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Moisture measurements in semiconductor process gases using cavity ring-down spectroscopy



Kristine A. Bertness, Susan Y. Lehman, Joseph T. Hodges


We have demonstrated the use of cavity ring-down spectroscopy to measure water concentrations in the nmol/mol (ppb) range in nitrogen and phosphine gases. To our knowledge, these measurements are the first successful application of this method to a toxic gas. Our experimental arrangement uses an external-cavity tunable diode laser operating at CW near the water absorption lines at 936 nm. The primary advantages of this technique are its high sensitivity combined with self-calibrating methodology and insensitivity to moisture in room air. The phosphine line is shared with a gas-source molecular beam epitaxy chamber, allowing us to measure real-time water concentrations during epitaxial crystal growth. We have found that even high levels of moisture in phosphine do not produce large increases in oxygen concentration in AlInP grown by this method. Our lowest detectible concentration is approximately 10 ppb of water in nitrogen gas, which rises to approximately 200 ppb in phosphine because of background modulations from weak phosphine absorption lines in the same wavelength region.
Gases & Technology Magazine


cavity ring-down spectroscopy, gas purity, gas-source molecular beam epitaxy, moisture, phosphine, water


Bertness, K. , Lehman, S. and Hodges, J. (2003), Moisture measurements in semiconductor process gases using cavity ring-down spectroscopy, Gases & Technology Magazine, [online], (Accessed April 24, 2024)
Created March 1, 2003, Updated February 19, 2017