Measurement of NO_<i>x</i> concentration at ppb level in high-purity gases based on chemiluminescence method

Abstract

High-purity gases are widely used in semiconductor device manufacturing and fuel cell industries. However, the impurities have a significant influence on the processing accuracy directly. Thus, it is particularly necessary to carry out the concentration diagnosis of key trace impurity gases. In this work, an integrated system for the simultaneous detection of trace NO/NO_<i>x</i> is designed based on the chemiluminescence spectrum theory and the catalytic conversion mechanism of nitrogen oxides. The test experiments reveal that the measurement system has the advantages of high linearity (<i>R</i>² = 0.99967), high sensitivity, low detection limit (~25 ppt), and easy operation. Subsequently, the measurement method for NO_<i>x</i> with different high-purity gases are established considering the quenching effects of different background gases on fluorescence and phosphorescent. The detection system is then used to measure the ppb-level NO_<i>x</i> impurities in four commonly used high-purity gases (Ar, O₂, CO₂, N₂) in the laboratory. The results show that the NO impurity in CO₂ gas is the highest, approximately 9 ppb,but relatively low, 0–4 ppb, in the other high-purity gases. The NO₂ impurities in all four high-purity gases are very low (< 6 ppb). Finally, the NO_<i>x</i> impurity content values in high-purity gases are evaluated and analyzed based on the gas preparation and purification approach. The aim of the work is to provide a reliable diagnostic approach and data basis of the impurity composition for the fuel cell, semiconductor and other cutting-edge technological fields.