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. 11/8/00

Experimental TCP Setup Planar Probe Monochromator Plasma 30 cm Inductive Coil 19 cm OES (PMT) Langmuir Probe Mass Spectrometer 11/8/00

Instability windows Inductive Capacitive Capacitive Unstable in most of discharge conditions used in etching Instability linked to average attachment rate 11/8/00

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 11/8/00

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 11/8/00

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 11/8/00

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 11/8/00

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 11/8/00

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. 11/8/00