RATIOMETRIC AUTOTUNING ALGORITHM FOR RF PLASMA GENERATOR

摘要

An RF plasma system employs frequency tuning to change the frequency of an RF generator within a frequency range to match the impedance of a plasma chamber. Forward power and reflected power magnitudes are obtained from a bidirectional sensor. The ratio of reflected power to forward power is obtained for one frequency, and then the frequency is changed. The tuning algorithm compares the ratio of reflected to forward power at the new frequency with the ratio obtained earlier. If this ratio is smaller, the frequency is changed again in the same direction, but if larger, then the frequency is changed in the other direction. These steps are iterated until the ratio of reflected to forward power reaches a minimum. The tuning algorithm can be implemented in hardware or in software.