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Lecture 8.0. Silicon Crystal Growth. Silicon Mfg. - old. Produce Silicon metal bar Zone Refining – n times To get purity Cut off impure end Use pieces to fill crystallization apparatus Grow Mono-Crystal of large size. Zone Refining. 0=x-Ut, k=C S /C L.

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Lecture 8.0

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Lecture 8.0

Silicon Crystal Growth


Silicon Mfg. - old

  • Produce Silicon metal bar

  • Zone Refining – n times

    • To get purity

  • Cut off impure end

  • Use pieces to fill crystallization apparatus

  • Grow Mono-Crystal of large size


Zone Refining

0=x-Ut, k=CS/CL

Co=solute concentration in melt or of solid on first pass

Co=0x+L Cs(x)dx - ox-L kCL(x)dx


Si-Fe Phase Diagram


Si-O Phase Diagram


Crystal Growth


Silicon Mfg. - new

  • Produce ultra pure Silicon cylinder

  • Use pieces to fill crystallization apparatus

  • Grow Mono-Crystal of large size


Melt is maintained with a given impurity concentration

Melting Point is decreased

Solid produced has a given impurity concentation

Add Dopants to Silicon Grown


Ultra-pure Silicon Production

  • Si + 3HClSiHCl3 +H2

    • fluidized bed reactor at 500 to 700K

    • Condense chlorosilane, SiHCl3

  • Distillation of liquid SiHCl3

  • SiHCl3+H2Si + 3HCl at 1400K

  • Si vapor Deposits on Si mandrel in a purged fed batch reactor heated to 700K

  • Results Large diameter Si with impurities at 10 ppt or 14-9’s pure


12” (30 cm) Boule


Crystal Growth


Czochralski Crystal Growth Apparatus

  • Figure 4. Today's Czochralski growth furnace, or crystal puller, is a far more sophisticated apparatus than that built by Gordon Teal nearly 50 years ago. It is however fundamentally identical. A crystal is pulled from a feedstock of molten material by slowly withdrawing it from the melt. Czochralski pullers often possess provisions for adding to the melt during a single pull so that crystals larger than what can be obtained in a single charge of the crucible may be produced. Today crystals of a 12-inch diameter are possible, and the industry will spend billions to adopt this new size in the coming years. This figure was taken directly from the Mitsubishi Semiconductor

    • website: http://www.egg.orjp/MSIL/ english/index-e.html!


Czochralski Growing System


12” (30 cm) Boule


Crystal Growth Steps

  • Induce Supersaturation

    • Sub cooled melt

    • S=exp[THf/(RT2)dT]

  • Nucleation

  • Growth at different rates on each Crystal Face

  • Results in crystal with a particular Crystal Habit or shape


Nucleation

  • Free Energy

    • GTOT=GvV + A

  • Critical Size

    • R*=2AVm/(3vRgT lnS)

  • Nucleation Rate

  • J=(2D/d5)exp[-G(R*)/(RgT)]

  • D=diffusion coefficient

  • d= molecular diameter


Surface Nucleation

  • Surface energy, , is replaced by  cos , where  is the contact angle between phases

  • Geometric factors changed

  • Units #/(cm2sec)

  • Surface Nucleation

    • Limits growth of flat crystal surfaces


Crystal Growth

  • Boundary Layer Diffusion

  • Surface Diffusion

  • Edge Diffusion

  • Kink Site Adsorption

  • Loss of Coordination shell at each step


Crystal Growth Rate Limiting Steps

  • Boundary Layer Diffusion

  • Surface Diffusion

  • Surface Nucleation

    • Mono

    • Poly

  • Screw Disslocation

  • Edge Diffusion

  • Kink Site Adsorption

  • Loss of Coordination shell


Screw Surface Growth


Fluxes

  • Boundary Layer

  • Surface

  • Edge


Mass Transfer to Rotating Crystal

  • Local BL-MT Flux

  • J[mole/(cm2s)] = 0.62 D2/3(Co-Ceq) n-1/6w1/2

  • J[mole/(cm2s)] = 0.62 D2/3 Ceq(S-1) n-1/6w1/2

    • Franklin, T.C. Nodimele, R., Adenniyi, W.K. and Hunt, D., J. Electrochemical Soc. 135,1944-47(1988).

    • Uniform, not a function of radius!!

  • Crystal Growth Rate due to BL-MT as Rate Determining Step


Heat Transfer to Rotating Crystal

  • Local BL-HT Flux

  • J[mole/(cm2s)] = h(Teq-T)/Hf

  • J[mole/(cm2s)]

    • = 0.62 k -1/3 n-1/6w1/2 (Teq-T)/Hf

  • Franklin, T.C. Nodimele, R., Adenniyi, W.K. and Hunt, D., J. Electrochemical Soc. 135,1944-47(1988).

  • Uniform, not a function of radius!!

  • Crystal Growth Rate due to BL-HT as Rate Determining Step


  • Crystal Habit

    • Equilibrium Shape

      • h1/1=h2/2=h3/3

    • Kinetic Shape

      • h1=G1(S)*t

      • h2=G2 (S)* t

      • h3=G3 (S)* t


    Crystal Faces

    • Flat Face

    • Stepped Face

    • Kinked Face

    • Diffusion Distances to Kink sites are shorter on K &S Faces


    Crystal Habit


    Wafers Cut from Boule & Polished


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