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Solid State Devices
SMU
Fall 2013
An Overview of
Microelectronic Fabrication
and
Semiconductor Technology
August 27, 2014
Historical Trends
Silicon Wafer Size
• Early Wafers - 1, 1.5, 2
Inch Diameters
• Wafer Size has Increased
Steadily
• 200 mm (8”) Wafers in
Production
• 300 mm (12”) Coming on
Line Now (> 3B$/Fab)
• 450 mm Planned
Larger Wafers
Lower Die Cost
• Cost to Process a Wafer is
Relatively Fixed for a Given
Process
• Larger Wafer Lower Cost/Die
Historical Trends
Memory Density (Bits/Chip)
• Moore’s Law - Exponential
Increase in Chip Complexity
• ISSCC Research Benchmarks
•1967 - 64 bit Memory
•1984 - 1Mb Memory
•1995 - First 1 Gb Memory
Historical Trends
Microprocessor Complexity (Trans./Chip)
• ISSCC Benchmarks
•1971 - 2000 Transistors
•1988 - 1M Transistors
•1998 - 100M Transistors
Historical Trends
Memory Feature Size (mm)
• Feature Size Decreases by 2X
approximately every 5 years
• Each New Process Generation
Doubles Density - Reduction of
Feature Size by 0.707
• The Original Nanotechnology
• Feature size now 70-90 nm
• Transistors Operate Normally to at
Least 6 nm
• Diameter of human hair ~ 40 – 120
µm (1000 nm = 1 µm)
Now (2015): ~ 20 to 30 nm gate lengths
Semiconductor Industry
Roadmap - ITRS
Each new process generation doubles chip density by scaling feature size by 0.7.
NMOS Transistor
Top View and Cross-Section
Conducting
Channel Region
• N-Channel Metal-Oxide
Semiconductor Transistor
• n- and p-type
semiconductor regions
• Thick and thin oxides
• Etching Openings
• Polysilicon gate
• Metal (Al)
Interconnections
Basic NMOS Process
Key Steps
•Oxidation
•Photolithography
•Implantation
•Diffusion
•Etching
•Film Deposition
CMOS Technology
N-Well Technology Cross-Section
Oxidation
Photolithography
Implantation
Diffusion
Etching
Film Deposition
• Complementary MetalOxide Semiconductor
Technology
• Dominant Technology in
Integrated Circuits Today!
• Requires both NMOS and
PMOS Transistors
Bipolar Transistor
Top View and Cross-Section
Active
Transistor
Region
• Bipolar Junction Transistor
(BJT)
• Standard Buried Collector
Process (SBC)
• n- and p-type semiconductor
regions
• Thick and thin oxides
• Etching Openings
• Metal (Al) Interconnections
Standard Buried Collector (SBC) Process
Key Steps
•Oxidation
•Photolithography
•Implantation
•Diffusion
•Etching
•Film Deposition
Processing Summary
•
•
•
•
•
wafer cleaning
thermal oxidation, Ch 3 (or CVD, Ch6)
lithography, Ch 2
diffusion, Ch 4 (or ion implantation, Ch 5)
metal deposition, Ch 6
followed by
• wafer level testing
• packaging, Ch 8
Review 3311 MOSFET Traveler
Go To Materials Basics Slides
Cubic Lattice Structures
3D
(z=1)
(0)
(y=1)
(x=1)
a
Simple Cubic
2D
3 September 2009
Body Centered Cubic
Face Centered Cubic
Diamond Lattice
• two face-centered-cubic lattices
• displaced along the body diagonal of the larger cube by
one quarter of the body diagonal.
The diamond lattice therefore is a face-centered-cubic lattice with a basis
containing two identical atoms.
a/4 offset square lattice
3 September 2009
a/4 offset FCC lattice
Diamond & Zincblende
3 September 2009
InP or GaAs
Explain this structure in
Terms of FCC lattices
What atom is group III?
What atom is group IV?
3 September 2009
Arrangement of III&V Atoms
If we grow a III-V crystal structure, how do the atoms bond to one another?
Where do they go relative to one another?
3
2
1
3 September 2009
STM of InP/InGaAs/InP
• Periodic atomic arrangement…
H.Chen, et. al, J. Appl. Phys. 89 4815 (2001)
3 September 2009
Atomic spacing and
energy levels
electrons in free space
Energy, E
vacuum energy level
electrons are bound
4p
4s
3s, 3p, 3d
2s, 2p
1s
~1-2A
crystal
3 September 2009
spacing between
atoms
≥10A
isolated atom
Properties of electrons in
semiconductor crystals
• Quantum Mechanical ► no longer Classical
– Behave as particles
