  The effect of a uniform magnetic field on particle transport in low-pressure
radio frequency (RF) capacitively coupled plasma (CCP) has been studied using a
particle-in-cell (PIC) model. Three distinct regimes of plasma behavior can be
identified as a function of the magnetic field. In the first regime at low
magnetic fields, asymmetric plasma profiles are observed within the CCP chamber
due to the effect of E x B drift. As the magnetic field increases,
instabilities develop and form self-organized spoke-shaped structures that are
distinctly seen within the bulk plasma closer to the sheath. In this second
regime, the spoke-shaped coherent structures rotate inside the plasma chamber
in the - E x B direction, where E and B are the DC electric and magnetic field
vectors, respectively, and the DC electric field exists in the sheath and
pre-sheath regions. The spoke rotation frequency is in the MHz range. As the
magnetic field strength increases further, the rotating coherent spokes
continue to exist near the sheath. The coherent structures are, however,
accompanied by new small-scale incoherent structures originating and moving
within the bulk plasma region away from the sheath. This is the third regime of
plasma behavior. The threshold values of the magnetic field between these
regimes were found not to vary with changing plasma reactor geometry (e.g.,
area ratio between ground and powered electrodes) or the use of an external
capacitor between the RF-powered electrode and the RF source. The threshold
values of the magnetic field between these regimes shift toward higher values
with increasing gas pressure. This paper provides guidance on the upper limit
of the magnetic field for instability-free operation in low-pressure CCP-based
semiconductor deposition and etch systems that use the external magnetic field
for plasma uniformity control.
