Metrology for trace water in ultra-pure process gases

Water vapour is a hard to eliminate contaminant for the speciality gases industry. Within a European market set to be worth more than €20 BN a year by 2027, ultra-pure gases, such as argon, nitrogen, and hydrogen, are valued for protecting processes such as semiconductor manufacturing, where optimising failure rates offers prized competitive advantage.

Trace water contamination of just a few parts per billion (ppb) can result in circuit failures; the target is for measurements of water vapour in gases to span nine orders of magnitude. This presents a significant measurement challenge for gas producers and analytical instrument makers. Industry roadmaps see no let-up in demand for increased performance, specifying demand for methods delivering measurements in the fraction range between five parts per million and five ppb. While mid-to-high range measurements have been investigated and standards exist, current methods are inaccurate in some temperature and pressure ranges and for several carrier gases, while existing optical methods rely on some questioned extrapolations.

The project has developed a range of optical methods, including for gases other than nitrogen, down to 5 ppb, a primary method to measure amount fractions down to 50 ppb, and validate chilled-mirror hygrometers down to -105 C. An inter-comparison of trace water measurements was then proposed to encourage the take-up of the developed technologies and measurement infrastructure in the measurement supply chain.

The resulting new sensors and primary standards will offer improved measurement accuracy for gas producers and analytical instrument makers, and confer competitive advantage for European high-technology industries.