ESD Evaluation of the Emerging MuGFET Technology

C. Russ et. al 2005 ESD/EOS Conference

Slide 2

Oh No! Is ESD Going to be MuGGed by Yet Another Technology Development??

Dr. MuGFETGive me your ESD!

Slide 3

Purpose of this work

• Introduce the exciting new Multi-Gate Advanced Transistor Technology called the “MuGFET” and assess its sensitivity to high current ESD behavior

• Investigate suitable ESD protection methods for this new technology

Slide 4

Outline

Introduction: MultiGate FETs (MuGFETs)

ESD Characterization

– Fully depleted (FD) MuGFETs

– Partially depleted (PD) planar FETs

– Diodes

Failure analysis

Protection approaches

Conclusions

Slide 5

Introduction (1)

Classical FET in Bulk Si

SD

GL W

• Scaling expected to become difficult due to Short Channel Effects (32nm node and beyond)

SiO 2

Si

Gate

current current

Slide 6

Introduction (2)

Planar FET Device in SOI

SD

GL W

• Low junction capacitance speed!

• Good body control in fully depleted SOI– Requires costly wafers with ultra-thin Si-film

SiO 2

Si

Gate

current current

Slide 7

Introduction (3)MuGFET Device (or “Fin”-FET)

SD

GL

SiO 2

Si

Gate

• Channel enclosed by multiple (2, 3, 4) gates Best body control (fully depleted) Suppression of Short Channel Effect

• Best candidate for continued technology scaling

current

2 gates @ sides: double-gate

3 gates @ sides+top: tri-gate

current

W

Slide 8

Introduction (4)

S DG

finS D

G

fintop gate electrode

WFIN

Fu

lly

de

ple

ted

BOX

gate

side gate electrodes

HFIN

top gate electrode

WFIN

Fu

lly

de

ple

ted

BOX

gate

side gate electrodes

HFIN

Fu

lly

de

ple

ted

• Fin height: 60-88nm (present), 30-40nm (target)

• Fin width: 50nm (present), 20-30nm (target)

• Capability to carry ESD current?

Slide 9

Outline

Introduction: MultiGate FETs (MuGFETs)

ESD Characterization

– Fully depleted (FD) MuGFETs

– Partially depleted (PD) planar FETs

– Diodes

Failure analysis

Protection approaches

Conclusions

Slide 10

Test structures

SCGS

Lg

MD

R

Wgeo

LGATE

SOURCE

DRAINN+

GA

TE

N+

Planar SOIpartially depleted (PD)

Wgeo

SOURCE

GA

TE

Wfin=50nm

200nm

Lg

a S

pitchLGATE

DRAINN+

N+

MuGFETfully depleted (FD)

a D

Slide 11

Test structures

CAp+ n+

G

Gated diode

• NMOS and Gate diodes available as MuGFET (‘Fin’) and planar SOI types

• Fin width = 50nm, Fin heights = 88 and 60nm

• Nickel silicided (no silicide blocking)

SDn+ n+

G

NickelSilicide

NMOS

Buried oxide Buried oxide

Slide 12

MuGFET: Grounded Gate NMOS

• Unprecedented high ESD sensitivity failure instantaneous after breakdown!

• L pushes out breakdown, but no snapback visible

Slide 13

MuGFET: MOS-diode, Gate tied high

• Gate biasing allows moderate MOS current flow

• Damage occurs as soon as Vbd of GGNMOS-case is reached non-uniform current flow?

Slide 14

Planar PD SOI NFET: Grounded Gate

• More robust (~2mA/um), reproducible and scalable

• Very steep on-characteristics

• L pushes out BD, minor snapback occurs

Slide 15

• Excellent ESD performance (Fin-type and planar)!

• Fin-type diodes show less sensitivity to tsi

Gated Diodes: Fins + Planar (fwd. mode)

It2 [mA/um]

film thickness tsi

88nm 60nm

Fin-type

500 fins

Wsi=25um

16.8 15.2

Planar

W=50um11.6 9.6

Slide 16

0

0.01

0.02

0.03

0.04

0.05

4 5 6 7 8 9 10

FinFETp-typeFinFETn-typeplanarp-typeplanarn-type

curr

ent [

A]

voltage [V]

It2• Breakdown voltage

much higher than for any FET

• Fin-type diodes in BD do not show premature failure as seen in NFETs resistive ballasting

Gated Diodes: Fins + Planar (rev. mode)

Slide 17

Outline

Introduction: MultiGate FETs (MuGFETs)

ESD Characterization

– Fully depleted (FD) MuGFETs

– Partially depleted (PD) planar FETs

– Diodes

Failure analysis

Protection approaches

Conclusions

Slide 18

Failure Analysis: NFETs

S D

G

90nm

PlanarPD SOI

• Planar device: uniform damage along gate width– reasonable ESD performance

• MuGFET: localized damage of neighboring fins– extremely low ESD performance

D80nm

ESD

SDS

G G

metal

MuGFET

No

dam

age

Slide 19

Failure Analysis: Diodes (fwd. mode)

• MuGFET diode: uniform damage of fins– high ESD performance– intrinsic current capability of technology reached

C

metalmetal poly

500nm

A

ESD

Mu

GF

ET

AC

metalmetal poly

500nm

Pla

nar

• Planar diode: no failure in silicon (contact failure?)

