Improved Double-Probe Technique for Spatially Resolved Diagnosis of Dual-Frequency Capacitive Plasmas ⁄

The conventional double-probe technique was improved with a combination of self-powering and radio-frequency (RF) choking. RF perturbations in dual-frequency capacitively coupled discharge were effectively eliminated, as judged by the disappearance of self-bias on the probes. The improved technique was tested by spatially resolved measurements of the electron temperature and ion density in both the axial and radial directions of a dual-frequency capacitive plasma. The measured data in the axial direction were compared with simulation results, and they were excellently consistent with each other. The measured radial distributions of the ion density and electron temperature were influenced significantly by the lower frequency (LF) power. It was shown that superposition of the lower frequency to the higher frequency (HF) power shifted the maximum ion density from the radial center to the edge region, while the trend for the electron temperature profile was the opposite. The changing feature of the ion density distribution is qualitatively consistent with that of the optical emission intensity reported.