Eur. Phys. J. AP 11, 71-76 (2000)
https://doi.org/10.1051/epjap:2000146

Influence of particulates generated in a CH₄ low pressure radiofrequency discharge on dc negative self bias voltage

LASEP, Faculté des Sciences, Université d'Orléans, Site de Bourges, rue G. Berger, BP 4043, 18028 Bourges Cedex, France

Corresponding author: Veronique.Massereau@univ-orleans.fr

Received: 6 December 1999
Revised: 4 May 2000
Accepted: 8 June 2000
Published online: 15 July 2000

Abstract

The formation and the behavior of particulates have been studied in a pure methane rf plasma (13.56 MHz) for pressures in the range 20−150 Pa. The generated particulates are evidenced using laser light scattering. They are mainly observed at the sheath boundaries where they are suspended in well defined traps. Particulate appearance times at the upper sheath boundary have been determined using the 90° scattered light intensity at 514.5 nm. The appearance time of particulates is sensitive to the working pressure: the higher the pressure, the shorter the appearance time. In our experimental conditions, no particulates are observed in the cloud near the biased electrode for pressures lower than 30 Pa. The negatively charged particulates induce changes in the electrical characteristics of the discharge. The generation and the behavior of particulates are correlated with the time evolutions of the laser beam extinction and of the absolute value of the dc self bias voltage during an experiment.