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

The dependence of ion flux, ion energy distribution and neutral density of a planar radiofrequency (RF) driven inductively coupled plasma source on pr essure and power is analysed using a plasma monitor and a Faraday cup. The ion Aux is about 7 mA cm(-2) at 5 Pa and 300 W and increases as RF power an d argon pressure increase. The ion energy distribution consists of a single peak with a full width at half maximum of 3 eV for a discharge power in th e range from 50 to 300 W and for a pressure in the range from 0.5 to 5 Pa. This indicates that inductive coupling mainly drives the discharge while ca pacitive coupling between coil and plasma is weak. A significant decrease i n Ar neutral density is observed when the plasma is ignited. The Ar depleti on increases with increasing RF power and increasing Ar base pressure and r eaches 30% at 5 Pa and 300 W. The contributions of the different mechanisms resulting in an Ar depletion are estimated and compared. The decrease in n eutral density cannot be explained by the ionization of Ar atoms only but i s significantly attributed to the heating of Ar atoms by collisions with en ergetic particles. The increase in neutral gas temperature is estimated and found to be in reasonable agreement with measurements of the gas temperatu re reported previously by other groups.