Karen Kirkby, Justin Hamilton Surrey Ion Beam Centre, University of Surrey

PhD Presentation 20th December 2007

IAEA CRP Chiang Mai 2007

Karen Kirkby, Justin Hamilton

Surrey Ion Beam Centre, University of Surrey

The role of the Buried Oxide in SOI Structures Dopant Diffusion and Activation



Thank you • PhD Students

– Justin Hamilton, Jim Sharp, Max Kah• Post Docs

– Andy Smith• Colleagues at Surrey

– Roger Webb, Russell Gwilliam, Brian Sealy, Nick Cowern (Newcastle)• IRC-irst, Trento

– Massimo Bersani and Damiano Giubertoni, Salvatore Gennaro• Bologna

– Andrea Parisini• Toulouse

– Fuccio Christiano• Applied Materials

– Erik Collart (UK)



ContentsContents• IntroductionIntroduction• Experimental DesignExperimental Design• Experimental ResultsExperimental Results

SOI Vs Bulk Si TempSOI Vs Bulk Si TempEffect of the buried interfaceEffect of the buried interfaceOptimisation & ModellingOptimisation & Modelling

• ConclusionsConclusions



• Smaller• Faster• Cheaper

Miniaturisation: why?Miniaturisation: why?



Transistor size , device per chip

Gordon Moore noticed in 1965: number of devices on a chip doubled every 18-24 months & predicted this trend would continue

Device down-scaling:Device down-scaling:



Silicon-on-Insulator (SOI)Silicon-on-Insulator (SOI)

• Silicon wafer with a buried Oxide (BOX)

• Advantages of SOI over Bulk SiIncreased SpeedReduced Power ConsumptionIncreased radiation toleranceImmunity from latch-up

• Industry is moving towards SOI

BOXBOX

SiSi

BOXBOX

SiSi



Down-scaling of MOS devices causes leakage current (short channel effects)

Down-scaling challenges:Down-scaling challenges:

• High activation level• Shallow penetration of dopants

S/D extension

Substrate

Lg

Xj

Ultra shallow source/drain extension regions require:



Challenge for further down-scalingChallenge for further down-scaling

2005 ITRS requirements for p-type layers and future trends

• High activation level 800 ohms/sq• Shallow penetration of dopants 15nm

0300600900

120015001800

Junction depth @ 1E18cm-3 (nm)

RS (

ohm

s/sq

) Lg=28nmLg=20nm

Lg=14nm

0 128

Lg=10nm

A 50nm MOSFET in production from a 90nm process (courtesy

of Intel)

4

SOI





• High activation level 1200 ohms /sq• Shallow penetration of dopants 8-10nm


of Intel)



Why pre-amorphisation?Avoids Boron channelling

Improves Boron activation

Solid Phase Epitaxy!

PAI & SPEPAI & SPE

No Channelling in a-Si

Depth (nm)

Con

cent

ratio

n (c

m-3

)

Channelling Tail in c-Si



F. Cristiano et al, Mat. Sci. Eng. B, 114-115, p174 (2004)

A. Michel et al, Appl. Phys. Lett, 50, 7, p417 (1987)

Transient Enhanced Diffusion (TED)

Boron de-activation

Implant damage:Implant damage:• Implant B in c-Si

• Frenkel Pairs

• Plus One Model

(schematic representation)(schematic representation)



depth

Amorphisation threshold

Amorphisation

(destruction of crystal structure)

I

V

Ge PAI

Net excess interstitials after local

recombination of I with V

No point defects survive

I

ImplantB

Pre-amorphisation & SPERPre-amorphisation & SPER

• Ge amorphises Si

• B implanted

• I & V recombine

• Net excess I


(con

cent

ratio

n)

10 16

10 18

10 20

10 22

depth



B initially shallow

and above solubility

SPEre-growth

Pre-amorphisation & SPERPre-amorphisation & SPER

• Ge amorphises Si

• B implanted

• I & V recombine

• Net excess I

• SPE re-growth

• EOR defect band


(con

cent

ratio

n)

10 16

10 18

10 20

10 22

depth



De-activation & diffusionDe-activation & diffusion


(con

cent

ratio

n)

10 16

10 18

10 20

10 22

depth

BICs

• I flux toward surface

• BIC formation

• TED

• What happens in SOI material?

I flux

TED

BOX



Experimental DesignExperimental Design

• PAI at a dose of 1x1015cm-2 Ge, with energies of 8keV & 20keV, bulk Si & SOI



BO

X

20 keV GeB

55 nm38 nm

Surface

19 nm

8 keV Ge BO

XB

55 nm



Experimental DesignExperimental Design• PAI at a dose of 1x1015cm-2 Ge, with

energies of 8keV & 20keV, bulk Si & SOI

• Implanted with 500eV Boron at dose of 2x1013cm-2, 2x1014cm-2 and 2x1015cm-2

• Re-growth study (570ºC for 30 – 150s), check for wafer re-crystallisation

• Activation & diffusion study, isochronal anneals (700ºC – 1000ºC for 60s)



Experiment OneExperiment One

Do SOI and bulk Si samples experience a difference in temperature when

annealed together?



