Commonly used Plasma Sources

In the previous sections and we discussed already that the glow discharge is loosing continously energy when electrons and ions escape to the wall. On the other hand we defined in the same sections the plasma to be in a steady state, means a mechanism that feeds energy back to the plasma must exist. In all discharges relevant to semiconductor manufacturing the balance is achieved by coupling electromagnetic power to the plasma. Hereby the few always existing electrons are accelerated until they aquire enough kinetic energy to create new electron/ion pairs by inelastic collisions with neutral atoms or molecules. Nearly all energy is transfered to the electrons, due to their significant higher mobility which was already discussed in section .

The term plasma source denotes the mechanism and/or apparatus that transforms the supplied electromagnetic energy into acceleration of electrons. This kinetic energy sustains the plasma by electron impact ionization. Actually, in discharges relevant to semiconductor manufacturing there are four basic mechanisms/apparatus applied. Three of them will be discussed briefly in the following sections, namely capacitive, inductive and wave heated discharges. Chapman [1] gives a good introduction to capacitive discharges, the graduate level book of Lieberman and Lichtenberg [5] as well as Popov [6] address all three kind of sources mentioned above.

The fourth, the DC discharge is historically important, but actually due to the necessity of driving a constant current through the sheaths not applicable for plasma etching/deposition of insulators. Instead is is used for the sputtering of conductive materials like aluminum, tungsten or titan. As my personal knowledge (and interest?) is not so big for sputtering processes, I'd like to point you for a more thorough understanding to the literature, the books of Chapman [1] as well as Franz [3] provide a good introduction and further references.