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This work focuses on the comparison between a zero-dimensional (0D) global model (LoKI) and a one-dimensional (1D) radial fluid model for the positive column of oxygen DC glow discharges in a tube of 1 cm inner radius at pressures between 0.5 Torr and 10 Torr. The data used in the two models are the same, so that the difference between the models is reduced to dimensionality. A good agreement is found between the two models on the main discharge parameters (gas temperature, electron density, reduced electric field and dissociation fraction), with relative differences below 5%. The agreement on other species average number densities, charged and neutral, is slightly worse, with relative differences increasing with pressure from 11% at 0.5 Torr to 57% at 10 Torr. The success of the 0D global model in describing these plasmas through volume averaged quantities decreases with pressure, due to pressure-driven narrowing of radial profiles. Hence, in the studied conditions, we recommend the use of volume-averaged models only in the pressure range up to 10 Torr.

The experimental and theoretical study of radiofrequency capacitively coupled plasma discharge afterglow has been carried out. Temporal dynamics of Ar metastable and resonance states densities are measured by the absorption method with separate capacitive discharge as a radiation source. The collision radiative model is applied to calculate the corresponding dynamics of Ar excited states in the afterglow with electron density and temperature obtained from self-consistent particle in cell simulation. Different temporal dynamics for metastable and for resonance states densities are revealed and explained. The numerical results and experimental data on Ar excited state dynamics are in good agreement with each other. The decrease in vacuum ultraviolet photon fluxes from the discharge to the substrate is shown. The possible damage free time for plasma treatment of specific dielectric film in a pulsed discharge regime is estimated.

Oxygen molecules in the lowest metastable state, O2(a 1Δ g ), play an important role in oxygen plasmas due to their high reactivity and significant concentrations. The accumulation of high densities of O2(a 1Δ g ) occurs due to its low quenching rate. This paper demonstrates the existence, at high gas temperatures (700–1700 K), of fast quenching of O2(a 1Δ g ) by O(3P) atoms, a process that has not been considered in previous models. Experiments were carried out at oxygen pressures of 10–100 Torr in an 81 MHz CCP discharge in a quartz tube with external electrodes. This setup provides high absorbed power density, leading to both high gas temperatures and significant O(3P) densities. We observe that the O2(a 1Δ g ) density is significantly limited at high gas temperatures by rapid quenching by atomic oxygen. The results were interpreted using a self-consistent 1D discharge model. The observations can only be explained by the inclusion of a rapid quenching reaction: O2(a 1Δ g ) + O(3P) → O2(X3Σ g −) + O(3P), with an activation energy in the range of 0.54–0.69 eV. The rate constant was determined over a wide range of discharge conditions (P = 20–100 Torr and T g = 800–1700 K), giving values between 3 × 10−11 exp(−8000/T) cm3 s−1 to 1.5 × 10−11 exp(−6300/T) cm3 s−1. A possible mechanism for this process is discussed. Measurements of the density of metastable O2(b 1Σ g +) molecules also indicated the existence of quenching by atomic oxygen, with a somewhat lower activation energy of ∼0.32 eV. The variations of the measured [O2(b 1Σ g +)]/N mole-fraction could be fitted by the model using a rate constant 2 × 10−11 × exp(−3700/T) cm3 s−1 for this process. These quenching processes of metastable O2(a 1Δ g ) and O2(b 1Σ g +) molecules by oxygen atoms are important for oxygen plasmas and could have a significant impact on the kinetics of oxygen-containing mixtures at higher gas temperatures, for example in plasma-assisted combustion or in high-pressure plasma processing reactors.

An experimental measurement of the density of excited argon states 1s5, 1s4, 1s3, and 1s2 was carried out for an rf capacitive discharge in argon at a frequency of 13.56 MHz and 81 MHz for two pressures of 50 and 100 mTorr in a wide range of discharge applied power. A collision-radiative model was developed to calculate the densities of 1s states from the known electron density and the electron energy distribution function. The electron energy distribution function is obtained from a self-consistent discharge simulation based on the Particle in cell with Monte Carlo collisions model. It is shown that the calculated densities of the metastable states of argon are in good agreement with the experimentally measured ones. The calculated resonance state densities are underestimated.

