Pressure Broadening of H2O Absorption Lines in the 1.3 μm Region Measured by Continuous Wave-Cavity Ring-Down Spectroscopy: Application in the Trace Detection of Water Vapor in N2, SiH4, CF4, and PH3:

A continuous wave cavity ring-down (cw-CRD) spectrometer has been developed for the measurement of trace levels of water vapor by absorption spectroscopy at wavelengths in the vicinity of 1358 nm and 1392 nm. The speed of data acquisition and selectivity make cavity ring-down spectroscopy potentially more useful than current techniques for measurement of trace water in process gases and vacuum environments used for semiconductor manufacture where water vapor contamination has a detrimental effect on the final product. The pressure broadening coefficients (γ) for bath gases N2, air, and Ar and semiconductor process gases SiH4, PH3, and CF4 were determined for a range of absorption lines in the 2v1 and v1 + v3 bands of H2O. For the transitions investigated, the concentration of water vapor in the sample gas varied from 1.7 × 1012 to 2.9 × 1015 molecule cm−3 in N2 at a total pressure of <10 mbar and was mixed with the bath gas of increasing pressure up to ∼200 mbar. The values of γ quantify the reduction in ...