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In RF sputtering, high frequency alternating current is applied to a vacuum chamber and a target. It is used for metals, ceramics, silica, oxides, metal oxides, nitrides, insulators, etc.
Radio frequency (RF) refers to high frequencies. As it uses alternating current, the direction of particle acceleration alternates with the voltage. Electrons on the chamber side flow into the circuit, and electrons on the target side lose an escape and gather in high density. This causes the target side to be negatively biased, causing the ions to hit the target and sputter off.