EE-5-58(TO)
VLSI TECHNOLOGY
Epitaxial Growth
Chandan Yadav
Electrical Engineering, IIT Jammu
Issues to address…
 Epitaxial growth
 Epitaxial Growth Techniques
Epitaxial growth
Why to study epitaxial layer growth
https://www.cityu.edu.hk/phy/appkchu/AP6120/3.PDF
Epitaxial growth
Why to study epitaxial layer growth
‒ In semiconductor device and IC fabrication, realization of
many thin films are required, epitaxial layer is one of them.
e.g. application in fabrication of transistors.
Micrograph of fabricated
p-MOSFTET →
Image source: S. E. Thompson et al. “A 90-nm Logic Technology Featuring Strained-Silicon” IEEE TED, Nov. 2004
Epitaxial growth
Why to study epitaxial layer growth
‒ In semiconductor device and IC fabrication, realization of
many thin films are required, epitaxial layer is one of them.
Image source: Z. Liu et al. “Selective epitaxial growth of monolithically integrated GaN-based light emitting diodes with
AlGaN/GaN driving transistors” Appl. Phys. Lett. 104, 091103 (2014)
Epitaxial growth
Why to study epitaxial layer growth
– Radical changes in materials' properties can be created over small
distances within the same crystal e.g.
 Growth of lightly doped single crystal silicon on top of heavily
doped single crystal silicon.
 Want to create very sharp PN boundary
 Buried Epi layer in bipolar transistors.
Epitaxial growth
Epitaxy – A word derived from two Greek words
“Epi”
On
Crystalline
substrate
Arrangement
Epitaxy
Epitaxy → “to arrange upon” or
“oriented overgrowth”
Epitaxial growth → A growth of a
single crystal film on surface of a
crystalline substrate e.g. a single
crystal Si layer on crystalline
substrate.
Si
 Epitaxy can be homoepitaxy or
heteroepitaxy.
Epi or Epitaxial layer: Refers to
“grown crystalline layer” on top of
crystalline substrate.
Epitaxial
growth
Greek words
Crystalline Epi
substrate layer
“taxis”
Example
Epitaxial growth
Is epitaxial growth is different than crystal growth
/ No)

using CZ and FZ method ? (Yes
Crystal Growth with CZ or FZ:
Epitaxy:
 Single crystal silicon ingot.
 grow a single crystal layer on
 Make single crystal Silicon
a crystalline substrate.
wafers (substrate) from the
grown ingot.
ingot
Example
Image source: WaferPro
Crystalline
substrate
Epi
layer
Example
Epitaxial Growth
Epitaxial growth Techniques
– A few epitaxial growth process:
 Chemical Vapour Deposition (CVD)
› Plasma enhanced
› Rapid thermal
› Metallorganic
› Ultrahigh Vacuum
› Atomic layer
› Optical and X-ray assisted

Physical Vapour Deposition (PVD) methods
› Molecular beam epitaxy
› Ion Beam epitaxy
 Liquid Phase Epitaxy
 Thermal chemical vapour deposition or Vapor-Phase Epitaxy (VPE) is a
subset of CVD.
 VPE is a most commonly used method for Silicon epitaxy in IC production
© Epitaxial Silicon Technology
Epitaxial Growth
Epitaxial growth Techniques
‒ Chemical Vapour Deposition (CVD):
 CVD is a process whereby an epitaxial layer is formed from a
gaseous phase via a chemical reaction.
 CVD performed at atmospheric pressure is called APCVP.
 CVD performed at low pressure (10-100 Pa) is called LPCVD.
‒ Vapor-Phase Epitaxy (VPE) is a subset of CVD.
Epitaxial Growth
CVD Technique
‒ Requirements: A reaction chamber (reactor).
: Reactants in gaseous form.
‒ Reactors consists of susceptor, heater name in CVD are
based on the susceptors design:
 Susceptor is analogous to crucible in CZ crystal growth
method.
 Susceptor provide mechanical support to substrate.
 In radiated heating reactor, susceptor also serve as a source
of thermal energy for chemical reactions.
1. Horizontal reactor
Epitaxial Growth
CVD Technique

