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Non-contaminating Electron Density Monitor for RF Induction Plasmas

IP.com Disclosure Number: IPCOM000108112D
Original Publication Date: 1992-Apr-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 1 page(s) / 56K

Publishing Venue

IBM

Related People

Hopwood, JA: AUTHOR [+2]

Abstract

Disclosed is a method of determining the electron density in a radio frequency (RF) induction plasma in which no additional contaminates are introduced into the plasma.

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This is the abbreviated version, containing approximately 57% of the total text.

Non-contaminating Electron Density Monitor for RF Induction Plasmas

       Disclosed is a method of determining the electron density
in a radio frequency (RF) induction plasma in which no additional
contaminates are introduced into the plasma.

      In a production setting where plasma processing of materials is
used, it is desirable to monitor the properties of the plasma to
ensure product quality and process repeatability.  The density of
electrons is one such measure of plasma performance.  Currently
electron density can be determined by Langmuir probes which,
unfortunately, contaminate and perturb the plasma.  Alternately,
microwave interferometry is used at considerably greater expense.
The method described below is both inexpensive and non-contaminating.

      The magnetic flux probe is a well-known device which consists
of a small loop of wire which terminates a transmission line (1).  It
is also understood that electromagnetic waves with frequencies which
are less than the electron plasma frequency decay exponentially
within a plasma (2).  The rate of spatial decay of the wave increases
with increasing electron density.  By measuring the spatial decay of
the electromagnetic wave, it is possible to monitor electron density
in a plasma.  Since it is not necessary for the probe to directly
contact the plasma, it is placed inside a dielectric tube.
Dielectrics (quartz, pyrex, alumina, etc.) are commonly used in
plasma processing apparatus, so it is...