AVS 50th International Symposium
    Plasma Science and Technology Monday Sessions
       Session PS-MoM

Paper PS-MoM11
3-Dimensional Modeling of Pulsed Inductively Coupled Plasmas: A Method to Improve Uniformity@footnote 1@

Monday, November 3, 2003, 11:40 am, Room 315

Session: Critical Dimension Etching
Presenter: P. Subramonium, University of Illinois at Urbana-Champaign
Authors: P. Subramonium, University of Illinois at Urbana-Champaign
M.J. Kushner, University of Illinois at Urbana-Champaign
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Continuous wave (CW) operation of inductively coupled plasma (ICP) reactors having asymmetric pump ports or feedstock gas injection may produce asymmetric densities of radicals and fluxes to the substrate. These asymmetries are often intensified by positive feedback between regions of higher conductivity producing higher power deposition and higher ionization rates, which in turn increase the conductivity. Pulsed ICPs have been investigated as a means to extract negative ions to the substrate to reduce charging damage. Pulsed ICPs may also provide a means to reduce or eliminate asymmetries by reducing this positive feedback. In this paper, results from a 3-dimensional model for pulsed ICPs having such asymmetries will be discussed. As these long-term phenomena are difficult to resolve in multi-dimensional plasma equipment models a computationally parallel hybrid model has been developed to both speed the calculation and to better represent the physical processes. Results for pulsed ICPs in Ar, Ar/Cl@sub 2@, Ar/C@sub 2@F@sub 6@ gas mixtures will be discussed while varying pulse repetition frequency (5 - 20 kHz), duty cycle (10% - 70%), power (200 - 800 W) and pressure (5 - 20 mTorr). We found that the non-uniformities in species densities which feedback through the plasma conductivity are generally reduced during the afterglow of the pulsed plasma. In the afterglow, without the nonuniform source function, diffusion smooths the plasma density profile, providing a more uniform set of initial conditions for the next power pulse. The ionization source during the subsequent power pulses is therefore more uniform. As a result, time averaged plasma properties for pulsed plasmas are more uniform compared to CW excitation. Uniformity generally improves with decreasing duty cycle and decreasing repetition rate. @FootnoteText@ @footnote 1@ Work supported by Semiconductor Research Corporation and National Science Foundation.