Direction of the flow of gas with respect to the semiconductor surface is
useful to identify vertical and horizontal reactors
2. Pancake reactor
3. Barrel reactor
Substrate
Susceptor
Epitaxial Growth
CVD Technique
‒ Steps involved in CVD mechanism can be listed as:
 Reactants (gases and dopants) are transported to the
substrate region.
 They (reactance) are transferred to the substrate surface,
where they are adsorbed.
Adsorption phenomenon
absorption
 A chemical reaction occurs catalyzed at the surface, followed
by growth of the epitaxial layer.
 Gaseous products are desorbed into the main gas stream.
Desorption: release of adsorbed molecule on the surface
 Reaction byproducts are transported out of the reaction
chamber.
Epitaxial Growth
CVD Technique
– A simplified model of Si deposition from trichlorosilane
(TCS) and silicontetrachloride (STC).
Silicon sources in gaseous form
A mass transport of gas flow
SiCl4
B Gas phase reaction
SiH2Cl2
C mass transport of precursors to growth surface
D adsorption of the precursor to the growth surface SiHCl3
E surface diffusion to growth sites
SiH4
F incorporation of Si to the growing film
G Desorption of the byproducts of the surface reaction
H Mass transport of byproducts in the main gas flow.
Silicon Tetrachloride
Dichlorosilane
Trichlorosilane
Silane
Fig.: Schematic of processes during CVD.
*adsorbed SiCl2
High-temperature CVD processes for crystalline silicon thin-film and wafer solar cells, Dissertation,. 2008
Epitaxial Growth
VPE Technique
– It’s a subset of CVD and commonly used to grow crystalline Si
(1) Gas
phase
decomposition
(2) Transport to the wafer
surface
(3) Adsorption at the surface
of growth species
(4) Diffusion
(5) Decompose
(6) By-products desorption.
Fabrication Engineering at the Micro- and Nanoscale
Epitaxial Growth
VPE Technique
– Crystalline Si epitaxial layer growth
 Silicon tetrachloride (SiCl4) was first commonly used precursor.
›
Requirement: substrate temperature must be high > 1150ºC
›
Issue: Dopant redistribution at this high temperature
›
At low temperature 600ºC, it is often used for polysilicon deposition.
SiH4(g)  Si(s) + 2H2(g)
 Growth rates from SiHCl3, SiH2Cl2, and SiH3Cl have all been
developed at relatively lower temperature than SiCl4 requirement.
›
Reactant component in all these materials is SiCl2
 Dichlorosilane (SiH2Cl2 or DCS) is currently the most commonly
employed source
›
›
SiCl2 formation takes place at a relatively lower temperature
It has Highest efficiency (ratio of deposited Si and Si in reactant gas).
Fabrication Engineering at the Micro- and Nanoscale
Epitaxial Growth
VPE Technique
– Crystalline Si epitaxial layer growth


Chlorine can etch of the substrate
etch mechanism depends on the square of the HCl.
Si(s) + 2HCl(g) ⇌ SiCl2(g) + H2(g)
Adding gaseous HCl slows the net deposition rate by increasing the etch rate.
etching
Fabrication Engineering at the Micro- and Nanoscale
Epitaxial Growth
CVD Technique
‒ CVD chemical reaction for Silicon epitaxial growth:
• At low temperature growth rate is expressed by Arrhenius function:
EA  activation energy
the same rate limiting process may be
involved for each reaction
In region B: temperature is high and Surface
reaction is faster than the rate at which the
reactant species reach.
Growth is limited to mass transport.
© HANDBOOK OF CHEMICAL VAPOR DEPOSITION(CVD) Principles, Technology, and Applications, 2nd Ed.
Epitaxial Growth
Metal organic CVD (MOCVD)
‒ What is MOCVD:
Definition: MOCVD grows thin semiconductor films on solid
wafers using organometallic compounds as source materials.
Primary Use: Fabrication of advanced electronic and
optoelectronic devices.
Key Applications: LEDs (lighting, billboards), laser diodes
(CD, DVD, HD-DVD/BD), cell phone transistors (HBTs), and
solar cells (satellites).
Vendors: AIXTRON, Thomas Swan, VEECO (Emcore), NipponSanso, etc.
Epitaxial Growth
Metal organic CVD (MOCVD)
MOCVD has several names that are
semiconductor industry and academia
used
interchangeably
in
the
1. MOVPE: Metal Organic Vapor Phase Epitaxy
This is often considered the most technically precise term, as the goal
is to achieve epitaxy (the highly ordered, crystalline growth of one
layer on another).
2. OMVPE: Organometallic Vapor Phase Epitaxy
This is another very common and technically accurate term, simply
swapping the order of "Metal Organic" to "Organometallic."
3. OMCVD: Organometallic Chemical Vapor Deposition
This name is less common than MOCVD or MOVPE but highlights the
process as a form of the broader class of CVD techniques.
Epitaxial Growth
Metal organic CVD (MOCVD)
‒ Why MOVPE:
The use of MOVPE is driven by its ability to meet the demanding
requirements of advanced semiconductor devices. It has following
advantages:
High-Volume Manufacturing (High Throughput) and no ultra high
vacuum
•
•
It can accommodate multiple wafers simultaneously i.e. useful for mass
production
Higher growth rate due to chemical reaction based process.
High quality of grown layers
•
•
•
High Purity and Crystalline Quality
Versatility in Materials
Complex Multilayers (Heterostructures)
Precise Control and Flexibility
•
•
Abrupt/sharp Interfaces
Dopant control.
Epitaxial Growth
Metal organic CVD (MOCVD)
Primarily used for II-VI, and III-V semiconductors, special
metallic oxides and metals.
Adopted from: ECE 6450 - Dr. Alan Doolittle, Georgia Tech
Epitaxial Growth
Metal organic CVD (MOCVD)
‒ Basic principle of MOVPE Process:
Step1: Precursor Supply (Vapor Transport)


