Investigations of Pulse-to-Pulse Instabilities and Abnormal Electron Growth in Highly Electronegative Inductively Coupled Plasmas

Electronegative pulsed inductively coupled plasmas (ICPs) are commonly used for surface modification in microelectronic fabrication. Pulsed ICPs are prone to E-H transitions, which depend on reactor geometry, power pulse profile, pressure, and gas mixture. E-H transitions in ICPs sustained in Ar/Cl₂ mixtures were computationally investigated using the Hybrid Plasma Equipment Model (HPEM). The E-mode is particularly strong due to a decrease in electron density resulting from thermal attachment during the interpulse afterglow. During these simulations (base case: 30 mTorr, pulse repetition frequency 13.33 kHz, 30% duty cycle, 350 W average power), startup instabilities causing anomalous electron growth during the E-H transitions were observed for various operating conditions—mostly with large Cl₂ mole fractions. We found that the instabilities are pulse periodic and pulse-to-pulse patterns (anomalous or normal growth of electron density) vary with the operating conditions. We will discuss results from the computational investigation for instabilities occuring at the onset of the power pulse and pulse-to-pulse patterns for various operating conditions, including the substrate bias. The correlation between the instability and electron energy-dependent attachment reactions will be discussed. The fluxes, energy, and angle distributions of charged particles to the wafer and dielectric window will be discussed.