Helmholtz-Alliance LIMTECH. page 1

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1 Helmholtz-Alliance LIMTECH page 1

2 C1: Magnetic flow control in growth and casting of photovoltaic silicon (HZDR, TUBAF) Solidification of Solar-Si Si-crystal growth by Czochralski (Cz) 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 page 2

3 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 page 3

4 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. page 4

5 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 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 photoconductivity ( minority carrier lifetime) page 5

6 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) Growth chamber Control unit (voltage, power, frequency max. 250V,20kW,10kHz) Translation/Rotation stage with growth setup (crucible, susceptor, insulation) Induction coil (10 windings, diameter/height of 200/150mm) page 6

7 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; Si 3 N 4-x O x coated SiO 2 crucible insulation susceptor crucible melt crystal Ar,CO (4) (5) (2) (1) (3) Phenomena/Interface reactions: (1) incorporation/segregation (N complexes, C s, O i ) (2) supersaturation/precipitation (SiC / SiO 2 / Si 3 N 4 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 page 7

8 C1: Magnetic flow control in growth and casting of photovoltaic silicon Turbulente Auftriebsströmung Experiments with GaInSn to model the flow and T-distribution in Cz page 8 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

9 Turbulente Auftriebsströmung C1: Magnetic flow control in growth and casting of photovoltaic silicon Transition from large-scale buoyancy driven turbulence to small-scale RMF-driven turbulence at Ta = Ta tr Temperature fluctuation, K ( a ) ( b) T r =0 H T = T o c T = T h ω o z H o B o B R o r time, s T = 30K, Ta = , right: RMF + DC, Ha = 105, blue: uniform DC, red: cusp DC Significant reduction of T-fluctuations by RMF attractive for crystal growth page 9

10 Exp. Strömungsmodellierung Modellexperimente mit Ga oder GaInSn: Code-Validierung Numerische Cz-Simulationen sollten an Modellexperimenten validiert werden, die Strömungs- und Temperaturmessungen erlauben wichtig für Turbulenzmodellierung! Modellexperimente in Behältern mit 90/178 mm: Gr bis zu ca Vergleich: Cz-Si in 14 -Tiegel mit T = 20K: Gr = Strömungen im Modell repräsentativ für Strömungen im Cz-Si-Tiegel Modellsysteme: Zylinder, modifiziertes Rayleigh-Bénard, generisch, einfaches T-Steuer, Cz ähnlich, keine Rotation (TSE1) Cz-Tiegel, mit Rotation, T bis zu 200K (TSE2) page 10

11 Experimentelle Strömungsmodellierung Versuchsstand TSE2 in MULTIMAG Drehdurchführung Kühlwasser Motor für Kristallrotation Schleifring für Messdaten Hohlwelle MULTIple MAGnetic field facility Kristalldummy Spulensysten Tiegel page 11

12 Experimentelle Strömungsmodellierung Versuchsstand TSE2 in MULTIMAG Drehtisch Motor für Tiegelrotation Syphon- Drehdurchführung Thermo- element- Tripods Schutzgas Schmelze Zu- und Ablauf Thermalöl page 12