Time-Resolved Measurements of the E-to-H Mode Transition in Electronegative Pulse-Modulated Inductively Coupled Plasmas
M Edamura, Eric C. Benck, Yicheng Wang
Time-resolved measurements of electronegative pulse-modulated inductively coupled plasmas (ICPs) were carried out using various measurement techniques. It was experimentally clarified that the structure of an Ar/CF4 plasma during an afterflow dynamically changes passing through three stages when the period of the afterglow is long enough: (1) Electron density and temperature suddenly decrease because of the reaction of electron attachment to fluorine atoms. Fluorine negative ions increases by electron attachment, but the sheath potential still exists and the negataive ions are confined in the bulk plasma region. Since the charge neutrality should be maintained, the density of positive ions is almost constant during this stage. (2) The sheath potential gradually disappears and the density of all the charged particles (electrons, positive and negative ions) decrease because of increased loss to the wall surface. (3) The sheath structure has disappeared completely and the plasma consists of mainly postive and negative ions and is dominated by ambipolar diffusion. The density of the positive ion decreases slightly by the loss to the wall by ambipolar diffusion. The presence of these stages during the afterglowis very important to understand the behaviors of pulsed ICPs with E-to-H mode transitions. The state of a plasma at the end of an afterglow determines the discharge characteristics of the pulsed ICPs (e.g., the appearance of an E mode, the duration of the E mode, stability of the plasma). Since most of the charged particles are lost on the chamber surface in the afterglow, behaviors of the pulsed plasma are strongly affected by the chamber surface condition. This makes it difficult to realize reproducible processes using pulsed plasmas. However, from a different point of view, the measurements of the transient phenomena of the afterglowmakes it possible to monitor the chamber surface condition, which is important for most plasma processes.
, Benck, E.
and Wang, Y.
Time-Resolved Measurements of the E-to-H Mode Transition in Electronegative Pulse-Modulated Inductively Coupled Plasmas, Journal of Vacuum Science and Technology A
(Accessed November 30, 2023)