TDLS Analysis Of Water Vapour Traces in Semiconductor Process Gas

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

“…Kastle et al first demonstrated the detection of moisture in ammonia using a tunable lead salt diode laser and a 10-m multipass White cell. 6 To avoid the effect of ammonia absorption, the strongest H 2 O absorption lines in the mid-infrared spectral region were not selected, but two H 2 O absorption lines at 1923.162 and 1922.342 cm -1 were utilized, at which the absorption of NH 3 molecules were relatively small. As a result, a detection limit of a few ppm was obtained.…”

“…This is because moisture is a component of air and has many strong absorption lines in most spectral regions employed for detection. Mid-infrared lead salt tunable diode laser spectrometry is another method that is suitable for trace moisture detection in reactive and corrosive gases. , These lasers make possible direct access to convenient spectral regions for the absorption measurements of fundamental vibrational bands of many molecules. The disadvantage of mid-infrared lead salt spectrometry is that the detectors and laser diodes have to be operated under cryogenically cooled conditions; besides, the output power of laser is relatively small.…”

“…However, only a few measurements of trace moisture in NH 3 with laser absorption spectroscopy have been reported, because ammonia has many absorption bands interfering with H 2 O absorption lines from the near-infrared to mid-infrared spectral region, as mentioned below. Kastle et al first demonstrated the detection of moisture in ammonia using a tunable lead salt diode laser and a 10-m multipass White cell . To avoid the effect of ammonia absorption, the strongest H 2 O absorption lines in the mid-infrared spectral region were not selected, but two H 2 O absorption lines at 1923.162 and 1922.342 cm -1 were utilized, at which the absorption of NH 3 molecules were relatively small.…”

High precision trace humidity measurements with a fibre-coupled diode laser absorption spectrometer at atmospheric pressure

“…Most of the published spectrometer developments focus on atmospheric water vapour measurements [3,4], in which high temporal resolution is required. Other authors reported on the application of diode laser spectrometers for the detection of moisture concentrations in waste incinerators [5] or to monitor trace moisture impurities in industrial gases [6][7][8], for which the low cross sensitivity for acid gases is of special interest. Only very few publications deal with detailed analysis of the standard uncertainty, stability and reproducibility of laser spectrometers.…”