Metal-organic and hydride gases (e.g. Trimethylgallium and Arsine for
GaAs growth) are introduced into a reaction chamber using a carrier gas
(like H₂ or N₂).
These vapors transport the required elements to the heated substrate
surface.
Step2: Chemical Decomposition (Surface Reaction)


When the precursors reach the heated substrate, thermal decompose
takes place i.e. pyrolysis process.
The constituent atoms (metals and nonmetals) react on the surface to
form the desired epitaxial semiconductor layer.
Step3: Byproduct Removal and Layer Growth


The deposited atoms bond to the surface and a new crystalline epitaxial layer
is grown.
The reaction byproducts (such as CH₄, H₂, etc.) are carried away by the gas
flow.
Epitaxial Growth
Metal organic CVD (MOCVD)
‒ Simplified presentation of a crystal growth process
Epitaxial Growth
Metal organic CVD (MOCVD)
Fig.: A large-scale commercial MOCVD systems
https://www.sciencedirect.com/topics/chemical-engineering/metallorganic-chemical-vapor-deposition
Epitaxial Growth
Metal organic CVD (MOCVD)
 Ternary metal-oxy-chalcogenides (Bi2O2Se bismuth oxyselenide)
triphenyl bismuth
dimethyl selenide
precursors
M. Kang et al. “Low-Temperature and High-Quality Growth of Bi2O2Se Layered Semiconductors via Cracking Metal–Organic
Chemical Vapor Deposition, ACS Nano, 2021
Epitaxial Growth
Molecular Beam Epitaxy (MBE)
‒ Inventor: Bell Lab, Arthur and Alfred Cho
‒ MBE involves the direct physical transport of the material to
be grown, or its components, to a heated substrate.
 Epitaxial growth is achieved by directing/bombarding
atomic and molecular beams from effusion cell to
substrate in a well-controlled, ultra high vacuum system.
–
MBE is performed in high or ultra high
vacuum (10−8 to 10−12 Torr) conditions.
– Mean free path is very long (can be
hundreds of meters).
– The evaporated material travels in a
straight line (a molecular beam) toward
a hot substrate.
– The beam reach to substrate to
grow/deposit a film of the evaporated
material.
Fig.: Basic Principle of MBE.
Epitaxial Growth
Molecular Beam Epitaxy (MBE)
– The final composition of grown film depends on:



Temperature and surface atomic structure of substrate.
Flux ratio of individual component reaching to substrate.
Speed of atomic arrival.
– Advantages:



It can be used to prepare high quality, defect-free, and highly uniform
semiconductor crystals of a wide array of compounds.
Precise control over film thickness is possible.
Low temperature process.
– Disadvantages:



It is highly expensive and complicated system
Slow deposition rate
The thickness rises then strain energy is too high and defects are
generated.
Epitaxial Growth
Molecular Beam Epitaxy (MBE)
‒
Effusion
cell:
Source beams are
obtained by thermal
evaporation
from
high purity elements,
which are placed in
crucibles known as
effusion cells.
Figure Source: T. D. Brown, PhD Diss, GaTech 2003 – attributed
to A. S. Brown in Encyclopedia of Advanced Materials 1990.
Schematic of MBE growth chamber
Epitaxial Growth
Molecular Beam Epitaxy (MBE)
‒ Works under ultra high vacuum (UHV) conditions (~10-11
torr)
‒ Slower growth rate.
‒ better thickness and heterojunction control.
‒ High cost.
‒ The relationship between the mean free path (λ in cm) of
traveling molecules and chamber pressure (P in Pa) is
0.66

P
References
Griffin “Silicon VLSI
Technology:Fundamentals, Practice and Modeling”, Prentice Hall Upper
Saddle River NJ, 2000.
2. G. S. May, S. M. Sze “Fundamentals of Semiconductor Fabrication” John
Wiley & Sons, 2004
3. R.C. Jaeger, Introduction to Microelectronic Fabrication, Prentice Hall,
Second Edition, 2013
1. J.
Plummer,
M.
D.
Deal,
and
P.
B.