Unstable behavior of plasma in inductive discharges

Summary form only given. Instabilities in a transformer coupled plasma (TCP) source have been studied. An inductive discharge has been created by a 13.56 MHz RF-driven planar inductive coil mounted on the top of an aluminum cylindrical vacuum chamber. Electronegative gases such as O/sub 2/ and SF/sub 6/ and their mixtures with Ar have been used as operating gases. To detect plasma instabilities, time-resolved diagnostics have been used including optical emission spectroscopy and Langmuir probe measurements of the ion current. Instabilities have been observed in a transition region where the discharge changes its mode from capacitive (E-mode) to inductive (H-mode). Frequencies of plasma fluctuations (fluctuations of the ion current or intensity of the light emitted from the plasma) were in the range of 1 Hz-0.9 MHz for operating gas pressures of 2.5-20 mTorr and an absorbed power of 150-600 W. These plasma instabilities may be related to a hysteresis-like behavior of the inductive discharge in the E-H transition region and associated with the balance of power absorbed and lost by electrons.