Effects of substrate bias on electron energy distribution in magnetron sputtering system

Abstract

In the downstream region of an unbalanced magnetron argon discharge, the influences of substrate bias (i.e., the condition of plasma boundary) on electron energy distribution function and plasma characteristics were investigated through the experiments using a single Langmuir probe. In a steady state with the grounded substrate, it could be found that the electron current flowing to the substrate compensates for the ion current flowing to the cathode due to the axial magnetic field such that the substrate plays the role of the actual anode. The potential of the anode sheath could be controlled by applying a dc voltage to the substrate, and the nonlinear behavior of the plasma potential with respect to the dc substrate voltage caused the distinctive evolution of the potential of the anode sheath. It was found that a transition of the electron energy distribution function from a bi-Maxwellian distribution at small dc voltages to a Maxwellian distribution at highly negative dc voltages occurs with decreasing the substrate bias voltage. This phenomenon was discussed in view of the role of the substrate as an electron loss boundary and the cooling mechanism of electrons in bulk plasmas. (C) 2004 American Institute of Physics.