silicon crystal growth

8/12/2019 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

silicon crystal growth

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