Measurements of Time Varying Plasma Potential, and Electron Temperature and Density in a 13.6 MHz RF Discharge

J. Vac. Sci. Technol., A, 7, 972-976 (1989).

Wilson, J. L., Caughman, J. B. O., Nguyen, P. L., Ruzic, D. N.

Argon plasma measurements were conducted in a commercial capacitively coupled etcher operating at 400 mTorr with 60-W coupled power at 13.56 MHz. Time varying floating potential was measured using a capacitively coupled probe which uses a capacitive voltage divider and a field effect transistor buffer amplifier. Average floating potential was obtained from a high-input-impedance Langmuir probe. The floating potential was found to be sinusoidal, [21 sin(wt)–4]V±1.5 V, with a maximum of 17±1.5 V and a minimum of –25±1.5 V. From these data and the use of a low-input-impedance Langmuir probe, a calibrated instantaneous I–Vcharacteristic is used to obtain plasma potential andelectron temperature. Plasma potential was found to be sinusoidal, [21 sin(wt)+30]V±1.6 V, with a maximum of 51±1.6 V and a minimum of 9±1.6 V. Electron temperatures were 6.58±0.19 eV at maximum plasma potential and 6.49±0.19 eV at minimum plasma potential. The electron density for this experiment was determined to be 1.48±0.83×10¹⁰ electrons/cm³ .