Available data on the kinetic processes in H2-O2-O2(a 1Δ g ) mixtures are analyzed theoretically, and the ranges in which the rate constants of these processes can vary are determined. The processes of energy transformation in an O2(a 1Δ g )-H2-H-HO2 system in the approximations of the fast and slow (in comparison with the vibrational relaxation time of the HO2 radical) quenching of the electronically excited state are considered. The experiments on the quenching of singlet delta oxygen (SDO) molecules O2(a 1Δ g ) excited in a microwave discharge at a temperature of 300 K and pressure of 6 Torr in a lean hydrogen-oxygen mixture are simulated (by a lean fuel mixture is meant a mixture in which the ratio of the fuel to the oxidizer mass fraction is less than the stoichiometric ratio, which is 2: 1 for a hydrogen-oxygen mixture). It is shown that, over the experimental observation times, the SDO quenching frequency depends on the concentration of molecular hydrogen, the residual odd oxygen fraction in the gas flow, and the ratio between the rate constants of kinetic processes involving HO2 and HO2* radicals. Simulations of the microwave discharge and the transport of excited oxygen along the drift tube make it possible to determine the residual odd oxygen concentration in the gas flow. Recommendations on the choice of the rate constants for the O2(a 1Δ g ) + HO2)A″, v3″ = 0) ↔ O2 + HO2*(A′, v3′ = 1), HO2*(A′v3′ ≤ 1) + O2(a 1Δ g ) → HO2*(A′,v3′ ≥ 6) + O2, and HO2*(A′,v3′ ≤ 1) + O2(a 1Δ g ) → H + O2 + O2 processes are given. It is shown that, in the case of slow quenching in a H2-O2-O2(a 1Δ g ) mixture at a low temperature, the intensity of hydrogen oxidation is enhanced due to the reaction + HO2*(A′,v3′ ≤ 1) + O2(1Δ) → H + O2 + O2.

Results of experiments on the quenching of singlet delta oxygen (SDO) O2(a 1Δ g ) in lean hydrogen-oxygen mixtures at temperatures of 500–1020 K and pressures of 26–90 Torr behind the shock front are analyzed theoretically. The processes affecting SDO quenching are simulated taking into account the temporal characteristics of the experiment and various mechanisms of energy transformation in an O2(a 1Δ g )-H2-H-HO2 system. It is demonstrated that the approximations of both fast and slow (in comparison with the vibrational relaxation time of the HO2 radical) quenching of the electronically excited state of the radical are in good agreement with the experimental data on the effective rate constant of SDO deexcitation at temperatures of up to 700 K. It is shown that the available data on the kinetics of reactions involving SDO in H2-O2-O2(a 1Δ g ) mixtures overestimate the SDO quenching rate in comparison with the experimental results obtained at temperatures above 850 K. The decrease in the rate constant of the reaction H + O2(a 1Δ g )→ products by one order of magnitude makes it possible to match the simulation results to the experimental data. The existence of the processes restoring SDO in the presence of atomic hydrogen that are not considered in the current models of the H2-O2-O2(a 1Δ g ) kinetics is supposed.

Influence of electron excited singlet delta oxygen (SDO) molecules produced in direct current (DC) glow discharged plasma on the induction length decrease in the H2-O2 mixture has been studied via ...

The kinetic processes occurring in an electric-discharge oxygen-iodine laser are analyzed with the help of a 2D (r, z) gasdynamic model taking into account transport of excited oxygen, singlet oxygen, and radicals from the electric discharge and their mixing with the iodine-containing gas. The main processes affecting the dynamics of the gas temperature and gain are revealed. The simulation results obtained using the 2D model agree well with the experimental data on the mixture gain. A subsonic oxygen-iodine laser in which singlet oxygen is generated by a 350 W transverse RF discharge excited in an oxygen flow at a pressure P = 10 Torr and the discharge tube wall is covered with mercury oxide is simulated. The simulated mixing system is optimized in terms of the flow rate and the degree of preliminary dissociation of the iodine flow. The optimal regime of continuous operation of a subsonic electric-discharge oxygen-iodine laser is found.

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.

This work is devoted to the study of the possibility of obtaining the highest O2(a 1 � g) yield in ED SOG at the high absolute O2(a 1 � g) concentration needed for developing a powerful oxygen–iodine laser pumped by electric discharge. A singlet oxygen was produced in a transversal rf discharge in the pressure range 10–30 Torr of pure oxygen in the small-diameter (7 mm) quartz tube with HgO coating of the inner walls for removing atomic oxygen to eliminate fast O2(a 1 � g) quenching. It is shown that pd scaling (p—pressure, d—tube diameter) of the rf discharge actually allows an increase of the absolute O2(a 1 � g) density. The increase in the rf frequency from 13.56 to 81 MHz results in the essential increase of the O2(a 1 � g) yield (beyond 15% at such a high oxygen pressure as 15 Torr), but the subsequent transfer to the higher rf frequency of 160 MHz only slightly influences the maximally obtained O2(a 1 � g) yield. The effect of the NO admixture on the O2(a 1 � g) production has been also studied. The rate constant of O2(a 1 � g) quenching by NO k NO = (8.5 ± 1.5) × 10 −17 cm 3 s −1 was directly measured. The NO admixture (up to 20%) resulted in the noticeable increase in the O2(a 1 � g) yield mainly at low energy inputs. But this gain in the O2(a 1 � g) concentration drops with increasing energy input. Nevertheless it is shown that by combining the O2 + NO mixture with the HgO coating of the discharge tube walls one can provide the O2(a 1 � g) yield on the level of ∼21% at 10 Torr, ∼17% at 20 Torr and ∼13% at 30 Torr of O2 with the efficiency of ∼4–6%. The analysis of the NO admixture influence on the discharge structure and O2(a 1 � g) production has been carried out by using the 2D model. It was found that at the low energy input the NO admixture acts as an easily ionized species that enlarges the region occupied by plasma. Thus, in the O2 + NO discharge the normal current density is lower than in the pure oxygen discharge. As a result a higher energetic efficiency of O2(a 1 � g) production is also observed in the case of the O2 + NO mixture and the low energy input. In order to provide the optimal conditions for O2(a 1 � g) production (with regard to the yield and efficiency) in the continuous wave transversal VHF discharge at such high oxygen pressures as of 10–30 Torr it is necessary to find out the range of energy inputs where the VHF discharge operates in the regime of normal current density on the boundary with the abnormal regime and to remove atomic oxygen produced in the discharge by some volume or surface processes.

