Models/modeling plasma processing

Thus, making use of modern methods of theoretical atomic spectroscopy and available computer programs, one is in a position to fulfill more or less accurate purely theoretical (ab initio) or semi-empirical calculations of the energy spectra, transition probabilities and of the other spectroscopic characteristics, in principle, of any atom or ion of the Periodical Table, their isoelectronic sequences, revealing in this way their structure and properties, to model the processes in low- and high-temperature plasma. Such calculations could be done prior to the corresponding experimental measurements, instead of them, or after them to help to interpret the interesting phenomena found in experimental studies. 

Additional growth considerations, as well as process modeling and plasma diagnostics underlying plasma-enhanced CVD are further discussed by Hess and Graves in Chapter 8, which is specifically devoted to plasma processing. 

Graves, D. B., Kushner, M. X, Gallagher, X W, Garscadden, A., Oehrlein, G. S., and Phelps, A. V, Database Needs for Modeling and Simulation of Plasma Processing. National Research Council, Panel on Database Needs in Plasma Processing, National Academy Press, Washington, DC, 1996. 

The development of a qualified down-scale model of a process module is integral to the approach of process validation using bench-scale experiments, as described earlier. We have developed down-scale models of process steps ranging from various types of process chromatography for protein purification to separation by precipitation and filtration. These down-scale models have been utilized to evaluate the effects of relevant process parameters on product-quality attributes. The normal logical sequence of process development, of course, is bench scale to pilot scale to full scale. However, for many plasma protein purification processes, a reverse order needs to be followed. As licensed full-scale processes already exist, the full-scale process steps need to be scaled down to construct small process models in order to evaluate the robustness of process parameters on the product without impacting full-scale production. These models can also be utilized to evaluate process changes, improvements, and optimizations easily and economically. 

Plasma processing reactors normally operate with the wafer biased at radio frequencies, typically in the range 0.1 to 13.56 MHz. Even if the ions injected at the sheath edge were monoenergetic, an lED would result in an RF (time-dependent) sheath, even in the absence of collisions. The literature on RF sheaths is voluminous. Both fluid [170-175] and kinetic (e.g., Monte Carlo) [176-180] simulations have been reported. One of the most important results of such simulations is the lED. The ion angular distribution (IAD) [74, 75] and sheath impedance (for use in equivalent circuit models) [32] are also of importance. 

D. P. Lymberopoulos, Modeling and Multidimensional Simulation of Plasma Processing Reactors, Ph.D. Thesis, University of Houston (1995). 

---