Abstract: A reactor comprising a plate-shaped cathode that is horizontally arranged and connected to an alternating voltage, in a ground connected casing, and gas inlet and gas outlet lines. The cathode is equipped with means for generating local magnetic fields restricted to the region of the individually supported substrates. The cathode can be furthermore have holes or openings in which are arranged substrate holders shiftable or movable vertically to relate to the substrate surface.The substrates are etched in the reactor by means of a plasma which is produced from at least one reactive gas. Each substrate is exposed to at least one local magnetic field. If a mostly chemically etchable material is to be etched in the presence of a mostly physically etchable material, to a much stronger extent than the latter, the advantageous etching speed ratio can be set in that the substrates are additionally raised over the cathode surface.