Boron Diffusion in Silicon CEC Inha University Chi-Ok Hwang.

Boron Diffusion in Silicon

CECInha UniversityChi-Ok Hwang

Transient Enhanced Diffusion

• Modeling dopant diffusion using Arrhenius turns out to be incorrect experimentally;

• “+1” model: ① for sub-amorphizing implants, independe

nt of both dose and implant temperature, that is, of the number of Frenkel pairs (Defects and Diffusion in Silicon Processing by Chen et al. in 1997,ibid by Giles et al. in 1997)) ② incorrect at very low dose, high mass or very high energy implants.

)/exp()( 0 kTEDTD a

Transient Enhanced Diffusion

• When the defect density is relatively small, the faster diffusing species can reach the surface before encountering the opposite type defect.

• During annealing of higher energy or larger mass implants it is possible that vacancies may exist even after recombination.

I and V Example(Density Effect)

When the defect density is relatively small, the faster diffusing speciescan reach the surface before encountering the opposite type defect.

I and V Example(Energy or Mass Effect)

During annealing of higher energy or larger mass implants it is possible that vacancies may exist even after recombination

Interstitials Peak : 100Å

Vacancies Peak : 105Å

Separation : 5Å

Interstitials Peak : 200Å

Vacancies Peak : 210Å

Separation : 10Å

Initial Damage

Initial Damage

Transient Enhanced Diffusion

• TED is nearly independent of the ion-implant damage for initial times and after some period the enhancement goes away ⇒ The excess interstitial concentration remains approximately fixed during TED and drops to its equilibrium value. ⇒ “rod-like” or “{311}” defects.

• The amount of TED is larger at lower temperatures ⇒ The duration of TED is much shorter at higher temperatures.

Vacancy MechanismBVVBs

Kick-out Mechanism

is

i

BIB

BBI

BIIB

)/exp( TkEP Bb

)/exp( TkEP Bb

Kick-out Mechanism(Zhu etc, PRB 54(7), 4741

(1996)

Interstitialcy Mechanism• Alippi etc, PRB 64, 075207 (2001) -B in a substitutional site -SiB complex -B into an interstitial position -B into the closest lattice site kicking out a SiI(silicon self

-interstitial) (SiI diffuses away or stays bound to the boron atom)• Windl etc, PRL 83(21), 4345 (1999)• Sadigh etc, PRL 83(21), 4341 (1999)

SBSiSiBenergylowestXBSi Tdis )(

Terms

• Density-Functional based Tight-Binding Molecular Dynamics (DF-TBMD)

• Tight-binding approximation: it is assumed that the electrons are tightly bound to the nuclei.

Interstitialcy Mechanism(Alippi etc, PRB 64, 075207, 2001)

Interstitialcy Mechanism(Alippi etc, PRB 64, 075207, 2001)

Interstitialcy Mechanism(Alippi etc, PRB 64, 075207, 2001)

Interstitial Sites

Sadigh etc, PRL 83(21), 4341 (1999)

Boron Interstitial Clusters

Boron Cluster Models

Vacancy Cluster Model

1

1

nn

nn

VIV

VVV

Coupled Diffusion