Yu. A. Mankelevich

Microcrystalline, nanocrystalline, and ultrananocrystalline diamond chemical vapor deposition: Experiment and modeling of the factors controlling growth rate, nucleation, and crystal size

Ar∕CH4∕H2 gas mixtures have been used to deposit microcrystalline diamond, nanocrystalline diamond, and ultrananocrystalline diamond films using hot filament chemical vapor deposition. A three-dimensional computer model was used to calculate the gas phase composition for the experimental conditions at all positions within the reactor. Using the experimental and calculated data, we show that the observed film morphology, growth rate, and across-sample uniformity can be rationalized using a model based on competition between H atoms, CH3 radicals, and other C1 radical species reacting with dangling bonds on the surface. Proposed formulas for growth rate and average crystal size are tested on both our own and published experimental data for Ar∕CH4∕H2 and conventional 1% CH4∕H2 mixtures, respectively.

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.

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.

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%.

Measurement and modeling of Ar∕H2∕CH4 arc jet discharge chemical vapor deposition reactors II: Modeling of the spatial dependence of expanded plasma parameters and species number densities

Detailed methodology and results are presented for a two-dimensional (r,z) computer model applicable to dc arc jet reactors operating on argon/hydrogen/hydrocarbon gas mixtures and used for chemical vapor deposition of micro- and nanocrystalline diamond and diamondlike carbon films. The model incorporates gas activation, expansion into the low pressure reactor chamber, and the chemistry of the neutral and charged species. It predicts the spatial variation of temperature, flow velocities and number densities of 25 neutral and 14 charged species, and the dependence of these parameters on the operating conditions of the reactor such as flows of H2 and CH4 and input power. Selected outcomes of the model are compared with experimental data in the accompanying paper [C. J. Rennick et al., J. Appl. Phys. 102, 063309 (2007)]. Two-dimensional spatial maps of the number densities of key radical and molecular species in the reactor, derived from the model, provide a summary of the complicated chemical processing tha...

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.

Coagulation of dust grains in the plasma of an RF discharge in argon

Results are presented from experimental studies of coagulation of dust grains of different sizes injected into a low-temperature plasma of an RF discharge in argon. A theoretical model describing the formation of dust clusters in a low-temperature plasma is developed and applied to interpret the results of experiments on the coagulation of dust grains having large negative charges. The grain size at which coagulation under the given plasma conditions is possible is estimated using the developed theory. The theoretical results are compared with the experimental data.

Dust particle coagulation mechanism in low-pressure plasma: rapid growth and saturation stage modeling

Developed polarization-induced ion flow asymmetry (PIFA) mechanism of dust particle coagulation in a low-pressure, low-temperature plasma is used for simulation of experimentally observed coagulation dynamics. The PIFA mechanism provides a new self-consistent description of basic coagulation stages and phenomena: threshold start, rapid growth and saturation phase. The derived analytical expressions for the cross-sections of two negatively charged particle interactions in low-temperature plasma show that coagulation rate coefficients can exceed gas kinetic coefficients by ten times, in agreement with experimental measurements of particle growth rates. Using the PIFA mechanism we have numerically simulated the clustering process for real experimental conditions and studied the effects of plasma parameters on particle size distributions. Calculated results are in good agreement with experimentally observed coagulation trends and peculiarities.

Interaction of F atoms with SiOCH ultra low-k films. Part II: etching

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.

Measurement and modeling of Ar∕H2∕CH4 arc jet discharge chemical vapor deposition reactors. I. Intercomparison of derived spatial variations of H atom, C2, and CH radical densities

Comparisons are drawn between spatially resolved absorption spectroscopy data obtained for a 6.4kW dc arc jet reactor, operating with Ar∕H2∕CH4 gas mixtures, used for deposition of thin, polycrystalline diamond films, and the results of a two-dimensional (r,z) computer model incorporating gas activation, expansion into the low pressure reactor, and the chemistry of the neutral and charged species. The experimental measurements, using either cavity ring-down spectroscopy or diode laser absorption spectroscopy, determined absolute number densities of H(n=2) atoms, and column densities of C2(aΠu3), C2(XΣg+1), and CH(XΠ2) radicals, with vibrational and rotational quantum state resolutions, and their variation with height through the horizontally propagating arc jet plume. Spectra were also analyzed to obtain temperatures and local electron densities [from Stark broadening of H(n=2) absorption lines]. The experimental data are directly compared with the output data of the model that returns spatially inhomogen...