The Materials Processing Group has ongoing tasks that involve model and code development for the study of plasma reactors used in semiconductor processing. The ultimate goal is the development of a virtual reactor. The main thrust of this research is in the development of the Semiconductor Equipment Modeling Software (SEMS) code, a continuum Navier-Stokes solver. It is important to note that high-density plasma reactors operate at pressures on the order of 0.1 to 10 mTorr where rarefaction can be significant to the degree that the constitutive relations used in continuum fluid dynamics (CFD) techniques become invalid. A usefulalternative is the more accurate but more expensive direct simulation Monte Carlo method (DSMC) designed for such low gas pressure flowfields. Research is underway to develop a parallel plasma version of the DSMC method. This tool will then be used for benchmarking the SEMS code being developed concurrently and for the investigation of critical plasma processes in semiconductor manufacturing.
As an adjunct to this work, DSMC simulations of non-plasma applications of interest to the semiconductor industry and/or NASA are being conducted. One such project involved a collaborative effort with Motorola, Inc. to characterize the rarefied flow through showerheads by deriving pressure drop versus velocity correlations that can then be used to provide accurate inlet conditions for reactor scale simulations where the showerhead is approximated as a porous medium. Other applications such as ion thrusters are being considered.
Finally, work is underway to validate the SEMS code through comparison to experiment of various reactive mixtures. Part of this research involves the study of electronegative CF4 plasmas. In the process of simulating the flowfields in a GEC (Gaseous Electronics Conference) reference cell and comparing to in-house experimental Langmuir probe measurements, the importance of modeling of gas heating through exothermic reactions became apparent. Further model validation is underway. The link to the SEMS simulations page displays some of the results obtained for CF4 and other gases.
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