Electronic Gases

Gases play a versatile role in a wide range of process steps in the manufacture of semiconductors and solar cells.

For example, electronic gases are used for etching, doping, layer removal and cleaning process chambers.

However, this increasing consumption of electronic gases also has its downside – the conventional cleaning gases sulphur hexafluoride (SF6) and nitrogen trifluoride (NF3) are harmful to the climate.

An NF3 molecule has a global warming potential around 11,000 times greater than that of a carbon dioxide molecule, and an SF6 molecule 22,000 times greater.

Linde is rising to this challenge by developing solutions to prevent these gases being released into the atmosphere – either by recycling or through alternative applications using more eco- friendly gases.

We have devised a process, for example, to recycle unused SF6 from the epitaxy chamber, feeding it back to the production process following purification. This closed-loop technology recaptures 100 percent of the residual gas for cost-effective reuse while simultaneously preventing their release into the atmosphere.

Two of these SF6 recycling systems are already in operation in German solar cell plants.

Another option is to eliminate the use of greenhouse gases in cleaning entirely, instead generating the active cleaning agent, fluorine (F2), directly where it is required. In contrast to NF3, pure F2 does not contribute to global warming.

Tests in Linde’s development laboratory in San Marcos, California, have shown that pure F2 makes cleaning faster and significantly more effective. It is also possible to switch from NF3 to a F2 generator without major modifications to existing distribution systems. So with a simple switch, a plant can increase its productivity and cut its NF3 consumption entirely.

Linde had already developed these technologies at the end of the 1990s and has been gathering experience with onsite fluorine generators for semiconductor customers since 2003.

In summer 2007, the trade journal EUROAsia Semiconductor recognised Linde’s on-site F2 generator with its Materials–Improvement Award 2007. In 2008, Linde was proud to receive an innovation prize from the prestigious Institute of Engineering and Technology (IET).