• No effect of PAI energy on the re-growth rateNo effect of PAI energy on the re-growth rate

RBS – RBS – Re-growth RatesRe-growth Rates

• Re-growth rate increases with Boron doseRe-growth rate increases with Boron dose

Boron 8keV Ge Bulk 8keV Ge SOI 20keV Ge Bulk 20keV Ge SOI0 N/A N/A 0.27 0.26

2x1013cm-2 0.35 0.37 0.37 0.392x1014cm-2 0.4 0.42 0.4 0.442x1015cm-2 0.52 0.48 0.52 0.50

Re-growth Rate (nm/sec)

B dose incr.

• No real difference between Bulk Si and SOINo real difference between Bulk Si and SOI

Table of re-growth rate for increasing Boron doseTable of re-growth rate for increasing Boron dose

J.J. Hamilton, et al. Nucl. Instr. and J.J. Hamilton, et al. Nucl. Instr. and Meth. in Res. B 237, 107 (2005).Meth. in Res. B 237, 107 (2005).



Experiment TwoExperiment Two

What are the electrical and structural differences between SOI and bulk Si?



Hall MeasurementsHall MeasurementsBulk Si & SOI implanted with Boron at a dose 2x1015 cm-2 and

pre-amorphised with 8keV Ge – EOR at 20nm

Small difference between 8keV SOI Vs bulkSmall difference between 8keV SOI Vs bulk J.J. Hamilton, et al. Appl. Phys. J.J. Hamilton, et al. Appl. Phys. Lett. 89, 42111 (2006).Lett. 89, 42111 (2006).

700 750 800 850 900 950 10000

400

800

1200

1600

2000

2400S

heet

Res

ista

nce

(ohm

s/sq

.)

Temperature ºC

Bulk Si SOI



700 750 800 850 900 950 10000

300

600

900

1200

1500

1800S

heet

Res

ista

nce

(ohm

s/sq

.)

Temperature ºC

Bulk Si SOI

PAI & SPER Bulk Si Vs SOIPAI & SPER Bulk Si Vs SOIBulk Si & SOI implanted with Boron at a dose 2x1015 cm-2 and

pre-amorphised with 20keV Ge – EOR at 40nm

Less deactivation for 20keV SOI Vs bulkLess deactivation for 20keV SOI Vs bulk

~850ohm/sq.

~550ohm/sq.

35% reduction in ∆RsSOI than ∆RsSI

J.J. Hamilton, et al. Appl. Phys. J.J. Hamilton, et al. Appl. Phys. Lett. 89, 42111 (2006).Lett. 89, 42111 (2006).



SIMS MeasurementsSIMS MeasurementsBulk Si & SOI implanted with Boron at a dose 2x1015 cm-2 and pre-amorphised with 8 & 20keV Ge + annealed at 800ºC for 60s

8keV 20keV

0 10 20 30 40 50 60 70 80

1E17

1E18

1E19

1E20

1E21

Ge 8 keV - bulk Ge 8 keV - SOI

11B

CO

NC

EN

TRA

TIO

N (a

t/cm

3 )

DEPTH (nm)

103

104

105

106

107

0 10 20 30 40 50 60 70 80

1E17

1E18

1E19

1E20

1E21

Ge 20 keV - bulk Ge 20 keV - SOI

11B

CO

NC

EN

TRA

TIO

N (a

t/cm

3 )

DEPTH (nm)

103

104

105

106

107

Higher level of out diffusion for 20keV SOI Vs bulk SiHigher level of out diffusion for 20keV SOI Vs bulk SiLess B trapping in 20keV SOI Vs bulk SiLess B trapping in 20keV SOI Vs bulk Si



55nm

20keV20keV

40nm

CC DD

40nm

surface

800800ººC for 60s anneal for 8 & 20keV Ge in SOI & Bulk SiC for 60s anneal for 8 & 20keV Ge in SOI & Bulk Si

20nm55nm

Bulk SiBulk Si SOISOI

8keV8keV

AA BBBOXBOX

EOR defects EOR defects

20nm

BOXBOXEOR defectsEOR defects



0 10 20 30 40 50 60 701E17

1E18

1E19

1E20

1E21

As-implanted 20 keV Ge Bulk Si 20 keV Ge SOI

11B

CO

NC

EN

TRA

TIO

N (a

t/cm

3 )

DEPTH (nm)

