Generation of vacancy-related defects during focused swift-ion beam implantation of silicon

I.Capan1, M.Jakšić1, Ž. Pastuović1,2, Rainer Siegele2, David Cohen2

1Ruđer Bošković Institute, Zagreb, Croatia2 Centre for Accelerator Science, IER, ANSTO, 1 New Illawarra Rd, Lucas heights NSW 2234, Australia

Split, 8-10 October 2012 Silicon Detector Workshop 2

Introduction

Influence of high energies/high fluences of particles on silicon-based detectors;

Can heavier ions offer cost effective simulation of radiation damage produced in semiconductor detectors by p, n, e?

Ion beams dense regions of vacancies and interstitials in bulk semiconductor clustering;

Electrically active cluster-related damage in silicon: Structure? Capture kinetics?

Split, 8-10 October 2012 Silicon Detector Workshop 3

40 60 80 100 120 140 160 180 200 220 240 260 280 300

0.0

0.1

0.2

0.3

0.4

0.5

Si ion implantation Neutron irradiation (/ 3.5) 4 MeV electrons (/ 4)

C, p

F

Temperature, K

Introduction

RD’s in n-type CZ Si

V2(=/-)

V2(-/0)

VO

?

VOVO

VVVV

Split, 8-10 October 2012 Silicon Detector Workshop 4

Introduction Divacancy & ion mass effect

Split, 8-10 October 2012 Silicon Detector Workshop 5

Introduction

Models for interpretation of the DLTS observed mass effect:

(i) the lattice distortation and strain due to accumulated damage produced by heavy ions in the highly localized collision cascades can prevent, to a large extent, the electronic bond switching. The effect increases with ion mass because a density of elastic energy deposition, i.e. primary defect generation rate increases and causes larger distrortation and strain in the crystal lattice. Since the electronic bond switching is a thermally activated process, V2(=/-) peak is more influenced by the lattice strain than V2(-/0) peak (V2(=/-) defect has a low activation temperature of 115K ), PRB 55 (1997);

Split, 8-10 October 2012 Silicon Detector Workshop 6

Introduction Models for interpretation of the DLTS observed mass

effect:

(ii) suppression of the DLTS signal from shallow states is due to a local depletion of the carrier concentration in the dense defect cascade region which leads to incomplete occupation of the shallow states such as VO and V2(=/-) in heavy ion implanted n-Si, PRB 65 (2002);

(iii) additional electrically active defects, e.g., vacancy-clusters (Vx, x>2) that artificially enhance the V2(-/0) signal, J. Appl. Phys. 93 (2003);

Split, 8-10 October 2012 Silicon Detector Workshop 7

Experiment The materials used in our experiment were phosphorus-

doped Czohralski-grown (CZ) silicon wafers with initial resistivities of (1–2) cm.

The Au/n-Si Schottky diodes were formed by thermal evaporation of gold on etched Si surface

The samples (D=1mm) were uniformly irradiated at RT with scanning focused 8.3 MeV Si3+ ion micro-beam (I=5 fA @ F=4x1012 ions/cm-2s-1) up to dose of 1010 cm-2.

Deep traps were characterized with depth resolving deep level transient spectroscopy (DLTS).

Split, 8-10 October 2012 Silicon Detector Workshop 8

Results CV

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.51E13

1E14

free

car

rier

con

cent

ratio

n (c

m-3

)

depth (mm)

Depth profile

Averaged energy loss profiles of 8.3 MeV Si ions implanted in 100nm Au/n-Si Schottky diode (TRIM) w threshold for dense vacancy regime (PRB79)

0 1x104 2x104 3x104 4x104 5x1040.01

0.1

1

10

100

1000

8.3 MeV Si

en

erg

y lo

ss (

eV

//io

n)

depth ()

NON-ionization (NIEL) ionization (LET)

Threshold for 1.2 v/A/ion = 25.2 eV/A/ion (Td=21eV)25.2

DLTS scan

Split, 8-10 October 2012 Silicon Detector Workshop 9

Results DLTS

100 150 200 250

-0.06

-0.04

-0.02

0.00

DL

TS

sig

nal (

pF)

Temperature (K)

8.3 Si MeV

52 54 56 58 60 62

-9

-8

-7

-6

-5

ln(e

/T2 )

1/kT

V2(-/0)

Ec-0.40 eV

Activation energy VO VV VP

0.170.23

0.420.45XX

Low-doped material!

??

Is it a point-likeIs it a point-like defect?defect?

Split, 8-10 October 2012 Silicon Detector Workshop 10

Results DLTS Capture kinetics

-5 -4 -3 -2 -10.06

0.08

0.10

0.12

0.14

0.16

DL

TS

am

plit

ude

(pF

)

log (tp)

Tmax = 188 K

8.3 MeV Si+

1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.01

0.000

0.002

0.004

0.006

)exp(1

t

CC

Point-like defect kinetics!Point-like defect kinetics!

PRB 79 075206

Split, 8-10 October 2012 Silicon Detector Workshop 11

Results Defect depth profiling with DLTS

VV X1 X2

0.420.53

Two new deep defect states from interstitial-rich region emerge!

??

Two DLTS spectra (@ Two DLTS spectra (@ -1 – -0.2 V -1 – -0.2 V & @& @ -5 – -3 V-5 – -3 V) combined!) combined!

Vacancy- rich region

Interstitial-rich region

0.78

Split, 8-10 October 2012 Silicon Detector Workshop 12

Results Laplace DLTSLDLTS measured at 225K, i.e. the activation energy of VV (-/0) ~0.4 eV for: a)Vacancy-rich region (-2, -1 V)b)Interstitial-rich region (-5, -2.8 V)

Si : SiT=225K(Ec-0.4 eV)

LDLTS spectra from as implanted and annealed (180C 40min) sample measured at 225K for: a)Vacancy-rich region (-2, -1 V)b)Interstitial-rich region (-5, -2.8 V)

Split, 8-10 October 2012 Silicon Detector Workshop 13

Conclusions

VO and V2(=/-) completely suppressed 0.40 eV vacancy-related defect 0.40 eV cluster-related defect And the model is ...

Split, 8-10 October 2012 Silicon Detector Workshop 14

TODO

Scanning capaictance microscopy (SCM)