Characteristics of a Large-Diameter Surface-Wave Mode Microwave-Induced Plasma

A large-diameter unmagnetized argon plasma is generated by an Okamoto cavity operated in a surface-wave mode. A quartz discharge tube (16 cm inner diameter, 12 cm long) is placed inside the cavity. An argon plasma is produced in the discharge tube and effuses in a process chamber. The electron density, electron temperature, ion current density and floating potential in the chamber are measured as a function of spatial position using a Langmuir probe. An electron density over 1011 cm-3, with an electron temperature in the range of 2–3 eV and a floating potential with respect to the chamber wall of less than 5 V is obtained at pressure in the mTorr range with 2.45 GHz, 700 W input microwave power. A high ion current density (over 10 mA/cm2) of uniformity (standard deviation/average) within 4.4% over 16 cm is achieved.