1996 年 44 巻 2 号 p. 165-174
Semiconductor fabrication field requires screening technology, for external air leakage inspection in a clean room gas delivery system which can inspect all inspection points in one gas line in one process. Recent advances in welding technology have meant that the occurrence of a leak at welding point is now extremely uncommon. Inspection costs of a gas delivery system can therefore be decreased by applying such a screening process. The detection sensitivity required for screening of the air component is ppt level or below.
The atmospheric pressure ionization mass spectrometer (APIMS) was applied to the screening process using the argon carrier gas. Trace nitrogen which previously could not be detected by the APIMS, could be detected by mixing hydrogen in the argon gas. The detection sensitivity was increased over 100 times compared to the oxygen detection since there is a large amount of nitrogen in air and the proton transfer reaction for nitrogen ionization having a larger rate constant than the charge transfer reaction for oxygen ionization. N2H+ intensity shows a sudden increase with H2 concentration because the rate constant, in the rate-determining step for N2H+ formation in higher H2 concentrations, is larger than that in the lower H2 concentrations. The optimum H2 concentration is 3-10% for obtaining the higher sensitivity.
It is expected that the application of APIMS technique will greatly reduce the costs associated with the leak inspection.
