Chemical Vapor Deposition
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Chemical Vapor Deposition
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Chemical Vapor Deposition - Thin Film Materials Processing - Lecture Slides, Slides of Material Engineering
These are the Lecture Slides of Thin Film Materials Processing which includes Vaporization, Vapor Pressure Curves, Thermal Desorption, Molecular Binding Energy, First Order Desorption, Desorption Rate, Real Surfaces, Diffusion of Gas Particles etc. Key important points are: Chemical Vapor Deposition, Degree of Crystallinity, Growth Kinetics, Stagnant Film Model, Boundary Layer Theory, Gas Transport, Surface Reaction, Frequency Factor, Activation Energy
Typology: Slides
2012/2013
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Chemical Vapor Deposition
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Chemical Vapor Deposition
Chemical Vapor Deposition - a
technique for depositing thin film of
materials on wafers or other
substrates. Source gases are
introduced into a reaction chamber
and energy is applied through heat,
plasma generation, or other
techniques that result in the
decomposition of the source gas
and reaction the chemicals to form a
film.
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Degree of Crystallinity
Amorphous - no recognizable long range order to the positioning of atoms within the material
Polycrystalline (poly) - intermediate case, crystalline subsections that are disjoint relative to each other
Crystalline (epitaxial) - atoms are arranged in an orderly three- dimensional array
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5-Step CVD Process
GAS Flow
adsorbate
or
adatom
Substrate
weak e-
Reactants
Products
Stagnant
layer
1 Diffusion across stagnant layer
2 Adsorption on surface
3 Surface reaction, migration film formation
4 Desorption of Products
5 Diffusion of products back into gas stream
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Growth Kinetics - Stagnant Film Model
original silicon surface
F
Cs
Cg
Main Gas Flow
s
Diffusion flow
Stagnant Layer
Gas Stream^ (linear gradient)
Epi Growth Wafer
F
Cs - Surface reactant concentration D = Diffusivity
Cg - Gas stream reactant concentration
surface reaction flow
F1 = D ( Cg - Cs ) s
Diffusivity times the concentration gradient
D
s
= hg = gas phase mass transfer coefficient
F1 = hg (Cg - Cs ) (^) F2 = Ks C (^) s For steady state Epitaxial Growth
F1 = F Therefore Cs = hg Cg Ks + hg^ F1 > F2 reaction limited F1 < F2 mass transport limited
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Gas Transport -- Boundary Layer Theory
Fluid Mechanics of Gas Flows
Gas moving down a tube of diameter d in the x
direction at a velocity v
A diffusion boundary layer s(x) is formed whose
thickness increases as the gas moves down the
tube
2
1
v
x
x
η = the gas viscosity
ρ = the gas mass density
v = gas stream velocity
diffusion boundary layer δ (x)
wafers
reactor chamber
d (^) v MAIN GAS FLOW
x Graphite Susceptor
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