Influence of inhomogeneous magnetic field on the characteristics of very high frequency capacitively coupled plasmas

Abstract

The effect of inhomogeneous magnetic field on the spatial structure of very high frequency (VHF) plasmas is investigated for different coil configurations, gas pressures, high frequency bias powers, and degrees of electronegativity. The simulation results show that the electron density peaks in the center of the chamber for VHF plasmas due to the standing electromagnetic wave effect. On application of a magnetic field, the density increases near the wafer edge and decreases at the chamber center. The radial magnetic field component is found to limit electron loss to the electrodes and locally enhance the electron density. The axial magnetic field component limits plasma diffusion in the radial direction helping preserve the effect of improved electron confinement by the radial magnetic field. The peak electron density decreases with increasing magnetic field as the plasma moves toward the electrode edge occupying a larger volume. The effect of magnetic field becomes weaker at higher pressure due to the increased electron-neutral collisions which reduce the effectiveness of electron confinement around the magnetic field lines. The impact of magnetic field on plasma profile is somewhat weaker in an electronegative Ar/CF4 plasma because of the presence of less mobile and unmagnetized negative ions.