D. G. Voloshin

Experimental and Theoretical Study of Ion Energy Distribution Function in Single and Dual Frequency RF Discharges

Ion energy distribution functions (IEDFs) at the electrodes in single frequency (SF) and dual frequency (DF) radio-frequency discharges in Ar at pressures of 20 and 45 mtorr are measured and calculated. A numerical simulation of the IEDF on the base of a self-consistent particle-in-cell model with Monte Carlo collisions was performed. In addition, a semianalytical model was developed to calculate the IEDF in collisionless and collisional SF and DF plasmas. The IEDF width for the intermediate frequency case was determined from both experimental and theoretical results. The possibility of frequency decoupling is discussed.

Two modes of capacitively coupled rf discharge in CF4

Capacitively coupled rf discharge in pure CF4 was studied using a one-dimensional self-consistent particle-in-cell Monte Carlo model. Two different discharge modes are observed depending on the discharge conditions: the regime of electronegative plasma with high-electron temperatures in the bulk, and the regime of electropositive plasma with abnormally low electron temperatures in the bulk. The characteristic features of the two discharge modes are considered. A sharp transition from the former to the latter mode is observed with an increase in applied voltage. The dependence of the transition voltage on gas pressure is analyzed. In the studied range of gas pressures, the existence of a high-temperature mode in an electronegative gas like CF4 is suggested by the balance between the ionization rate and attachment rate in the bulk region. As a result, the transition voltage increases with gas pressure because of the increased relative role of electron attachment. It is shown that the differences in the used electron cross-section sets may noticeably affect the simulation results and the discharge properties. Three different electron cross-section sets for CF4 are considered. In particular, the transition voltage between the two discharge modes differs essentially for different cross-sections used. In order to analyze the fundamental causes of this difference, a detailed comparison of three cross-section sets was done on the basis of the Monte Carlo calculation of swarm parameters in constant electric fields.

Experimental and theoretical study of dynamic effects in low-frequency capacitively coupled discharges,

A low-frequency capacitively coupled radio-frequency (rf) discharge in Ar excited at 1.76 MHz is studied both experimentally and theoretically. Experimental measurements of electron concentration, discharge voltage and current are presented for a wide range of rf input powers. The rf current shape is nonsinusoidal, close to the triangle one. The evolution of Ar(2p1) emission excitation function in the interelectrode gap during an rf cycle is measured using the phase-resolved optical emission spectroscopy technique. Theoretical study is based on the particle-in-cell Monte Carlo collision numerical simulation. Specific dynamic features of the low-frequency discharge are discussed. The important role of secondary electrons in discharge maintenance and power balance is shown. This study is crucial for understanding dual-frequency discharges with a corresponding value of low frequency.

Experimental and Theoretical Studies of Radical Production in RF CCP Discharge at 81-MHz Frequency in

In this paper, the experimental and theoretical studies of RF capacitive-coupled-plasma (CCP) discharge at frequency of 81 MHz in Ar/CF4 and Ar/CHF3 mixtures were carried out. The density distributions of CF2, F, and H radicals in the interelectrode gap were measured by the spatially resolved emission and absorption spectroscopies. In the CHF3/Ar discharge, the measurements of plasma density and electron temperature were also carried out by using the probe technique. The experimental data were analyzed on the base of the self-consistent simulation of RF CCP discharge. The multipurpose hybrid approach was used in which the self-consistent particle-in-cell MC method is applied to describe the behavior of electrons and ions, whereas the behavior of neutral species is treated by the fluid model, taking into account the complicated plasma chemistry in the Ar/CF4 and Ar/CHF3 mixtures. The comparative analysis of the experimental and simulation results has shown that, in the Ar/CF4 plasma, the main source of CF2 radicals is the electron-impact dissociation of CF4, whereas the chain reactions with H and F atoms play a crucial role in CFx radical production in Ar/CHF3 with the chain branching being caused by electron-impact dissociation of HF. The good agreement between the calculated and experimental densities of CF2, H, and F radicals shows that the present model correctly describes the chain mechanism. The results of probe measurements in the CHF3/Ar discharge also agree well with the calculated plasma density and mean electron energy in the bulk. At the same time, the simulation revealed the rather lower electronegativity as compared with the known literature data. The simulation has shown that the electron attachment to CF2 radicals may strongly increase the negative-ion density. The direct measurements of negative ions together with CFx densities are necessary to make clear the question. The results of this paper directly indicate that the kinetics of electron attachment and detachment to polymeric neutral products and radicals is of great importance for the correct description of fluorocarbon-plasma electronegativity.

