A plasma reactor (1) for treating a substrate (40), comprises at least two electrodes (20, 30) arranged within the reactor (1) defining an internal process space (13) there between, whereas the two electrodes (20, 30) are located opposed to each other and parallel with respect to a first surface (20a) of the electrodes (20, 30). Further it comprises a gas inlet (11) and a gas outlet (12) for transporting gas in and out of the plasma reactor (1), a radiofrequency generator (21) connected to at least one of the electrodes (20, 30). At least one of the electrodes (20, 30) has a corrective layer having a non planar shape along a surface (20a) facing the internal process space (13) which has in a first cross section along a radius of the electrode (20) a profile comprising three consecutive and adjacent segments, namely a first, a second and a third segment, where the third segment is adjacent to an edge of the electrode (20) and whereas medium gradient in the first segment is less than a medium gradient in the second segment and a medium gradient in the second segment is larger than a medium gradient in the third segment. An electrode (20) shaped in the above described manner provides for uniform plasma intensity along the surface of the substrate (40) and therefore provides for a treating which is homogenous and features uniform thickness. This invention further allows a compact construction of the vacuum treatment apparatus (1).