Will be helpful for VLSI Designer

1. Epitaxial Deposition
Abu Syed Md. Jannatul Islam
Lecturer, Dept. of EEE, KUET, BD
1
Department of Electrical and Electronic Engineering
Khulna University of Engineering & Technology
Khulna-9203

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Epitaxy
 The term Epitaxy comes from the
Greek word meaning ‘ordered
upon’.
 Epitaxy means the growth of a
single crystal film on top of a
crystalline substrate.
 For most thin film applications
(hard and soft coatings, optical
coatings, protective coatings) it is
of little importance.
 However, for semiconductor thin
film technology it is crucial.

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Homoepitaxy:
 The film and the substrate are the same material.
 Often used in Si on Si growth (A on A)
 Epitaxially grown layers are purer than the substrate and can be doped
independently of it.
Types of Epitaxy
Heteroepitaxy:
 Film and substrate are different materials.(Growth of AlAs on Si or GaAs
on Si).
 Trying to grow a layer of a different material on top of a substrate leads to
unmatched lattice parameters.
 This will cause strained or relaxed growth and can lead to interfacial
defects.
 Such deviations from normal would lead to changes in the electronic,
optic, thermal and mechanical properties of the films.
 Allows for optoelectronic structures and band gap engineered devices.

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Ordered, crystalline growth
Epitaxial growth
Epitaxial Growth
NOT epitaxial
 High Quality Film (1μm or less
thickness) deposited on a high
quality substrate.
 To ensure high crystalline quality,
the lattice parameters of the thin
layer should match with that of the
substrate (to minimize strain).

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 While Si is not the ideal material from an electronic and optical point of view, its
abundance, ease of processing and availability of a good native oxide have made it
the backbone of semiconductor industry.
 Combining Si substrates with compound semiconductor films would enable higher
optoelectronic functionality and higher speeds. However, there are severe lattice
mismatch and chemical compatibility issues between Si and most III-V alloys that
preclude direct growth.
 Metal-Semiconductor Hetero-epitaxy: Metal-semiconductor structures are used for
contact applications. While not essential, epitaxial growth allows increased electron
mobility through a junction.
 Epitaxial growth is useful for applications that place stringent demands on a
deposited layer:
 High purity, Low defect density, Abrupt interfaces, Controlled doping profiles
 High repeatability and uniformity, Safe, efficient operation
 Can create clean, fresh surface for device fabrication
Why Epitaxial Growth

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 Engineered wafers
 Clean, flat layer on top of less ideal
Si substrate
 On top of SOI structures
 Ex.: Silicon on sapphire
 Higher purity layer on lower quality
substrate (SiC)
 In CMOS structures
 Layers of different doping
 Ex. p- layer on top of p+ substrate to
avoid latch-up
Why Epitaxial Growth
 To make layer which is not available in nature
 Very important in III-V semiconductor production
 Bipolar Transistor (Needed to produce buried layer)
 III-V Devices (Interface quality key, Hetero-junction
Bipolar Transistor, LED, Laser).

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Steps:
 Absorption of ad atoms
 Surface diffusion
 Crystal growth
 Evaporation of adatoms
Parameters:
 Growth temperature
 Growth pressure
 Flow amount of reactants
 Substrate and treatment
Epitaxial Growth Steps & Parameters

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Scheme of Epitaxial Deposition

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Epitaxial Deposition Techniques
Epitaxial growth can be performed at temperatures
considerably below the melting point of the substrate crystal.
A variety of methods are used to provide the appropriate
atoms to the surface of the growing layer.
 Vapor Phase Epitaxy/Chemical vapor deposition (grown
from Vapor)
 Liquid phase epitaxy (grown from a Melt)
 Molecular beam epitaxy (an evaporation of the elements in
a Vacuum)
With this wide range of epitaxial growth techniques, it is
possible to grow a variety of crystals for device applications,
having properties specifically designed for the electronic and
optoelectronic device being made.

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Liquid Phase Epitaxy
 Reactants are dissolved in a molten solvent at high temperature
 Substrate dipped into solution while the temperature is held
constant
 Example: SiGe on Si
 Bismuth used as solvent
 Temperature held at 800°C
 High quality layer
Molecular Beam Epitaxy
 Very promising technique
 Beams created by evaporating solid source in UHV
 Not ideal for large area layers or abrupt interfaces
 Thermodynamic driving force relatively very low
Epitaxial Deposition Techniques

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 MOMBE---means when Metel Organic Source used for MBE
 Sputtering---the layer quality is very poor. Thus it is used for making
contact with the help of metal related source.
 HVPE---Hydride Vapor Phase Epitaxy
 Pulse laser Deposition (PLD)
 Reactive Evaporation
 Electron Beam Plasma Technique
 Solvo thermal Method
Epitaxial Deposition Techniques
*Advantages, Disadvantages, and Applications of all these
techniques are very much important. Please collect all the
information……………….

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Techniques Strengths Weaknesses
LPE (liguid phase epitaxy) Simple, High purity Scale economies Inflexible,
Non-uniformity
HVPE( hydride vapor
phase epitaxy)
Well developed Large scale No Al alloys Complex
process/reactor control difficult,
Hazardous sources
MBE Simple process, Uniform,
Abrupt interface In-situ
monitoring
As/P alloy difficult, Expensive ,
Low throughput
MOCVD/OMVPE/OMCVD
MOVPE
Most flexible, Large scale
production Abrupt interface
Simple reactor, High purity,
selective in situ monitoring
Expensive sources Most
parameters to control Accurately
Hazardous precursors
Overview of Epitaxy Techniques