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.

A 2D self-consistent simulation of an rf discharge in a gas flow in pure oxygen over a wide range of discharge parameters was carried out. The simulation was made at the experimental conditions of Part I of this paper for the discharge tube with an HgO coating where the most effective production of O2(a?1?g) was experimentally observed. The simulation goal is to study the features of transversal rf discharge self-organization at different rf frequencies, 13.56 and 81?MHz, to reveal the most optimal conditions for both the O2(a?1?g) yield and its energy efficiency. It was shown that the energy part absorbed by electrons increases with the frequency. The spatial discharge structure was studied at both frequencies. It was revealed that at the higher rf of 81?MHz the discharge operates in a mode of the normal current density even at high input powers. The kinetic processes which determined both O2(a?1?g) loss and production at experimental conditions were studied and discussed. The increase in rf frequency from 13.56 to 81?MHz reveals an increase in the SO yield and efficiency. It also connects with the decreasing of input energy losses in the sheaths.

The scaling on pressure for a discharge singlet oxygen generator based on the rf discharge excitation of O2 flow is studied in the context of the problem of oxygen?iodine laser pumping. With this aim, the evolution of O2(a?1??g) and molecules as well as O(3P) atoms in 13.56 and 81?MHz discharges at pressures up to 15?Torr has been investigated in detail. It is shown that fast quenching of O2(a1?g) by atomic oxygen with increasing pressure and energy input causes rapid saturation of the O2(a1?g) density in the discharge and limits the O2(a?1??g) yield on a rather low level of a few per cent. Covering of the discharge tube walls with mercury oxide for fast catalytic removal of oxygen atoms allows us to greatly increase the O2(a?1??g) yield as well as to avoid fast quenching of O2(a?1??g) in the early afterglow. It enables us to succeed in obtaining the rather high O2(a?1??g) yields at such high pressure as 10?15?Torr. So the singlet oxygen yield is ~10?12% at ~10?Torr. The transition to the higher frequency of 81?MHz even increases greatly the O2(a?1??g) yield up to ~16%.

A capacitive coupled radio-frequency plasma at argon pressure of 100 mtorr, 13.56 and 81 MHz frequency and high specific input powers has been studied both experimentally and theoretically. The different numerical models were developed and used for simulation. It was shown that the main ionization source in low frequency (LF) discharge at all studied powers is due to secondary electrons emitted from the electrode by ion impact. The high-frequency (HF) discharge at the same powers is operated in alpha-mode. Applicability of fluid and kinetic models for simulation of LF and HF discharges are studied on the base of our experimental data

A one-dimensional particle-in-cell Monte Carlo (PIC-MC) model for a capacitively coupled rf discharge in methane with the kinetic approach of electron and ion behaviour is presented. To make a computation reasonably fast only two main ion species, and , have been taken into consideration. The ion energy distribution functions (IEDF) near the substrate have been calculated for different discharge parameters. The IEDF of differs substantially from the IEDF of at low frequency because of the resonant charge transfer for . The elastic scattering of ions on different neutral products originating in the plasma becomes essential for ion spectra at high frequencies. It was shown that the discharge frequency has an influence on the electron density and the electron energy as well as on the dissociation rate. The ion and radical fluxes to the substrate have been calculated for different gas pressures and discharge frequencies. The results of the present model were compared with the data calculated by means of the hybrid PIC-MC–fluid model (Ivanov et al 2002 J. Appl. Phys. 91 6296) in which for the ions the drift–diffusion approximation is being used. It is shown that the kinetic approach for the ion motion results in a decrease in the charge fluxes to the substrate. A correlation between the IEDF and the experimental deposition rate of diamond-like carbon films has been analysed.

