Ion Implantation CEC, Inha University Chi-Ok Hwang

Ion Implantation Ion implantation (introduced in 1960’s) 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

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

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

Ion implantation

Ion Implantation Limitations -complex machine operations -safety issue to the personnel Ion implantation profiles -range, R -projected range, R p -projected straggle, ΔR p -projected lateral straggle, ΔR ⊥

Ion Implantation Simulation size: cascade size ( cm 3 (M.-J. Caturla etc, PRB 54, 16683, 1996) ) atoms (J.B. Gibson etc, PR 120(4), 1229, 1960) - a few hundreds of thousands of atoms (J. Frantz etc, PRB 64, , 2001) Time scales - thermal vibration periods of atoms in solids: 0.1 ps ( 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 /cm 3 (5.43Å unit cell, 8/unit cell) ion dose: ions/cm 2

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)

Ion Implantation ion implantation Potential: BCA - nuclear stopping power; elastic collision V ij (r) = Z i Z j e 2 /r Φ(r) Φ(r); screening of the nuclei due to the electron cloud ① Thomas-Fermi ② ZBL; universal screening potential - electronic stopping power; frictional force ③ Stillinger-Weber potential

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

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)

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

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 ion’s energy is relatively low The percentage of the interstitials and vacancies surviving the recombination decreases as the implant energy increases

Kinchin-Pease Model E d ; displacement threshold energy (15 eV) Number of point defects Net increase of point defects N; local defect density N α ; critical defect density for amorphization f; fraction of defects surviving the recombination within one recoil cascade

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