Download - Silicon Crystal Growth
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Lecture 8.0
Silicon Crystal Growth
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Silicon Mfg. - old
Produce Silicon metal bar
Zone Refiningn times
To get purity
Cut off impure end
Use pieces to fill crystallization
apparatus
Grow Mono-Crystal of large size
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Zone Refining
0=x-Ut, k=CS/CL
Co=solute concentration in melt
or of solid on first pass
Co=0x+L Cs(x)dx - o
x-L kCL(x)dx
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Si-Fe Phase Diagram
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Crystal Growth
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Silicon Mfg. - new
Produce ultra pure Silicon cylinder
Use pieces to fill crystallization
apparatus
Grow Mono-Crystal of large size
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Add Dopants to
Silicon Grown
Melt is maintainedwith a givenimpurityconcentration
Melting Point isdecreased
Solid producedhas a givenimpurityconcentation
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Ultra-pure Silicon Production
Si + 3HClSiHCl3+H2 fluidized bed reactor at 500 to 700K
Condense chlorosilane, SiHCl3
Distillation of liquid SiHCl3
SiHCl3+H2Si + 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 14-9s pure
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12 (30 cm) Boule
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Czochralski Crystal Growth
Apparatus Figure 4. Today's Czochralsk i gr owth furnace,
or crystal pul ler, is a far more so phist icatedapparatus than that bui l t by Gordon Tealnearly 50 years ago. It is howeverfund amental ly identical. A cry stal is pul ledf rom a feedstock of mo l ten mater ia l by slowly
wi thdrawing i t from the mel t . Czochralsk ipul lers of ten possess prov is ions for adding tothe mel t during a single pul l so that crystalslarger than w hat can be ob tained in a singlecharge of the crucib le may be pr oduced.Today crystals of a 12-inch diameter arepossible, and the industry wi l l spend bi l l ionsto adopt this new size in the coming years.
This f igure was taken direct ly from theMitsubishi Semiconductor
websi te: http:/ /www .egg.or jp/MSIL/
english/ index-e.html!
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Czochralski Growing System
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12 (30 cm) Boule
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Crystal Growth Steps
Induce Supersaturation
Sub cooled melt
S=exp[THf/(RT2)dT]
Nucleation
Growth at different rates on each
Crystal Face Results in crystal with a particular
Crystal Habit or shape
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Nucleation
Free Energy
GTOT=GvV + A Critical Size
R*=2AVm/(3vRgT lnS) Nucleation Rate
J=(2D/d5)exp[-G(R*)/(RgT)] D=diffusion coefficient
d= molecular diameter
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Surface Nucleation
Surface energy, ,is replaced by cos, where is thecontact anglebetween phases
Geometric factorschanged
Units #/(cm2sec)
Surface Nucleation Limits growth of flat
crystal surfaces
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Crystal Growth Rate
Limiting Steps Boundary Layer
Diffusion
Surface Diffusion
Surface Nucleation Mono
Poly
Screw Disslocation
Edge Diffusion Kink Site Adsorption
Loss of Coordinationshell
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Screw Surface Growth
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Fluxes
Boundary
Layer
Surface
Edge
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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
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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 asRate Determining Step
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Crystal Habit
Equilibrium Shape
h1/1=h2/2=h3/3 Kinetic Shape
h1=G1(S)*t
h2=G2 (S)* t
h3=G3 (S)* t
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Crystal Faces
Flat Face
Stepped Face
Kinked Face
Diffusion Distances
to Kink sites areshorter on K &S
Faces
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Crystal Habit
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Wafers Cut from Boule & Polished