Silicon Crystal Growth 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=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

Si-Fe Phase Diagram

Si-O Phase Diagram

Crystal Growth

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

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

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

12” (30 cm) Boule

Crystal Growth

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: http://www.egg.orjp/MSIL/ english/index-e.html!

Czochralski Growing System

12” (30 cm) Boule

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

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

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

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

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

Screw Surface Growth

Fluxes Boundary Layer Surface Edge

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. 135,1944-47(1988). Uniform, not a function of radius!! Crystal Growth Rate due to BL-MT as Rate Determining Step

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. 135,1944-47(1988). Uniform, not a function of radius!! Crystal Growth Rate due to BL-HT as Rate Determining Step

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

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

Crystal Habit

Wafers Cut from Boule & Polished