0 10 20 30 40 50 60 70

1E17

1E18

1E19

1E20

1E21

As-implanted 20 keV Ge Bulk Si 20 keV Ge SOI

11B

CO

NC

EN

TRA

TIO

N (a

t/cm

3 )

DEPTH (nm)

800ºC

SIMS MeasurementsSIMS MeasurementsBulk Si & SOI implanted with Boron at a dose 2x1015 cm-2 and

pre-amorphised with 20keV Ge + annealed for 60s at 800ºC & 850ºC

850ºC

Significant less B trapping in SOI Vs Bulk SiSignificant less B trapping in SOI Vs Bulk Si J.J. Hamilton, et al. Appl. Phys. J.J. Hamilton, et al. Appl. Phys. Lett. 89, 42111 (2006).Lett. 89, 42111 (2006).



Interstitia

l Flux

20keV Ge Bulk

20keV Ge SOI

BOX

Interstitial Flux

20keV Ge Bulk

20keV Ge SOI

BOX

De-activation & TED

Back interface sink for I Faster EOR dissolution

Physical MechanismPhysical Mechanism




Experiment ThreeExperiment Three

Optimisation of amorphisation

conditions in SOI



Experimental DesignExperimental Design

• PAI at a dose of 1x1015cm-2 Ge, with energies of 8, 20, 24, 32 & 36keV, both Si & SOI

• Implanted with 500eV Boron at dose of 2x1015cm-2

• Isochronal annealing study (700ºC – 1000ºC for 60s)



PAI dose of 1x1015cm-2 Ge, both Si & SOI+ 500eV Boron at dose of 2x1015cm-2Surface

20nm

8keV Ge

BO

X

55nm

B

40nm

20keV Ge

55nm

BO

XB

45nm

24keV Ge

BO

X

B

55nm

32keV Ge

55nm

BO

X

~55nm

B



XTEM MeasurementsXTEM MeasurementsSOI and Bulk Si implanted with Boron at a dose 2x1015 cm-2 and pre-amorphised with 32keV Ge as-implanted + annealed at 700ºC for 60s

Re-growth has occurred, therefore has recrystallisedRe-growth has occurred, therefore has recrystallised

Defect trapping within the BOX interface in SOIDefect trapping within the BOX interface in SOI

EOR defects

SOI – as-implantedSOI – as-implanted SOI – annealedSOI – annealed Bulk Si – annealedBulk Si – annealed

~4nm~4nm



0 10 20 30 40 50 60 701E17

1E18

1E19

1E20

1E21

1E22 Bulk Si SOI

B C

ON

CE

NTR

ATI

ON

(at/c

m3 )

DEPTH (nm)

SIMS MeasurementsSIMS Measurements

EOR defect band overlaps BOXEOR defect band overlaps BOX

Bulk Si & SOI implanted with Boron at a dose 2x1015 cm-2 and pre-amorphised with 32keV Ge, annealed at 850ºC for 60s

BO

X in

terfa

ce



700 750 800 850 900 950 10000

400

800

1200

1600

2000

She

et R

esis

tanc

e (R

s)

Temperature (ºC)

8keV Ge 20keV Ge

700 750 800 850 900 950 10000

400

800

1200

1600

2000

She

et R

esis

tanc

e (R

s)

Temperature (ºC)

8keV Ge 20keV Ge 24keV Ge 32keV Ge

700 750 800 850 900 950 10000

400

800

1200

1600

2000

She

et R

esis

tanc

e (R

s)

Temperature (ºC)

8keV Ge 20keV Ge 24keV Ge

700 750 800 850 900 950 10000

400

800

1200

1600

2000

She

et R

esis

tanc

e (R

s)

Temperature (ºC)

8keV Ge

Van Der Pauw ResistivityVan Der Pauw ResistivitySOI implanted with Boron at a dose 2x1015 cm-2 and

pre-amorphised with 8, 20, 24 & 32keV Ge – EOR at 20, 40, 45 & ~55nm

Less than 80ohm/sq. RS peak deactivation for 32keV (from 700ºC to 850ºC)

29%

51% 57%

Minimal deactivation for Minimal deactivation for the 32keV PAIthe 32keV PAI



0 10 20 30 40 501E17

1E18

1E19

1E20

1E21

1E22

As-implanted 8keV

B C

ON

CE

NTR

ATI

ON

(at/c

m3 )

DEPTH (nm)0 10 20 30 40 50

1E17

1E18

1E19

1E20

1E21

1E22

As-implanted 8keV 20keV

B C

ON

CE

NTR

ATI

ON

(at/c

m3 )

DEPTH (nm)0 10 20 30 40 50

1E17

1E18

1E19

1E20

1E21

1E22

As-implanted

B C

ON

CE

NTR

ATI

ON

(at/c

m3 )

DEPTH (nm)