The production and transport dynamics of O2(a?1?g) and molecules as well as O(3P) atoms has been studied in an O2 flow excited by a 13.56?MHz RF discharge in a quartz tube at pressures of 1?20?Torr. It has been shown that the densities of O2(a?1?g) and O(3P) are saturated with increasing energy input into the discharge. The maximum yield of singlet oxygen (SO) and the O2 dissociation degree drops with pressure. It is demonstrated that depending on the energy input the RF discharge can exist in three modes: I?in the spatially homogeneous mode or ?-mode; III?in the substantially inhomogeneous mode, when plasma jets are present outside the discharge; and II?in the transient mode between modes I and III. In this paper only the homogeneous mode of RF discharge in the O2 flow is considered in detail. A self-consistent model of the ?-mode is developed, that allows us to analyse elementary processes responsible for the production and loss of O2(a?1?g) and molecules as well as O(3P) atoms in detail. To verify both the kinetic scheme of the model and the conclusions, some experiments have been carried out at lower flow velocities and higher pressures (?10?Torr), when the stationary densities of O2(a?1?g), and O(3P) in the discharge area were established not by the escape of particles but by the losses due to the volumetric and surface reactions. The density under these conditions is determined by the balance of production by both direct electron impact and electronic excitation transfer from metastable O(1D) atoms and deactivation by oxygen atoms and tube walls, including quenching by ozone in the afterglow. The O(3P) density is determined by the balance between the production through O2 dissociation by electron impact and heterogeneous loss at the wall recombination. The stationary density of O2(a?1?g) is provided by the processes of O2(a?1?g) production by direct electron impact and loss owing to quenching by the tube walls at a low pressure below 4?Torr, as well as by three-body recombination with oxygen atoms with increasing pressure above 7?Torr. The analysis of O2(a?1?g) three-body quenching by oxygen atoms showed that this process could actually have a high rate constant and be able to provide a fast SO deactivation at high pressures. The approximate value of the rate constant?(1?3) ? 10?32?cm3?s?1 has been obtained from the best agreement between the simulated and experimental data on transport dynamics of O2(a?1?g) molecules and O(3P) atoms. It is shown that the RF discharge ?-mode corresponds to a discharge with an effective reduced electrical field in a quasi-neutral plasma of about ~ 30?Td, which makes possible a rather high efficiency of SO production of ~3?5%.

The effect of the nonlocal nature of the electron distribution function on the dissociation rate of oxygen molecules in a dc glow discharge is studied. The concentration of oxygen atoms and the probability of their loss at the discharge tube wall are measured as functions of the discharge parameters by means of the timeresolved actinometric method involving argon atoms. An analysis of the measurement data in terms of both a discharge model in which the effect of the nonlocal nature of the electron energy spectrum is taken into account and a model in which this effect is ignored makes it possible to thoroughly investigate the balance of oxygen atoms in the discharge. The production rate of O(3 P) atoms and their concentration in the plasma are calculated with allowance for the nonlocal nature of the electron energy distribution function. The calculated values agree well with the experimental data and differ substantially from those obtained using a spatially homogeneous distribution function.

Experimental measurements of current-voltage relationship in RF CCP discharge in argon at 81 MHz have been performed by cylindrical Langmuir probes technique. Two different probe radii have been used: 50 and 250 μm. The high plasma density 1010–1011 cm-3 has been estimated at specific input power under study. The experimental data on nonmonotonic behavior of probe current with pressure were observed firstly for conditions of RF discharge plasmas. To analyze the probe measurements the fast numerical model for ion current collected by a cylindrical probe has been developed. This model is based on the particle-in-cell with Monte-Carlo collision method for ions motion and Boltzmann relation for electrons. The features of probe data at studied conditions were discussed. The comparative analysis of different collisionless approaches for plasma density calculation from ion probe current is done. It is shown that in general collisionless theories underestimate the plasma density value. For correct evaluation of plasma density experimental I-V probe measurement should be supplied by the numerical simulation. It was demonstrated that the collisionless analytical theory of orbital motion can formally give correct results on plasma density at some plasma conditions even when ion collisions take place. The physical reasons of this accidental validity are explained.

The kinetics of the production and loss of CF2 and CF radicals in a glow discharge in pure CF4 is investigated by the laser-induced fluorescence method. The effective rate constants for electron-impact dissociation of CF4 molecules along the pathways toward CF2 and CF radicals are determined within a wide range of the reduced electric field (80–250 Td). It is shown that, along with the direct electron-impact dissociation of CF4, the radicals are also produced via the dissociation of the CxFy polymer fluorocarbon particles that form in the plasma. A detailed analysis of the kinetics of the radical production and loss in a modulated discharge made it possible to evaluate the contribution of the electron-impact dissociation of CF4 to the production of radicals and, consequently, to determine the dissociation rate constants $$k_{CF_2 } $$ and k CF. A comparison of the obtained $$k_{CF_2 } $$ and k CF values with the results of calculations by the Monte Carlo method and the literature data on the cross sections for electron-impact dissociation of CF4 molecules enabled the normalization of these cross sections in the threshold region and the construction of the model cross sections for the electron-impact dissociation of CF4 into neutral products. The calculated cross sections allow a satisfactory description of the experimental results throughout the entire range of E/N under study. A significant scatter (up to 100%) in the experimental data on $$k_{CF_2 } $$ and k CF at low values of E/N is related to the considerable contribution of the CxFy polymer molecules (and, probably, CxF y + ions and fluorocarbon grains) to the production of CF2 and CF radicals both in the plasma volume and on the surface of a fluorocarbon film covering the discharge tube wall.

