lecture 8.0
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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
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
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!
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
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