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1Challenge the future
To do list.add extra slide about the coupling, at pressure level.Burn CD
2Challenge the future
Wafer transport and gas separation in a contact-less Spatial Atomic Layer Deposition track.
Candidate: Gonzalo Ramirez Troxler
Committee: Dr. ir. R.A.J van OstayenDr. E.H.A GrannemanProf.ir. R. Munnig SchmidtDr. R. Delfos
3Challenge the future
Outline• Introduction and motivation
• Solar Cells Market and challenges.
• Solar cells, recombination velocity and passivation.
• Atomic Layer Deposition• Levitrack System
• Working principle
• Thesis goals: fine tuning stage.• Modelling
• Thin Film Flow
• Concentration of Species• Results
• CFD model
• Prototype system to measure position of wafer• Conclusions and recommendations
4Challenge the future
IntroductionSolar Cells Market
• 1,600% growth of MW installed last decade.
• Resources depletion.
• Ecological impact.
Outlook
5Challenge the future
Introduction
Challenge: To position Solar Cells as a major actor in the power generation scenario.
Cost Reduction and Increase efficiency.
Motivation
Surface Passivation using aluminium oxide - Al2O3
6Challenge the future
Introduction
Levitrack: • Contact-less transportation track• Substrates levitate and layers of Al2O3 are deposited
(ALD).• High Throughput.• Low cost of construction.
LEVITECH and LEVITRACK
Levitech BV is a Dutch based company that develops novel solutions for the IC and Solar Cells Industry. Spin-off of ASM International.
7Challenge the future
IntroductionSolar cell and passivation
With silver print all rear fingers are short-circuitedand no light is transmitted though the back
With silver print all rear fingers are short-circuitedand no light is transmitted though the back
Front
Rear
Ag contacts
n++
ARC SiNx
Al lines
4444
p-Si
Al2O3
p++Al-BSF
Front Rear
Back-sheet foil
Surface Passivation increase efficiency of solar cell:
• Increase lifetime of charge carriers.
8Challenge the future
IntroductionAtomic Layer Deposition (ALD)
Initial surface
9Challenge the future
IntroductionAtomic Layer Deposition (ALD)
TMA reacts with hydroxyl groups
10Challenge the future
IntroductionAtomic Layer Deposition (ALD)
TMA saturates surface.
11Challenge the future
IntroductionAtomic Layer Deposition (ALD)
Purge using N2.
12Challenge the future
IntroductionAtomic Layer Deposition (ALD)
H2O reacts with methyl groups and Al.
13Challenge the future
IntroductionAtomic Layer Deposition (ALD)
H2O saturates the surface forming Al2O3.
14Challenge the future
IntroductionAtomic Layer Deposition (ALD)
Purge using N2.
15Challenge the future
IntroductionSpatial Atomic Layer Deposition (1)
Single Reactor
Spatial ALD N2
TMA
H2O
16Challenge the future
IntroductionSpatial Atomic Layer Deposition (2)
Single Reactor 12 meter Spatial ALD
Track
Layer height: 10 nm
Time: 5 min Time: 5
min
X 5
17Challenge the future
LEVITRACKWorking principle (1)
18Challenge the future
LEVITRACKWorking principle (2)
0.5 mm
19Challenge the future
LEVITRACKWorking principle (3)
156 mm
156 mm
20Challenge the future
LEVITRACKWorking principle (4)
21Challenge the future
LEVITRACKThesis goal: fine tuning stage.
The aim of this thesis is to study and improve this 4-m test setup, in order to demonstrate stable transport, while minimizing the
mixing of precursor gases.
• Stable transport: no damage on wafers.
• Mixing of precursors: TMA and H2O need to be always separated on space.
22Challenge the future
Modelling
• Multiphysics• Fluid Flow• Concentration of species• Surface Chemistry• Heat transport• Structural mechanics
CFD Model
23Challenge the future
ModellingThin film flow (1)
Navier-Stokes equations + Continuity equation.
Reynolds’ equation
Unknowns: 3 velocities and pressure.
Unknown: pressure
Assumptions:• Lubricant isoviscous.• Low Reynolds number. (Negligible
Inertia force)• Negligible body forces.
24Challenge the future
Modelling
• Height average velocity.• N2-O2 model.• Stationary.
Concentration of species
Thin Film Flow
Concentration of Species.
One way coupling.
25Challenge the future
Results and discussionCFD Model (1)
OutVolume
Top VolumeGap
Bottom VolumeGap
Exhaust
26Challenge the future
Results and discussionFlat surface track: benchmark
Mixing requirement not fulfilled.
Flat surface
27Challenge the future
Results and discussionFlat surface track: improvement to geometry
100% groove
70% groove
28Challenge the future
Results and discussion100% grooves
Mixing requirement fulfilled.
100% grooves
.
29Challenge the future
Results and discussion100% grooves: Flying height
30Challenge the future
Results and discussion70% grooves
Mixing requirement not fulfilled.
Fh = 140 μm
70% grooves
.
31Challenge the future
Results and discussionFlat surface vs. 100% grooves
32Challenge the future
Results and discussionFlat surface vs. 70% grooves
33Challenge the future
Results and discussionGrooved surface track (5)
No Groove
70% Groove 100% Groove
Mixing Requirement
34Challenge the future
LEVITRACKThesis goal: fine tuning stage.
The aim of this thesis is to study and improve this 4-m test setup, in order to demonstrate stable transport, while minimizing the
mixing of precursor gases.
35Challenge the future
Results and discussion
• Design system to measure separation of the of the wafer to the lateral wall.
Lateral gap measurement system (1)
36Challenge the future
Results and discussionLateral gap measurement system (2)
37Challenge the future
Conclusions and recommendations
It was developed:
• Fast and accurate enough CFD model to predict the pressure profile and spread of precursors inside the track.• As reference 3d NS model takes 2 day per model, while
the thin film flow model 10-20 minutes.
• System to measure the lateral gap.• Submitted to be patented.
It was found:
• Alternative geometry, which fulfils the mixing requirement.
Conclusions
38Challenge the future
Conclusions and recommendations
• Include dynamics of the wafer in the model.
• Implement and study lateral stability with proposed measurement system.
• Integration of the deposition process to the model.
Recommendations
39Challenge the future
40Challenge the future
Back Up slides
41Challenge the future
Back up slidesSolar cell and passivation (1)
+
-
+ ++ ++ + ++ +
----- ----
1.- N-type and P-type junction together.2.- Creation of the depletion region.3.- Light adsorbed by the silicon.4.- Creation of electron-holes pairs.
-
+5.- Hole->p-type. Electron->n-type Electron-hole pair tries to recombine.6.-Electrones conducted.
42Challenge the future
P1 systemWorking principle (4)
43Challenge the future
Modelling Analytical model
• A negative pressure difference decrease the wafer velocity.
• 0.1 mbar 20% reduction of expected velocity.
• Analytical model developed in Levitech.
• Simple approach.
44Challenge the future
Model ValidationModel validation (1)
7 mbar
3 mbar
5 mbar
10 mbar
45Challenge the future
Model ValidationModel validation (2)
1 8 10 12 30
• Velocity: 0 [m/s]:• Row 8: in front of the
wafer.
• Row 10: on the edge of the wafer.
• Row 12: Below the wafer.
46Challenge the future
Model ValidationModel validation (3)
47Challenge the future
Results and discussion
• Channel effect.• Load asymmetry
• Variation of the flying height (100μm).
• Reduce transportation velocity.• Needs to be further studied in the
functional prototype.
Summary of grooved geometry
48Challenge the future
Results and discussionLateral gap measurement system (3)