Two layer barrier on polymeric substrate

Plasma treatment apparatus for treating a substrate (6) comprising at least two opposing electrodes (2, 3) and a treatment space (5). The at least two electrodes (2, 3) are connected to a plasma control unit (4) for generating an atmospheric pressure glow discharge plasma in the treatment space (5). A gas supply device (8) provides a gas mixture in the treatment space (5). In operation,a first layer of inorganic material is deposited on a polymeric substrate using a gas composition comprising oxygen having a concentration of 2 % or less, while the power supply provides an energy of 30 J/cm2 or less. A second layer of inorganic material is deposited on the first layer using a gas composition comprising oxygen having a concentration of 3 % or higher. During the second layer formation the power supply provides an energy of 40 J/cm2 or higher