B2 - Schoonover, Inc.

PPM 422 Plasma Process Monitor
Residual Gas and Process Gas Analyzers
PPM 422 Plasma Process Monitor
User Advantages
♦ Detection of neutral particles and of positive and negative ions from
the plasma
♦ Energy analysis of neutral particles and of positive and negative ions
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♦ Measurement of radicals
♦ End point detection of plasma processes
♦ Large dynamic range
♦ High measuring speed
The PPM 422 is a differentially pumped mass spectrometer unit with
integrated energy analyzer for measuring neutral particles, positive and
negative ions, as well as for energy analysis of ions and neutral particles
in plasma processes.
The extraction orifice is located near the plasma. It can be floating or
biased. Directly behind the extraction orifice, there is a lens and the ion
source with 2 filaments, followed by a lens and the energy analyzer. An
additional lens focuses the ions into the mass filter. The mass filter, the ion
source, the lens system, the energy analyzer, and the deflection unit are
isolated to ground and may be biased up to 500 V.
The PPM is operated with the Balzers Quadstar TM software package
specially optimized for this application.
1 Turbo pump
2 Secondary electron
multiplier SEM
3 Deflection unit
4 Quadrupole
mass filter
5 Extraction orifice
6 Safety shield
against arcing
7 Entrance lens
8 Ion source
9 Transfer lens
10 Energy analyzer
Mass spectrum of positive ions
Mass spectra of positive ions from a plasma reveal detailed information of the various species
contained in a plasma, and therefore allow an insight into plasma chemistry. The basis for
reactive ion etching is the conversion of the material to be removed into volatile reaction products
which can be pumped away. An example is the etching of tungsten in SF6 plasma where metallic
tungsten is converted into WF6. This reaction product can be recognized in the mass spectrum
by means of the various dissociation products (WF5+, WF4+, WF3+, WF2+).
Mass spectrum of negative ions
Negative ions are a major component in a plasma with electro-negative species like fluorine,
chlorine, oxygen or hydrogen. In certain plasma processes like plasma polymerization, the
negative ions play a key role, which is partly due to the very long residence time of negative ions
in the glow region. Therefore, detection of negative ions is highly desirable. The figure shows
a mass spectrum of negative ions from a SF6 plasma in the mass range 100-200 amu.
Besides the peaks due to the etch gas SF6, one can recognize various peak groups related
to the etched molybdenum.
Note: Contact the sales office nearest you for ordering information.
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