[en] 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, CH₄⁺ and CH₅⁺, have been taken into consideration. The ion energy distribution functions (IEDF) near the substrate have been calculated for different discharge parameters. The IEDF of CH₄⁺ differs substantially from the IEDF of CH₅⁺ at low frequency because of the resonant charge transfer for CH₄⁺ . 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

[en] The O(³P) atom loss has been studied in O₂ RF plasma in the quartz tube in the intermediate pressure range (10–100 Torr) when the transition from the surface to volume loss is observed. Space- and time-resolved actinometry on Ar and Kr atoms was used to study O(³P) atom loss. The research has shown that such a transition actually takes place. However, it was revealed that the gas temperature plays a significant role in this. Gas temperature was measured spectroscopically using the band emission. It was demonstrated that the gas temperature in the plasma volume was rather high (>1200 K) due to the high values of the specific input RF power which in turn led to a significant O(³P) loss rate decrease in the discharge volume. The atomic oxygen loss is limited by the O(³P) surface recombination as well as by the volume recombination in a thin layer near the wall. It leads to a low integral loss rate and provides a high oxygen dissociation degree. Analysis based on measured [O(³P)]/N, T _gas, O₃ spatial profiles and surface loss model including recombination with chemisorbed and physisorbed atoms has revealed the importance of both surface and volume losses. High values of the specific input RF power also lead to increase of the gas temperature near the wall and the temperature of the internal tube surface. As a result, the O atom surface loss rate increases and the volume loss rate near the wall decreases, so overall the contributions of both O(³P) volume and surface recombination are comparable at pressures up to 100 Torr. The O(³P) loss kinetics at intermediate pressures appears to be a rather complex phenomenon and requires at least 1D or even 2D modeling for its correct description. Using global models under similar conditions may lead to dubious results in a detailed study of kinetic mechanisms and processes, but it can be useful for a simple analysis of experimental results. (paper)

[en] The applicability of actinometry for measuring the absolute concentration of O, N and F atoms in discharge plasma was studied. For this purpose, concentrations of these atoms were measured downstream of an ICP plasma by means of the actinometry method and of appearance potential mass-spectrometry (APMS). Comparison of the results showed good agreement between the two methods. Since the excitation cross sections of electron states O(3p ³P) and O(3p ⁵P) applied in actinometry are well tested, this allows using the APMS method for absolute calibration of the theoretical excitation cross sections for N and F atoms. As a result, total excitation cross sections ${\mathrm{\sigma <!--\; ??\; -->}}_{\text{e}}^{\text{total}}$ of the atomic levels N(3p ⁴P^o), F(3p ²P^o) and F(3p ⁴D^o) have been obtained for the first time. Since different types of electron energy distribution function (EEDF) were observed (Maxwellian, bi-Maxwellian and Druyvesteyn) the influence of these possible EEDF types on actinometric coefficients $C_{\text{Ar}}^X$ (X  =  O, N, F), that link the ratio of the atom and actinometer intensities $I_X/I_{\text{Ar}}$ with that of their concentrations [X]/[Ar], was also analyzed. It was shown that at the same ionization rate (effective electron temperature) the excitation rate constants $k_{\text{e}}^{X,\text{Ar}}$ are highly sensitive to the shape of EEDF, whereas actinometric coefficients $C_{\text{Ar}}^X$ depend on it only slightly. Dependence of actinometric coefficients on electron temperature $C_{\text{Ar}}^X\left(T_{\text{e}}\right)$ is positive if the emitting level of the X-atom is lower than that of the actinometer, and negative if vice versa. The energy difference between the emitting states of O and Ar atoms is maximal (∼3 eV), so that $C_{\text{Ar}}^{\text{O}}\left(T_{\text{e}}\right)$ is not constant for a whole range of electron temperatures typical for discharge plasmas (∼2–8 eV). For nitrogen atoms $C_{\text{Ar}}^{\text{N}}\left(T_{\text{e}}\right)$ varies considerably with T _e only when T _e  <  4 eV. In the case of fluorine atoms the energy difference of emitting F and Ar states is only ∼1 eV and coefficient $C_{\text{Ar}}^{\text{F}}\left(T_{\text{e}}\right)$ is nearly constant in a wide region of T _e  >  1.5 eV. (paper)

[en] 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.

