Abstract: In a known plasma-chemical coating apparatus, a plasma chamber is provided within which at least one linear antenna is arranged for producing a plasma by means of electromagnetic power, in which a supply for a carrier gas terminates and which comprises a plasma exit opening in the direction of a treatment chamber for a plasma-assisted modification of a substrate. Starting from this, to achieve cleaning cycles as in coating apparatuses with comparatively slow coating processes, it is suggested according to the invention that the plasma exit opening is configured as an elongated narrowing and defined preferably on both sides by cylinders which extend in parallel with each other and are rotatable about their cylinder axis, and that a cleaning zone is respectively provided for each of the cylinders, into which an area of the outer surface of the respective cylinder which is to be cleaned can be introduced by rotation about the cylinder axis.