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M.H.Nemati Sabanci University
Ion Implantation M.H.Nemati Sabanci University
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Ion Implantation 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+ 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 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 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
After Annealing Before Annealing
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Ion Implantation: Hardware
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 Electrical System Gas Cabin Analyzer Magnet Vacuum Pump
Ion Source 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 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
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
Ion source Extraction electrode Analyzer magnet Post acceleration Plasma flooding system End analyzer
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Ion Beam Line Suppression Electrode Analyzer Magnet Vacuum Pump
Ion Source Beam Line Extraction Electrode Post Acceleration Electrode Vacuum Pump Plasma Flooding System 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 Ion Beam Smaller m/q Ratio Larger m/q Ratio Right m/q Ratio
Magnetic Field (Point Outward) Flight Tube
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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 N-Well P-Epi P-Wafer
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Implantation Process: S/D Implantation
Low energy (20 keV), high current (>1015/cm2) P+ Photoresist n+ n+ STI USG P-Well N-Well P-Epi P-Wafer
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Process Issues 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
Ion source Extraction Analyzer magnets Post acceleration Charge neutralization system Beam stop
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Summary of Ion Implantation
Well High energy, low current Source/Drain Low energy, high current Vt Adjust Low energy, low current LDD Low energy, low current
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