A surface model was developed for diamondlike-carbon film deposition, and was connected in a self-consistent way with a one-dimensional plasma chemistry and physics model for a CH4 radio-frequency (rf) discharge. The surface model considers the adsorption of multiple species (CH3, CH2, and H), and solves for the surface coverage of each species. Comparison is also done with a one-adsorbed-species model. Deposition is assumed to take place via direct ion incorporation, and ion-induced stitching of adsorbed neutrals; film removal takes place via etching and sputtering. The effects of ion flux/energy and surface temperature are examined in detail: At high ion energies direct ion incorporation dominates, in spite of competition with sputtering; at intermediate energies stitching prevails, while for lower ion energies etching can become largest. Mass balances are written at the surface–gas interface, permitting the determination of the effective sticking coefficients of the reacting neutrals. The sticking coefficients calculated from the surface model are fed back into the gas-phase chemistry model to recalculate the neutral densities. The process is repeated until a self-consistent solution is obtained. It is shown that the effective sticking coefficient of a neutral changes drastically from a low value for the plasma-off (or low ion energy) state, to a high value for the plasma-on and high ion energy state, resulting in higher consumption at the surface. The results show that it is imperative for meaningful results to solve surface and gas-phase chemistry models in a self-consistent way, a fact demonstrated by successful comparison with experimental data for the deposition rate and the gas-phase densities.

A combined plasma physics and chemistry simulator is presented and applied for rf methane discharge in the 100 mTorr pressure range. The simulator consists of a self-consistent fluid model for charged species physics, a public-domain Boltzmann equation solver for dc field calculation of the electron energy distribution function (EEDF), and a generalized one-dimensional gas-phase chemistry model. The methane discharge shows an electropositive and capacitive behavior analogous to that of noble gases, with negative ion densities one order of magnitude less than those of electrons. Electron densities and energies compare favorably with literature values of probe measurements. The high-energy tail of the EEDF in methane has fewer electrons than the Druyvensteyn or Maxwell distribution. The chemistry model was applied for four species, namely, CH4, CH3, CH2, and H, and the densities predicted are on the order of 1015, 1012, 1010, 1013 atoms/cm3 respectively, at 140 mTorr. Their density profiles compare favorably with literature experimental data. Detailed analysis of the contribution of each reaction, and sensitivity analysis reveals the major creation and loss pathways for each chemical species.

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A methane discharge fluid model is developed, and subsequently combined with a simple gas-phase chemical kinetics model. The aim is to provide better understanding of the charged species dynamics, and their interaction with the gas-phase kinetics in a CH4 plasma. Swarm data are used as input in the fluid model, which predicts the ion and electron densities, electric fields and ionization rates as a function of space and time in the radio-frequency period. Results show that, due to detachment, the negative ion density in CH4 is of order 10-2 that of electrons; a capacitive discharge behaviour is observed analogous to that of an electropositive gas. The effects of electrode spacing (2-6 cm), gas pressure (80 mTorr to 1 Torr) and radio-frequency current (2.2-3.4 mA cm-2 0.06-0.15 W cm-2) are studied and compared successfully with experimental data. The time-averaged, spatially-resolved electron density and energy, the set of cross sections for CH2 and CH3 dissociation, together with an assumption about the form of the electron energy distribution function, are subsequently used as input in a simplified one-dimensional gas-phase kinetic model. The model predicts the CH2 and CH3 spatial profiles, which compare well with experimental data.

A global model has been developed for low-pressure (3-20 mTorr), radio-frequency (rf) (13.56 MHz) inductively coupled plasmas (ICPs), produced in SF 6 /Ar mixtures. The model is based on a set of mass balance equations for all the species considered, coupled to the discharge power balance equation and the charge neutrality condition. Simulations are used to show the impact of operating conditions, such as the rf power, the pressure and the percentage of argon in the mixture, on the evolution of charged and neutral species. Langmuir probe and optical emission spectroscopy measurements are used to determine the electron temperature and the densities of electrons, ions and atomic fluorine in the SF 6 /Ar ICPs under study. These data are compared with simulation results obtained from the global model. A satisfactory agreement is found between the simulation results and the measured values of the electron density and temperature, for rf powers in the range 900-1700 W, regardless of the percentage of argon in the mixture. Predictions for the atomic fluorine density (∼10 14 cm −3 ) are in good agreement with experiment, for various rf powers.

In order to fabricate the structures with high aspect ratio (depth/width), it is necessary to develop plasma etching processes with a very accurate feature control and improvements in etching rates. We have developed an etching simulator which takes into account the main plasma–surface interactions in a SF6/O2 plasma etching on silicon substrate process. In this article, the role of oxygen on final trench topography and etching rate evolution is discussed. The presented results show that the notion of balance between the passivation regime and the etching processes has great consequences in topographic and kinetic trench characteristics. In particular, a good correlation has been established between the roughness on the trench sidewalls and zones of underpassivation.

A global model has been developed for low-pressure, inductively coupled plasma (ICP) SF6/O2/Ar mixtures. This model is based on a set of mass balance equations for all the considered species, coupled with the discharge power balance equation and the charge neutrality condition. The present study is an extension of the kinetic global model previously developed for SF6/Ar ICP plasma discharges [Lallement et al., Plasma Sources Sci. Technol. 18, 025001 (2009)]. It is focused on the study of the impact of the O2 addition to the SF6/Ar gas mixture on the plasma kinetic properties. The simulation results show that the electron density increases with the %O2, which is due to the decrease of the plasma electronegativity, while the electron temperature is almost constant in our pressure range. The density evolutions of atomic fluorine and oxygen versus %O2 have been analyzed. Those atomic radicals play an important role in the silicon etching process. The atomic fluorine density increases from 0 up to 40% O2 where it reaches a maximum. This is due to the enhancement of the SF6 dissociation processes and the production of fluorine through the reactions between SFx and O. This trend is experimentally confirmed. On the other hand, the simulation results show that O(3p) is the preponderant atomic oxygen. Its density increases with %O2 until reaching a maximum at almost 40% O2. Over this value, its diminution with O2% can be justified by the high increase in the loss frequency of O(3p) by electronic impact in comparison to its production frequency by electronic impact with O2.

Level set approach to simulation of feature profile evolution in a high-density plasma-etching systemThe kinetics of high aspect ratio, anisotropic silicon etching in a SF 6 -O 2 plasma is investigated with a combination of Monte Carlo simulations and inductively coupled plasma etching experiments. The spontaneous reaction of atomic fluorine is dominant at room temperature and Knudsen transport of the radicals is the only limitation in narrow structures. At low temperatures ͑typically between Ϫ125 and Ϫ95°C͒ oxygen passivation becomes effective and anisotropic profiles are obtained because the oxygen passivation can only be removed by the directional ion bombardment. The input parameter settings for the Monte Carlo model are based on measurements with plasma diagnostics. Simulations show that anisotropy is controlled by the oxygen sidewall passivation which depends on the oxygen flux, the oxygen adsorption coefficient, and the aspect ratio. The simulated trench profiles and the aspect ratio dependent etch rate are consistent with the experimental results. Experimentally the etch rate behavior can be tuned from aspect ratio dependent to aspect ratio independent by decreasing the ion flux. This effect can be described well by the recently developed chemically enhanced ion-neutral synergy model. It turns out that aspect ratio independent etching is obtained if the downwards depletion of fluorine radicals due to Knudsen transport is compensated by an increase of the available reaction sites.