Less harmful alternatives to hydrofluorinatedcarbons (HFCs) are likely to replace conventional fluorinated gases (F-gases) across many industries, but they are expected to remain a fixture of semiconductor manufacturing for the foreseeable future.
“Why are people concerned about these things? Firstly, they’re very potent greenhouse gases,” explained Stephen Harrison, Founder and Managing Director of sbh4, during a gasworld webinar.
Many have a high global warming potential (GWP), a measure of how much energy the emission of one tonne of a gas will absorb over a given period relative to the emission of one tonne of carbon dioxide (CO2).
One of the worst offenders is sulphur hexafluoride, a gas widely used as an insulator and arc-quenching medium. Despite its effectiveness, it has a GWP of around 24,000, meaning a tonne emitted warms the atmosphere roughly 24,000 times more than a tonne of CO2 over the standard assessment period.
“That is how potent they are,” said Harrison. “They’re forever chemicals and they don’t really disintegrate … [which is why] people are concerned about them.”
In response, the EU is enforcing a strict phase-down that aims to eliminate the placing of HFCs on the market by 2050.
There are also efforts to replace them with less harmful chemicals such as hydrofluoroolefins (HFOs).
“There are some very good alternatives to the really nasty F-gases … we can use HFOs, which are olefins, which have a double bond in the middle of them.”
Despite containing fluorine, HFOs feature a carbon-carbon double bond that allows them to break down much more readily in the atmosphere under ultraviolet light than conventional F-gases.
And as sustainability targets draw closer, companies are taking notice.
One of the industry’s leading manufacturers, Chemours, has developed a lineup of HFO-based refrigerant blends used to replace older, higher-GWP alternatives in supermarkets, chillers and heat pumps.
Automotive giant Volkswagen has gone a step further, rejecting HFO-based refrigerants in favour of natural refrigerants such as CO2 for some mobile air-conditioning and heat pump systems.
The picture is very different in semiconductor manufacturing, where F-gases play a critical role in etching and cleaning processes.
Semiconductor devices continue to shrink, increasing the performance requirements for used in production.
“And it’s difficult to find substitutes when the performance of the molecule is so critically important, and getting more important, so I don’t think we’re going to see F-gases coming out of the wafer fab anytime soon,” said Harrison.
Instead, the industry is increasingly focused on preventing emissions from reaching the atmosphere in the first place.
“The F-gases are effectively destroyed using plasma and other technologies,” explained Harrison, likening the process to hitting them with the biggest possible chemical hammer.
F-gases are essential during the chip production process© Shutterstock
These molecules are broken down using highly energy-intensive plasma processes, with the fluorine captured in liquid form for safe disposal.
While refrigerants are increasingly being replaced, Harrison sees a different path for electronics-related F-gases.
“I see it much more as a ‘let’s make sure we clean them before they exit the wafer fab’ kind of story.”
Companies such as Taiwan Semiconductor Manufacturing Company use point-of-use abatement systems involving combustion, dry scrubbers, catalytic systems and hybrid thermo-oxidation methods. According to the company, these systems achieve destruction and removal efficiencies of 90 to 99% for regulated pollutants.
Similar approaches have been proposed for its Arizona facilities, where point-of-use abatement technologies are expected to reduce fluorinated greenhouse gas emissions by around 90%.
