Lecture 8.0Lecture 8.0

Silicon Crystal Growth

Silicon Mfg. - oldSilicon Mfg. - old

Produce Silicon metal barZone Refining – n times– To get purity

Cut off impure endUse pieces to fill crystallization

apparatusGrow Mono-Crystal of large size

Zone RefiningZone Refining

0=x-Ut, k=CS/CL

Co=solute concentration in melt or of solid on first passCo=0x+L Cs(x)dx - ox-L kCL(x)dx

Si-Fe Phase DiagramSi-Fe Phase Diagram

Si-O Phase DiagramSi-O Phase Diagram

Crystal GrowthCrystal Growth

Silicon Mfg. - newSilicon Mfg. - new

Produce ultra pure Silicon cylinderUse pieces to fill crystallization

apparatusGrow Mono-Crystal of large size

Add Dopants to Add Dopants to Silicon GrownSilicon Grown

Melt is maintained with a given impurity concentration

Melting Point is decreased

Solid produced has a given impurity concentation

Ultra-pure Silicon ProductionUltra-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 14-9’s pure

12” (30 cm) Boule12” (30 cm) Boule

Crystal GrowthCrystal Growth

Czochralski Crystal Growth Czochralski Crystal Growth ApparatusApparatus 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 SystemCzochralski Growing System

12” (30 cm) Boule12” (30 cm) Boule

Crystal Growth StepsCrystal Growth Steps

Induce Supersaturation– Sub cooled melt– S=exp[THf/(RT2)dT]

NucleationGrowth at different rates on each

Crystal FaceResults in crystal with a particular

Crystal Habit or shape

NucleationNucleation

Free Energy– GTOT=Gv V + A

Critical Size– R*=2AVm/(3vRgT lnS)

Nucleation Rate J=(2D/d5)exp[- G(R*)/(RgT)]

D=diffusion coefficient d= molecular diameter

Surface NucleationSurface 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 GrowthCrystal Growth

Boundary Layer Diffusion

Surface Diffusion Edge Diffusion Kink Site

Adsorption

Loss of Coordination shell at each step

Crystal Growth Rate Crystal Growth Rate Limiting StepsLimiting Steps

Boundary Layer Diffusion

Surface Diffusion Surface Nucleation

– Mono– Poly

Screw Disslocation Edge Diffusion Kink Site Adsorption Loss of Coordination

shell

Screw Surface Growth Screw Surface Growth

FluxesFluxes

Boundary Layer

SurfaceEdge

Mass Transfer to Rotating CrystalMass Transfer to Rotating Crystal

Local BL-MT Flux J[mole/(cm2s)] = 0.62 D2/3(Co-Ceq) -1/6

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

– 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 CrystalHeat Transfer to Rotating Crystal

Local BL-HT Flux J[mole/(cm2s)] = h(Teq-T)/Hf

J[mole/(cm2s)]

• = 0.62 k -1/3 -1/6 (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 HabitCrystal Habit

Equilibrium Shape– h1/1=h2/2=h3/3

Kinetic Shape– h1=G1(S)*t

– h2=G2 (S)* t

– h3=G3 (S)* t

Crystal FacesCrystal Faces

Flat Face Stepped Face Kinked Face

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

Crystal HabitCrystal Habit

Wafers Cut from Boule & PolishedWafers Cut from Boule & Polished