^COONH^sub 2^ present in the sample or calibration standard so that all CO2 is analyzed in its free form. Several commercial cylinder sources maintained at room temperature were analyzed by this method, and in all cases, equilibrium concentrations of