Spatially resolved electron density distribution in an RF excited parallelplate plasma reactor by 1 mm microwave interferometry

The electron distribution in the argon plasma of a capacitively coupled par allel plate reactor (13.56 MHz) is measured with spatial resolution. The li ne-of-sight integrated electron density is obtained with a quasi-optical he terodyne interferometer operating at the wavelength lambda = 1 mm. The elec tron density distribution is measured in a sequence of planes between the e lectrodes whereby the radial distribution is determined in each plane by Ab el inversion. This allows us to generate an (r, z) mapping of the electron density. The lateral resolution is 6.5 mm in the focal region; the phase re solution amounts to 7 x 10(-5) of a period so that a line density of 2 x 10 (14) m(-2) represents the lower limit of applicability. The spatial distributions are compared with electron density measurements a t similar discharges by other groups and with probe measurements in the mid plane of our discharge.