EMPIR project generates first stable trace level Hydrogen Chloride gas standards

A new dynamic gas standard for HCl has been developed in the 1–15 nmol mol-1 range – a major cause of production loss in semiconductor manufacturing

Europe has 9 % of the world share of the semiconductor manufacturing industry, representing 25 billion euro, with aims to increase this to 20 % by 2025.

In this industry even small amounts of contaminants can cause detrimental defects to products and processes. Since 1997, there have been 24 major production losses due to Airborne Molecular Contamination (AMC), each with a value of up to 80 million euro.

Hydrogen Chloride (HCl) is a highly reactive and toxic gas released by processes such as etching in the microelectronics industry. Without appropriate monitoring it can accumulate in clean rooms, causing chemical contamination layers such as haze on the wafer and corrosion on instrumentation.

Monitoring instrumentation for HCl must be accurately calibrated using traceable gas reference materials. However, due to HCl’s reactivity, it readily adsorbs onto the wetted surfaces of the cylinder making gravimetric preparation of static standards highly challenging. The lack of traceable static mixtures is one of the biggest obstacles to advancing the science.

New dynamic calibration standard for HCl

The National Physical Laboratory (NPL), the National Metrology Institute (NMI) for the UK, with the help of the consortium, solved this problem in the EMPIR project Metrology for Airborne Molecular Contaminants II (17IND09, MetAMC II). During the project NPL developed a dynamic standard for HCl down to the 1-15 nmol mol-1 detection range using a 2-step dilution system based on a sonic nozzle array. The new gas calibrant is also SI traceable as it is linked to primary reference materials (PRMs) that are gravimetrically prepared.

Dynamic standards differ from static in that they are generated using a continuous flow of gas with a known generation rate that is defined by both the amount fraction of the static PRM being diluted and the dilution ratio from the combination of selected sonic nozzles. During operation the surfaces become passivated with HCl meaning losses due to adsorption or condensation become negligible once the system has reached equilibrium. In addition, the input concentration of the HCl can be varied – providing a wide dynamic range.

The development of the new standard was disseminated at several high-profile events including STEM for Britain 2023 and Chemistry of the Whole Environment Research. The work was also presented to the Science and Technology Advisory Council and representatives of former BEIS and UKRI.

A single stage dilution system for HCl developed in the project has also allowed NPL to participate in key comparison CCQM-K175 organised by the Gas Analysis Working Group (GAWG) of the Consultative Committee on amount of Substance (CCQM). The aim is to ensure the equivalency in the measurement capability of NMIs to measure 30 µmol mol-1 HCl in nitrogen. This is necessary to support industry specifically with compliance to the Industrial Emissions Directive (2010/75/EU) as this is a relevant HCl amount fraction emitted from industrial installations. It is also important as it provides the SI traceability to the NPL dynamic standard. This comparison is ongoing and is expected to be accepted for equivalence and published later this year. Following this NPL will submit new calibration and measurement claim (CMC) for 10 – 100 µmol mol-1 for HCl measurements based on the results.

The dynamic gas standard technique can also be extended to other gases that currently have no low-level calibration standards – such as highly reactive ammonia which is harmful to health and is extensively released by agriculture and intensive farming practices.

Other project developments

Published a good practice guide on the handling and use of static HCl materials, with an introduction from VSL, the NMI of the Netherlands on YouTube.

Published a specification document for the different spectroscopy techniques used for Airborne Molecular Contaminants
The economic benefit of the work of the project in detection of airborne molecular contamination has been calculated by the project consortium to be estimated as 8 million euro in 2026 and 40 million euro in 2031.

As well as helping Europe achieve a 20 % market share in the semiconductor manufacturing industry by 2025 the project’s work on spectroscopic techniques are anticipated to have other applications, such as diagnosis tools for diseases, mapping the atmospheric composition of planets.

This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

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