Electronic products also have an ecologic footprint - that's common knowledge today. What may come as a surprise, however, is that the largest share of a product's CO2 emissions - around 80% - does not occur during the use phase, but rather during production. But what is the reason for this? This is impressively demonstrated by the example of semiconductor production. In this field, deep etching is a key basic process for creating microstructures in a silicon wafer. For this purpose, the extremely climate-damaging gas sulfur hexafluoride (SF6) is used - one of the main reasons for the poor eco-balance.
This is where a research team from the Fraunhofer Institute for Electronic Microsystems and Solid State Technologies EMFT comes in: They want to reduce the amount of required process media by optimizing the technology process. They are also looking for alternatives to the harmful fluorine gas. As part of the project SUMSi, funded by the German Federal Ministry of Education and Research (BMBF), the team is developing two novel plasma sources for deep silicon etching, that allow significantly smaller process chambers: a so-called INCA source - an inductively coupled plasma array - and a microwave-excited, planar plasma rod source.
Both plasma source variants have already been successfully tested in the plasma etching chamber at Fraunhofer EMFT using the so-called "Bosch process". Simply put, the process is based on a regular alternation between passivation and Si etching and is a standard in industrial production to manufacture microstructures. The scientists used three different process media: C4F8 (passivation gas), SF6 (climate-damaging etching gas) and a FAN gas mixture (climate-friendly etching gas, mixture of F2/Ar/N2). The etch rates - i.e. the material removal per time - were comparable or even higher with SF6 than with the currently used systems. The more climate-friendly alternatives rank currently even lower, due to the significantly lower fluorine content.
Considering the enormous CO2 savings potential, there is no doubt that the research team will continue to work on this topic: An initial estimate shows that using alternative, more climate-friendly gases would decrease the CO2 equivalent of the Bosch process by more than a factor of 10. Therefore, the search for more environmentally friendly process solutions has just begun and will be intensively continued at Fraunhofer EMFT.