A method for measuring plasma parameters and dielectric film thickness by analyzing transient voltages for deposition plasma processing monitoring

Abstract

An electrical method is proposed to measure the dielectric film thickness, electron temperature, and plasma density for deposition plasmas. In this method, a square voltage is applied to a flat probe coated with a dielectric film, and the transient voltage of a series capacitor connected to the probe is measured. The thickness of the dielectric film is obtained from the transient voltage because the applied voltage is divided across the dielectric film and the series capacitor. The deposited dielectric film causes a change in transient voltage of the series capacitor. A circuit model with a nonlinear sheath, a series capacitor, and the dielectric films is suggested to obtain plasma density and electron temperature. The time response of transient voltage is related to plasma density, electron temperature and total capacitance of the series capacitor and the dielectric film. Two square voltages with different amplitudes were applied to measure plasma density and electron temperature. Experiments were conducted in inductively coupled plasma. Various capacitors were used to replace the dielectric films, and a flat probe coated with Al2O3 was used to verify the measurement of dielectric film thickness, showing the high accuracy of our method. In addition, the electron temperature from our method is in good agreement with that from electron energy distribution functions, and the plasma density is in good agreement with that from orbital motion limited theory. Therefore, this method would be useful for monitoring plasma parameters and deposited film thickness in industrial plasma processing.