Transition from E to H mode discharge in pulse-modulated inductively coupled plasmas

Time-resolved measurements of pulse-modulated inductively coupled plasmas were carried out by using a Langmuir probe. It was found that under a certain set of conditions (a mixture of 20% O-2 and 80% Ar, a pressure of 2.67 Pa, an rf power of 200 W, a pulse frequency of 500 Hz, and an rf-off time of 100 mus), a plasma transits from E mode (capacitive coupling mode) to H mode (inductive coupling mode) after the rf-off time. With a shorter rf-off time of 50 As, the plasma returned to H mode without passing through E mode. Whether H mode or E mode appears after the rf-off time depends on the electron density at the end of the afterglow. Namely, the restoration to H mode after the if-off time occurs if the plasma has an adequate electron density, and E mode occurs if-electron density is not enough to sustain H mode. It was also found that electron temperature decreases and plasma potential increases gradually during E mode because of the change of the electron-energy distribution. The change of the plasma reduces the impedance mismatching gradually and increases the electron density until the transition to H mode occurs. Such mode transition behavior strongly depends on the basic characteristics of the plasma processing apparatus during continuous discharge and also on the condition of the chamber wall. (C) 2003 American Vacuum Society.