1. M.H.Nemati Sabanci University
Ion Implantation
M.H.Nemati
Sabanci University

2. Ion Implantation
Introduction
Safety
Hardware
Processes
Summary

3. Introduction Dope semiconductor Two way to dope
Diffusion
Ion implantation
Other application of ion implantation

4. Dope Semiconductor: Diffusion
Isotropic process
Can’t independently control dopant profile and dopant concentration
Replaced by ion implantation after its introduction in mid-1970s.

5. Dope Semiconductor: Ion Implantation
Used for atomic and nuclear research
Early idea introduced in 1950’s
Introduced to semiconductor manufacturing in mid-1970s.

6. 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.

7. Ion Implantation, Phosphorus
SiO2
Poly Si n+ n+
P-type Silicon

8. Ion Implantation Control
Beam current and implantation time control dopant concentration
Ion energy controls junction depth
Dopant profile is anisotropic

9. Stopping Mechanism Ions penetrate into substrate
Collide with lattice atoms
Gradually lose their energy and stop
Two stop mechanisms

10. 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

11. 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

12. Channeling Effect Lattice Atoms Channeling Ion Collisional Ion q
Wafer Surface

13. 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

14. 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

15. 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.

16. Thermal Annealing
Lattice Atoms
Dopant Atom

17. Thermal Annealing
Lattice Atoms
Dopant Atom

18. Thermal Annealing
Lattice Atoms
Dopant Atom

19. Thermal Annealing
Lattice Atoms
Dopant Atom

20. Thermal Annealing
Lattice Atoms
Dopant Atom

21. Thermal Annealing
Lattice Atoms
Dopant Atom

22. Thermal Annealing
Lattice Atoms
Dopant Atom

23. Thermal Annealing
Lattice Atoms
Dopant Atoms

24. Implantation Processes: Annealing
After Annealing
Before Annealing

25. Ion Implantation: Hardware
Gas system
Electrical system
Vacuum system
Ion beamline

26. 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

27. Ion Implanter Electrical System Gas Cabin Analyzer Magnet Vacuum Pump
Ion Source
Beam Line
Electrical System
Vacuum Pump
Plasma Flooding System
Wafers
End Analyzer

28. 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

29. Ion Implantation: Electrical System
High voltage system
Determine ion energy that controls junction depth
RF system
Some ion sources use RF to generate ions

30. 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

31. 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.

32. Ion Implantation: Beamline
Ion source
Extraction electrode
Analyzer magnet
Post acceleration
Plasma flooding system
End analyzer

33. 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

34. 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

35. Ion Implantation: Extraction
Extraction electrode accelerates ions up to 50 keV
High energy is required for analyzer magnet to select right ion species.

36. 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

37. Analyzer Ion Beam Smaller m/q Ratio Larger m/q Ratio Right m/q Ratio
Magnetic Field (Point Outward)
Flight Tube

38. Ion Implantation: The Process
CMOS applications
CMOS ion implantation requirements
Implantation process evaluations

39. Implantation Process: Well Implantation
High energy (to MeV), low current (1013/cm2) P+
Photoresist
N-Well
P-Epi
P-Wafer

40. Implantation Process: VT Adjust Implantation
Low Energy , Low Current B+
Photoresist
USG
STI
P-Well
N-Well
P-Epi
P-Wafer

41. 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

42. 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

43. Process Issues Wafer charging Particle contamination
Elemental contamination
Process evaluation

44. Ion Implantation: Safety
One of most hazardous process tools in semiconductor industry
Chemical
Electro-magnetic
Mechanical

45. 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.

46. Summary of Ion Implantation
Ion source
Extraction
Analyzer magnets
Post acceleration
Charge neutralization system
Beam stop

47. 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