Periodic formation and propagation of double layers in the expanding chamber of an inductive discharge operating in Ar∕SF6 mixtures

Inductive reactors are routinely used for etching of silicon and various metals in the microelectronic industry. The plasma is excited by flowing a rf current in a coil which launches a decaying wave into the plasma through a dielectric window. When operating in the high plasma density regime the inductive H mode, they provide high ion fluxes with adjustable ion energies by means of an additional rf biasing of the wafer holder. However, when the power applied to the coil is low, the H mode cannot be sustained and the discharge operates in a capacitive E mode due to the high voltage across the coil with respect to the grounded walls. The transition between the E mode and the H mode by increasing the input power is the first source of instability of inductive reactors when electronegative gases are used. This phenomenon, referred as the source instability, has been described and modeled in a series of recent papers. 1–8