A wafer-type monitoring apparatus that can simultaneously measure the two-dimensional (2D) distributions of substrate temperature and plasma parameters is developed. To measure the temperature of the substrate, a platinum resistance temperature detector is used. The plasma density and electron temperature are obtained using the floating harmonics method, and incoming heat fluxes from the plasma to the substrate are obtained from the plasma density and electron temperature. In this paper, 2D distributions of the substrate temperature, plasma density, and electron temperature are obtained simultaneously for the first time in inductively coupled plasma. The shapes of the 2D distributions of the substrate temperature and incoming heat flux are similar to each other, but some differences are found. To understand that, an energy balance equation for the substrate is established, which shows good agreement with the experimental results. This apparatus will promote the understanding of surface reactions, which are very sensitive to the temperatures and plasma densities in plasma processing.

The floating probe method (FPM) applicable for processing plasma diagnostics was developed for the measurement of ion density and electron temperature (J. Appl. Phys. 101 033305). When an AC voltage is applied to a floating probe, harmonic currents are generated due to the nonlinearity of the sheath. The electron temperature and ion density are obtained using the harmonic currents and the voltage across the sheath. However, in the FPM, when the sensing resistance becomes similar to the sheath resistance, iterative calculations must be performed to compensate for the voltage reduction across the sheath due to the sensing resistor. In this paper, the voltage across a DC blocking capacitor is measured to directly obtain the voltage across the sheath. Therefore, it is not necessary to compensate for the voltage reduction across the sheath through iterative calculations. The electron temperature was increasingly overestimated as the capacity of the DC blocking capacitor became smaller. This overestimation was caused by the capacitive load effect and was compensated for using a correction for the second harmonic current. The measured electron temperature and ion density were compared with those from electron energy distribution functions (EEDFs) in an inductively coupled plasma, and they were in good agreement.

A measurement method immune to radio frequency (RF) fluctuations is proposed for obtaining electron temperature and plasma density in RF discharges. The self-bias voltage formed by applying a square voltage to a floating planar probe and its fundamental frequency current are measured to obtain electron temperature and plasma density. To investigate the change in electron temperature due to RF distortion, the case with and without RF filters is compared, and our method is least affected by RF fluctuations compared to the conventional methods: electron energy probability function (EEPF) and floating harmonic method (FHM). When the RF powers and the gas pressures change, the electron temperature and the ion density measured from our method agree well with those measured from the FHM. Although our method and the EEPF are slightly different due to the depletion of the EEPF at high energy (near the floating potential), the trends of the three methods (our method, FHM, and EEPF) agree well under all conditions. In our method, the electron temperature was investigated with and without correction for the increase in the ion current at probe tip radii of 5 and 1 mm. When correcting the increase in ion current due to the sheath expansion, the electron temperature is not overestimated and does not change in the planar probe with a small radius. This can be useful in plasma monitoring system where an RF filter cannot be installed, or the probe tip must be made small.

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.

No abstract