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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

Lecture 8.0

Silicon Crystal Growth

silicon mfg old
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
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

silicon mfg new
Silicon Mfg. - new
  • Produce ultra pure Silicon cylinder
  • Use pieces to fill crystallization apparatus
  • Grow Mono-Crystal of large size
add dopants to silicon grown
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
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
czochralski crystal growth apparatus
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!
crystal growth steps
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
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 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 growth2
Crystal Growth
  • Boundary Layer Diffusion
  • Surface Diffusion
  • Edge Diffusion
  • Kink Site Adsorption
  • Loss of Coordination shell at each step
crystal growth rate limiting steps
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
fluxes
Fluxes
  • Boundary Layer
  • Surface
  • Edge
mass transfer to rotating crystal
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
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
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
Crystal Faces
  • Flat Face
  • Stepped Face
  • Kinked Face
  • Diffusion Distances to Kink sites are shorter on K &S Faces
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