[en] A technique employing electron beams generated by an open gas discharge is proposed for measuring the light efficiency of phosphor coatings of cathodoluminescent screens. The total light efficiencies of various phosphor coatings in the medium excitation energy range (ε < 7 keV) are estimated with allowance for both the direct radiation flux outgoing from the phosphor screen and the backward radiation flux propagating along the exciting electron beam. The possibility is demonstrated of creating a high-luminance (∼20000 cd/m²) cathodoluminescent source with a light efficiency of ∼60 lm/W.

[en] Low-pressure RF plasma in fluorohydrocarbon gas mixtures is widely used in modern microelectronics, e.g. in the etching of materials with a low dielectric constant (low-k) materials). The multifold experimental and theoretical study of a radio frequency capacitively coupled plasma at 81 MHz in Ar/CF₄/CHF₃ has been carried out at 50 mTorr and 150 mTorr gas pressures. A wide set of experimental diagnostics together with hybrid PIC MC model calculations were applied to a detailed study of the plasmas. Measurements of the F atoms, HF molecules and CF_x radicals, electron density, electronegativity and positive ion composition were performed. Absolutely calibrated VUV spectrometry was carried out to measure the VUV photon fluence towards the electrode. This combined experimental and model approach allowed us to establish the fundamental mechanisms of the charged and neutral species elementary reactions. Dissociative charge transfer reactions and fluoride transfer reactions influence the main ion (CF${}_3^{+}$, CHF${}_2^{+}$) composition in Ar/CF₄/CHF₃ plasma a lot. The mechanisms of heavy ion formation in Ar/CHF₃ are also discussed. The important role of additional attachment mechanisms (besides dissociative attachment to the feedstock gases, CF₄, CHF₃) was analyzed. The catalytic chain mechanism, including the HF molecules, which defines the CF_x kinetics in Ar/CHF₃ plasma, was validated. This multifold approach enabled us to determine the complicated plasma chemical composition of the active species as well as the fluxes of VUV photons at the surface of the processed material, and is a result that is important for understanding low-k damage. (paper)

[en] This work is devoted to the study of the possibility of obtaining the highest O₂(a ¹Δ_g) yield in ED SOG at the high absolute O₂(a ¹Δ_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 ¹Δ_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 ¹Δ_g) density. The increase in the rf frequency from 13.56 to 81 MHz results in the essential increase of the O₂(a ¹Δ_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 ¹Δ_g) yield. The effect of the NO admixture on the O₂(a ¹Δ_g) production has been also studied. The rate constant of O₂(a ¹Δ_g) quenching by NO k_q^NO = (8.5±1.5)x10^-17 cm³s^-1 was directly measured. The NO admixture (up to 20%) resulted in the noticeable increase in the O₂(a ¹Δ_g) yield mainly at low energy inputs. But this gain in the O₂(a ¹Δ_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 ¹Δ_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 ¹Δ_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 ¹Δ_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 ¹Δ_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

