page 1

Helmholtz-Alliance LIMTECH

page 2

directional solidification of mc-Si

in a high-vacuum induction furnace (TUBAF):

- varying electromagnetic stirring

- variation of gas phase properties

- detailed studies on impurity transport

Model experiments for Cz

Numerical simulations

Si-crystal growth by Czochralski (Cz)Solidification of Solar-Si

C1: Magnetic flow control in growth and casting of photovoltaic silicon(HZDR, TUBAF)

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Helmholtz-Allianz LIMTECH

C1 – Magnetic flow control in growth and casting of photovoltaic silicon

Partners

HZDR, Institute of Fluid Dynamics (IFD), Dr. G. Gerbeth (PI)

TUBAF, Institute of Non-Ferrous Metallurgy and Purest Metals (INEMET),

Prof. M. Stelter/Dr. O. Pätzold

Part A (INEMET, IFD)

Defect engineering in multi-crystalline silicon grown from an inductively

heated melt under different flow conditions

Part B (IFD)

Flow modelling for Czochralski growth of single-crystalline silicon

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Helmholtz-Allianz LIMTECH

C1 – Magnetic flow control in growth and casting of photovoltaic silicon

Part A – Defect engineering in multi-crystalline silicon grown from an inductively

heated melt under different flow conditions

Main objectives:

Investigation, clarification and optimisation of the impurity interaction in growth of

multi-crystalline silicon from well-mixed and poorly mixed melts with focus on

i) the solution and/or evaporation of impurities at the melt – crucible and

melt – atmosphere interfaces

ii) the formation and agglomeration of inclusions in melt and crystal

iii) the axial and radial segregation of impurities in the crystal

Flow control:

Electro-magnetic and mechanical flow control to establish particular melt mixing by

i) changing of the effective Lorentz force in the melt by the material, dimensions,

and configuration of the susceptor

ii) mechanical rotation of the growth setup including the melt crucible.

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Helmholtz-Allianz LIMTECH

Working packages:

Numerical modeling of the growth system including

i) global thermal modeling of the induction furnace

ii) local simulation of the melt flow and impurity transport

iii) thermodynamic modeling of the global phase and species equilibrium as well as of

selected impurity reactions in the crystal/melt – growth crucible – atmosphere system.

Growth and wetting experiments under systematically varied conditions

(melt flow, composition of crucible/substrate coating, composition of the atmosphere)

Characterisation of the crystals including Fourier transform IR spectroscopy (� substitutional

carbon, interstitial oxygen), IR microscopy (� precipitates), and microwave-detected photo-

conductivity (� minority carrier lifetime)

C1 – Magnetic flow control in growth and casting of photovoltaic silicon

Part A – Defect engineering in multi-crystalline silicon grown from an inductively

heated melt under different flow conditions

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Helmholtz-Allianz LIMTECH

High-vacuum induction furnace for directional solidification of multi-crystalline

silicon ingots by the vertical Bridgman method

Control unit

(vacuum, gas flow, stage)

Control unit

(voltage, power, frequency

max. 250V,20kW,10kHz)

Growth chamber

Translation/Rotation stage with growth

setup (crucible, susceptor, insulation)

Induction coil (10 windings,

diameter/height of 200/150mm)

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Helmholtz-Allianz LIMTECH

Scheme of the main impurity interaction during growth of multi-crystalline Si ingots

Components of the setup:

- Graphite susceptor; Graphite-containing insulation; Si3N4-xOx coated SiO2 crucible

insulation

susceptor

crucible

melt

crystal

● ● ●

(1)

(2)

(3)

(4)

(5)

Phenomena/Interface reactions:

(1) incorporation/segregation

(N complexes, Cs, Oi)

(2) supersaturation/precipitation

(SiC / SiO2 / Si3N4 inclusions)

(3) convective/diffusive transport

(4) solution of coating and crucible

(O/C/N/metal contamination)

(5) evaporation/incorporation/precipitation

CO + 2Si(l) ↔ SiC + SiO

CO + Si(l) ↔ [C]Si +[O]Si + Si(l)[Si]Si + [O]Si ↔ 2 SiO

Ar,CO

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Turbulente AuftriebsströmungExperiments with GaInSn to model the flow and T-distribution in Cz

C1: Magnetic flow control in growth and casting of photovoltaic silicon

Cz-model with a 7“ crucible

perfectly fits to large-scale Si case

independent rotation of crucible and crystal

Superposition of various

AC and DC magnetic fields

Goal: Control of large-scale, non-axisymmetic

buoyant structures

Links: A4, C2, YIG

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Turbulente Auftriebsströmung

Transition from large-scale buoyancy driven turbulence tosmall-scale RMF-driven turbulence at Ta = Tatr

∆T = 30K, Ta = 3.2×106,

right: RMF + DC, Ha = 105, blue: uniform DC, red: cusp DC

time, s

Tem

pera

ture

flu

ctu

ati

on

, K

( )a ( )b

−0.5

0.5

−1

0

1

−6

−4

−2

0

2

4

6

0 5 10 15 0 15 30 45

Significant reduction of T-fluctuations by RMF⇒⇒⇒⇒ attractive for crystal growth

Ro

ωo

=T Tc

Ho

Bo

=T Th

r

z

B

=0T

r

−Ho

C1: Magnetic flow control in growth and casting of photovoltaic silicon

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Modellexperimente mit Ga oder GaInSn: Code-Validierung

Exp. Strömungsmodellierung

Modellexperimente in Behältern mit ∅ 90/178 mm:

Gr bis zu ca. 2 ×109

Vergleich:

Cz-Si in 14“-Tiegel mit ∆T = 20K: Gr = 1.3 ×109

⇒ Strömungen im Modell repräsentativ für

Strömungen im Cz-Si-Tiegel

Numerische Cz-Simulationen sollten an Modellexperimenten

validiert werden, die Strömungs- und Temperaturmessungen

erlauben

⇒ wichtig für Turbulenzmodellierung!

Modellsysteme:

• Zylinder, modifiziertes Rayleigh-Bénard, generisch,

einfaches T-Steuer, Cz ähnlich, keine Rotation (TSE1)

• Cz-Tiegel, mit Rotation, ∆T bis zu 200K (TSE2)

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Versuchsstand TSE2 in MULTIMAG

Experimentelle Strömungsmodellierung

MULTIple

MAGnetic

field

facility

Drehdurchführung

Kühlwasser

Motor für

Kristallrotation

Schleifring für

Messdaten

Hohlwelle

Kristalldummy

Spulensysten

Tiegel

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Versuchsstand TSE2 in MULTIMAG

Experimentelle Strömungsmodellierung

Thermo-

element-

Tripods

Schutzgas

Schmelze

Drehtisch

Motor für

Tiegelrotation

Syphon-

Drehdurch-

führung

Zu- und Ablauf

Thermalöl