Ion Implantation Ted Mechanisms
# Transient Enhanced Diffusion: Step 13 — Point Defect-Mediated Dopant Migration
During high-temperature RTA, implantation damage creates an excess of point defects (vacancies and interstitials). Step 13 explores Transient Enhanced Diffusion (TED) — the accelerated dopant migration mediated by these excess defects. Vacancies, in particular, enhance dopant diffusion by providing fast migration paths. An implanted dopant can hop to a neighboring vacancy and move one lattice site at a time. With excess vacancies from implant damage, dopant diffusion can increase 10–100x compared to intrinsic diffusion, causing severe profile broadening. TED is the dominant diffusion mechanism during the first few minutes of RTA, when point defects are most abundant. Step 13 explains TED physics and methods to suppress it.
## 1. Vacancy-Mediated Diffusion and the Point Defect Gradient
During implantation, vacancies and interstitials are created in pairs by ion collisions. Interstitials diffuse rapidly to the surface or recombine with vacancies. Vacancies diffuse more slowly and accumulate near the implant peak (where damage is maximum). During RTA warm-up, these vacancy clusters are activated thermally and become mobile. A dopant surrounded by vacancies experiences frequent vacancy-dopant exchanges, moving rapidly through the crystal. The point defect concentration [V] (and [I]) decays exponentially as defects diffuse out and recombine. TED intensity therefore decreases with annealing time, faster at higher temperature.
## 2. Real Diagram: TED-Dominated Profile Broadening
## 3. TED Suppression: Halo Implants and Carbon Co-Implantation
TED can be suppressed by point defect engineering: introduce excess interstitials (which recombine with and annihilate vacancies) via a light co-implant or halo implant — a low-energy implant of the same dopant type, offset spatially to create interstitials in regions where TED would otherwise cause broadening. Alternatively, carbon implants (which preferentially bind to vacancies) can suppress vacancy-mediated diffusion by tying up vacancies in immobile complexes.
## 4. Real Diagram: Vacancy-Mediated Diffusion and the Point Defect Gradient
## Transient Enhanced Diffusion's Place in the Process Lineage
TED mechanisms is step 13 of the ion implantation series — explaining the dominant diffusion process during rapid annealing. Steps 14–25 continue through electrical activation, defect management, and process optimization.