The particle contamination and the plasma perturbation by the probe invasion in the plasma, as the electrical Langmuir probes, should be minimized in the plasma processing. Since the floating probe method can be minimized to the probe contact to the plasma, it becomes attractive to monitor the plasma properties. For the floating probe method, the plasma properties are analyzed from the AC coupled current signals flown in the system of probe circuit. The main current is consisted of a displacement current through the stray capacitance of probe system and a conduction current through the probe sheath. Thus the current signal is sensitive to the capacitance of probe system and the driving frequency, so the accuracy of measurement can be improved with the minimization of the displacement component in the current signal. Here it is introduced that the accuracy of measurement can be achieved from the conduction sheath current obtained from the extrapolation of the harmonics of current signals which are taken at the several different bias frequencies. In addition, the driving frequency of probe can be optimized with the consideration of the sensing resistance, the sheath resistance, and the stray capacitance. The improvement of accuracy in the plasma density and temperature measurements was demonstrated for the various operating pressures and powers.

10.3938/jkps.55.1841