-1 -1 2 ) .s .V (cm Low Field Mobility µ 0

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Guidelines for MOSFET Device Guidelines for MOSFET Device

Optimization accounting Optimization accounting

for L

for L - - dependent Mobility dependent Mobility Degradation

Degradation

G. Bidal^1,2, D. Fleury^1,2, G. Ghibaudo², F. Boeuf¹ and T. Skotnicki¹.

1STMicroelectronics, 850 rue Jean Monnet, 38920 Crolles Cedex, France;

2IMEP, 3 parvis Louis Néel, BP 257, 38016 Grenoble Cedex 1, France;

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Outline Outline

• Introduction

• Methodology used in this work

– Low field apparent mobility – µ-degradation modeling

• Experimental results

– Impact of technological modules

• Guidelines for transport enhancement

– How close to ballistic ?

– Benchmark of studied technological modules

• Conclusion

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Outline Outline

• Introduction

• Methodology used in this work

– Low field apparent mobility – µ-degradation modeling

• Experimental results

– Impact of technological modules

• Guidelines for transport enhancement

– How close to ballistic ?

– Benchmark of studied technological modules

• Conclusion

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Metal gate

Mobility crisis in highly scaled Mobility crisis in highly scaled

devices devices

0 50 100 150 200 250 300 350 400 450

0.01 0.1 1

Effective Channel Length Leff (µm) Low Field Mobility µ0 (cm2 .V-1 .s-1 ) electrons

holes

squares: data from [1]

circles: data from [2] • Experimental evidence of

carriers’ mobility diminution as L_g is scaling down [K.M.Cao IEDM 99, K.Rim IEDM 02, M.Zilli EDL 07, Ramos ESSDERC 06]

• Observed on:

Poly-Si gate

SiO₂ dielectric

High-K dielectric

Strained Unstrained

Doped channel Undoped channel Bulk

SOI FinFET

[2]: A.Cros et al., IEDM 06 [2]: F.Andrieu et al., VLSI 05

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Motivation

1.00E-05 1.00E-04 1.00E-03 1.00E-02

0.01 0.1 1 10

µ_short x2

Same long channel mobility

Velocity limit Mobility limit

log L_eff (µm)

1.E- 1.E- 1.E- 1.E-

• If mobility is high enough and only in this case, the

mobility term 1/(µ₀E_lateral) can become negligible and the transport will be mainly

driven by the limiting velocity

• Any mobility enhancement will get us closer to the

limiting velocity

) /(

1 /

1

0

lim lateral

gt ox

dsat WC V v E

I = × + µ

From T.Skotnicki et al., IEEE TED’08

I

_ON

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• Many possible explanations…

- long range CS from S/D

[M.Cassé et al., VLSI 2008]

- CS from the high-K [V.Barral et al., SNW 2008]

- neutral defects due to S/D I/I

[A.Cros et al., IEDM 2006]

- etc.

Purpose of this work

• … that may be mixed !

Final mobility

• Purpose of this work is not to diagnose the mechanisms of this mobility degradation, but to identify key technological modules that may help to reach a higher short channel mobility

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How to ?

0 50 100 150 200 250 300 350 400 450

0.01 0.1 1

Effective Channel Length Leff (µm) Low Field Mobility µ0 (cm2 .V-1 .s-1 ) electrons

holes

squares: data from [1]

circles: data from [2]

• By fitting experimental results by an empirical model in order to provide a simple

benchmarking tool between the different technologies

[2]: A.Cros et al., IEDM 06 [2]: F.Andrieu et al., VLSI 05

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Outline Outline

• Introduction

• Methodology used in this work

– Low field apparent mobility – µ-degradation modeling

• Experimental results

– Impact of technological modules

• Guidelines for transport enhancement

– How close to ballistic ?

– Benchmark of studied technological modules

• Conclusion

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Low field mobility

0 20 40 60 80 100 120 140 160

0.0E+0 5.0E-7 1.0E-6 1.5E-6

Inversion Charge Density (C.cm^-2) Effective Mobility µeff (cm2 .v-1 .s-1 )

L_eff reduction = µ_effreduction = µ₀ reduction

Lines : Y-function Symbols: Split CV

µ₀=µ_eff(Q_inv≈0)

• Y function and split C(V) methods give similar results, except under V_th

• L_eff shrink implies µ₀ degradation and µ_eff degradation

2 2 1

0

. .

1 _gt _gt

eff V V

µ µ

θ

θ +

= +

eff d

inv

eff d

eff Q V W

L µ I

. .

= .

2 2 1

0

. .

1 _gt _gt

eff V V

µ µ

θ

θ +

= +

eff d

inv

eff d

eff Q V W

L µ I

. .

