Green Pro: Semiconductor manufacturing processes with improved sustainability

Approximately 80 % of the CO2 footprint of average electronic components is created already during their production. A Fraunhofer EMFT research team is working on optimizing semiconductor manufacturing processes in order to minimize the use of climate-damaging process gases. In this context, the scientists are also testing more climate-friendly alternatives to etching gases used as standard today.

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.

They want to reduce the amount of process media required by optimizing the technology process and the processing plant. They are also working on alternatives to the harmful fluorine gas. As part of the Federal Ministry of Research, Technology and Space (BMFTR) project GreenPro, the team is developing two new types of plasma sources for deep etching silicon that allow significantly smaller process chambers: an INCA source - an inductively coupled plasma array - and a microwave-excited, flat plasma rod source. The researchers are also designing the associated demonstrator system.

Both variants of the plasma sources are tested in advance in the plasma etching chamber at the Fraunhofer EMFT in the so-called “Bosch process” and then installed in the demonstrator. 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 etching rates - i.e. the material removal per time - were comparable to or even slightly below the current standard gas SF6 in the first experiments using the climate-friendly alternatives, but the process optimizations are still missing.

The research team is convinced that the initially estimated reduction in CO2 equivalent by a factor of 10 for the Bosch process can be achieved in the next three years by using alternative, more climate-friendly gases and optimizing the plasma sources. The search for environmentally friendly process solutions for the manufacture of semiconductor products has only just begun and is being intensively pursued at the Fraunhofer EMFT.