D. V. Lopaev

The mechanism of low-k SiOCH film modification by oxygen atoms

The interaction of oxygen atoms with three types of plasma enhanced chemical vapor deposition low-k SiOCH films is studied. The samples were treated by O atoms in the far plasma afterglow conditions in a special experimental system designed for this study. The experimental system allowed avoiding the effect of ions and vacuum ultraviolet (VUV) photons on surface reactions and controlling the oxygen atom concentration over the samples. Fourier-transform infrared spectroscopy, x-ray fluorescence, and atomic force microscopy techniques were used to analyze the changes occurring in low-k films. Monte Carlo model for O atom interaction with low-k material that includes penetration, recombination, and reactions with methyl groups was developed. It is shown that the surface recombination on the pore wall surface determines the profile and penetration depth of O atoms into the films. The reaction of O atoms with methyl groups has lower probability and therefore proceeds in the background mode.

Pressure scaling of an electro-discharge singlet oxygen generator (ED SOG)

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.

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.

Modification of organosilicate glasses low-k films under extreme and vacuum ultraviolet radiation

Degradation of chemical composition of porous low-k films under extreme and various vacuum ultraviolet emissions is studied using specially developed sources. It is shown that the most significant damage is induced by Xe line emission (147 nm) in comparison with Ar (106 nm), He (58 nm), and Sn (13.5 nm) emissions. No direct damage was detected for 193 nm emission. Photoabsorption cross-sections and photodissociation quantum yields were derived for four films under study. 147 nm photons penetrate deeply into low-k films due to smaller photoabsorption cross-section and still have sufficient energy to excite Si-O-Si matrix and break Si-CH3 bonds.

Recombination of O and H Atoms on the Surface of Nanoporous Dielectrics

The interaction of O and H atoms with SiOCH nanoporous low-dielectric-constant (low-k) films is studied in the far plasma afterglow in the absence of ion and photon fluxes on the surface. The loss probabilities of O and H atoms are directly measured by plasma-induced actinometry. Modification of low-k films during the experimental scans was studied by the Fourier transform infrared spectroscopy technique. The model of O- and H-atom recombination in nanoporous materials was developed to analyze the experimental data. It is shown that the main mechanism of the O and H loss is their surface recombination. The consumption of these atoms in the reactions with the carbon-containing hydrophobic groups has a minimal contribution. Thus, the surface recombination defines a damage depth in low-k films. It was shown that the oxygen atoms lead to the noticeable removal of CH3 groups. On the contrary, hydrogen atoms do not break Si-CH3 bonds, allowing the avoidance of plasma damage in the case of the hydrogen-plasma-based resist strip in appropriate conditions.

Discharge singlet oxygen generator for oxygen–iodine laser: I. Experiments with rf discharges at 13.56 and 81 MHz

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%.

Discharge singlet oxygen generator for oxygen–iodine laser: II. Two-dimensional modelling of flow oxygen rf plasma at 13.56 and 81 MHz power frequency

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.

Surface recombination of oxygen atoms in O 2 plasma at increased pressure: I. The recombination probability and phenomenological model of surface processes

This work deals with the study of oxygen atom loss on a quartz surface in a glow discharge plasma in pure O2 at increased pressures (5?50?Torr). O atom loss probabilities are obtained from the radial distributions of oxygen dissociation degree measured by the actinometry method. It is shown that the applicability of the actinometry method at high pressures requires the knowledge of the spatial distribution of a reduced electric field for the correct calculation of the electronic excitation rates of oxygen and actinometer atoms. The analysis of the obtained data within the framework of a simple phenomenological model of the surface processes revealed that O atom surface recombination with physisorbed oxygen atoms and molecules (producing O2 and O3, respectively) is the main loss channel for oxygen atoms in O2 plasmas at increased pressures. The oxygen atom loss probability can noticeably grow in comparison with the case of low pressure due to the essential increase in the surface occupation degree by physisorbed atoms and molecules.

Surface recombination of oxygen atoms in O 2 plasma at increased pressure: II. Vibrational temperature and surface production of ozone

Ozone production in an oxygen glow discharge in a quartz tube was studied in the pressure range of 10?50?Torr. The O3 density distribution along the tube diameter was measured by UV absorption spectroscopy, and ozone vibrational temperature TV was found comparing the calculated ab initio absorption spectra with the experimental ones. It has been shown that the O3 production mainly occurs on a tube surface whereas ozone is lost in the tube centre where in contrast the electron and oxygen atom densities are maximal. Two models were used to analyse the obtained results. The first one is a kinetic 1D model for the processes occurring near the tube walls with the participation of the main particles: O(3P), O2, O2(1?g) and O3 molecules in different vibrational states. The agreement of O3 and O(3P) density profiles and TV calculated in the model with observed ones was reached by varying the single model parameter?ozone production probability on the quartz tube surface on the assumption that O3 production occurs mainly in the surface recombination of physisorbed O(3P) and O2. The phenomenological model of the surface processes with the participation of oxygen atoms and molecules including singlet oxygen molecules was also considered to analyse data obtained in the kinetic model. A good agreement between the experimental data and the data of both models?the kinetic 1D model and the phenomenological surface model?was obtained in the full range of the studied conditions that allowed consideration of the ozone surface production mechanism in more detail. The important role of singlet oxygen in ozone surface production was shown. The O3 surface production rate directly depends on the density of physisorbed oxygen atoms and molecules and can be high with increasing pressure and energy inputted into plasma while simultaneously keeping the surface temperature low enough. Using the special discharge cell design, such an approach opens up the possibility to develop compact ozonizers having high ozone yield at the low energy cost of O ? O3 conversion.

Removal of amorphous C and Sn on Mo:Si multilayer mirror surface in Hydrogen plasma and afterglow

Removal of amorphous carbon and tin films from a Mo:Si multilayer mirror surface in a hydrogen plasma and its afterglow is investigated. In the afterglow, the mechanism of Sn and C films removal is solely driven by hydrogen atoms (radicals). Probabilities of Sn and C atoms removal by H atoms were measured. It was shown that the radical mechanism is also dominant for Sn atoms removal in the hydrogen plasma because of the low ion energy and flux. Unlike for Sn, the removal mechanism for C atoms in the plasma is ion-stimulated and provides a much higher removal rate.