Specific Process Knowledge/Etch/DRIE-Pegasus/System-description: Difference between revisions

Connecting a RF generator to an AC circuit in order to drive a plasma in a dry etch tool is not as trivial as one might expect. One cannot just connect an RF generator to a coil, put a certain power through and expect that a plasma generated will automatically absorb all energy. It is not possible: At RF frequencies cables become inductors so circuits must be carefully constructed.

Most RF power generators are designed to transfer power into a 50 ohm load. This means that the circuit, in addition to the coil that has a certain inductance and resistance will also require additional electrical components if the total 50 ohm impedance criteria is to be met (unless the inductance and resistance of the coil are carefully chosen and constant). If the impedance is off, part of the power will be dissipated elsewhere in the circuit as reflected power - for instance as localized heating of RF cables due to standing waves. One must therefore have a way of controlling the circuit impedance.