Transcript Ion Implantation

Ion Implantation
M.H.Nemati
Sabanci University
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Ion Implantation
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Introduction
Safety
Hardware
Processes
Summary
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Introduction
• Dope semiconductor
• Two way to dope
– Diffusion
– Ion implantation
• Other application of ion implantation
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Dope Semiconductor: Diffusion
• Isotropic process
• Can’t independently control dopant profile
and dopant concentration
• Replaced by ion implantation after its
introduction in mid-1970s.
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Dope Semiconductor: Ion Implantation
• Used for atomic and nuclear research
• Early idea introduced in 1950’s
• Introduced to semiconductor manufacturing
in mid-1970s.
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Dope Semiconductor: Ion Implantation
• Independently control dopant profile (ion
energy) and dopant concentration (ion
current times implantation time)
• Anisotropic dopant profile
• Easy to achieve high concentration dope of
heavy dopant atom such as phosphorus and
arsenic.
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Ion Implantation, Phosphorus
SiO2
Poly Si
n+
P+
n+
P-type Silicon
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Ion Implantation Control
• Beam current and implantation time control
dopant concentration
• Ion energy controls junction depth
• Dopant profile is anisotropic
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Stopping Mechanism
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Ions penetrate into substrate
Collide with lattice atoms
Gradually lose their energy and stop
Two stop mechanisms
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Two Stopping Mechanism
• Nuclear stopping
– Collision with nuclei of the lattice atoms
– Scattered significantly
– Causes crystal structure damage.
• electronic stopping
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Collision with electrons of the lattice atoms
Incident ion path is almost unchanged
Energy transfer is very small
Crystal structure damage is negligible
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Implantation Processes: Channeling
• If the incident angle is right, ion can travel long
distance without collision with lattice atoms
• It causes uncontrollable dopant profile
Lots of collisions
Very few collisions
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Channeling Effect
Lattice Atoms
Channeling Ion
Collisional Ion
q
Wafer
Surface
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Implantation Processes: Channeling
• Ways to avoid channeling effect
– Tilt wafer, 7° is most commonly used
– Screen oxide
– Pre-amorphous implantation, Germanium
• Shadowing effect
– Ion blocked by structures
• Rotate wafer and post-implantation diffusion
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Implantation Processes: Damage
• Ion collides with lattice atoms and knock them
out of lattice grid
• Implant area on substrate becomes amorphous
structure
Before Implantation
After Implantation
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Implantation Processes: Anneal
• Dopant atom must in single crystal structure
and bond with four silicon atoms to be activated
as donor (N-type) or acceptor (P-type)
• Thermal energy from high temperature helps
amorphous atoms to recover single crystal
structure.
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Thermal Annealing
Lattice Atoms
Dopant Atom
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Thermal Annealing
Lattice Atoms
Dopant Atom
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Thermal Annealing
Lattice Atoms
Dopant Atom
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Thermal Annealing
Lattice Atoms
Dopant Atom
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Thermal Annealing
Lattice Atoms
Dopant Atom
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Thermal Annealing
Lattice Atoms
Dopant Atom
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Thermal Annealing
Lattice Atoms
Dopant Atom
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Thermal Annealing
Lattice Atoms
Dopant Atoms
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Implantation Processes: Annealing
Before Annealing
After Annealing
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Ion Implantation: Hardware
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Gas system
Electrical system
Vacuum system
Ion beamline
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Implantation Process
Gases and Vapors:
P, B, BF3, PH3, and AsH3
Next Step
Implanter
Select Ion:
B, P, As
Select Ion
Energy
Select Beam
Current
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Ion Implanter
Gas Cabin
Ion
Source
Electrical
System
Analyzer
Magnet
Vacuum
Pump
Beam
Line
Electrical
System
Vacuum
Pump
Plasma Flooding
System
Wafers
End Analyzer
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Ion Implantation: Gas System
• Special gas deliver system to handle
hazardous gases
• Special training needed to change gases
bottles
• Argon is used for purge and beam
calibration
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Ion Implantation: Electrical System
• High voltage system
– Determine ion energy that controls junction depth
• High voltage system
– Determine ion energy that controls junction depth
• RF system
– Some ion sources use RF to generate ions
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Ion Implantation: Vacuum System
• Need high vacuum to accelerate ions and
reduce collision
• MFP >> beamline length
• 10-5 to 10-7 Torr
• Turbo pump and Cryo pump
• Exhaust system
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Ion Implantation: Control System
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Ion energy, beam current, and ion species.
Mechanical parts for loading and unloading
Wafer movement to get uniform beam scan
CPU board control boards
– Control boards collect data from the systems,
send it to CPU board to process,
– CPU sends instructions back to the systems
through the control board.
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Ion Implantation: Beamline
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Ion source
Extraction electrode
Analyzer magnet
Post acceleration
Plasma flooding system
End analyzer
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Ion Beam Line
Suppression Electrode
Vacuum
Pump
Ion
Source
Extraction
Electrode
Post Acceleration
Electrode
Plasma Flooding
System
Analyzer
Magnet
Beam
Line
Vacuum
Pump
Wafers
End Analyzer
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Ion implanter: Ion Source
• Hot tungsten filament emits thermal electron
• Electrons collide with source gas molecules
to dissociate and ionize
• Ions are extracted out of source chamber and
accelerated to the beamline
• RF and microwave power can also be used to
ionize source gas
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Ion Implantation: Extraction
• Extraction electrode accelerates ions up to
50 keV
• High energy is required for analyzer magnet
to select right ion species.
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Ion Implantation: Analyzer Magnet
• Gyro radius of charge particle in magnetic field
relate with B-field and mass/charge ratio
• Used for isotope separation to get enriched U235
• Only ions with right mass/charge ratio can go
through the slit
• Purified the implanting ion beam
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Analyzer
Magnetic Field (Point Outward)
Ion Beam
Larger m/q Ratio
Flight Tube
Smaller m/q Ratio
Right m/q Ratio
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Ion Implantation: The Process
• CMOS applications
• CMOS ion implantation requirements
• Implantation process evaluations
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Implantation Process: Well
Implantation
• High energy (to MeV), low current (1013/cm2)
P+
Photoresist
N-Well
P-Epi
P-Wafer
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Implantation Process: VT Adjust
Implantation
Low Energy , Low Current
B+
Photoresist
USG
STI
P-Well
N-Well
P-Epi
P-Wafer
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Lightly Doped Drain (LDD) Implantation
• Low energy (10 keV), low current (1013/cm2)
P+
Photoresist
USG
STI
P-Well
P-Epi
N-Well
P-Wafer
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Implantation Process: S/D Implantation
• Low energy (20 keV), high current (>1015/cm2)
P+
Photoresist
STI
n+
n+
P-Well
USG
N-Well
P-Epi
P-Wafer
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Process Issues
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Wafer charging
Particle contamination
Elemental contamination
Process evaluation
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Ion Implantation: Safety
• One of most hazardous process tools in
semiconductor industry
• Chemical
• Electro-magnetic
• Mechanical
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Summary of Ion Implantation
• Dope semiconductor
• Better doping method than diffusion
• Easy to control junction depth (by ion
energy) and dopant concentration ( by ion
current and implantation time).
• Anisotropic dopant profile.
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Summary of Ion Implantation
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Ion source
Extraction
Analyzer magnets
Post acceleration
Charge neutralization system
Beam stop
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Summary of Ion Implantation
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Well
Source/Drain
Vt Adjust
LDD
High energy, low current
Low energy, high current
Low energy, low current
Low energy, low current
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