Abstract

A Fourier transform infrared spectroscopic method has been developed for the determination of trace moisture in HCl gas. Calibration of moisture was performed as a two-step process. First, an FT-IR spectrometer equipped with a 10-m-pathlength cell was placed in series with a DuPont 5700 Moisture Analzyer to yield an absorbance vs. concentration curve of H₂O in N₂. In the second step, the moisture analyzer was replaced with a water scrubber, and the correlation of molar absorbance values for moisture in HCl vs. moisture in N₂ was obtained through dilution of a fixed-concentration moist nitrogen stream into alternate streams of dry HCl and N₂ gas. The effects of hydrogen bonding with the HCl matrix on H₂O absorbance bandwidth and intensity were investigated at 2 cm⁻¹ and 0.5 cm⁻¹ spectral resolutions for the O-H stretching absorbance region. Matrix correlation data resulted in a linear calibration of moisture in HCl gas for the 0.1-25 ppm range. The infrared methodology has been further utilized to characterize the performance of several HCl gas purifiers designed for use in semiconductor applications. The in-line configuration of this method permits direct quantitation of HCl gas dryer efficiency, capacity, and flow rate specifications. Instrumental considerations including corrosion-resistant optics, inert seals, fittings, valves, purge techniques, and calibration procedure details and results are discussed.

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