National Academies Press: OpenBook

Database Needs for Modeling and Simulation of Plasma Processing (1996)

Chapter: Incident Flux and Desorbing Flux Analysis

Suggested Citation:"Incident Flux and Desorbing Flux Analysis." National Research Council. 1996. Database Needs for Modeling and Simulation of Plasma Processing. Washington, DC: The National Academies Press. doi: 10.17226/5434.
Page 34

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HETEROGENEOUS PROCESSES 34 present in the plasma environment are a result of the response of the initial surface to the incident species profile. It is likely that certain specific surfaces may be produced only in the plasma environment. Because of this characteristic it is not possible to draw on databases that were developed for other technological fields, as is possible in the area of electron impact processes, for example. If information is available, e.g. thermochemical data for solids in the 1985 JANAF thermochemical tables,1 its use may be questionable, at least for direct ion-surface interactions, because of departures from thermodynamic equilibrium due to ion bombardment. An important review of the fluorine-silicon system and to a lesser extent of other systems has been published by Winters and Coburn.2 They present their survey as a summary of "the status of this virtually unexplored field of surface chemistry." The fluorine-silicon model system can serve as a prototype of the complexities encountered in plasma-surface chemistry. Not all information available on the important key applications has been reviewed in a similar fashion. Surface processes related to poly-Si etching have at least been studied by several investigators using C12 and HBr gases.3 For SiO2 etching in high-density fluorocarbon plasmas many studies exist, but little surface chemistry work has been performed.4 The surface processes related to silicon dioxide PECVD have been studied by attenuated- total reflectance IR.5 TECHNIQUES FOR IMPROVING THE DATABASE Approach A two-fold experimental approach appears most promising in improving the database in this field. First, detailed measurements on actual plasma processing systems need to be made. Second, controlled investigations of the different surface science aspects of the plasma etching or deposition process need to be made in an ultrahigh- vacuum (UHV) apparatus using well-controlled and well-characterized beams of different plasma species at the relevant energies. These can interact with the substrate one at a time, two at a time, and so on. The measurements performed under each approach are listed in Table 4.1. Measurements On Realistic Plasma Reactors Incident Flux and Desorbing Flux Analysis Regarding the incident flux, we would like to know the identities and energies of species incident on the surface; how these species interact with the surface and with each other; the importance of angular effects; scaling with process parameters; and reaction probabilities.

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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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