Plasma treatment apparatus and method

A plasma treatment apparatus comprising a chamber earthed, a vacuum pump for exhausting the chamber, a suscepter on which a wafer is mounted, a shower electrode arranged in the chamber, opposing to the suscepter, a unit for supplying plasma generating gas to the wafer on the suscepter through the shower electrode, a first radio frequency power source for adding radio frequency voltage, which has a first frequency f1, to both of the suscepter and the shower electrode, a second radio frequency power source for adding radio frequency voltage, which has a second frequency f2 higher than the first frequency f1, at least to one of the suscepter and the shower electrode, a transformer whose primary side is connected to the first radio frequency power source and whose secondary side to first and second electrodes, and a low pass filter arranged in a circuit on the secondary side of the transformer, and serving to allow radio frequency voltage, which has the first frequency f1, to pass through it but to cut off radio frequency voltage, which has the second frequency f2, while plasma is being generated.