Consequences of photodetachment in pulsed Ar/O₂ and Ar/Cl₂ inductively coupled plasmas

Pulsed electronegative inductively coupled plasma (ICPs) are now used for high volume manufacturing (HVM) microelectronics fabrication.  Pulsed ICPs in electronegative gases typically undergo a mode transition from the capacitive (E-mode) to the inductive (H-mode) at the beginning of each power pulse due to the decrease in electron density in the attaching gas mixture during the interpulse afterglow.  The E-H transition produces plasma waves and high energy ion bombardment of the window under the antenna which leads to process variability and erosion of the window.  Methods to control the E-H transition (e.g., duty cycle, gas mixture) are somewhat limited due to their effect on other aspects of the process such as etch selectivity.  In this work, we discuss results from a computational investigation of photo-detachment of electrons from negative ions as a means to control E-H transitions.  The electrons produced by photo-detachment contribute to plasma conductivity which accelerates the onset of the H-mode.  This investigation was performed using the Hybrid Plasma Equipment Model (HPEM) with Ar/O₂ and Ar/Cl₂ gas mixtures at tens of mTorr with a pulsed laser producing photodetachment from the O^- or Cl^- negative ions.  Comparisons are made to experimental measurements of plasma properties in similar ICPs using pulsed lasers to produce photo-detachment