Trace Water Vapor Detection in Nitrogen and Corrosive Gases by FTIR Spectroscopy

Abstract

A commercial Fourier transform infrared spectrometer (modified to improve the purge) and a long-path gas cell were used to demonstrate a detection limit of about i0 ppb for water in N2, HCI, and HBr. This technology is being developed as an in-line monitor to extend the life of gas delivery systems and improve wafer yields in the semiconductor industry. The reported detection limit includes an improvement of about a factor of three achieved by applying quantitative multivariate calibration to the problem. Methods are discussed to compensate for background moisture in the beam path. Also, discussed are the choice of operating parameters to optimize the instrumental performance. Surprisingly, resolving the narrow water absorption bands (FWHM = 0.20 cm -1) is not necessary to achieve optimal sensitivity. In fact, optimal sensitivity is achieved at 2 to 4 cm i resolution, allowing the use of an inexpensive interferometer in the final instrument. A calibration over the range of 40 to 2000 ppb of water in N2 has been performed and found to be in good agreement with published spectral data. Finally, an improved instrument design is discussed which is projected to have a lower detection limit and a shorter collection time.

Quantitative Analysis of Trace Moisture in N2 and NH3 Gases with Dual-Cell Near-Infrared Diode Laser Absorption Spectroscopy

“…Some optical detection methods have been reported for analysis of trace moisture in halide gases. Fourier transform infrared spectrometer (FT-IR) with a multipass white cell was utilized for trace moisture measurements in HCl and HBr. , In these measurements, however, the effect of residual moisture absorption in the beam path outside the sample cell cannot be neglected even in a purge box. This is because moisture is a component of air and has many strong absorption lines in most spectral regions employed for detection.…”

Trace Water Vapor Analysis in Specialty Gases: Sensor and Spectroscopic Approaches

“…For many gases, including the hydrogen halides and the carbon and nitrogen oxides, one or both regions are available for water vapor analysis [54][55][56][57][58][59][64][65][66]. An example of the analysis of a low-purity nitric oxide sample is shown in Figure 7.11.…”

“…20 L/min dry nitrogen). Other approaches investigated to minimize or account for background water vapor include bench evacuation or the use of a specially designed optical system that allows sequential measurement of water vapor in the bench alone or in the gas cell alone to reference out the water vapor in the bench [56][57][58][59]. Note that auto-or self-referencing methods that are used for background spectral removal from within the gas cell (discussed in more detail in Chapter 3) still require a low and steady-state level of water vapor in the bench purge [60].…”

Al2O3-coated microcantilevers for detection of moisture at ppm level

“…However, the sensitivity cannot compete with other mature techniques yet. The detection limit of moisture is of the ppb level with electrolytic technique [18] or optical techniques such as FTIR spectroscopy [19] or semiconductors [20].…”