Mechanisms for the production and loss of CF2 and CF radicals in a glow discharge in pure CF4 are investigated by the time-resolved laser-induced fluorescence method. The fluorocarbon polymerization processes are shown to contribute significantly to the production of radicals both in the plasma volume and on the surface of the discharge tube. The effective frequencies of both the volume and surface processes of radical production and loss are determined. An analysis of these frequencies allowed us to study the polymerization mechanism in a CF4 plasma at a high relative concentration of F atoms and low ion energy. It is shown that, at elevated pressures, when the density of CxFy polymer particles in the plasma volume becomes comparable with the density of simple fluorocarbon radicals, the electron-impact dissociation of these particles is the main channel for the production of CF2 and CF radicals. Another source of CF2 and CF radicals is related to the reactions of CnF2m+1 unsaturated fluorocarbon particles both in the plasma volume and on the surface of a fluorocarbon film arising on the discharge tube wall. The CxFy fluorocarbon polymer particles form both in the discharge volume and on the fluorocarbon filmsurface also in the course of the film destruction. At lowered pressures, the main channel for the production of CF2 and CF is the direct electron-impact dissociation of CF4 molecules, whereas the loss of these radicals at the tube wall is the main loss channel. The probabilities of the heterogeneous losses of CF2 and CF radicals on the heavily fluorinated surface of the fluorocarbon film at low ion energies are determined. Under these conditions, the surface recombination of the Fch chemisorbed fluorine atoms and CF x ph physisorbed radicals with the production of an activated complex is shown to be the most probable mechanism for the heterogeneous losses of CF2 and CF. The approximate activation energies for the production of Fch · CF 2 ph and Fch · CFph surface complexes are found to be 750±70 K and 1030±100 K, respectively.

A self-consistent hybrid model of discharge in a plasma display cell is proposed, which provides an adequate description of a nonlocal electron distribution in nonstationary cases. A comparative analysis of the results of calculations based on the hybrid (nonlocal) and local models reveals considerable differences both in the discharge structure and in the emission dynamics.

Low-k dielectric films can be substantially damaged during plasma processing. High energy UV and VUV photons emitted by plasma play the key role in damaging the porous low-k films directly or indirectly by stimulating chemical reactions with radicals in plasma and plasma afterglow. The different ULK samples (k: 2.0-2.2, porosity: 30-50%, pore radius: 1-2 nm) were studied by exposing to five radiation sources at various wavelengths (VUV: 193 nm, 147 nm, 104-106 nm, 58.3 nm, and EUV: 13.5 nm). Time-spatial behavior of the ULK damage as a function of photons fluence was studied by FTIR spectroscopy and XRF analysis. It is shown that the degree of damage depends on wavelength of UV light. The major UV damage was observed at the wavelengths below 193 nm. The maximum damage corresponds to 147 nm while the degree of damage at 58.3 nm was much smaller. In the case of organosilicate (OSG) based ULK materials, the degree of damage, as a rule, increases with porosity. Organic low-k materials are damaged more than OSG at 193 nm, but at shorter wavelengths (147, 106, 58.3 and 13.5 nm) they are more stable than OSG. One-dimensional model for radiation absorption and dynamics of CH3 group destruction in ULK films was developed. The cross-sections of photons absorption and photo-stimulated Si-CH3 bond breaking in ULK films for 13.5 -147 nm wavelength range were derived from a combined experimental and modeling study. The obtained values allow to simulate the VUV/EUV induced modifications of low-k materials with different composition, to understand better the mechanisms of plasma damage and to generate ideas for controllable modifications of low-k materials.

Single (SF) and dual frequency capacitively coupled plasma (DF CCP) in (0–50%) H2/Ar mixtures was studied numerically with 1D hybrid (Particle-in-cell with Monte Carlo Collision + fluid) model. In SF (81 MHz) discharge the effect of hydrogen dilution is studied for the fixed discharge input power. Mechanisms of the plasma density decrease and variation of ions composition with H2 percentage are discussed. The effect of low-frequency voltage on plasma density, ions composition, ions fluxes, and ions energy was studied in DF CCP (1.76–81 MHz) discharge in 5% H2/Ar gas mixture at low (20 mTorr) and high (100 mTorr) pressures.

Spectra in the vacuum-ultra violet range (VUV, 30 nm–200 nm) as well as in the ultra-violet(UV) and visible ranges (UV+vis, 200 nm–800 nm) were measured from Ar/CF3I and Ar/CF4 discharges. The discharges were generated in an industrial 300 mm capacitively coupled plasma source with 27 MHz radio-frequency power. It was seen that the measured spectra were strongly modified. This is mainly due to absorption, especially by CF3I, and Ar self-trapping along the line of sight, towards the detector and in the plasma itself. The estimated unabsorbed VUV spectra were revealed from the spectra of mixtures with low fluorocarbon gas content by means of normalization with unabsorbed I* emission, at 206 nm, and CF band (1B1(0,v',0)A1(0,,0)) emission between 230 nm and 430 nm. Absolute fluences of UV CF emission were derived using hybrid 1-dimensional (1D) particle-in-cell (PIC) Monte-Carlo (MC) model calculations. Absolute calibration of the VUV emission was performed using these calculated values from the model, which has never been done previously for real etch conditions in an industrial chamber. It was seen that the argon resonant lines play a significant role in the VUV spectra. These lines are dominant in the case of etching recipes close to the standard ones. The restored unabsorbed spectra confirm that replacement of conventional CF4 etchant gas with CF3I in low-k etching recipes leads to an increase in the overall VUV emission intensity. However, emission from Ar exhibited the most intense peaks. Damage to low-k SiCOH glasses by the estimated VUV was calculated for blanket samples with pristine k-value of 2.2. The calculations were then compared with Fourier transform infrared (FTIR) data for samples exposed to the similar experimental conditions in the same reactor. It was shown that Ar emission plays the most significant role in VUV-induced damage.

