VACANCY-IMPURITY INTERACTIONS IN

ION-IMPLANTED SILICON

Peter J. SimpsonThe University of Western Ontario

J. Rideout, A.P. Knights McMaster University

Outline• Ion induced defects•Positron annihilation•Chemical “fingerprints”•Migration energies

Vacancy production• silicon implantation into silicon at 500keV generates

~2900 vacancy-interstitial pairs per ion (SRIM)

• silicon monovacancies are mobile at room temperature

• vacancies pair with each other or with impurities (dopants, oxygen)

• ~at room temperature, ~90% of the vacancies produced recombine with interstitials

Positron Annihilation

= g(p)shifted

Totalmomentum

Gamma ray spectrum

503 505 507 509 511 513 515 517 519

coun

ts

gamma ray energy (keV)

Positrons are trapped by defects

“S”harpness parameter

Figure by Maik Butterling

Positron accelerator

Example: ion-implanted silicon

0 5 10

0.91

0.97

1.03

0.94

1.00

Silicon implanted with 11.6 MeV Au ions

va

lenc

e el

ectr

on p

aram

eter

(als

o ca

lled

"S p

aram

eter

")

Depth (microns)

1e13 1e12 5e10 1e10 5e9 virgin silicon

Measuring vacancy concentrations

109 1010 1011 1012 1013

1017

1018

1019

Implanted ions: Au Ge

Def

ect c

once

ntra

tion

(cm

-3)

Ion fluence (cm-2)

A closer look at annihilation spectra…

Chemical “fingerprints”

Arsenic in silicon

Various fluorides

0 1 2 3 40.5

1.0

1.5

2.0

2.5

3.0 NaF LiF MgF2

Momentum (a.u.)

n(p)

/ n G

e(p)

F-doped silicon

0.0 0.5 1.0 1.5 2.0 2.5 3.00.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

pL(atomic units)

n(p)

/nSi

(p)

"As implanted" FZ 10 min anneal @ 650oC 30 min anneal @ 650oC

“Reconstruction”

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0.91.01.11.21.31.41.51.61.71.81.92.02.12.22.32.42.5

pL (atomic units)

n(p)

/nSi

(p)

Experimental 62.2% (Fluoride)+38.7% (Bulk-Si)

FZ 30 min @650oC

New apparatus

In situ ion implantation/positron spectroscopy

Positron Source and Moderator (Ti/Pt)

Ramp annealing of 10keV argon implant1-5 ohm-cm boron-doped silicon

260K

480K

Isothermal annealing

Arrhenius plot

Ea ~0.2eV

Summary• Interplay among vacancies, interstitials and impurities

provides complex microscopic behaviour that drives materials properties

• Positron annihilation can provide pieces of the puzzle to understand this

Void formation threshhold:Implant 325 keV He, anneal 800oC.

0 10 20 30 40 50 60

0.96

0.98

1.00

1.02

1.04

1.06

FZ n-type

no

rmal

ized

S p

aram

eter

positron energy (keV)

1x1015 3x1015 6x1015 1x1016

Void formation threshhold

0 10 20 30 40 50 60

0.96

0.97

0.98

0.99

1.00

Cz p-type

norm

aliz

ed S

par

amet

er

positron energy (keV)

1x1015

3x1015

6x1015

1x1016

Void formation threshhold

0 1 2 3 4 5 6 70.96

0.97

0.98

0.99

1.00

1.01

1.02

1.03

1.04

1.05

N

orm

aliz

ed S

Par

amet

er

Depth (m)

FZ n-type Cz p-type Cz n-type

Annealing ambient

0 10 20 30 400.94

0.96

0.98

1.00

1.02

1.04

1.06FZ n-type

no

rmal

ized

S p

aram

eter

positron energy (keV)

N2 10 min O2 10 min N2 70 min O2 70 min

Applications

• Irradiation• Aging• Fatigue• Thermal history• Thin film growth• Porosity

• Semiconductors• Metals• Polymers• Ceramics

Ion implantation creates vacancies and interstitials, and introduces impurities