SIMS MeasurementsSIMS MeasurementsSOI implanted with Boron at a dose 2x1015 cm-2 and

pre-amorphised with 8, 20 & 32keV Ge, annealed at 800ºC for 60s

0 10 20 30 40 501E17

1E18

1E19

1E20

1E21

1E22

As-implanted 8keV 20keV 32keV

B C

ON

CE

NTR

ATI

ON

(at/c

m3 )

DEPTH (nm)

32keV PAI shows highest level 32keV PAI shows highest level of activation, least TED and of activation, least TED and largest junction abruptnesslargest junction abruptness



32keV Ge SOI

BOX

20keV Ge Bulk

20keV Ge SOI

BOX

Physical MechanismPhysical Mechanism


De-activation & TED

Back interface sink for I Faster EOR dissolution

Interstitial Flux



BOX InterfaceSurface

d

ModellingModelling

x d - x

Centroid

L1

1

L2

1

,1 Lx

CD EORII

2

,2 Lxd

CD EORII

2

21 Ld

LxdF

= fraction of interstitials Flowing towards the surface


IAEA CRP Chiang Mai 2007J.J. Hamilton, et al. Appl. Phys. J.J. Hamilton, et al. Appl. Phys. Lett. 91, 92122 (2007).Lett. 91, 92122 (2007).

40 35 30 25 20 15 10 5 00

2x1013

4x1013

6x1013

8x1013

1x1014

L2 = / Nc

Dos

e of

exc

ess

Si i

nter

stiti

als

that

flow

to

war

ds th

e su

rface

(cm

-2)

Remaining crystal thickness after amorphization (nm)

40 35 30 25 20 15 10 5 00

2x1013

4x1013

6x1013

8x1013

1x1014

L2 = / Nc L

2 = 100

Dos

e of

exc

ess

Si i

nter

stiti

als

that

flow

to

war

ds th

e su

rface

(cm

-2)


40 35 30 25 20 15 10 5 00

2x1013

4x1013

6x1013

8x1013

1x1014

L2 = / Nc L

2 = 100

L2 = 30

Dos

e of

exc

ess

Si i

nter

stiti

als

that

flow

to

war

ds th

e su

rface

(cm

-2)


40 35 30 25 20 15 10 5 00

2x1013

4x1013

6x1013

8x1013

1x1014

L2 = / Nc L

2 = 100

L2 = 30

L2 = 10

Dos

e of

exc

ess

Si i

nter

stiti

als

that

flow

to

war

ds th

e su

rface

(cm

-2)


40 35 30 25 20 15 10 5 00

2x1013

4x1013

6x1013

8x1013

1x1014

L2 = / Nc

L2 = 100

L2 = 30

L2 = 10

L2 = 0

Dos

e of

exc

ess

Si i

nter

stiti

als

that

flow

to

war

ds th

e su

rface

(cm

-2)


40 35 30 25 20 15 10 5 00

2x1013

4x1013

6x1013

8x1013

1x1014

0.0

4.0x1013

8.0x1013

1.2x1014

1.6x1014

2.0x1014

L2 = / Nc

L2 = 100 L

2 = 30

L2 = 10 L

2 = 0

Dos

e of

exc

ess

Si i

nter

stiti

als

that

flow

to

war

ds th

e su

rface

(cm

-2)


Rel

ativ

e de

activ

ated

B d

ose

(cm

-2)

Deactivated B

ModellingModelling





• High activation level 1200 ohms /sq• Shallow penetration of dopants 8-10nm


of Intel)

• High activation level 1200 ohms /sq (800 ohms/sq)• Shallow penetration of dopants 8-10nm (20 nm)



ConclusionsConclusions

Very promising for future USJ applications in SOIVery promising for future USJ applications in SOI

Negligible B de-activationNegligible B de-activationShallow, abrupt junctionShallow, abrupt junction

Two Mechanisms:Two Mechanisms:• BOX acts as a sink for interstitials, with near BOX acts as a sink for interstitials, with near

zero value for recombination lengthzero value for recombination length• EOR overlaps BOX, reducing initial I number to EOR overlaps BOX, reducing initial I number to

interact with Binteract with B

Very little c-Si is required to seed re-growthVery little c-Si is required to seed re-growth

SOI and Bulk Si experience same anneal temp.SOI and Bulk Si experience same anneal temp.



Acknowledgements:Acknowledgements:E.J.H. Collart

Applied Materials

M. Bersani, D. Giubertoni and S. GennaroITC-irst

A. ParisiniCNR-IMM

B. ColombeauChartered Semiconductors

Justin HamiltonJ. A. Sharp, A. J. Smith, N. Bennett and M. Kah

University of Surrey

Nick CowernUniversity of Newcastle



Any Questions?Any Questions?

Documents

Karen Kirkby, Justin Hamilton Surrey Ion Beam Centre, University of Surrey