Photoemission optogalvanic spectroscopy: An i n s i t u method for plasma electrode surface characterization

Abstract

Photoemission optogalvanic spectroscopy (POGS) is shown to be useful for plasma electrode surface characterization. A pulsed ultraviolet laser is used to induce photoemission from the electrode surface in a radio frequency plasma reactor and the increase in plasma current is detected. The photoemission process is first characterized in vacuum and then compared to that in several plasma gases using Al and Si electrodes. In vacuum, the laser-induced photoemission signal is generally consistent with space-charge-limited current. When below the space-charge limit, the magnitude of the photoemission signal depends upon laser wavelength and power, surface composition, and film thickness. The removal of SiO2 from Si and the contamination of Al in fluorine-containing plasmas is monitored using this technique. A large increase in the POGS signal is observed as the oxide is removed from Si or when a fluorinated Al surface is exposed to an O2 plasma. The POGS signal decreases with fluorine exposure with both Al and Si. We are continuing to explore the utility of this technique as an endpoint detector and in situ contamination monitor.