Kh Bai

Pressure and helium mixing effects on plasma parameters in temperature control using a grid system

Pressure and He mixing effects on plasma parameters in electron temperature control using a grid system are investigated. Electron temperature is higher in lower pressure, when the electron temperature is high and not controlled. Electron density can be increased by about three times by decreasing the source gas pressure from 20 to 1 mTorr, and by about two times by He mixing in the temperature controlled region (diffusion region), while the electron density is decreased in the source region. This electron density increase is mainly due to the increase of the high energy electron population, and the measured electron energy distribution functions clearly show this.

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.

Electron temperature analysis of two-gas-species inductively coupled plasma

The electron energy distribution functions and electron temperatures are measured in Ar/He and Ar/Xe inductively coupled plasma with various mixing ratios. The electron temperature does not change linearly with the mixing ratios; instead it increases abruptly near PHe/PAr+He=1 and decreases rapidly near PXe/PAr+Xe=0. A simple model using a two-ion-species fluid model is suggested to explain the electron temperature variations, and it agrees well with the experimental results.

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.

Control and analysis of ion species in N2 inductively coupled plasma with inert gas mixing

We control the ion density ratio of [N+]/[N2+] and investigate the relation between the ion ratio and the plasma parameters in inductively coupled plasma. We measure the electron energy distribution functions and the ion ratio in a N2/He,Ar,Xe mixture system as a function of mixing ratio. We can control the ion ratio from 0.002 to 1.4, and the ion ratio is a strong function of electron temperature. We can calculate the ion ratio using a simple model, and the obtained results agree well with the measured values in N2/He,Ar, but there is a large discrepancy in the N2/Xe discharge. The non-Maxwellian structure of the electron energy distribution functions may be the reason for the discrepancy.

Electron temperature control with a small mesh number grid in inductively coupled plasmas

The electron temperature is controlled to 0.6 eV with a small mesh number (the number of the grid wire per 2.54 cm) grid in Ar 1.3 Pa inductively coupled plasma. The key factor in determining the electron temperature is different for different mesh numbers: when the mesh number is large, the key factor is the potential difference between the plasma potential in region II and the grid bias voltage, but when the mesh number is small the plasma potential difference between regions I and II is the key factor. Furthermore, in such cases, the electron density in region II increases with discharge pressure, which is the opposite of what occurs when the mesh number is large. The measured electron energy probability functions show a bump structure for some conditions. This could be explained by the low electron–electron or electron–neutral collision frequencies due to the low electron density and operating pressure.

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.

Paradoxical sheath width variation in transversely magnetized capacitive coupled plasma

We investigated r.f. sheath width variation in transversely magnetized capacitive coupled plasma. While increasing the magnetic field, a paradoxical sheath width variation was observed. Although the electron density decreases with increasing magnetic field, the r.f. sheath width (S0∝1/√ne) decreases with increasing magnetic field. This paradoxical result originates from the overlooking of the axial electron density profile variation by the magnetic field.

On inductively coupled plasmas for next-generation processing

Abstract The electron heating mechanism in ICP is briefly reviewed in the collisionless regime. We suggest a parallel resonance antenna (PRA) that by varying capacitance in a capacitor ( C v ) as an external parameter can control not only the antenna current distribution, but also plasma uniformity. Radial plasma uniformity can be controlled and optimized by controlling coil currents between the coil segments, operating pressure, and chamber geometry in a recently developed antenna system. These results are consistent with the previous modeling paper [Appl. Phys. Lett. 77 (2000) 492].