The process of ozone production and loss during the oxygen photodissociation upon the absorption of radiation from an excimer lamp with a wavelength of 172 nm was studied by experimental and theoretical methods. Analysis of the experimental data within the framework of a one-dimensional numerical model showed evidence for the presence of a previously unknown mechanism of the heterogeneous ozone loss in a flow of atomic oxygen.

An analytical approach is used to calculate an ion energy distribution function (IEDF) in a dual frequency (DF) collisionless rf discharge in argon. Three possible limit regimes for frequency relations in the DF discharge are discussed. The analytical IEDF is obtained for the intermediate-frequency case, which is most applicable in plasma-processing technologies. The analytical expressions for an ion spectrum width as well as for the minimum and maximum ion energies are derived. The analytical theory is compared with a particle-in-cell Monte Carlo numerical simulation and also with the results of a semianalytical model.

Radio frequency capacitively coupled plasma (RF CCP) sustained at RF frequencies of 27 MHz in an Ar–CF4–CF3I gas mixture is studied experimentally and theoretically. The RF CCP in Ar–CF4–CF3I is simulated by using a 1D hybrid particle-in-cell–fluid numerical model. We pay special attention to the changes in plasma structure and fluxes to the electrode, negative ion and neutral radical production with admixture of CF3I in Ar–CF4 plasma. With CF3I admixture the plasma becomes strongly electronegative as a result of the high electron attachment rate to the CF3I molecule. The atomic fluorine density becomes extremely low with addition of CF3I molecules due to the large volume loss in the reaction CF3I + F → CF3 + IF. Optical emission spectrometry data on CF2 emission at the wavelength of 250 nm indicate the essential sources of CF2 in CF3I-containing plasma in the studied conditions, although direct dissociation channels for the CF3I molecule with CF2 production have not been studied. Evaluation of CF2 density in Ar–CF4–CF3I plasma was first carried out on the basis of the actinometry technique and numerical simulation. The possible mechanism of ultra-low-k film damage in the studied conditions is also discussed.

The etch mechanism of porous SiOCH-based low-k films by F atoms is studied. Five types of ultra-low-k (ULK) SiOCH films with k-values from 1.8 to 2.5 are exposed to F atoms in the far downstream of an SF6 inductively coupled plasma discharge. The evolution of etching with an F dose was studied using various techniques of surface and material analysis such as FTIR, XPS, EDS and SE. It is revealed that the etch mechanism is connected with surface fluorination and formation of –CHxFy species on the surface due to H abstraction by F atoms from –CH3 groups. It is shown that the etching includes two phases. The first one is observed at the low F doses and is connected with chemical modification and etching of walls in the topmost pores, which finishes when the walls are fully etched. At the same time, the additional etching in the underlying pores due to F penetration forms the etch depth profile, after that the second etching phase starts. This phase is characterized by the higher etch rate due to the propagation of the etch depth profile further into the film. The preliminary treatment of pore walls inside porous channels effectively accelerates etching many times compared to non-porous material. The acceleration depends on the modification depth, which in turn is a function of pore structure and interconnectivity as well as the F atom reaction mechanism. The combined random walk (Monte-Carlo) & kinetics model developed to describe F penetration inside SiOCH films together with reactions of F atoms leading to –CHxFy depletion and opening SiOx bonds for F access allowed relating the increased etch rates with increasing the total number of F atom collisions inside interconnected pores. The etch mechanism of SiOCH films is found in many respects to be similar to the SiO2 etch mechanism on the elementary level, but as whole it is ruled by the SiOCH structure: porosity degree, pore size, pore interconnectivity as well as structural features of SiOx bonds.

