Electron energization via ExB drift generation in rf magnetrons operated at a low pressure

Sputtering via rf magnetrons is an important film deposition technology used

primarily when the target is nonconductive. To reduce interaction of the sputtered

particle fluxes with the working gas, such a technology is commonly applied at a low pressure.

It appears that it is still not completely clear how a population of highly energetic electrons

above the ionization threshold is produced under such circumstances. For instance, in contrast to

dc magnetrons, where secondary electrons accelerated in the cathode fall can significantly

contribute to the group of energetic electrons, this mechanism is of minor importance for

rf magnetrons. This work discusses a possible mechanism dominating the electron energization in

rf magnetrons based on results of simulations conducted with an implicit electrostatic energy-conserving PIC/MCC code.

It is argued that such a mechanism is caused by an essentially collisionless generation of a strong

ExB drift (aka "Hall heating"). This happens due to the fact that electrons are sufficiently

magnetized and their motion across magnetic field lines is impeded, so that they can interact

with very strong electric fields in the sheath or pre-sheath areas during time evolution of the latter.

Such a mechanism is essentially different from both the Ohmic and the sheath heating in unmagnetized CCP

discharges, therefore we propose to name the new heating mode "mu-mode" to stress its electron

magnetization origin.