Comparison of electron density measurements in planar inductively coupled plasmas by microwave interferometer and Langmuir probe

Summary form only given, as follows. A Langmuir probe and a heterodyne microwave interferometer have been used to characterize a planar inductively coupled ion source operated in one of two configurations. In the normal configuration, moly extraction grids are used to form a beam of ions with energy over the range 50-500 eV. Alternately, the source is operated without grids resulting in a diffuse plasma which can be probed just outside the source. We have investigated probe tip orientations parallel and perpendicular to the plasma flow under both configurations. In the experiments, spatially resolved electron densities measured by Langmuir probe are fitted to a polynomial, spatially integrated, and compared with the line-integrated plasma density measured with the microwave interferometer. Results indicate that the two density measurements, extended over a broad range of input RF power, differ in the range of a few percent to approximately 30%. In addition to presenting measured data under various plasma conditions, the effects of probe tip orientation and other factors contributing to the total measurement errors are discussed.