A hybrid fluid dynamic/kinetic model is presented which describes the sheath and the presheath regions of dc or rf driven low pressure gas discharges in a realistic and self-consistent way. The model assumes an infinite extended sheath parallel to the electrode, allowing a one-dimensional spatial description. It provides for the presence of multiple positive ion species and their collisional interactions with the neutral background, and takes into account the possibility of a nonharmonic modulation of the sheath potential and the application of an external dc bias; in this work, the model is applied to a two-species capacitively coupled argon and oxygen plasma. The input required by the model consists of the fluxes of the incoming ions, of the modulating current, and of the pressure, the composition, and the temperature of the background gas. On output, the model provides the values of the electric field and of the particle densities within the sheath and the presheath, the total voltage drop across the sheath, and also the energetically and angularly resolved distributions of the positive ions and the energetic neutrals which impinge the material substrate at the boundary. In general, the model is able to treat dc discharges as well as capacitively and/or inductively coupled rf discharges, it thus covers most of the plasmas used in very large scale integration microelectronics manufacturing and other surface modification techniques. Using the model, studies of the energy distributions of the incoming ions have been performed for a wide range of parameters, and the effects of varying process conditions have been investigated. At low and intermediate pressures (p<50 mTorr), the distribution functions of rf driven discharges exhibit a characteristic bimodal structure; this structure disappears with increasing pressure as ion-neutral collisions become significant. A comparison of calculated ion energy distributions with experimental measurements on capacitively coupled argon and oxygen discharges shows excellent quantitative agreement. In addition to the ion energy distribution, the angular distributions of the incident ions at various energies are also discussed as a function of the neutral gas pressure. It turns out that the details of the angular distribution not only depend on the field structure of the sheath itself but also on that of the presheath. The results of the presented model are therefore more reliable than those of previous models which restricted themselves to the sheath region. This high physical accuracy of the presented model, together with its flexibility and its high execution speed, allows its use as a tool for technology-oriented computer-aided design in the microelectronics industry.

In very large scale integrated microelectronics fabrication magnetically enhanced reactive ion etch (MERIE) reactors are established for many dry etch processes of conducting or dielectric materials. Angularly and energetically resolved distributions of the surfaces incident particles (ions and neutrals) as well as the fluxes of ions and neutrals play an essential role for feature scale profile evolution. The focus of this work is set on the calculation of the neutral to ion fluxes ratio. Therefore the MERIE reactor’s boundary sheath is simulated by the technology-oriented computer aided design simulation tool hybrid plasma sheath model (HPSM). HPSM consists of a self-consistent coupling of a fluid dynamical part to a Monte Carlo part. The sheath and presheath regions are described in one unified model. Energetic neutrals impinging the surface can be monitored in addition to the positive ion species. Simulations with parameters in the range of about 100 mTorr, rf voltages of a few 100 V, magnetic fields of about 90 G, and plasma powers of about 1000 W are presented. The simulations show that the flux of the energetic neutrals compared to the flux of the ions is not neglectable and that the neutral flux makes an important contribution to the energy budget of the surface impinging particles.

An approach is presented which allows to predict important characteristics of plasma based surface modi®cation techniques like reactive ion etching (RIE), plasma etching (PE), ionized metal vapor deposition (IPVD), or plasma enhanced physical vapor deposition (PECVD). In a ®rst step, the electrical ®eld in the vicinity of the substrate is calculated by means of a self-consistent plasma boundary sheath model. In a second step, this ®eld is used to calculate the energy and angular distribution of the ions impinging the surface. The knowledge of this distribution allows a more realistic prediction of essential process properties like the maximum aspect ratio of an etch process, or the obtainable conformality of a deposition step.

We investigate the reactive ion etching of amorphous silicon by halides using a hierarchy of models on different time and length scales. The feature evolution is modeled using a two- dimensional cell based Monte-Carlo feature scale simulator. The fluxes, the energy distributions, and the angular distributions of the wafer-incident particles are provided by a hybrid plasma sheath simulator. The relevant surface reaction rates are calculated by a molecular dynamics simulator using a Stillinger-Weber representation of the interatomic potential. Our investigations show that the surface reaction rates are strongly determined by the particular surface morpho- logy, which, in turn, is strongly influenced by the kinetic properties of the impinging particles. Thus, we link the molecular dynamics simulator into the model as a whole.As results, we present calculations for the etching of amorphous silicon by fluorine, chlorine, and bromine. A Stillinger-Weber representation of the bromine and the silicon-bromine potential which was not yet available in literature is additionally developed. We discuss the different morphologies of halogenated silicon surfaces as a consequence of the energy distri- bution and the angular distribution of the impinging particles. Comparisons of the sputter yield functions of bare amorphous silicon surfaces and corresponding halogenated surfaces exhibit considerable differences, qualitative as well as quantitative.

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