1 Challenge the future To do list. add extra slide about the coupling, at pressure level. Burn CD

1Challenge the future

To do list.add extra slide about the coupling, at pressure level.Burn CD


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


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


IntroductionSolar Cells Market

• 1,600% growth of MW installed last decade.

• Resources depletion.

• Ecological impact.

Outlook


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


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.


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.


IntroductionAtomic Layer Deposition (ALD)

Initial surface



TMA reacts with hydroxyl groups



TMA saturates surface.



Purge using N2.



H2O reacts with methyl groups and Al.



H2O saturates the surface forming Al2O3.



Purge using N2.


IntroductionSpatial Atomic Layer Deposition (1)

Single Reactor

Spatial ALD N2

TMA

H2O


IntroductionSpatial Atomic Layer Deposition (2)

Single Reactor 12 meter Spatial ALD

Track

Layer height: 10 nm

Time: 5 min Time: 5

min

X 5


LEVITRACKWorking principle (1)



0.5 mm



156 mm

156 mm




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.


Modelling

• Multiphysics• Fluid Flow• Concentration of species• Surface Chemistry• Heat transport• Structural mechanics

CFD Model


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.


Modelling

• Height average velocity.• N2-O2 model.• Stationary.

Concentration of species

Thin Film Flow

Concentration of Species.

One way coupling.


Results and discussionCFD Model (1)

OutVolume

Top VolumeGap

Bottom VolumeGap

Exhaust


Results and discussionFlat surface track: benchmark

Mixing requirement not fulfilled.

Flat surface


Results and discussionFlat surface track: improvement to geometry

100% groove

70% groove


Results and discussion100% grooves

Mixing requirement fulfilled.

100% grooves

.


Results and discussion100% grooves: Flying height


Results and discussion70% grooves

Mixing requirement not fulfilled.

Fh = 140 μm

70% grooves

.


Results and discussionFlat surface vs. 100% grooves


Results and discussionFlat surface vs. 70% grooves


Results and discussionGrooved surface track (5)

No Groove

70% Groove 100% Groove

Mixing Requirement


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.


Results and discussion

• Design system to measure separation of the of the wafer to the lateral wall.

Lateral gap measurement system (1)


Results and discussionLateral gap measurement system (2)


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


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



Back Up slides


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.


P1 systemWorking principle (4)


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.


Model ValidationModel validation (1)

7 mbar

3 mbar

5 mbar

10 mbar



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.




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


Results and discussionLateral gap measurement system (3)

Documents

1 Challenge the future To do list. add extra slide about the coupling, at pressure level. Burn CD