Wavelength-Modulation Laser Hygrometer for Ultrasensitive Detection of Water Vapor in Semiconductor Gases

Published

February 1, 2001

Author(s)

D C. Hovde, Joseph T. Hodges, Gregory E. Scace, J A. Silver

Abstract

The ability to quantify trace amounts of water vapor in semiconductor process gases is critical to quality control plasma etching and other semiconductorfabrication techniques. This paper demonstrates a first-principles method for the measurement of subnanomole per mode (par-par-billion by volume or ppb)levels of water vapor based on wavelength modulation absorption spectrosocpy with a diode laser light source. Humidity levels as low as 5 nmol/mol of watervapor in air are measured with a sensitivity of better than 0.2 nmol/mol. The sensitivity, linearity, and stability of the technique are determined in experimentsconducted at NIST using the Low Frost-Point Hunidity Generator (LEPG) over the range 5 nmol/mol to 2.5 umol/mol of water vapor in air. Operation in otherindustrially relevant process gases is domonstrated. The pressure broadening coefficients for water broadened by helium (0.0199(6) cm-1 atm-1 HWHM) and byhydrogen chloride (0.268(6) cm-1 atm-1 HWHM) are reported for the water line at 1392.5 nm.

Citation

Applied Optics

Volume

40

Issue

No. 6

Pub Type

Journals

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Keywords

absorption, absorption spectroscopy, diode laser, helium, humidity, hydrogen chloride, partial pressure

Citation

Hovde, D. , Hodges, J. , Scace, G. and Silver, J. (2001), Wavelength-Modulation Laser Hygrometer for Ultrasensitive Detection of Water Vapor in Semiconductor Gases, Applied Optics, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=830613 (Accessed October 9, 2025)