1. Silicon Crystal Growth
Lecture 8.0
Silicon Crystal Growth

2. 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

3. 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

4. Si-Fe Phase Diagram

5. Si-O Phase Diagram

6. Crystal Growth

7. Silicon Mfg. - new Produce ultra pure Silicon cylinder
Use pieces to fill crystallization apparatus
Grow Mono-Crystal of large size

8. Add Dopants to Silicon Grown
Melt is maintained with a given impurity concentration
Melting Point is decreased
Solid produced has a given impurity concentation

9. 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

10. 12” (30 cm) Boule

11. Crystal Growth

12. 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: english/index-e.html!

13. Czochralski Growing System

14. 12” (30 cm) Boule

15. Crystal Growth Steps Induce Supersaturation Nucleation
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

16. Nucleation Free Energy Critical Size Nucleation Rate
GTOT=Gv V + 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

17. 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

18. Crystal Growth Boundary Layer Diffusion Surface Diffusion
Edge Diffusion
Kink Site Adsorption
Loss of Coordination shell at each step

19. 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

20. Screw Surface Growth

21. Fluxes
Boundary Layer
Surface
Edge

23. Mass Transfer to Rotating Crystal
Local BL-MT Flux
J[mole/(cm2s)] = 0.62 D2/3(Co-Ceq) n-1/6 w1/2
J[mole/(cm2s)] = 0.62 D2/3 Ceq(S-1) n-1/6 w1/2
Franklin, T.C. Nodimele, R., Adenniyi, W.K. and Hunt, D., J. Electrochemical Soc. 135, (1988).
Uniform, not a function of radius!!
Crystal Growth Rate due to BL-MT as Rate Determining Step

24. 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-1/6 w1/2 (Teq-T)/Hf
Franklin, T.C. Nodimele, R., Adenniyi, W.K. and Hunt, D., J. Electrochemical Soc. 135, (1988).
Uniform, not a function of radius!!
Crystal Growth Rate due to BL-HT as Rate Determining Step

25. Crystal Habit Equilibrium Shape Kinetic Shape h1/1=h2/2=h3/3
h1=G1(S)*t
h2=G2 (S)* t
h3=G3 (S)* t

26. Crystal Faces Flat Face Stepped Face Kinked Face
Diffusion Distances to Kink sites are shorter on K &S Faces

27. Crystal Habit

28. Wafers Cut from Boule & Polished