Ik-Jin Choi

Measurement of electron temperature and ion density using the self-bias effect in plasmas

For novel plasma diagnostics, the rf floating probe was revisited. For inducing the self-bias effect, ac bias voltage (∼kilohertz) was applied through a dc blocking capacitor between a probe and a signal generator. The dc self-bias potential was changed not only with ac bias voltages but also with electron temperatures, and therefore, the electron temperature was derived from the variations in the self-bias potential with and without ac bias voltage. The harmonic component of the probe contains information about the ion flux, and using a fast Fourier transform analysis of the probe current, the ion density was derived from the first harmonic current of the probe. The experimental results were compared with a single Langmuir probe. The electron temperature and the ion density were in good agreement with those from the Langmuir probe. Because the amplitude of the ac bias voltage is very low (<3 V), local ionizations affected by a high bias-voltage can be neglected.

Double probe diagnostics based on harmonic current detection for electron temperature and electropositive ion flux measurement in RF plasmas

A double probe diagnostic using an ac bias signal between both probe tips was developed. The electron temperature and electropositive ion flux were derived by analyzing the first and third harmonic currents of the probe. The double probe was compared with the floating-type single probe at various RF powers and pressures in an inductively coupled plasma. The electron temperature and electropositive ion flux measured from the double probe agreed with the measurements from the floating-type single probe. This methodology can be applied to an electrically isolated diagnostic system for processing plasmas.

Effect of DC Bias on the Plasma Properties in Remote Plasma Atomic Layer Deposition and Its Application to HfO2 Thin Films

This work was supported by the National Program for Tera-Level Nanodevices of the Ministry of Science and Technology of Korea as one of the 21st Century Frontier Programs.

Wireless wafer-type probe system for measurement of two-dimensional plasma parameters and spatial uniformity

A wireless wafer-type probe system was developed to measure two-dimensional plasma parameters and uniformity. The apparatus uses double probe theory with a harmonic detection method. The plasma parameters, such as the electron temperature, ion density and ion flux, are derived by using the amplitudes of the first and third harmonic currents. The experiment was conducted in an inductively coupled plasma. The measurements of the wireless wafer-type probe were compared with a floating-type Langmuir probe and a similar trend was observed. As the inner and outer antenna current ratio changes, the wireless wafer-type probe was able to measure the evolution of the two-dimensional ion density profiles. Since the wireless wafer-type probe system was electrically isolated and designed to operate stand-alone in the chamber, it can be installed in plasma chambers without any external controllers. This plasma diagnostic system shows promise for processing plasmas.

Electron density and electron temperature measurement in a bi-Maxwellian electron distribution using a derivative method of Langmuir probes

In plasma diagnostics with a single Langmuir probe, the electron temperature Te is usually obtained from the slope of the logarithm of the electron current or from the electron energy probability functions of current (I)-voltage (V) curve. Recently, Chen [F. F. Chen, Phys. Plasmas 8, 3029 (2001)] suggested a derivative analysis method to obtain Te by the ratio between the probe current and the derivative of the probe current at a plasma potential where the ion current becomes zero. Based on this method, electron temperatures and electron densities were measured and compared with those from the electron energy distribution function (EEDF) measurement in Maxwellian and bi-Maxwellian electron distribution conditions. In a bi-Maxwellian electron distribution, we found the electron temperature Te obtained from the method is always lower than the effective temperatures Teff derived from EEDFs. The theoretical analysis for this is presented.

Pulsed floating-type Langmuir probe for measurements of electron energy distribution function in plasmas

A floating type Langmuir probe was studied to measure the electron energy distribution function (EEDF) in plasmas. This method measures the current (I)-voltage (V) curve with rising and falling variations based on a floating potential by using charge-discharge characteristics of the series capacitor when a square-pulse voltage is applied. In addition, this method measures the EEDF by using the alternating current (ac) superposition method. The measured EEDFs were in good agreement with results from a conventional single Langmuir probe. This technique could be applied as a plasma diagnostic method in the capacitively coupled plasma where the plasma potential is extremely high or the processing plasma where the deposition gas is used.