This work is devoted to the experimental and theoretical study of rf frequency influence on the discharge structure and the O 2 (a 1 D g ) yield in a rf discharge in the tubes with HgO coating for removing atomic oxygen to avoid fast O 2 (a 1 D g ) quenching. Two series of experiments were carried in two discharge sets up: 1 - tube of large diameter of 14 mm, electrode length of 30 cm; 2 - tube of small diameter of 7 mm, electrode length of 10 cm. In the first series, the increase of rf frequency from 13.56 MHz to 81 MHz resulted in the singlet oxygen (SO) yield Y >15% at such high oxygen pressure as 10 Torr. 2D self-consistent model was developed to simulate the rf discharges in gas flow in a wide rage of discharge parameters both with and without HgO coating. Results of the simulation agreed very well with the experimental data. It is shown that at the high rf frequency the discharge operates in a mode of the normal current density so that the energy absorbed by electrons from the rf field increases with the frequency. In the second series we scaled up the rf discharge on the pd parameter ( p -pressure, d -tube diameter) to increase the oxygen pressure. The pd discharge scaling at the high rf frequency allowed to reach the O 2 (a 1 D g ) yield Y > 15% at oxygen pressure up to ~17 Torr. The effect of NO admixture on the O 2 (a 1 D g ) production has been studied in series 2 at rf frequency of 160 MHz. NO admixture (5÷20%) results in the noticeable increase in the O 2 (a 1 D g ) yield in comparison with the discharge tube without HgO coating. It is shown that combination of O 2 + NO mixture with HgO coating of the discharge tube walls provides the most optimal O 2 (a 1 D g ) production with the efficiency up to 7-10 % and allows to reach the threshold yield in 15 % at oxygen pressure even above ~20 Torr.

Quasi two-dimensional (r,z) model of large bore copper vapor laser (CVL) was developed. Full set of heat and species (charged and neutral) transfer equations, Maxwell equations and electron energy balance equation were solved for different pulse repetition rate in a temporally self- consistent manner, with the long term evolution of plasma kinetics followed over multiple excitation/afterglow cycles. Electron rate constants were for the first time taken from the realistic EEDF, which was the result of solving Boltzmann equation in two-term approximation with charged particle collisions taken into account. Laser radiation power was calculated together with external circuits (several magnetic switches are included) self-consistently. Our model includes the plasma-chemical and neutral kinetic processes in Cu/Ne/H 2 /HCl mixtures. Two-dimensional thermal radiation transfer was taken into account for the first time. The influence of skin-effect and H 2 /HCl additives on CVL characteristics was studied. Detailed hydrogen rotational and vibrational kinetics taken into account in a CVL model allows us to explain experimental results: radial redistribution of laser power, wall temperature increase, prepulse electron temperature and concentration decrease with hydrogen. The model was used for designing new laser system. After that this laser was constructed and gives first results lately. The laser shows good agreement with predictions, in already realized pure Cu mode (without any admixtures) it gives 105 W, whereas the prediction was 117 W.

The production and loss kinetics of CF2 and CF radicals in the CF4 glow discharge were studied with using the time— resolved LIF technique. The effective rate constants of the CF4 dissociation into the chanhels with CF2 and CF production were determined in a wide range of reduced electric field: 80-250 Td. It is shown that besides of the CF4 dissociation by direct electron impact there is also another source conditioned by fluorocarbon plasma polymerization processes. The detailed analysis of growth and decay dynamics of radical concentrations at the discharge modulation has allowed us to separate different channels of the radical production and consequently to determine the constants of CF4 dissociation rate by electron impact KCF2 KCF and A comparison of received KCF2 and KCF with calculations made on the base of solving the Boltzman equation by Monte-Carlo technique with using the available data on electron scattering cross-sections on CF4 molecules, has in part allowed us to renormalize the partial dissociation cross-sections near the threshold and to build up the model cross-sections of neutral dissociation of CF4 by electron impact It is shown, that the polymerization processes substantially contribute (particularly at low values of E/N) to production of radicals, as in a plasma volume, and on a surface of the discharge tube. The analysis of the obtained data on characteristic frequencies (times) of these processes has allowed us to study mechanisms of fluorocarbon's polymerization in CF4 plasma in conditions of high relative concentration of fluorine atoms and low ion energy. So it is shown, that with increasing pressure, when the concentration of polymer fragments CxFy in bulk of plasma is comparable with concentration of simple fluorocarbon radicals CFx (x=1-3), the dissociation of these fragments by electronic impact and the reactions of unsaturated fluorocarbon fragments CnF2m+1 as in volume, and on a surface of a fluorocarbon film, covering discharge tube walls become the main production channels of CF2 and CF. Since with lowering pressure a major channel of CF2 and CF destruction is connected with their heterogeneous losses on tube walls, the surface loss probabilities of CF2 and CF radicals in conditions of the fluorinated fluorocarbon film surface are determined. It is shown, that the most probable mechanism of heterogeneous loss of CF2 and CF under these conditions is the surface recombination of chemisorbed fluorine atoms Fch and physadsorbed radicals CFxPh (x=1-2) through the formation of an activated surface complex. The analysis of the experimental data with using this approach has allowed us to estimate the approximate values of activation energies for the formation of the surface complexes Fch. CF2ph and Fh. CFPh - 750 ± 70 K and 1030 ± 100 K respectively.

At present neither of available sets of CF4 electron scattering cross sections does enable one to interpret satisfactory the CF4 dissociation in discharge plasma. We have undertook the investigation directed to determine the self-consistent set of CF4 neutral dissociation cross-sections which would allows one to describe correctly the F and CFx(x=1–3) production rates in the discharge. We suggest to carry out a series of experiments on a study of CF and CF2 radical as well as F atom kinetics in positive column of CF4 DC discharge. It is the first work from this series the aim of which was to determine a rate constant of CF4 electron impact dissociation into CF2 radical production channel (e + CF4 ⇒ CF2 + products). The rate constant was determined monitoring the CF2 absolute concentration dynamics in modulated DC discharge by differential UV adsorption technique and laser induced fluorescence method. Following the experimental results and analysis of available data on electron scattering cross section sets on CF4 molecules we have attempted to specify the cross section for this CF4 dissociative channel.

