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Suggested Citation:"FINDINGS." National Research Council. 1996. Database Needs for Modeling and Simulation of Plasma Processing. Washington, DC: The National Academies Press. doi: 10.17226/5434.
Page 28

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28 DATABASE NEEDS FOR MODELING AND SIMULATION OF PLASMA PROCESSING challenge and even raises the question of whether this methodology is practicable. In situ fiber-coupled ellipsometry BOX3.l 36 monitoring has been accomplished by Tachibana et al. Radiative Surface Diagnostic Methods 4. A recent technique that might be applied on-line is Reflection/absorption surface desorption spectrometry, where the spectrometry may Multiple internal reflection be mass spectrometry or laser-induced .fluorescence Emission spectrometry. The former technique has been used with Ellipsometry reflected molecular beams to characterize surface reactions at Reflectance difference different surface temperatures and materials in molecular Photoluminescence beam epitaxy; recently the output of the mass spectrometer Optogalvanic spectroscopy Surface electromagnetic waves has been applied in the control loop replacing the signal from Second harmonic generation the oven temperature. Remarkable improvements have been Photoacoustic absorption obtained in the quality of multiple quantum wells Photothermal deflection manufactured in this way. A recent study37 employed a laser Photothermal displacement to desorb SiClx from the surface of a silicon wafer being Laser desorption and product analysis by etched in a high-plasma-density, low-pressure Ch helical mass spectrometry or spectroscopy resonator plasma. Then laser-induced fluorescence of SiCl in the gas phase was used to monitor the desorbed species. The results that were obtained include estimates of the chlorine content of the SiClx adsorbed layer under plasma etching conditions, and measurements of the thickness of this layer with the plasma reactor parameters. 5. Several other approaches have the potential to contribute to model development and validation in the longer term. Several laboratories are examining the use of in-surface ion energy analyzers, which directly provide the transfer function of the plasma sheath on the ions. Additionally it has been proposed that ion beam techniques such as elastic recoil detection and Rutherford backscattering might be applied in situ to determine surface atom coverage. Careful deconvolution of the results to allow for gas scattering would be required. 6. Use of the new array of methods for surface characterization is expanding rapidly. The atomic force microscope and its derivatives offer supreme precision in surface definition. These techniques will be very useful off-line when combined with surface scattering or radiative measurements. It is unlikely, however, that such methods will soon see on-line or plasma reactor control applications. A summary of the potential surface characterization techniques is given in Box 3 .1 . FINDINGS 1. There now exists a wealth of sensitive radiative and laser-based techniques that permit species concentration and temperature measurements in processing plasmas. Some have high spatial and temporal resolution. However, in most cases considerable effort is required to apply these methods to real reactors, and to thereby realize the full potential of the data they can provide by interactive comparisons with model predictions. 2. All spectroscopic diagnostic techniques depend on a database of atomic and molecular parameters. No technique can begin without a clear understanding of the spectral features observed, and a quantitative answer can sometimes be derived only with the help of one or more system parameters (such as absorption path length or .fluorescence collection efficiency) as well. 3. Some classes of data are more likely to motivate new diagnostic experiments than others. While the preexistence of the basic data needed to quantify an experiment can often be an incentive to carry out that observation, it is necessary to know the best spectral region in which to apply a given spectroscopic diagnostic. Thus, spectral databases are suggested as having particular value in initiating new investigations.

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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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