Self-bias

A capacitively decoupled high-frequency electrode (separated from the generator generator by a capacitor), which is operated at high frequency in the MHz range, receives a negative charge in the low-pressure plasma. The heavy positive ions are too inert to follow the high frequency of the alternating field but the light-weight electrons can follow easily. This gives the working electron an increasingly negative charge because the electrons cannot flow off due to the capacitive decoupling. This results in the formation of a bias voltage which accelerates the positive ions to these negatively charged electrode. A substrate supported on this negatively charged electrode will be bombarded by the ions. This effect is used for ion etching (physical etching).