US Patent 9117855 Polarity control for remote plasma

Methods of controlling the polarity of capacitive plasma power applied to a remote plasma are described. Rather than applying a plasma power which involves both a positive and negative voltage swings equally, a capacitive plasma power is applied which favors either positive or negative voltage swings in order to select desirable process attributes. For example, the plasma power may be formed by applying a unipolar oscillating voltage between an electrode and a perforated plate. The unipolar oscillating voltage may have only positive or only negative voltages between the electrode and the perforated plate. The unipolar oscillating voltage may cross electrical ground in some portion of its oscillating voltage.