Noble gas

Noble gases are the chemical elements helium, neon, argon, krypton, xenon and radon, which are characterised by the fact that the outermost electron shell of their atoms is completely filled with electrons. gefüllt ist. For this reason, noble gases do not form any bonds with other atoms because neither valence electrons can be released nor valence electrons of other atoms can be absorbed. Noble gases therefore always exist in atomic form and do not form molecules. If noble gases are used as process gases in plasma technology, they cannot form any radicalsbut only ions. bilden. Since excited atoms furthermore do not form any reactions with substrate atoms and molecules, no chemical plasma etching takes place. The particular importance of noble gases in plasma technology is due to the fact that they can be used every time purely physical ion etching is to be implemented. Above all, this is the case when the purpose is to achieve a fully anisotropic etching effect. From the group of noble gases, plasma technology almost exclusively uses argon. Due to their small mass, helium ions have only a minimal etching effect. For its bright yellow-orange plasma, neon is used in neon tubes. The heavy noble gases xenon, krypton and radon are very rare and thus rather expensive. Argon, on the contrary, is available in large quantities (0.93% of the earth atmosphere) at low costs and has a sufficiently large mass to ensure effective etching.