Active control of instabilities for plasma processing with electronegative gases

Feedback stabilization of instabilities was demonstrated in inductively coupled electronegative plasmas by modulating the radio frequency power in response to a feedback control signal. Two modes were observed and stabilized: a fast bursting mode (designated 'B' mode) and a slower oscillatory mode (designated 'O' mode). 'B' mode is a low duty-cycle non-linear phenomenon characterized by short (<1 µs) spikes on optical signals, at a pulse repetition rate of 10–40 kHz. 'O' mode is characterized by continuous oscillations in ion saturation current at lower frequency (200 Hz–1 kHz). Some parameter ranges exhibit both modes. Fluctuations in similar processing plasmas and having similar characteristics have previously been observed and identified with instability due to electron attachment to the electronegative neutral gas species.