Techniques for the measurement of trace moisture in high-purity electronic specialty gases

Abstract

The control of water vapor (moisture) contamination in process gases is critical to the successful manufacture of semiconductor devices. As specified moisture levels have become more stringent, there is a growing demand for more sensitive analytical methods. Instrumental methods currently being used or in development for measuring trace moisture at ppbv levels include Fourier transform infrared spectroscopy, tunable diode laser absorption spectroscopy, cavity ringdown spectroscopy, intracavity laser spectroscopy, electron impact ionization mass spectrometry, and atmospheric pressure ionization mass spectrometry. In addition, sensor-based technologies such as oscillating quartz crystal microbalances, and chilled mirror-, capacitor-, and electrolytic-based hygrometers operate in this regime. These approaches are presented and reviewed. As the success of each trace moisture method is dependent on the degree to which the different process gases interfere with the measurement process, important process gas applications of the techniques are highlighted. Advantages and disadvantages as well as future developments and trends are also presented.

Pulsed Discharge Helium Ionization Detector for Highly Sensitive Aquametry

“…[1][2][3][4][5][6][7] Although a variety of techniques for aquametry have been reported in the literature, 1,[8][9][10] only few have been adopted widely. 10 Several lab-scale detection techniques have been reported with ppbv to pptv levels of sensitivity. 37 However, these have remained bench-sized instruments or laboratory curiosities, and have not transitioned into a commercially viable product for widespread use.…”

“…Although the moisture LOD obtained using the PDHID-D2 did not match the higher sensitivity reported using TDLAS/NIR, 28 TDLAS hygrometers are expensive. 10 The range of RH values over which the PDHID-D2 was used overlapped with the range reported using competing technologies.…”

“…7 There are several methods for aquametry (measurement of water in solid, liquid and gaseous materials). 1,[8][9][10] Methods typically utilizing a fixed sample size include Karl Fischer titration (KFT), thermal conductivity detector (TCD), gravimetry, and ionization detectors. With varying sample size and limits of detection, each of these techniques also has advantages and disadvantages involving size, weight, and power/portability (SWAPP factors).…”

“…The PDHID-D2, due to its small footprint and low power requirement, has excellent SWAPP factors that could be combined with fully portable GC systems. 15,16 The relatively low cost (~$5000) 10 and commercial availability of the PDHID-D2 makes our technique applicable to field aquametry and/or applications that have limited sample size.…”

“…10 Some require laboratory-sized, bench-scale equipment, which is unsuited for field aquametry or applications in which only a small sample volume is available for analysis. In addition, commercially available sensors used for flowing samples are not configured for liquid aquametry.…”