Ion Implantation

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Ion Implantation

• CEC, Inha University
• Chi-Ok Hwang

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Ion Implantation

• Ion implantation (introduced in 1960s) vs
  chemical diffusion
• High accuracy over many orders of magnitude of
  doping levels
• Depth profiles by controlling ion energy and
  channeling effects
• Dopants into selected regions using masking
  material
• Both p- and n-type dopants
• Recovering implant-damaged Si crystalline via
  thermal annealing
• Definition of ion implantation
• CMOS energy range 0.2keV-2MeV

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Ion Implantaion

• Aspects of ion implantaion dose, dose
  uniformity, profiles (depth distribution),
  damage, damage recovery after annealing
• Dose
• Limitations
• -damage to the material structure of the target
• -shallow maximum implantation depth (1?)
• -lateral distribution of implanted species
• -throughput is typically lower than diffusion
  doping processes

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Ion Implantation

• Ion species and substrate
• Tilt and rotation
• Ion energy
• Dose rate
• Results dopant distribution, defect distribution

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Ion implantation
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Ion Implantation

• Limitations
• -complex machine operations
• -safety issue to the personnel
• Ion implantation profiles
• -range, R
• -projected range, Rp
• -projected straggle, ?Rp
• -projected lateral straggle, ?R?

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Ion Implantation

• Simulation size cascade size (10-25 cm3 (M.-J.
  Caturla etc, PRB 54, 16683, 1996) )
• - 1000 atoms (J.B. Gibson etc, PR 120(4), 1229,
  1960)
• - a few hundreds of thousands of atoms (J.
  Frantz etc, PRB 64, 125313 , 2001)
• Time scales
• - thermal vibration periods of atoms in solids
  0.1 ps (10-13 sec) or longer
• - cascade lifetime 10 ps (M.-J. Caturla etc,
  PRB 54, 16683, 1996)
• - ion implantation (secs annealing time
  secs-mins)
• Si density 5 x 1022 /cm3 (5.43Å unit cell,
  8/unit cell)
• ion dose 1014 -1018 ions/cm2

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Stopping powers

• Electric fields nuclear charge of the silicon
  atoms (short range interatomic force by screening
  effect, nuclear stopping) and valence electrons
  of the crystal (polarizational force, nonlocal
  electronic force)
• exchange of electrons with the silicon atoms
  (local electronic stopping)

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Ion Implantation

• ion implantation Potential BCA
• - nuclear stopping power elastic
• collision
• Vij(r) Zi Zje2 /r F(r)
• F(r) screening of the nuclei due to the
• electron cloud
• ? Thomas-Fermi
• ? ZBL universal screening potential
• - electronic stopping power frictional
• force
• ? Stillinger-Weber potential

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Ion Implantation

• Simulations of ion implantation
• - Full MD
• - Recoil Interaction Approximation (RIA) (1-100
  keV)
• - BCA valid for low-mass ions at incident
  energies from 1-15 keV (M.-J. Caturla, etc, PRB
  54, 16683, 1996)

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Ion Implantation

• Three phases of collision cascade
• - collisional phase (0.1-1 ps)
• - thermal spike (1 ns)
• - relaxation phase (a few thousands of fs)
• Measurements of depth profiling
• - Rutherford Backscattering Spectroscopy (RBS)
• - Secondary Ion Mass Spectroscopy (SIMS)
• - (Energy-Filtered) Transmission Electron
  Microscopy ((EF)TEM)

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BCA

• Primary recoil atoms,
• Binary scattering tables described by specifying
  the species involved in the collision, the impact
  parameter, and the ion energy
• Assuming that the potential energy of the ion at
  the start of the collision is negligible compared
  to its kinetic energy
• Neglecting multi-body interactions

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Kinchin-Pease Model

• Damage model damage generation, damage
  accumulation, defect encounters, amorphization
• Number of Frenkel pairs proportional to the
  nuclear energy loss
• Nuclear energy loss is deposited locally and
  induces local defects
• Holds only when the secondary ions energy is
  relatively low
• The percentage of the interstitials and vacancies
  surviving the recombination decreases as the
  implant energy increases

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Kinchin-Pease Model
Number of point defects
Ed displacement threshold energy (15 eV)
Net increase of point defects
N local defect density Na critical defect
density for amorphization f fraction of defects
surviving the recombination within one recoil
cascade
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Kinchin-Pease Model
Damage dechanneling defect encounter probability
Amorphization the critical density is taken to
be 10 of the lattice Density for all implant
species