The first international standard for vacuum gauges
Challenge
High (10⁻¹-10⁻⁶ Pa) and ultra-high (10⁻⁶-10⁻⁹ Pa) vacuum are indispensable in a range of high-technology industries including preventing atmospheric contamination during integrated circuit fabrication or the deposition of thin films for solar cell or electronic manufacturing.
Vacuum levels are measured by “ionisation gauges” (IG’s) but at the start of 2020 these instruments were not standardised, and commercial gauges differed in materials and geometries. These lacked long-term and transport stability and were mainly only calibrated for nitrogen gas. To quantify other gases, “sensitivity factors” were applied to measurements but this led to measurement uncertainties of 10 - 20%. This meant IGs were unable to comply with international standard ISO 21360-1 which requires an uncertainty of 3% on pressure measurements with these instruments.
Working with the company INFICON, the EMPIR project Ion Gauge (2017-2020) resolved these issues and produced a “standardised” IG which could measure vacuum pressure from 10-2 down to 10-6 Pa, with a 1% measurement uncertainty for nitrogen and only 2 - 3% for other gas types.
Standardisation bodies indicated that industry would benefit from a new technical specification on this new gauge design. This would allow conformity not only to ISO 21360-1 but also improve calibration uncertainty according to ISO 3567, and to ISO 27893.
Solution
In 2021, the ISO Gauge project started to develop a new technical standard for IGs and, in conjunction with the International Standards Organisation Technical Committee 112 (ISO TC 112), launched ISO NP TS 6737 and appointed the coordinator of ISO Gauge as project leader.
In June 2021, three partners from the previous Ion Gauge project, including INFICON, further optimised the new IG’s design for reliable operation. This included refining the influence of apertures, the effects of external magnetic fields, and the suitability of the cathodes to generate the electrons that ionise residual gases. The gaps between electrodes were sized to conform with IEC 61010 standards on safety requirements for electrical equipment and machining and welding tolerances were also defined to conform with standards ISO 2768-1 and ISO 13920.
After addressing further comments the final draft was approved and published in November 2023 as ISO/TS 6737 Vacuum technology — Vacuum gauges — Characteristics for a stable ionisation vacuum gauge.
Impact
INFICON is a leading company in vacuum instrumentation, gas analysis, thin film technology and protective particle coatings. The company’s expertise in vacuum instrumentation was integral to the development of the prototype standardised IG in the Ion Gauge project and the technical standard in the subsequent ISO Gauge project.
In 2022, INFICON has introduced the new IG to the market as the IRG080. This is the first gauge on the market that conforms to the ISO/TS6737 specification. Along with the low measurement uncertainties and wide measurement range (10-2 - 10-6 Pa) of the original prototype, it also has a high repeatability (<1 %), reproducibility (<1 %), and stability to storage and transport (<1 %). It can calibrate vacuum gauges or other instruments, such as quadrupole mass spectrometers - that analyse gas composition in industrial processes, environmental monitoring or research applications.
The IRG080 has been adopted by several National Metrology Institutes worldwide and had been selected by numerous R&D and calibration laboratories across industry and research, such as at CERN in Switzerland and ITER in France (international organisations which study fundamental physics and nuclear fusion respectively) to provide an accurate, stable and reliable reference. Outside the laboratory, industry is recognising the gauge as a reliable tool for in-situ calibration of vacuum-based coating processes.
The new ISO/TS6737 standard, and the freely released design of the standardised IG, will allow European industry to optimise a range of processes, including coating, semiconductor and EUV lithography, via the provision of a new traceable and more robust measurement tool.