\hbox{Ar/CF}_{4}

The effect of low-pressure He plasma on properties of nanoporous organosilicate glasses low-k films with 24% and 33% open porosity is studied. The influence of ions, VUV radiation, and metastable atoms are extracted separately using a special experimental system designed for this purpose. The low-k films treated in He plasma were exposed to O or H atoms in the downstream of high-pressure O2 or H2 rf discharge. The changes in chemical composition and structure occurring in low-k films were measured before and after all treatments. The loss probabilities of oxygen and hydrogen atoms on the low-k film surface were measured for both treated and pristine films. It is shown that the film pretreatment in He plasma leads to the noticeable densification of the top surface layer up to complete sealing all the films studied. The sealing layer prevents O atoms from deep penetration to the film bulk and carbon extraction. The sealing mechanism related to the joint impact of low-energy ions and VUV photons with metasta...

and

A gas-phase reaction model for and mixtures was developed. Self-consistent electron impact cross-section set for was introduced. The original total and partial dissociation cross sections were received. A developed gas-phase kinetic scheme was tested on the experimental data. An important role of the chain reactions in the kinetics of F and H atoms and radicals was revealed.

\hbox{Ar/CHF}_{3}

The yield of ozone in barrier discharges in oxygen–nitrogen mixtures containing 0.001 to 40% of nitrogen is investigated experimentally. Phenomena of the nonstationarity of processes of ozone generation that differ from the known ozone-zero phenomenon (OZP) apparent in the reduced efficiency of ozone generation in very high purity oxygen at long periods (from hours to tens of hours) of ozonator operation are found. It is established that the characteristic times (from minutes to tens of minutes) of ozone attaining stationary values after changes in the discharge parameters indicate slow adjustment of the surface condition of insulators and thus the heterogeneous decay of ozone to more rapidly changing flows of neutral and charged particles from gas discharge plasma on the surfaces of dielectrics. The possibility of such a scenario is confirmed using a new analytical approach and numerical calculations of the plasma–chemical kinetics of N2/O2 mixtures presented in the accompanying theoretical study.

Mixtures

The 2D numerical model of the ion current collection by a planar probe has been developed on the basis of a particle in cell with the Monte Carlo collision method for ion motion. This model is used to reveal the effects of ion collisions on the probe sheath area and spatial distribution of plasma density and to warn against current–voltage probe characteristic misinterpretation at plasma density measurements by commonly used Langmuir probe methods.

The effect of He plasma treatment on properties of organosilicate glass low-k films

Trifluoromethane (CHF3) is widely used in semiconductor processing. However, electron collision cross section set in CHF3 is not finally completed and verified yet. Cross section sets developed before were tested only in pure CHF3 and calculations with these sets do not describe swarm parameters in CHF3 diluted by Ar. In this work a numerical code based on the Monte Carlo method has been developed and used to calculate swarm parameters in pure CHF3 and Ar/CHF3 mixtures. Calculations in CHF3 diluted in Ar allowed us to validate the absolute value of vibration cross sections. The values and the shapes of momentum transfer, attachment and dissociation cross sections in CHF3 were renormalized on the base of the thorough analysis of all available experimental data and quantum-mechanical calculations. As a result physically well-grounded cross section set for CHF3 was developed and verified on various swarm experiments in CHF3 and CHF3/Ar mixtures.

Simulation of Gas-Phase Kinetics in

Two-dimensional numerical simulations of a dc discharge in a CH4/H2/N2 mixture in the regime of deposition of nanostructured carbon films are carried out with account of the cathode electron beam effects. The distributions of the gas temperature and species number densities are calculated, and the main plasmachemical kinetic processes governing the distribution of methyl radicals above the substrate are analyzed. It is shown that the number density of methyl radicals above the substrate is several orders of magnitude higher than the number densities of other hydrocarbon radicals, which indicates that the former play a dominant role in the growth of nanostructured carbon films. The model is verified by comparing the measured optical emission profiles of the H(n ≡ 3), C2*, CH*, and CN* species and the calculated number densities of excited species, as well as the measured and calculated values of the discharge voltage and heat fluxes onto the electrodes and reactor walls. The key role of ion–electron recombination and dissociative excitation of H2, C2H2, CH4, and HCN molecules in the generation of emitting species (first of all, in the cold regions adjacent to the electrodes) is revealed.