– Behave as waves
Particle Wave Duality
• Describe by a wavefunction
– Intensity = probability of finding the e-
Energy Bands
(Kronig-Penney Model Developed in EE 5310/7310)
• function of periodicity of the crystal
• Bloch Theorem:
– solutions to Schroedinger equation for a periodic potential
– yk(r) = uk(r) exp(ik r)
• uk(r) is period of crystal lattice
• uk(r) = uk(r + T)
• exp(ik r) is a plane wave
– Bloch Function
• one electron wavefunction
• sum of traveling waves
after Kittel, ‘Introduction to Solid State Physics’, 1996
ISBN 0-471-11181-3
potential energy of
an electron among
positive atom cores
U = potential
Atom nucleus
energy
a
x
after Kittel, ‘Introduction to Solid State Physics’, 1996
ISBN 0-471-11181-3
energy band diagram
Silicon
energy
*1 lattice spacing
N = 1, s = 1
-p/a
kx
p/a
Periodicity changes as look around
the crystal structure
after Kittel, ‘Introduction to Solid State Physics’, 1996 ISBN 0-471-11181-3
energy
Bandgap
-p/a
3 September 2009
kx
p/a
Direct vs Indirect Semiconductors
GaAs
direct
3 September 2009
Silicon
indirect
Impact of Temperature
On Bandgap
• temperature impact on crystal structure
– expand
– shrink
• Eg(T) = Eg(0) – AT2/(T+B)
– T in Kelvin
– A and B are contants
• specific to each crystal
after Kittel, ‘Introduction to Solid State Physics’, 1996
ISBN 0-471-11181-3
Bandgap vs Lattice Constant Chart
Material and Lattice Strain
• change in length over a pre-specified length
– e = dl/l
– if l = a (lattice constant length reference)
– e = da/a
• stress versus strain
– stress = force per unit area
– s = Ye
• Y = young’s modulus
• elastic strain
– rubberband-like
• inelastic strain
after Kittel, ‘Introduction to Solid State Physics’, 1996
ISBN 0-471-11181-3
strain in a crystal lattice
• uniaxial
• biaxial
• orthrhombic
elastic -> balance
z
y
x
• 3D strain effects
– exx , eyy ,ezz
– exy , eyz ,exz
• characterize in 1D
– ezz usually
lattice-matched strain
• tensile
• compressive
example of lattice-matched
strain
• SiGe/Si
– aSi = 5.431Å
– aGe = 5.66 Å
• for Si0.8Ge0.2
– a(Si0.8Ge0.2) ~ 0.8(5.431) + 0.2(5.66) ~ 5.48 Å
– e = da/a ~ (5.48-5.431)/5.431
– e ~ 0.90%
Critical Thickness
• crystal layer thickness beyond which the strained layer can
no longer withstand the strain energy (about 100 to 500
Angstrom%)
• Strain balancing: alternate layers of compressivelystrained layers with tensile-strained layers (allows
exceeding “critical thickness”)
• crystal will return to it’s natural state
– Relaxation
• generation of crystalline defects at point of relaxation
– lattice plane slippage
– during epitaxy
• “missing” atoms in lattice
• rough surface
Strain Impact on Energy Bands
• crystal lattice alteration
• via bloch’s theory
– period changes
– therefore energy bands will change
• most prominent changes
– energy level shifts
– band profile changes (can change effective mass of carriers!)
direct gap
III-V
Point Defects & Doping
Self Interstitial
Vacancy
Substutional
Substutional
Interstitial
3 September 2009
MBE Facility at IntelliEPI’s Facility in Richardson, Texas
– 7 MBE reactors:
• One Riber 7000 (7x6”)
• Three Riber 6000 (4x6”)
• Three Riber 49 (4x4”)
– First Riber7000 installation in IIIV industry
– Proprietary in-situ real-time
growth monitoring technology
– Dedicated operation and cleaning
facilities designed to handle
phosphorous for all MBE systems
Post-growth Characterization Capabilities
– Class 100 clean room: (2000 ft2)
– Characterization tools:
• X-ray diffraction
• PL mapping
• Surface particle scan
• Hall measurement
• Contactless resistivity
mapping
• Electro-chemical CV
profiling
• White light reflection
spectrometer
• Electrical CV profiling
• Mercury probe CV
– Large area device fabrication:
• Processing capability
• Probe station with DC
device characterization
IntelliEPI: III-V Compound Semicondutor Product Matrix
RF and microwave High Speed Digital

