Epitaxial growth

Question 1

Why is lower temperature epitaxy desireable?

Answer 1

With lower temperature the diffusivity decreases more rapidly than the growth rate.

Question 2

Explain the equation F = h_g(C_g- C_s) = k_sC_s (epitaxy).

Answer 2

The flux of deposition species across the gaseous boundary equals the flux of reactants consumed by the surface.

h_g= mass transport coefficient

k_s = surface reaction rate

C_g, C_s = concetration of growth species in gas and on wafer surface

Question 3

What is the expression for the growth rate in vapour-phase epitaxy?

Answer 3

R = h_gk_s/(h_g+k_s) * C_s/N

hg = mass transport coefficient

ks = surface reaction rate

Cg = concetration of growth species in gas

N = number density of atoms in crystal (5e22 cm^-3 for Si)

Question 4

Hva er RHEED?

Answer 4

RHEED = Reflection High Energy Electron Diffraction.

Metode for å overvåke wafer-overflaten under MBE. (Studere tykkelse og vekstrate)

Question 5

Hva er fordeler med MBE?

Answer 5

• Kan enkelt kontrollere tykkelsen.
• Kan gro mange lag.
• In-situ karakterisering (RHEED)
• Ingen giftige gasser

Question 6

Hva er ulemper med MBE?

Answer 6

• Vanskelig å lage komplekse overflater.
• Kan håndtere kun 4 stoffer på en gang.
• Ovale defekter på overflaten.