The Analysis of Trace Impurities in Nitrogen Gas by High Pressure Ionization Mass Spectrometry

Abstract

We developed high pressure ionization mass spectrometry (HPIMS) to monitor trace impurities in nitrogen ( N2) gas in order to establish an ultra-high purity (UHP) N2 supplying technology for ULSI fabrication. We also demonstrated that the oxygen ( O2), carbon dioxide ( CO2) and moisture ( H2O) in N2 can be measured with a high sensitivity and accuracy using HPIMS. The ion intensities of O2, CO2 and H2O in N2 with HPIMS was increased about one order of magnitude more than that with atmospheric pressure ionization mass spectrometry (APIMS). The excellent linearity between the ion intensity and O2 concentration was obtained with a correlation coefficient over 0.9999 in the range from 5 ppb to 50 ppb. The reproducibility and accuracy of measurement could be improved since the pressure of the ionization chamber was controlled precisely by using HPIMS.