High-speed plasma diagnostics based on the floating harmonic method in inductively coupled plasma and pulsed plasma

Abstract

The floating harmonic method is a diagnostic technique for obtaining plasma parameters, such as ion density and electron temperature, by applying a sinusoidal voltage to a floating probe. The typically applied frequency is in the kilohertz range. This method has been widely used in plasma diagnostics of semiconductor processes due to its robustness to RF fluctuations and fast measurement speed. However, recently, pulsed plasma has become common in semiconductor processes. As the plasma sheath is analyzed with a high-time-resolution diagnostic method such as phase-resolved optical emission spectroscopy, the development of high-speed plasma diagnostic techniques has become increasingly important. In this study, we investigated high-speed plasma diagnostic measurements based on the floating harmonic method. When the frequency of the voltage applied to the floating probe increases up to 1 MHz, the electron temperature can be underestimated due to the currents flowing through the capacitive sheath and the ceramic sleeve of the probe. We found that the displacement current of the probe sheath increases rapidly compared to the conduction current as the plasma density and electron temperature decrease. We also removed the additional harmonic currents flowing through the ceramic sleeve via two approaches. The plasma parameters obtained using the proposed method are in good agreement with the measurements performed using the floating harmonic method in the kilohertz range. Moreover, the electron temperature of the pulsed plasma was measured.