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

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

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

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

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

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

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

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

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