Epitaxial Growth

Epitaxial Growth
TALLINN UNIVERSITY OF TECHNOLOGY
Course : Communicative Electronics
Subject : Microelectronics (IED3030)
Harish Kumar Singh – 177319IVEM

Epitaxial Growth :
What? Why? Where
Thin crystalline overlay over crystalline
substrate/wafer
Lightly doped crystalline layer is grown over a
heavily doped substrate, to achieve higher
breakdown voltage and higher performance of
device
Epitaxy is used for integrated circuits, IGBT,
ultra-fast diodes, DMOS, low-signal transistors
and diodes and Power transistors and diodes
Substrate
Epitaxial Layer ( .5 to 20
micron)

Kinds of Epitaxy
Homoepitaxy
Substrate and epitaxial layer are of same material
Heteroepitaxy
Different epitaxial layer material compare to
bulk substrate layer
Material property requirement for Heteroepitaxy:
1) No chemical reaction b/w substrate and epitaxial
layer material
2) No latex mismatch : Different latex material cause
strain. Practically strain can be handle to the some
level of thickness.
3) No thermal mismatch: This also cause strain but can
be negotiable to the some level of thickness

Methods of Epitaxy
1) LPE ( Liquid Phase Epitaxy )
2 ) VPE ( Vapor Phase Epitaxy )
3) MBE ( Molecular Beam Epitaxy )
LPE and VPE involve chemical reactions
MBE involve no chemical reaction it’s based
on the principle of simple thermal evaporation

Liquid Phase Epitaxy
Liquid form epitaxial material will cool down,
cause insolubility which result in precipitate
Bring precipitate in contact with wafer with
controlled orientation result in thin single
layer epitaxial layer on bulky crystal.
This method is not used for Si because it’s
difficult to dissolve Si.

Vapor Phase Epitaxy
Use liquid with high vapor pressure to
generate Reactance Gas
Element present in Reactance Gas react with
the sample, result in deposition of epitaxy
layer on substrate

Boundary layer problem
with VPE
Near to Sample Velocity of Reactance gas is
approximately zero. This cause non-uniformity
in epitaxial layer growth on different substrate
sample.
This issue can be resolved using different
designs of reactor.

Reactor Design
1) Horizontal Reactor : Inclined sample
holder. So flow of reaction gas will always
parallel and equivalent for all samples in
reactor.
2) Vertical Reactor :
 Gas flow is normal to sample
 Reduce boundary layer problem
 Can’t hold to man samples

3) Cylindrical Reactor
Horizontal reaction because
gas flow is parallel to sample
Use for mass production
Cylinder can be rotated for
uniformity of deposition

Molecular Beam Epitaxy
No chemical reaction only physical evaporation
Advantage
Work at low temperature so avoid autodoping
Controlled evaporation gives precise control
on dopent incorporation and growth rate
No boundary layer problem
Disadvantage
Very costly and sophisticated

Electron Gun – For high level heating
Pump – Turbo molecular/ Cyro / Ion sublimation pump
not oil based pump because it cause oil vapor
Load lock system – Multi vacuum chamber system
for reload of sample
Effusion cell – Diffusion material evaporates from
effusion cell
Shutter – To control dopent incorporation and
epitaxial layer thickness
Mass Spectrometer – To measure gas composition in
chamber. To measure dopent level and layer quality.
Ion Gauge – Doping using Ion implantation give better
control over doping profile.
Sputter cleaning - Sample cleaning by focusing
argon beam on surface. Damage during cleaning
overcome by heating surface to 800-900 c

Autodoping Problem
Change in doping concentration of epitaxial
Layer. Two type of Auto doping.
1) Gas Phase Autodoping
On high temperature, dopent in substrate
diffuse and mix with gas stream, cause change
in concentration of epitaxial region
2) Solid State Outdiffusion
Dopent diffuse from higher concentration region
to Lower concentration region

Autodoping effect for
same type material

Pattern Shift & Distortion
Reason: Epitaxial layer growth is Anistropic
(depends on orientation) because of which
growth rate is non uniform, this give rise to
distortion

IIL – Integrated Injection
Logic
No biasing loading resistor at all because
resistor require lot of power and space on IC
CHIP. IIL have achieved high speed and less
power dissipation.
1. IIL logic gates are constructed using Bipolar junction transistor
only.
2. Basic logic units use multicollector npn transistors which are
powered from pnp tranistors
3. Due to obsence of resistors, it uses very small silicon chip area.
Even a complete microprocessor can be obtained in a single chip.
4. Easily fabricated and economical.
5. Power consumption is low and speed-power product is constant
(very small - 4pJ)
6. IIL has propgation delay about 1nS, power dissipation 1mW.

BiCMOS
BiCMOS is an evolved semiconductor
technology that incorporating two separate
technologies, namely bipolar junction transistor
and CMOS transistor in a single modern
integrated circuit.

 Advantages
Analog amplifier design is facilitated and improved by
using high impedance CMOS circuit as input and
remaining are realized by using bipolar transistors.
Since it is a grouping of bipolar and CMOS technologies we
can use BJT if speed is a critical parameter and we can use
MOS if power is a critical parameter
It has low power dissipation than bipolar technology alone
improved speed performance compared to CMOS
technology alone
It has the bidirectional capability (source and drain can be
interchanged as per requirement)
 Disadvantages
The fabrication process of this technology is comprised of
both
the CMOS and bipolar technologies increasing the
complexity.
Due to increase in the complexity of the fabrication
process, the cost of fabrication also increases.

Epitaxial Growth

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