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Suggested Citation:"CONCLUSIONS." National Research Council. 1996. Database Needs for Modeling and Simulation of Plasma Processing. Washington, DC: The National Academies Press. doi: 10.17226/5434.
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EXECUTIVE SUMMARY 2 3. Models of low-temperature, nonequilibrium plasmas, especially for the description of physical phenomena, have developed rapidly in the last 5 years. Computing power per unit cost continues to increase rapidly. However, few of the currently available plasma models can be easily used by process engineers. Although attempts have been made to model plasmas with realistic chemistries, the parameter space that can be addressed is limited. Only a handful of studies have been made that attempt to validate models of plasma processes with industrially relevant chemistries. Models that attempt to link the relevant length scales (from tool scale to feature scale to atomic scale) are just now emerging. Simulations can be no more accurate than the data and assumptions on which they are based. The lack of fundamental data for the most important chemical species is the single largest factor limiting the successful application of models to problems of industrial interest. 4. Heterogeneous (surface) processes are at the heart of plasma materials processing technology, but are in many cases much less well understood than are gas phase processes. Numerous etching and deposition profile evolution simulations are used in industry. These simulations generally use empirically derived rate coefficients that must be refit to experimental data whenever conditions change. Experimental diagnostics and modeling of plasma-surface processes based on first principles are rudimentary and require much development. Surfaces exposed to plasmas are often strongly modified by intense ion, photon, and radical species bombardment. Therefore, not only are the chemical and physical processes themselves strongly perturbed by plasma exposure, but in addition, the surfaces upon which the processes take place are unconventional in their structure and composition. 5. Electron collision cross section data are second only to data on heterogeneous processes in their importance to plasma processing. These data are sketchy at best for most species of interest, although some key species, such as SiH4 and CF4, have received considerable attention. Little information is available for dissociation products or for species in excited states. Recent progress in computational methods based on quantum scattering offers the possibility that the costly and time-consuming experiments may be augmented or even replaced by large-scale computation. 6. There now exists a wealth of sensitive radiative and laser-based techniques that permit species concentration and temperature measurements in processing plasmas. All spectroscopic diagnostic techniques depend on a database of atomic and molecular parameters. A comprehensive spectroscopic database is important to enabling unambiguous identification of a particular species in the plasma or on the surface. Spectroscopic measurements are usually the first step in measuring a rate coefficient or in testing a model prediction. The spectroscopic database therefore serves a dual role to provide both qualitative and quantitative information. Although the spectroscopic database is far from complete, especially for surface species, data are available in the literature that are relevant to plasma processing. However, these data are scattered throughout the technical and scientific literature, and in some cases their accuracy is in doubt. The ready availability and ease of spectroscopic database manipulation and storage will stimulate the development of new diagnostic techniques and the wider application of existing methods. 7. The database for ion-molecule and neutral-neutral chemistry varies considerably. For some species and reactions, the data are good. This is especially true for the cases in which there is overlap with processes occurring in the upper atmosphere or in some cases in chemical vapor deposition processes. In other cases, however, most notably for etching processes, there are few data available. 8. Thermochemical data are sketchy for many species of interest in plasma processing. These data are important in helping to establish boundaries for reaction pathways and for estimating reaction rate coefficients. Techniques, both experimental and computational, are generally available to obtain these quantities, but few efforts are under way at present to meet these needs. CONCLUSIONS 1. The major potential benefits of plasma modeling for chip manufacturers are better control over plasma processes, minimization of resources that would otherwise be devoted to optimizing plasma

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In spite of its high cost and technical importance, plasma equipment is still largely designed empirically, with little help from computer simulation. Plasma process control is rudimentary. Optimization of plasma reactor operation, including adjustments to deal with increasingly stringent controls on plant emissions, is performed predominantly by trial and error. There is now a strong and growing economic incentive to improve on the traditional methods of plasma reactor and process design, optimization, and control. An obvious strategy for both chip manufacturers and plasma equipment suppliers is to employ large-scale modeling and simulation. The major roadblock to further development of this promising strategy is the lack of a database for the many physical and chemical processes that occur in the plasma. The data that are currently available are often scattered throughout the scientific literature, and assessments of their reliability are usually unavailable.

Database Needs for Modeling and Simulation of Plasma Processing identifies strategies to add data to the existing database, to improve access to the database, and to assess the reliability of the available data. In addition to identifying the most important needs, this report assesses the experimental and theoretical/computational techniques that can be used, or must be developed, in order to begin to satisfy these needs.

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