[en] The transport dynamics of the metastable oxygen molecules O₂(a ¹Δ_g) and O₂(b¹Σ_g⁺) as well as O(³P) atoms in an oxygen flow excited by an RF discharge in a jet-mode has been investigated. The production and loss processes of these active species have been analysed by comparing experimental data with simulation results from a self-consistent model of the RF discharge jet-mode. It is shown that both atomic and singlet oxygen (SO) production occur mainly in the plasma jet areas outside the electrode zone. The interelectrode space provides the necessary boundary conditions for the plasma jet existence. The energy efficiency of O₂(a ¹Δ_g) production with RF discharge excitation of the oxygen flow was analysed in detail. It is demonstrated that the homogeneous discharge α -mode, where the O₂(a ¹Δ_g) excitation efficiency reaches ∼3-5%, is the optimal one for singlet oxygen pumping. The O₂(a ¹Δ_g) excitation efficiency drops below 1% at the transition from the α -mode to a jet-mode, though the maximum O₂(a ¹Δ_g) concentration is reached just in the jet-mode. At oxygen pressures less than 4 Torr and in the case of an RF discharge jet-mode with extremely fast gas cooling, it is possible to provide an SO yield over the threshold necessary for obtaining generation in an oxygen-iodine laser. However, it only results from the strong oxygen dissociation in the discharge. The O₂(a ¹Δ_g) excitation efficiency slightly increases with pressure owing to the decreasing mean electron energy in the discharge volume. With increasing pressure, O₂(a ¹Δ_g) quenching with the three-body recombination with atomic oxygen becomes more essential. The removal of atomic oxygen from the gas flow, for example by binding oxygen atoms with any molecular additives, is necessary for scaling the electro-discharged SO generator on pressure. The products of such 'binding' processes should not deactivate O₂(a ¹Δ_g). It is experimentally shown that the application of RF generators with a higher frequency (40 MHz instead of 13.56 MHz) allows us to increase the O₂(a ¹Δ_g) excitation efficiency by 30-40%

[en] O₂(a ¹Δ_g) production in a non-self-sustained discharge (ND) in pure oxygen and oxygen mixtures with inert gases (Ar and He) has been studied. A self-consistent model of ND in pure oxygen is developed, allowing us to simulate all the obtained experimental data. Agreement between the experimental and simulated results for pure oxygen over a wide range of reduced electric fields was reached only after taking into account the ion component of the discharge current. It is shown that the correct estimation of the energetic efficiency of O₂(a ¹Δ_g) excitation by discharge using the EEDF calculation is possible only with the correct description of the energy deposit into the plasma on the basis of an adequate discharge model. The testing of an O₂(a ¹Δ_g) excitation cross-section by direct electron impact, as well as a kinetic scheme of processes involving singlet oxygen, has been carried out by the comparison of experimental and simulated data. The tested model was then used for simulating O₂(a ¹Δ_g) production in ND in oxygen mixtures with inert gases. The study of O₂(a ¹Δ_g) production in Ar : O₂ mixtures with small oxygen content has shown that the ND in these mixtures is spatially non-uniform, which essentially decreases the energetic efficiency of singlet oxygen generation. While simulating the singlet oxygen density dynamics, the process of three-body deactivation of O₂(a ¹Δ_g) by O(³P) atoms was for the first time taken into account. The maximal achievable concentration of singlet oxygen in ND can be limited by this quenching. On the basis of the results obtained and the model developed, the influence of hydrogen additives on singlet oxygen kinetics in argon-oxygen-hydrogen mixtures has been analysed. The simulation has shown that fast quenching of O₂(a ¹Δ_g) by atomic hydrogen is possible due to significant gas heating in the discharge that can significantly limit the yield of singlet oxygen in hydrogen-containing mixtures

[en] The production and transport dynamics of O₂(a ¹Δ_g) and O₂(b¹Σ_g⁺) 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 ¹Δ_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 α-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 α-mode is developed, that allows us to analyse elementary processes responsible for the production and loss of O₂(a ¹Δ_g) and O₂(b¹Σ_g⁺) 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 ¹Δ_g), O₂(b¹Σ_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 O₂(b¹Σ_g⁺) density under these conditions is determined by the balance of O₂(b¹Σ_g⁺) 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 ¹Δ_g) is provided by the processes of O₂(a ¹Δ_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 ¹Δ_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) x 10^-32 cm³ s^-1 has been obtained from the best agreement between the simulated and experimental data on transport dynamics of O₂(a ¹Δ_g) molecules and O(³P) atoms. It is shown that the RF discharge α-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%