Plasma system designed or equipped specifically for etching in the oxygen plasma system.. The plasma stripper is particularly useful for removing photoresist masks following structuring. Photoresists are made of organic resins which are removed with excellent results by isotropic plasma etching in the oxygen plasma. Since photoresist layers can be thick, a high etching rate is required. The necessary high number of radicals can be generated particularly well by microwave excitation. Accordingly, a plasma stripper should preferably be equipped with microwave coupling. If the plasma excitation takes place outside of the treatment chamber, no ions are active, which is of advantage since it avoids charging and anisotropic etching of the substrate.