The charged species profiles have been studied in oxygen plasma of asymmetrically driven capacitively coupled rf discharge. The electron (ne),
and positive (p)
ion densities have been measured by Langmuir probe in a wide range of pressures (3–30 Pa) and interelectrode distances (2–10 cm). At small powers (ne<1015 m−3)
it was obtained that the electronegativity is high (n/ne ∼ 10)
and the electron density profile is flat in plasma bulk. The negative ion density profile is nearly flat in the ion–ion core, where n≫ne,
and falls off towards the plasma-sheath boundary with n ≈ 0
with the spatial scale π,
determined by the negative ion diffusion coefficient Dn
and detachment frequency γd.
As the pressure decreases, this spatial scale exceeds half of the interelectrode distance and the negative ion density profile tends to a parabolic one. The obtained spatial distributions of charged particles are compared with the results of self-consistent modeling by use of a fluid approach for ions, and kinetic equation for electrons. Numerical simulation results agree well with both theory predictions and measurement data. © 2000 American Institute of Physics.