HIGH ETCH RATE MODES IN MICROWAVE PLASMA-ETCHING OF SILICON IN HIGH MAGNETIC-FIELDS

High etch rate modes in microwave plasma etching were studied in a high magnetic field regime. The Si etch rate clearly showed two modes in which the local maxima appeared in the magnetic fields around B(c) = 875 G and 2B(c), and the second maximum at 2B(c) attained as high as 1500 A/min at 5 x 10(-5) Torr of NF3 with 600 W input power. The first mode was ascribed to the ECR, but exactly to the upper hybrid resonance because the magnetic field at which the ion current showed the maximum decreased at higher electron density. A measurement of the microwave field inside the plasma demonstrated that the phase velocity of the microwave changed continuously with the magnetic field centered on 2B(c). Since this was consistent with the dispersion of the whistler wave, the second mode was ascribed to the whistler mode resonance.