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A Microwave Interferometer for Density Measurement and Stabilization in Process Plasmas

Published online by Cambridge University Press:  22 February 2011

David I. C. Pearson,
G. A. Campbell,
C. W. Domier and
P. C. Efthimion
David I. C. Pearson
Affiliation:
Plasma and Materials Technologies, Inc., 222 W. Orange Grove Ave., Burbank, CA 91502.
G. A. Campbell
Affiliation:
Plasma and Materials Technologies, Inc., 222 W. Orange Grove Ave., Burbank, CA 91502.
C. W. Domier
Affiliation:
Institute of Plasma and Fusion Research, UCLA, Los Angeles, CA 90024.
P. C. Efthimion
Affiliation:
Princeton Scientific Consultants, P.O. Box 2181, Princeton, New Jersey 08540.
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Abstract

A low-cost heterodyne microwave interferometer system capable of measuring and/or controlling the plasma density over a dynamic range covering two orders of magnitude is demonstrated. The microwave frequency is chosen to match the size and density of plasma to be monitored. Large amplitude, high frequency fluctuations can be quantitatively followed and the longer-time-scale density can be held constant over hours of operation, for example during an inline production process to maintain uniformity and stoichiometry of films. A linear relationship is shown between plasma density and discharge current in a specific plasma device. This simple relationship makes control of the plasma straightforward using the interferometer as a density monitor. Other plasma processes could equally well benefit from such density control capability. By combining the interferometer measurement with diagnostics such as probes or optical spectroscopy, the total density profile and the constituent proportions of the various species in the plasma could be determined.

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