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Multi-scale modeling of molecular phenomena in plasma-assisted thin film deposition Ing. G.Abbate Prof.Dr.Ir. C.R.Kleijn Prof.Dr. B.J.Thijsse

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Outline Introduction & Background CFD Simulation & Continuum-Rarefied Transition Prediction The Hybrid CFD/DSMC Technique The Coupling Method BC to DSMC domain on the CFD/DSMC interface Results: The Shock Tube Problem Results Analysis Conclusions & Remarks Further Developments

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Introduction & Background The plasma-assisted thin film deposition processes are of great interest in micro-electronics, coating technology and manufacture of LDC A thermal plasma is generated at relatively high pressure (0.1-0.5 bar) The jet expands in a vacuum chamber (10 -100 Pa) Particles mean free path lenght increases Gas flow regime changes from Continuum to rarefied

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Continuum – Rarefied Flow Transition Prediction Temperature in the arc: 12000 K Pressure in the arc: 0.2 Bar Vessel pressure: 10 Pa Temperature in the arc: 12000 K Pressure in the arc: 0.2 Bar Vessel pressure: 100 Pa

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The Hybrid CFD/DSMC Technique When Kn > 0.05 Navier-Stokes equations are no longher valid When Kn < 0.05 Time & memory expences of DSMC are inadmissible A combined CFD/DSMC Technique is needed: - Kn CFD solver - Kn > 0.05 => DSMC

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The Coupling Method I Stage: PredictII Stage: Solve time: t i time: t i+1 CFD t coupling DSMCCFD Boundary conditions Solution Update

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BC to the DSMC domain on the CFD/DSMC interface Between CFD and DSMC regions an overlapping is considered On both Dirichelet BC coming from the other region are imposed Out of the overlappping region a “buffer cell” is considered where particles are genereted according to hydrodynamic values evaluated by the CFD solver Particles are convected during a DSMC time step Particles remaining in the buffer and particles leaveng the DSMC domain are deleted Particles entering the DSMC domain are incorporated in the DSMC algorithm

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Results: The Shock Tube Problem T= 12000 K P= 2000 Pa V= 0 m/s T= 2000 K P= 100Pa V= 0 m/s x L Ar 1-D Simulation

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Results Analysis: The Overlap Size The method does not depend on the overlap region size for an asymmetric overlap Instability effects can appear using a symmetric overlap

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Results Analysis: The Coupling Time Step The method does not depend on the coupling time step Instability effects can appear using a too long coupling time step

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Results Analysis: Number of Repeated Runs for the Ensamble Average The method does not depend on the number of repeated runs for the ensemble average

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Conclusions & Remarks A preliminary simulation of the flow field using the commercial code FLUENT have been run to predict Continuum-rarefied transition An adaptive hybrid CFD/DSMC method has been developed and applied to a shock tube problem to show the potential of the method to predict the flow field even where a CFD solver fails and much faster than a DSMC simulation An analysis of the results showd that the method is not dependent on the coupling time step, the number of DSMC runs for ensemble average and on the overlap region width asymmetric overlap If too big coupling time steps or a symmetric overlap are used instability effects can appear

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Furhter Developments Extension of the code to 2-D and 2-D axisymmetric flows Extension of the code to reacting flows (also dissociations & ionizations will be taken into account to simulate a plasma flow) Coupling gas flow simulations to molecular simulations of film growth Application of the code to the Plasma-assisted thin film deposition

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