Database Needs for Modeling and Simulation of Plasma Processing (1996)
Chapter: FINDINGS
Visit
NAP.edu/10766
to get more information about this book, to buy it in print, or to
download it as a free PDF.
Previous Chapter:
New Diagnostic Techniques
Next Chapter: REFERENCES
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.
|
BOX 3.1 Reflection/absorption Multiple internal reflection Emission Ellipsometry Reflectance difference Photoluminescence Optogalvanic spectroscopy Surface electromagnetic waves Second harmonic generation Photoacoustic absorption Photothermal deflection Photothermal displacement Laser desorption and product analysis by mass spectrometry or spectroscopy |
- challenge and even raises the question of whether this methodology is practicable. In situ fiber-coupled ellipsometry monitoring has been accomplished by Tachibana et al.36
- A recent technique that might be applied on-line is surface desorption spectrometry, where the spectrometry may be mass spectrometry or laser-reduced fluorescence spectrometry. The former technique has been used with reflected molecular beams to characterize surface reactions at different surface temperatures and materials in molecular beam epitaxy; recently the output of the mass spectrometer has been applied in the control loop replacing the signal from the oven temperature. Remarkable improvements have been obtained in the quality of multiple quantum wells manufactured in this way. A recent study37 employed a laser to desorb SiClx from the surface of a silicon wafer being etched in a high-plasma-density, low-pressure Cl2 helical 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.
- 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.
- 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
- 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.
- 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.
- 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.
Subscribe to Email from the National Academies
Keep up with all of the activities, publications, and events by subscribing to free updates by email.