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
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