ASML employees are taking a course to learn more about plasma physics for their work on EUV lithography systems.
"The EUV radiation in the scanner optics region of the EUV system also induces a plasma by the method of photoionization. The scanner optics region is not kept at very low vacuum but it is flushed by hydrogen gas at a background pressure of approximately 5 Pa. The hydrogen gas is ionized by the 92.4 eV photons of the EUV radiation, mostly through the single-photoionization process (ionization potential of H2 is 15.8 eV). Subsequently, the ejected electrons carry a high excess energy (76.4 eV) which leads to additional electron-impact ionization further contributing to the plasma generation. Moveover secondary electrons can be generated by the photo-electric effect. Overall, the plasma dynamics is pretty complex."
The hydrogen plasma serves some cleaning and de-oxidizing purposes. It is also used to remove Sn debris from the collector.
"The EUV-induced H2 plasma in the optics region is, however, not only beneficial and its interaction with the surfaces in the scanner needs to be carefully managed to avoid serious adverse effects: undesired etching of materials, surface roughening, diffusion into materials making them brittle, etc. This means that the plasma load on the materials close to the EUV beam should be taken into account by proper understanding of the effects and by controlling them. In terms of elementary reactions, this includes the surface interaction of hydrogen atoms and hydrogen ions as well as all kind of synergistic effects (between the various hydrogen plasma species and between the plasma species and EUV photons etc)."
"The EUV radiation in the scanner optics region of the EUV system also induces a plasma by the method of photoionization. The scanner optics region is not kept at very low vacuum but it is flushed by hydrogen gas at a background pressure of approximately 5 Pa. The hydrogen gas is ionized by the 92.4 eV photons of the EUV radiation, mostly through the single-photoionization process (ionization potential of H2 is 15.8 eV). Subsequently, the ejected electrons carry a high excess energy (76.4 eV) which leads to additional electron-impact ionization further contributing to the plasma generation. Moveover secondary electrons can be generated by the photo-electric effect. Overall, the plasma dynamics is pretty complex."
The hydrogen plasma serves some cleaning and de-oxidizing purposes. It is also used to remove Sn debris from the collector.
"The EUV-induced H2 plasma in the optics region is, however, not only beneficial and its interaction with the surfaces in the scanner needs to be carefully managed to avoid serious adverse effects: undesired etching of materials, surface roughening, diffusion into materials making them brittle, etc. This means that the plasma load on the materials close to the EUV beam should be taken into account by proper understanding of the effects and by controlling them. In terms of elementary reactions, this includes the surface interaction of hydrogen atoms and hydrogen ions as well as all kind of synergistic effects (between the various hydrogen plasma species and between the plasma species and EUV photons etc)."