= . Y-function:

Split C(V):

[J. Koomen et al., SSE, 1973]

[G. Ghibaudo et al., Electronics Letter, 1988]

[K.Romanjek et al., EDL, 2004]

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Empirical Model

0 50 100 150 200 250 300 350 400 450

0.01 0.1 1 10

Effective channel length L_eff (µm) Low field mobility µ0 (cm²V-1 s-1 )

αµ=0 αµ=0.05 αµ=0.1 αµ=1 µmax=µlong=200

µmax=µlong=300 µmax=µlong=400

eff µ

eff µ L

L µ

+ α

=

max 0

1 )

( Model : 1

(with 2 fitting

parameters)

eff µ

eff µ L

L µ

+ α

=

max 0

1 )

( 1

degradation factor

maximum mobility

• Zero degradation

corresponding to α_µ =0 does not exist: α_µ cannot be lower than

α_µ,bal given by the apparent

mobility reduction due to ballistic transport

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Fitting or not fitting ?

10 100 1000

0.01 0.1

effective channel length L_eff (µm) low field mobility µ0 (cm².V-1 .s-1 )

symbols: measured lines: model

nM OS

• Perfect fit is obtained on

experimental data at short gate length

• Bulk and Ultra thin Body (UTB) results

• PolySi/SiON and Metal/High-K results

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Outline Outline

• Introduction

• Methodology used in this work

– Low field apparent mobility – µ-degradation modeling

• Experimental results

– Impact of technological modules

• Guidelines for transport enhancement

– How close to ballistic ?

– Benchmark of studied technological modules

• Conclusion

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Impact of SiON thickness

0 50 100 150 200 250 300 350 400 450

0.01 0.1 1

α_µ=0.15 µmax=400

α_µ=0.25 µmax=290 symbols: measured

lines: model

nM OS

Poly-Si gate

DPN SiON Si substrate

17Å

Si substrate Poly-Si gate

DPN SiON ^12Å

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Impact of metal gate material

0 50 100 150 200 250 300 350 400

0.01 0.1 1

effective channel length L_{e ff} (µm) low field mobility µ0 (cm².V-1 .s-1 )

TaC gate TaN gate TiN gate α_µ=0.18

µ_max=360

α_µ=0.28 µ_max=300 symbols: measured

lines: model

Metal gate on

high-K TaC, TaN or

TiN

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Impact of UTB doping

0 50 100 150 200 250 300

0.01 0.1 1

undoped doped αµ=0.30

µmax=300

αµ=0.31 µmax=150 symbols: measured

lines: model

nM OS

UTB doped

or undoped

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Impact of junction formation

0 50 100 150 200 250 300 350 400 450 500

0.01 0.1 1

optimized S/D I/I

@1000°C

S/D I/I @1010°C α_µ=0.12

µ_max=500

α_µ=0.18 µmax=390 symbols: measured

lines: model

+ activation anneal Ion Implantation

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Impact of strain

0 50 100 150 200 250

0.01 0.1 1

α_µ=0.10 µ_max=200

α_µ=0.15 µ_max=90 w/ eSiGe stressors (PIS)

Ref. without stressors

discrepancy due to relaxed strain on long devices

pM OS

eSiGe eSiGe

x y

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Impact of crystal orientation

0 50 100 150 200 250

0.01 0.1 1

α_µ=0.16 µmax=230

α_µ=0.15 µmax=90 (100)/<110>

(110)/<110>

pM OS

(110)

<110>

L

_g

(100)

<110>

L

_g

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Outline Outline

• Introduction

• Methodology used in this work

– Low field apparent mobility – µ-degradation modeling

• Experimental results

– Impact of technological modules

• Guidelines for transport enhancement

– How close to ballistic ?

– Benchmark of studied technological modules

• Conclusion

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How close to the ballistic ?

• Boosting µ and reducing α is mandatory to reach high BR

0.025 0.075

0.125 0.175

0.225 0.275

25 275 525

0 10 20 30 40 50 60 70 80 90 100

Long channel mobility µmax

BallisticRate BR(%)

Deg rad

ation facto

r α

µ

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

0 200 400 600

µ_max [cm².V^-1.s^-1] αµ [nm.V.s.cm-2 ]

nMOS pMOS

α_µ,bal for electrons=0.04 α_µ,bal for holes=0.08

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Final benchmark & Guidelines

X2

= ++

Crystal orientation

x3 +

++

Process Strain

x2

= ++

Channel doping

x2 +

+ Junctions

x2 to x4 ++

+ Gate stack

Merit factor η=µ_max/α_µ impact

on αααα

µ

impact on µ_max Techno.

module

• Influence of each studied technological module is quantified

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Outline Outline

• Introduction

• Methodology used in this work

– Low field apparent mobility – µ-degradation modeling

• Experimental results

– Impact of technological modules

• Guidelines for transport enhancement

– How close to ballistic ?

– Benchmark of studied technological modules

• Conclusion

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