Method and apparatus for neutralization of ion beam using AC ion source

There is provided by this invention a unique ion source for depositing thin films on a substrate in a vacuum chamber that neutralizes the positive electric charges that develop on the substrate and vacuum chamber apparatus that may cause arcing and degradation of the film deposition. A power supply with a reversing voltage waveform is utilized that neutralizes the electric charge on the substrate and the vacuum chamber apparatus. A power supply applies an ac voltage to the anode of the ion source and a rectified ac voltage to the cathode. The ground terminal of the power supply is connected to the vacuum chamber. The rectifying circuit is comprised of zener diodes that clamp the voltage in the circuit from spikes during plasma ignition and a capacitor connected to negatively bias the cathode when there is no plasma discharge.