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

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

Introduction & BackgroundThe 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

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

The Hybrid CFD/DSMC TechniqueWhen 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 < 0.05 => CFD solver

- Kn > 0.05 => DSMC

The Coupling Method

I Stage: Predict II Stage: Solve

time: ti

time: ti+1

CFD

tcoupling DSMC CFD

Boundary conditions

Solution Update

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

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

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

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

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

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

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

Questions?