T.H. Chung

Global model and scaling laws for inductively coupled oxygen discharge plasmas

For inductively coupled oxygen rf discharge plasmas, a global model which consists of the energy and particle balance equations is formulated. The energy balance equation includes energy losses for electron-neutral elastic collision, excitation, ionization, dissociation, pair production, and charged particle wall loss. Particle balance equations are written for all species of interest. For a specified discharge length and diameter, absorbed power, pressure, electron temperature-dependent reaction rate coefficients and surface recombination constants, we solve these equations to determine the densities of all species and the electron temperature. We measure these parameters by the Langmuir probe method. According to the prevailing particle loss mechanism, the parameter space can be divided into a volume recombination-loss-dominated region and an ion-flux-loss-dominated region. Based on the global model equations, the scaling laws of plasma variables with the control parameters for the ion-flux-loss-dominat...

E-H mode transition in low-pressure inductively coupled nitrogen-argon and oxygen-argon plasmas

This work investigates the characteristics of the E-H mode transition in low-pressure inductively coupled N2-Ar and O2-Ar discharges using rf-compensated Langmuir probe measurements and optical emission spectroscopy (OES). As the ICP power increases, the emission intensities from plasma species, the electron density, the electron temperature, and the plasma potential exhibit sudden changes. The Ar content in the gas mixture and total gas pressure have been varied in an attempt to fully characterize the plasma parameters. With these control parameters varying, the changes of the transition threshold power and the electron energy distribution function (EEDF) are explored. In N2-Ar and O2-Ar discharges at low-pressures of several millitorr, the transition thresholds are observed to decrease with Ar content and pressure. It is observed that in N2-Ar plasmas during the transition, the shape of the EEDF changes from an unusual distribution with a flat hole near the electron energy of 3 eV in the E mode to a Max...

Velocity distributions in magnetron sputter

Results of the particle simulation of magnetron sputter are presented. Using a kinetic code, we obtain the spatial profiles of plasma density, potential, and velocity distribution function, along with the electron temperature, the ion density, the current density, and the deposition profiles at the anode surface. The result of simulation is compared with the Child-Langmuir law applied to the magnetron discharge and the global model. The velocity distribution function of electrons is Maxwellian, but that of ions is non-Maxwellian near the cathode with the majority in the energy range below 50 eV.

Electrostatic probe diagnostics of a planar-type radio-frequency inductively coupled oxygen plasma

An inductively coupled oxygen radio-frequency (13.56 MHz) discharge is investigated based on modeling and experiment. Experimental measurement is done at a range of gas pressure of 1–30 mTorr, and rf power of 100–1000 W. We measure most of the important plasma parameters such as the densities of charged species, electron temperature, plasma potential, and electron energy distribution function. The measured values are compared with the results of the spatially averaged global model. We observe a generally good agreement between the modeling and the experiment. The scaling features, the transition of the operating region, and the radial distributions of charged species are also discussed.

Two-Dimensional Fluid Simulation and Langmuir Probe Measurement of a Planar Inductively Coupled Oxygen Plasma

A two-dimensional (2D) self-consistent axisymmetric fluid simulation of an inductively coupled discharge of electronegative oxygen plasma with a one-turn antenna placed on the top of the dielectric roof is presented. The model equations include continuity equations, the Poisson equation, and an electron energy balance equation. For a planar inductive discharge, the electric field component Eθ (r, z) is calculated, assuming axisymmetric geometry. Considering a deep penetration of the induced rf field, the power deposition profile is formulated and used as the electron heating term in the electron energy balance equation. The 2D distributions of charged particle densities, electric potential, electron temperature, and ionization rate are calculated and compared with experiments. The effect of neutral gas pressure on plasma characteristics is investigated. As a result, for a relatively low pressure (5 mTorr) case, the ionization rate and charged particle densities are uniform in the radial direction, and for a medium pressure (20 mTorr) case, the ionization rate and the negative ion density are sharply maximized in the axial and radial directions. The results of the simulation agree reasonably well with the results of the spatially averaged global model and experimental results.

Modeling and Simulation of a Large-Area Plasma Source

A variant of transformer-coupled plasma, suitable for processing a large-area flat panel with good uniformity, is examined using various models and simulations. Using two-dimensional and one-dimensional fluid simulations, we present the detailed profiles of the plasma density, potential, electron temperature, electric field structure, and ion current density at the substrate. The average values compare reasonably well with those of a global (volume-averaged) model.

Two-dimensional fluid simulation of capacitively coupled RF electronegative plasmas

A two-dimensional self-consistent fluid simulation of capacitively coupled rf glow discharges of electronegative plasma with a cylindrically symmetric parallel plate electrode is presented. The model equations include continuity equations, a Poisson equation, and an electron energy balance equation. The two-dimensional distributions of charged particle densities, electric potential, electron temperature, and ionization rate are calculated. The effects of the applied rf voltage, the driver frequency, and the gas pressure on the discharge characteristics are investigated in detail.

Scaling characteristics of plasma parameters for low-pressure oxygen RF discharge plasmas

For a low-pressure (1-100 mtorr) oxygen RF discharge plasma, the scaling laws for the densities of charged species such as positive ion, negative ion, and electron are estimated in terms of external and internal plasma parameters for the ion-flux-loss-dominated region based on the global balance equations. The scaling formulas are compared with Langmuir probe measurement results performed on a planar inductively coupled oxygen plasma. The transition point from the ion-flux-loss-dominated region to the recombination-loss-dominated region moves to a lower pressure region as the absorbed power increases.

Effects of collisions and finite ion temperature on the sheath structure of cylindrical probes in low-pressure electronegative discharges

The spatial distributions of electric potential and velocity and density of positive ions are calculated in the surroundings of a negatively biased cylindrical probe immersed in electronegative plasmas. The model equations are solved on the scale of the electron Debye length. The solutions provide the variation of plasma variables along the distance from the plasma bulk region to the probe surface. The control parameters are the ratio of the negative ion density to the electron density, the ratios of the electron temperature to the positive and negative ion temperatures, and the ratio of the rate coefficient for the momentum transfer collision to that for the ionization. Especially, the effects of collision and finite temperature of positive ions are investigated. As the positive ion temperature increases, the sheath width decreases and the positive ion current collected by the probe increases. As the ratio of the rate coefficient for the momentum transfer collision to that for the ionization increases, the sheath edge approaches the plasma region, and the positive ion current to the probe decreases.

A particle-in-cell simulation of the breakdown and period doubling thresholds for a RF discharge Ar plasma

RF glow-discharge plasmas provide mild energetic ion bombardment of exposed surfaces. The characteristics of a 10 MHz RF glow-discharge Ar plasma are studied by particle-in-cell simulation. The model simulates a spherical plasma device using a one-dimensional plasma model. The code is used to determine the breakdown voltage, , for a given pd, where p is the gas pressure and d is the plasma discharge length. These values are then compared with Paschens law for the DC case. Also, the breakdown voltage as a function of driver frequency is investigated. Due to the nonlinear capacitance of the plasma, the current and voltage waveforms are found to contain higher harmonic components and sub-harmonic components. Above a certain power level of the driver, sub-harmonics which are indicative of a period-doubling (PD) bifurcation are found to become dominant. The PD thresholds for varying pd, the magnitude of the current and the voltage of the Fourier-analysed components as a function of applied RF voltages are calculated. The PD threshold is always higher than the breakdown threshold. Finally, the pressure-dependence of the sheath width is discussed.