Slide 20

Failure Analysis: Pulse Width vs. It2

It2 [mA]

Tpulse

100ns 500ns 2500ns

Planar NMOS W=50um

75-80 60-69 49-57

FinFET diode 500 fins, Wsi=25um

380 290 230

Planar diode W=50um

480 335 235

• ‘Wunsch-Bell’-unlike characteristics obtained• Planar MOS and FinFET diode:

– smaller sensitivity due to more heat sinking

Slide 21

Protection Approaches

0

0.5

1

1.5

0 1 2 3 4 5

FD MuGFET

PD planar

norm

aliz

ed

curr

ent [

mA

/um

]

voltage [V]

Lpoly=250nmplanar: W=50umFin: Wsi=500x50nm=25um

Vt1,FD

Vt1,PD

• Input protection: dual diode + power clamp approach• Output drivers: PD planar device as local clamp provides solution

integrated into process• Provides both performance and ESD protection

FD MuGFET driver

PD planarESD clamp

IOpad

Slide 22

ConclusionsNew issues for emerging Multigate technologies:– FinFET MOS: extremely ESD-susceptible

• Local burn-out of fins– Planar MOS: reasonable ESD hardness

• Uniform failure signature (even fully silicided!)• Available in same process• Lower trigger than FinFET local clamp

– Gate-biased MOS: • Possible as protection, BJT conduction must

strictly be avoided– Gated diodes (Fin-type and planar):

• Diodes needed in any protection scheme• FinFET diodes: high ESD currents possible!

Gate Dielectric Integrity along the Road Map of CMOS Scaling including Multi-Gate FET, TiN Metal Gate, and HfSiON High-k Gate Dielectric

T. Pompl et. al IRPS Conference

Infineon TechnologiesTexas Instruments

Slide 24

• Investigate:

Influences of multi-gate architecture and metal gate on gate dielectric reliability.

• Demonstrate:

Dielectric reliability trend along the road map towards a CMOS process using triple gate architecture, metal gate, and HfSiON gate dielectric.

Purpose

Slide 25

fully-depleted triple gate FET with poly-Si

gate and SiO2 (ISSG: 20 Å)

fully-depleted triple gate FET with TiN/poly-Si gate and SiO2

(ISSG: 17 Å)

fully-depleted triple gate FET with TiN/poly-Si gate and HfSiON

(ALD & post anneal in NH3, EOT: 10.5 Å,

20% Si, 7-8% N, bottom SiO2: 8 Å)

TEM Cross Sections of Vertical Silicon Fin

Slide 26

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

210-1-2

log(time (s))log(time (s))210-1-2

= 1.31

NFETtriple gatepoly, SiO

2

ln(-

ln(1

-F))

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

= 1.02

PFETtriple gatepoly, SiO

2

ln(-

ln(1

-F))

State of the art gate dielectric reliability can be achieved for CMOS processes using vertical multi-gate architectures.

The total length of tested top fin edge is 1.5 m per distribution.

High Volume TDDB checks for Weak Spots

Slide 27

10-1 100 101 102 103-5

-4

-3

-2

-1

0

1

2

Orientationon {100}substrate

0° 45° 90°

NFETtriple gatepoly, SiO

2

ln(-

ln(1

-F))

time (s)

No major influence on time to breakdown.Important also for SiO2 channel interface layer of high-k stacks.

Orientation of the silicon fin on {100} substrate:

SiO2 grown on silicon side walls with different crystal orientations.

Influence of Crystal Orientation

Slide 28

2.0 2.5 3.0 3.5 4.0 4.5100

101

102

103

104

105

EOT17Å

EOT20Å

EOT10.5Å

SiO2 & poly

SiO2 & TiN

HfSiON & TiNNFETtriple gate

t63%

(s)

gate voltage (V)

SiO2 & TiN: NFET meets standard reliability performance.HfSiON & TiN: NFET becomes more critical at stress level.

Expectations from thickness scaling of poly-Si/SiO2 towards

using 6.5 dec. in time per nm.

NFET: Time To Breakdown vs. Gate Voltage

17 Å

10.5 Å

Slide 29

-4.5 -4.0 -3.5 -3.0 -2.5 -2.0100

101

102

103

104

105

EOT10.5Å

EOT20Å

EOT17Å

SiO2 & poly

SiO2 & TiN

HfSiON & TiNPFETtriple gate

t63%

(s)

gate voltage (V)

SiO2 & TiN: PFET becomes more critical at stress level.HfSiON & TiN: PFET meets standard reliability performance.

PFET: Time To Breakdown vs. Gate Voltage

Expectations from thickness scaling of poly-Si/SiO2 towards

using 6.5 dec. in time per nm.

17 Å

10.5 Å

Slide 30

0 1 2 3

10-8

10-7

10-6

10-5

10-4

10-3

3

21

NFETtriple gate

gate

curr

ent (A

)

gate voltage (V)-3 -2 -1 0

10-8

10-7

10-6

10-5

10-4

10-3

321

1: SiO2 & poly, EOT=20Å

2: SiO2 & TiN, EOT=17Å

3: HfSiON & TiN, EOT=10.5Å

PFETtriple gate

gate

curr

ent (A

)

NFET: strong dependence of gate leakage on gate voltage needs to be considered for gate dielectric reliability.

1: SiO2 & poly-Si

2: SiO2 & TiN

PFET becomes equal to NFET

3: HfSiON & TiN

NFET gate leakage strongly increased compared to PFET.

Due to asymmetry of the high-k stack.

Gate Leakage Current vs. Gate Voltage in Inversion Biasing Mode

Slide 31

State of the art gate dielectric reliability can be achieved for CMOS processes using vertical multi-gate architectures.

GOX reliability trend along the road map of CMOS scaling will be dominated by metal gates and high-k dielectrics.

The use of metal gate increases gate leakage current density and reduces SiO2 reliability margin for PFET devices compared to poly-Si/SiO2.

NFET & HfSiON: the extrapolation of dielectric reliability to use conditions needs to consider the strong dependence of gate leakage on gate voltage.

PFET & HfSiON: the dielectric reliability meets the level of a standard poly-Si/SiO2 gate stack of same EOT.

Conclusions