Modification of ultra-low-k films by extreme ultraviolet (EUV) and vacuum ultraviolet (VUV) emission with 13.5, 58.4, 106, 147 and 193 nm wavelengths and fluences up to 6 × 1018 photons cm−2 is studied experimentally and theoretically to reveal the damage mechanism and the most ‘damaging’ spectral region. Organosilicate glass (OSG) and organic low-k films with k-values of 1.8–2.5 and porosity of 24–51% are used in these experiments. The Si–CH3 bonds depletion is used as a criterion of VUV damage of OSG low-k films. It is shown that the low-k damage is described by two fundamental parameters: photoabsorption (PA) cross-section σPA and effective quantum yield φ of Si–CH3 photodissociation. The obtained σPA and φ values demonstrate that the effect of wavelength is defined by light absorption spectra, which in OSG materials is similar to fused silica. This is the reason why VUV light in the range of ∼58–106 nm having the highest PA cross-sections causes strong Si–CH3 depletion only in the top part of the films (∼50–100 nm). The deepest damage is observed after exposure to 147 nm VUV light since this emission is located at the edge of Si–O absorption, has the smallest PA cross-section and provides extensive Si–CH3 depletion over the whole film thickness. The effective quantum yield slowly increases with the increasing porosity but starts to grow quickly when the porosity exceeds the critical threshold located close to a porosity of ∼50%. The high degree of pore interconnectivity of these films allows easy movement of the detached methyl radicals. The obtained results have a fundamental character and can be used for prediction of ULK material damage under VUV light with different wavelengths.

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.

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...

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.

Investigations of the discharge current shape in a low frequency single frequency discharge and in a dual frequency discharge are performed in this paper. For this purpose a Particle in cell with Monte-Carlo Collisions numerical simulation of the capacitively coupled discharge in argon, operated at frequencies of 1.76 MHz & 81 MHz, is carried out. As a result the non-sinusoidal, close to triangle shape of the discharge current is obtained even for the case of a symmetric discharge. The physical reason of such nonsinusoidal behavior of the discharge current is the dynamic structure of the discharge sheaths. Corresponding to the discharge current, the sheath edge motion is also non-sinusoidal and non-symmetric. These results may be important for the appropriate choice of the current and voltage waveforms in analytic modeling of single and dual frequency discharges.

A comparable analysis of continuous wave (CW) and pulse-periodic (PP) operation modes of an electro-discharge singlet oxygen generator (ED SOG) utilizing an 81?MHz discharge in the O2/NO mixture at elevated pressure (more than 10?Torr of O2) has been carried out. The discharge in both modes operates in the regime of the normal current density and therefore occupies only a part of the electrode's area depending on the inputted rf power. Due to the fact that the rf power in PP mode (during the pulse) is higher at the same energy input, the PP discharge can occupy a greater area compared with the CW discharge and is found closer to the boundary with the abnormal regime that is most effective for O2(a?1?g) production. Thereby it provides a higher O2(a?1?g) yield and efficiency with increasing pressure. The O2(a?1?g) yield of ~12% in PP mode of the O2/NO discharge has been realized with an efficiency of 12?18% against only ~9% and an efficiency of 8?12% in CW mode. This fact and the possibility to control additionally the duty cycle and pulsed rf power in PP discharge can be a prospective and useful means of optimizing the ED SOG in technological applications of an oxygen?iodine laser with electro-discharge pumping.

A one-dimensional particle-in-cell–Monte Carlo (PIC–MC) model was developed for a capacitively coupled rf discharge in a mixture of CH4 and H2. The electron behavior is kinetically simulated by solving Newton’s equations and treating the electron collisions with the Monte Carlo algorithm, whereas the behavior of the ions and radicals is treated by a set of continuity equations. The distinctive feature of this model is its self-consistency, i.e., the motion of the electrons is considered in the real electric field calculated from the Poisson equation, and not in the time-averaged electric field. The PIC–MC results were compared with the data calculated by means of a pure fluid model. In both models, exactly the same type of species, reactions, and cross sections are used. The results of both models, such as the electron energy distribution function, the average electron energy, and the densities of the various plasma species, are compared at a gas pressure of 0.14 Torr and a discharge frequency of 13.56 MHz, for the power ranging from 0.5 to 25 W. The nonstationary and nonlocal features of the electron energy distribution function are shown in the PIC–MC calculations. The effect of accumulation of low-energy electrons in the center of the discharge at higher input power P=25 W is observed in the PIC–MC model, in contrast with the fluid model. The mechanisms causing the accumulation of low-energy electrons, and the processes defining the stationary state of the discharge are analyzed. The applicability of the fluid model for the calculation of the density of different hydrocarbon radicals is discussed.