Ion flux, ion energy distribution and neutral density in an inductivelycoupled argon discharge

Abstract

The dependence of ion flux, ion energy distribution and neutral density of aplanar radiofrequency (RF) driven inductively coupled plasma source onpressure and power is analysed using a plasma monitor and a Faraday cup. Theion flux is about 7 mA cm-2 at 5 Pa and 300 W and increases as RF power andargon pressure increase. The ion energy distribution consists of a single peakwith a full width at half maximum of 3 eV for a discharge power in the rangefrom 50 to 300 W and for a pressure in the range from 0.5 to 5 Pa. Thisindicates that inductive coupling mainly drives the discharge while capacitivecoupling between coil and plasma is weak. A significant decrease in Ar neutraldensity is observed when the plasma is ignited. The Ar depletion increaseswith increasing RF power and increasing Ar base pressure and reaches 30% at5 Pa and 300 W. The contributions of the different mechanisms resulting in an Ardepletion are estimated and compared. The decrease in neutral density cannotbe explained by the ionization of Ar atoms only but is significantlyattributed to the heating of Ar atoms by collisions with energetic particles. Theincrease in neutral gas temperature is estimated and found to be in reasonableagreement with measurements of the gas temperature reported previously byother groups.