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Accueil > Séminaires et conférences > Séminaires, soutenances de thèses et HDR précédents > 2010 > Séminaires 2010 > Le vendredi 21 Mai à 14h

Le vendredi 21 Mai à 14h

Boris Legradic, Ecole Polytechnique Fédérale de Lausanne (EPFL)

Le vendredi 21 mai à 14h Ecole Polytechnique Palaiseau Salle de conférence du LIX

RF BREAKDOWN IN LOW PRESSURE GASES IN SMALL (MILLIMETRIC) GAPS WITH NON-PLANAR SURFACES

Résumé :

Small gaps are present in plasma-enhanced chemical vapor
deposition reactors to isolate the RF electrode from the
grounded parts of the reactor. These gaps are supposed to be
small enough so that no glow discharge can form (dark space
shielding), but wide enough to avoid problems of mechanical
tolerance and thermal expansion, as well as to limit large
capacitive currents and prevent metal vapor arcing due to
field emission. RF breakdown in these small gaps is of high
interest for the thin-film industry, since arcing and parasitic
plasmas in small gaps in PECVD reactors represent a failure
point preventing the upscaling to larger substrates and/or
higher power regimes for micro-crystalline silicon deposition.
This paper presents an experimental investigation into RF
breakdown for electrodes with holes or protruding features,
approximating the situation in real reactors, and providing
benchmark for fluid simulations using a drift-diffusion model
with a finite-element solver.
RF breakdown curves (voltage vs. pressure) have more
complex features than DC Paschen curves, but generally
show a steep left-hand branch at low pressures and a flatter
right hand branch at higher pressures. Introducing protrusions
or holes in parallel plate electrodes will lower the breakdown
voltage in certain conditions. However, experiments in argon
and hydrogen show that the breakdown curves are not
perceptibly influenced by the increased electric field at sharp
edges or ridges. Instead, both experiments and simulation
show that, in general, breakdown at high pressure will occur
at the protrusion providing the smallest gap, while
breakdown at low pressure will occur in the aperture
providing the largest gap. This holds true as long as the
feature in question is wide enough to provide breakdown :
Features that are too narrow will lose too many electrons due
to diffusion, either to the walls of the apertures or to the
surroundings of the protrusion, which negates the effect on
the breakdown voltage. The simulation could be developed
into a tool to aid the design of complex RF parts for darkspace
shielding.


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Tutelles : CNRS Ecole Polytechnique Sorbonne Université Université Paris Sud Observatoire de Paris Convention : CEA
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Mentions légales
Exploitant du site : Laboratoire de Physique des Plasmas, Ecole Polytechnique route de Saclay F-91128 PALAISEAU CEDEX
Hébergeur : Laboratoire de Physique des Plasmas, Ecole Polytechnique route de Saclay F-91128 PALAISEAU CEDEX
Directeur de la publication : Pascal Chabert (Directeur)