Radicals are generated in molecular process gases but also on substrates exposed to the plasma. This is primarily due to the ionising effect of the UV radiation of the plasma. This UV radiation splits molecular bonds, i.e. breaks off individual atoms or molecule fractions. Both split parts now have an unpaired bond which they try to fill again as soon as possible. For this reason, they are highly reactive and react immediately with the next particle in their range of influence which matches their unpaired bond. These split molecule parts with unpaired bond are referred to as radicals, and the unpaired bond as radical site. Polymers can be formed by the reactions and interlinking of radicals. The reaction of radicals of the process gas and the substrate leads to the formation of new molecules, which enter the gas phase and leave corresponding holes on the substrate. This is the functionality of plasma etching or plasma cleaning.