1. Instabilities in Electronegative Inductive Discharges
SFR Workshop
November 8, 2000
A. M. Marakhtanov, M. A. Lieberman,
A. J. Lichtenberg, and P. Chabert
Berkeley, CA
2001 GOAL: characterize instability using OES/actinometry and planar probe. Install the Z-scan sensor and explore the spectral RF signature of plasma instability by 9/30/2001.
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2. Experimental TCP Setup
Planar Probe
Monochromator
Plasma
30 cm
Inductive Coil
19 cm
OES (PMT)
Langmuir Probe
Mass Spectrometer
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3. Instability windows
Inductive
Capacitive
Capacitive
Unstable in most of discharge conditions used in etching
Instability linked to average attachment rate
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4. Frequency vs. Power and Pressure
90 mTorr
80 mTorr
SF6
65 mTorr
50 mTorr
40 mTorr
25 mTorr
10 mTorr
Instability frequency increases with increase of pressure and power
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5. Effect of Matching Network
SETTING 1 (LOW FREQ.)
SETTING 2 (HIGH FREQ.)
Ar / SF6 (1:1)
p = 5 mTorr
Prf = 500 W
f1 = 1.0 kHz
f2 = 8.5 kHz
In Ar/SF6 discharges the frequency depends on the settings of the matching network
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6. Determination of time varying densities from
planar and cylindrical probes currents
time (ms)
Ar / SF6 (1:1)
p = 5 mTorr
Prf = 550 W
f = 0.8 kHz
The negative ion fraction a can be deduced
from the saturation current ratio:
, where
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7. Results in (1:1) Ar/SF6 discharge
p = 5 mTorr
Prf = 500 W
f = 0.8 kHz
The electron density changes by a factor of 20 with fast rise and decay times
Positive and negative ion densities decay at the same rate
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8. Results in pure SF6 discharge
  5
SF6
p = 5 mTorr
Prf = 500 W
f = 12.9 kHz
  400
The electron density exhibit sharp peaks; the ion density is slightly modulated
The discharge spends a long time in low-density regime with   400
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9. 2002 and 2003 Goals
Characterize plasma instability using V-I-phase probe. Develop model for reduced electron temperature and density, by 9/30/2002.
Develop and test instability control. Reduce electron temperature and density in discharges, by 9/30/2003.
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