Method and device for treating a substrate by means of a plasma

In a method and device for treating a substrate by means of a plasma, the plasma is generated and accelerated at substantially sub-atmospheric pressure between a cathode and an anode of a plasma source (1) in a channel of system of at least one conductive cascaded plate between said cathode and anode. Said plasma is released from said plasma source to a treatment chamber (2) in which said substrate (9) is exposed to said plasma. The treatment chamber is sustained at a reduced, near vacuum pressure during operation. An alternating bias voltage is applied between said substrate and said plasma during said exposur