S. J. You

Mode transition for power dissipation induced by driving frequency in capacitively coupled plasma

We measured electrical characteristics of capacitively coupled plasma at low pressure (2.67 Pa) with different driving frequencies. From these measurements, we observed a significant change in discharge power characteristics during the frequency increase. While increasing the frequency, a square dependence of power characteristics (P∼I2) changes to a linear dependence (P∼I). This observed result reflects that a power dissipation mode transition from an ion-dominated dissipation mode to an electron-dominated dissipation mode takes place during the driving frequency increase. Both the results calculated from a simple sheath model and a particle-in-cell simulation are in a good agreement with the experimental data.

Nonlocal to local transition of electron kinetic property in magnetized plasma

The spatially resolved measurements of electron energy distribution functions (EEDFs) in a magnetized capacitive discharge reveal that the nonlocal electron kinetic property, the coincident property of the EEDFs of the total energy [kinetic energy (u) + potential energy(ϕ)] in different spatial positions, disappears as the magnetic field increases. This result can be understood as a transition of electron kinetic property from a nonlocal to a local regime induced by the magnetic field. This transition results from the fact that the magnetic field decreases the electron diffusion in the coordinates space but increases the electron diffusion in the energy space.

Effects of substrate bias voltage on plasma parameters in temperature control using a grid system

In this paper we investigate the effects of substrate bias voltage on plasma parameters in temperature control using a grid system in inductively coupled plasma. Electron temperature can be controlled from 2.5 eV to 0.5 eV at 1 mTorr Ar plasma using grid bias voltage, and the electron temperature is a strong function of substrate bias voltage. The main control parameter determining the electron temperature is the potential difference between grid-biased voltage and the plasma potential in the temperature controlled region (ΔφII,g). When substrate bias voltage is negative, plasma parameters do not vary with substrate bias voltage due to constant ΔφII,g

Power dissipation mode transition by a magnetic field

We measured electrical characteristics of transversely magnetized capacitively coupled plasma at low pressure (10 mTorr). From these measurements, we found that the power characteristics of the magnetized discharge were different from those of the unmagnetized discharge. As the magnetic field increases, a square dependence of power characteristic at high current changes to a linear dependence. This can be understood as a power dissipation mode transition by a magnetic field. A calculation from a simple sheath model agrees well with the experimental data.

Plasma parameters analysis of various mixed gas inductively coupled plasmas

The electron energy distribution functions and plasma parameters in various gas mixture discharges (N2,O2,CF4/He,Ar,Xe) are measured. When He is mixed, the electron temperature increases but the electron density is almost constant. The electron temperature increases rapidly near a He mixing ratio of 1, but it is almost constant when the mixing ratio is small. In Ar mixture discharge, the electron temperature is almost constant; the electron density increases rapidly near a mixing ratio of 1, but increases slightly when the mixing ratio is small. Mixing Xe increases the electron density and decreases the electron temperature. The electron density varies in a similar way with that of the Ar mixing case. A simple two-ion-species global model is used to analyze the plasma parameter variations as a function of mixing ratio, and it agrees well with the experimental results.

Correlation between excitation temperature and electron temperature with two groups of electron energy distributions

The relationship between the electron excitation temperature (Texc) determined by optical emission spectroscopy and the electron temperature (Te) using a rf-compensated Langmuir probe was investigated in argon capacitively coupled plasmas. In the experiment performed at the gas pressure range of 30 mTorr to 1 Torr and the rf power range of 5–37 W, the electron energy probability function (EEPF) obtained from the probe current versus voltage characteristic curve showed two energy groups of electrons. The measured EEPF demonstrated that the electron energy distribution changed from Druyvesteyn to single Maxwellian as the discharge current was increased and from bi-Maxwellian to Druyvesteyn as the pressure was increased. As a result, Texc showed a tendency identical to that of Te of the high energy part of electrons as pressure and rf power were varied. This suggests that electron temperature can be determined from the measured Texc through a calibration experiment by which the ratio between electron and exc...

Driving frequency effect on the electron energy distribution function in capacitive discharge under constant discharge power condition

A modern trend of VHF driven plasma sources in semiconductor processing stimulates a lot of studies concerning the driving frequency effect on plasma parameters in a capacitive discharge. In spite of abundant studies, the validation and application of these results in industrial plasma processing are still questionable because these studies were performed under a fixed rf voltage condition or an assumption of Maxwellian electron energy distribution, while the fixed discharge power condition and non-Maxwellian distribution are typical in industrial plasma processing. To resolve this problem, the authors investigated the driving frequency effect on plasma parameters (electron density and temperature) under the fixed discharge power condition by measuring the electron energy distribution functions, which are the most important factor in chemical reactions during the plasma processing. A remarkable result was observed—as the driving frequency increases, the electron temperature increases and the electron dens...

Low energy electron cooling induced by a magnetic field in high pressure capacitive radio frequency discharges

A study is conducted on a magnetic field effect on electron heating in capacitive rf discharges under a collisional regime, where the electron mean collision frequency is much higher than the rf frequency. The evolution of an electron energy distribution function (EEDF) over a magnetic field range of 0–30G in 300mTorr Ar discharges is measured and calculated for the investigation. A significant change in the low-energy range of the EEDF is found during the evolution. The observed result reveals the application of the magnetic field to the high-pressure capacitive plasma gives rise to a cooling effect on the low-energy electrons. This is in contrast to the low-pressure case where the magnetic field enhances the low-energy electron heating. The calculated result of the EEDF is in good agreement with the experiment.

The effects of mixing molecular gases on plasma parameters in a system with a grid-controlled electron temperature

Plasma parameter variations as a function of a mixing ratio in an electron temperature control system using a grid are investigated. Under the grid, the electron temperature, as well as electron density, is a strong function of a mixing ratio. The electron temperature decreases with a mixing ratio of molecular gases (O2 and CF4), and the large inelastic cross section of molecular gas is the reason for the decrease in the electron temperature. When the length of sheath around the grid wires is comparable to the space between the grid wires, only 10% mixing of CF4 decreases the electron temperature to 0.8 eV in 10 mTorr Ar/CF4 plasma.

Feature of electron energy distribution in a low-pressure capacitive discharge

The evolution of the electron energy distribution function is investigated in the low-pressure capacitive discharge under the collisionless electron heating regime, where the electron mean-free path is comparable to or larger than the system length. As the gas pressure decreases from 50 to 10 mTorr, a different feature of electron energy distribution with a plateau in the low-energy electron range, indicating the strong electron heating in that energy range, is found. This observed result can be explained in terms of collisionless heating from the interaction between the electron bouncing motion and the oscillating sheath [Y. M. Aliev, I. D. Kaganovich, and H. Schuter, Phys. Plasmas 4, 2413 (1997)]. A simple calculation of the electron energy distribution with the energy diffusion coefficient, including the electron bounce effect, is in good agreement with the experiment.