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 & 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
Continuum – Rarefied Flow
Transition Prediction
Temperature in the arc: 12000 K
Pressure in the arc: 0.2 Bar
Vessel pressure: 100 Pa
Temperature in the arc: 12000 K
Pressure in the arc: 0.2 Bar
Vessel pressure: 10 Pa
The Hybrid CFD/DSMC Technique
When Kn > 0.05
Navier-Stokes equations are no
longher valid
A combined CFD/DSMC Technique is
needed:
- Kn < 0.05 => CFD solver
When Kn < 0.05
Time & memory expences of DSMC
are inadmissible
- Kn > 0.05 => DSMC
The Coupling Method
I Stage: Predict
II Stage: Solve
Boundary conditions
time: ti
CFD
Dtcoupling
time: ti+1
Solution Update
DSMC
CFD
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
1-D Simulation
T= 12000 K
P= 2000 Pa
V= 0 m/s
Ar
L
x
T= 2000 K
P= 100Pa
V= 0 m/s
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?