Applications




Device Structure

(Red in Production mode)

RF components
in handsets
Automotive
radar
Defense related

GaAs pHEMT
GaAs mHEMT
InP HEMT
InP HBT




Optoelectronics
OC768- 40Gbps
network
OC192-10Gbps
network

Fiber optic
network light
sources and
Photo-detectors
InP HBT
InP HEMT
GaAs mHEMT

GaAs PIN
InP PIN
QWIP
Diode laser


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IntelliEPI: Thickness Uniformity
Across Platen for 7x6” MBE
Riber 7000 thickness uniformity
measured by white light reflection
103.0
No rmalized th ickn ess (%)
102.0
Ga
Al
101.0
7X6” platen
100.0
99.0
2,500Å GaAs
2,000Å AlAs
Outside wafer
Center wafer
98.0
97.0
0
50
100
150
Platen radial position (mm)
200
250
GaAs substrate
– Thickness variation across platen < 1% across 7X6” platen
configuration
– Si doping GaAs layer uniformity by contactless resistivity mapping:
• 6” wafer doping variation < 1%
• Difference from center wafer to outside wafer < 0.5%
Communications Technology Evolution
III-V semiconductors
from elements of
group III and group V
columns of Periodic
Table
•
III
IV
V
B
C
N
Al
Si
P
Ga
Ge
As
In
Sn
Sb
InP and GaAs are key enabling technology for all communications systems
– Wireless, telecomm, satellite, fiber optics, and other high frequency systems such as
collision warning radar system all require faster semiconductors like GaAs and InP
•
InP outperforms all existing RF/telecomm technology in terms of speed
– Wireless from 2GHz to 300 GHz with 2x breakdown voltage vs. SiGe, high gain, better
efficiency
– Current fastest flip-flop speed is 150 GHz (from IntelliEPI/Vitesse) vs. 96GHz of SiGe
Competing Building Blocks - Fiber optic network example
•
Internet is the main driving
force
– data, speed, bandwidth,
wireless
•
•
•
•
Both long-haul and local
networks shift to fiber optic
networks
2.5Gbps networks will be
replaced by 10Gbps (OC192)
2004-2005. GaAs is the major
semicon building block
40Gbps network will be the 2nd
largest in 2005 and will be
dominated by InP
Silicon will be dominant for
market adoption in the “late
majority” and “laggard” phases
High Speed Technology Race
InP Heterojunction
Bi-Polar Transistor (HBT)
0.25 mm
Base
Emitter
Collector
W. Hafez, et al, IEEE Elect. Dev. Lett.,
Vol 24, #7, pg 346, July 2003.
Ft > 150 GHz
*Partial slide Source: N. Pan, UCLA.
Divide by Two Circuit operating at 152 GHz!
IntelliEPI supplied materials.
•
Static digital flip-flop circuit fabricated by Vitesse using VIP2 process (InP DHBT)
*Data courtesy of Vitesse Semiconductor for DARPA-TFAST program.
Summary of Key Concepts
• Silicon: homojunctions
• Compound semiconductors enable an additional
degree of freedom along the growth direction
• MBE: ultra high vacuum deposition/crystal
growth process (MOCVD an alternative)
• Compound semiconductors suited for high speed
applications due to fast intrinsic electron mobility
• PHEMT analogous to FET
• HBT analogous to Si Bi-Polar Junction
Transistor (BJT)
End of Overview