Funnelling of rf current via a plasmoid through a grid hole in an rf capacitive plasma reactor

Abstract

The boundaries of capacitively coupled radio-frequency (rf) plasma reactors generally include at least one grounded metal grid or perforated plate for purposes of gas flow or diagnostic access. When increasing the rf power, an intense localized plasma (a plasmoid) can spontaneously ignite in a hole of a grounded surface. Experiments described here show that the plasmoid funnels rf current through the hole to the other side of the grounded plate, thereby increasing the effective grounded area in contact with the plasma. Hence, plasmoid ignition is always accompanied by a drop in the dc self-bias voltage of the rf electrode.The small area of the plasmoid aperture means that the rf current density passing through the plasmoid is very high, causing intense optical emission and strong local heating. Plasmoid ignition can therefore cause a loss of process reproducibility and potentially lead to melting and eventual destruction of reactor components.

Modeling of plasma processing reactors: review and perspective

“…Striations, plasmoids, rotating structures, and spatial constrictions are commonly observed in intermediate-pressure plasmas. 85,86 The presence of these phenomena indicates that kinetic effects might be relevant in these plasmas or that higher order moments need to be included in fluid models. There are few examples of the experimental characterization and modeling of these "non-idealities" in intermediate-pressure plasmas, so it is an area ripe for new modeling and experimental studies.…”

“…Fully kinetic simulations are however impractical due to the constraints on mesh resolution (and hence time step) due to small electron mean free path. Striations, plasmoids, rotating structures, and spatial constrictions are commonly observed in intermediate-pressure plasmas 85 , 86 . The presence of these phenomena indicates that kinetic effects might be relevant in these plasmas or that higher order moments need to be included in fluid models.…”

Optical diagnostics of dusty plasmas during nanoparticle growth

“…Plasmoids have been observed in several typical laboratory discharges [31][32][33][34][35][36][37][38] but their origin is still unclear. They seem to be favored by electric field disturbances as they are observed in grid holes [37] or preferentially close to guard rings encircling electrodes [31][32][33]. In this last case, the number of plasmoids can vary and their regular rotation around the circumference of the electrodes has been reported [31][32][33].…”

“…Indeed, the plasma is not globally changing during the rotation of these regions, it is just the places of enhanced emission that are moved. Plasmoids have been observed in several typical laboratory discharges [31][32][33][34][35][36][37][38] but their origin is still unclear. They seem to be favored by electric field disturbances as they are observed in grid holes [37] or preferentially close to guard rings encircling electrodes [31][32][33].…”

Unstable Plasmoids in Dusty Plasma Experiments

“…These unstable phenomena can be characterized by the appearance of small (a few mm) bright plasma spots that we formerly called plasma spheroids [3-6] but now we will use the more widespread term plasmoids [7,8]. These plasmoids originate from the electrodes and propagate through the discharge center following complex trajectories partly due to their mutual interactions.…”