AVS 46th International Symposium
    Plasma Science and Technology Division Monday Sessions
       Session PS-MoP

Paper PS-MoP18
Neutral Depletion and Transport Mechanisms in Large-Area High Density Plasma Sources

Monday, October 25, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: S.M. Yun, University of California, San Diego
Authors: S.M. Yun, University of California, San Diego
K. Taylor, University of California, San Diego
G.R. Tynan, University of California, San Diego
Correspondent: Click to Email
Plasma uniformity has been recognized as a significant parameter in large sized high density plasma processing tools. In this paper we show experimental and modeling results which indicate that significant neutral uniformity variations can also occur in high density plasma processing tools. The experiments are carried out in both inductively coupled plasma (ICP) and helicon plasma sources. The spatial distribution of reactive neutrals is measured using spatially resolved optical emission spectroscopy combined with Langmuir probe measurements of plasma density. The degree of on-axis neutral depletion is found to be determined by plasma density, neutral fill pressure, and neutral dissociation fraction. The observations can be explained by the "plasma pumping" effect, wherein electron impact ionization of neutral particles is followed by their rapid removal from the plasma by the presheath electric field. A one-dimensional neutral diffusion model that incorporates this mechanism provides reasonable agreement with our results. This net loss of neutral particles can result in a large (~50%) neutral density variation across 300mm wafers. The importance of neutral-surface interactions (i.e. the wall or wafer can be an effective source or sink of neutrals) is also examined.