1. Instabilities in Electronegative Inductive Discharges
SFR Workshop
May 24, 2001
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.
5/24/2001

2. Experimental TCP Setup
Planar Probe
Monochromator
Plasma
Inductive Coil
30 cm
19 cm
OES (PMT)
Langmuir Probe
Mass Spectrometer
5/24/2001

3. Upgraded TCP Coil and Matching Network
Rogowski coil
(RF current measurement,
fast time response)
3-turn water cooled
coil (high power)
Z-scan sensor
(V-I measurements)
5/24/2001

4. Instability Windows Instability linked to average attachment rate
Ar/SF6 (1:1)
Old TCP system
Inductive
SF6
Capacitive
Capacitive
SF6
Ar/SF6 (1:1)
Upgraded
TCP system
Inductive
Inductive
Capacitive
Capacitive
Instability linked to average attachment rate
5/24/2001

5. 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
5/24/2001

6. Global Model Equations
Negative ion balance
(slow time variation)
Electron balance
(medium)
Electron energy balance
(fast)
Charge neutrality at the walls
(n- not lost to walls)
Quasineutrality
(highly electronegative)
5/24/2001

7. Instability Condition
From negative ion balance, the logarithmic slope is
Therefore, a sufficient condition for instability is
a single equilibrium point at which
5/24/2001

8. Example of Phase Plane Motion
Integrate DE’s for n- , ne , and Te for a given initial condition
in the unstable regime
Theory
Experiment
Ar/SF6 , 5 mTorr
5/24/2001

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.
Publications
1. M.A. Lieberman, A.J. Lichtenberg, and M.A. Marakhtanov, Instabilities in Low-pressure Inductive
Discharges with Attaching Gases, Appl. Phys. Lett. 75, 3617 (1999)
2. P. Chabert, A.J. Lichtenberg, M.A. Lieberman, and A.M. Marakhtanov, Instabilities in Low-pressure
Electronegative Inductive Discharges (to appear in Plasma Sources Sci. Technol.)
5/24/2001