Quantum-size effects insub-10 nm fin width

InGaAs finFETs

Alon Vardi, Xin Zhao, and Jesús A. del Alamo

Microsystems Technology Laboratories, MITDecember 9, 2015

Sponsors: DTRA NSF (E3S STC) Northrop Grumman

Outline• Motivation• Process Technology• Electrical characteristics• Modeling• Conclusions

2

InGaAs planar Quantum-Well MOSFETs

High-Koxide

InGaAschannel

• InGaAs planar MOSFET performance matches that of High Electron Mobility Transistors (HEMT)

MITMOSFETs

del Alamo, CSICS 2015

3

InGaAs planar Quantum-Well MOSFETs -short-channel effects

• Short-channel effects limit scaling to Lg~40 nm• 3D transistors required for further scaling

0.01 0.1 1 100

200

400

600

800

DIBL

(mV/

V)Lg(µm)

tc ↓

tc=12 nm

3 nm

Lin, IEDM 2014

0.01 0.1 1 10

100150200250300350400

S min (m

V/de

c)

Lg(µm)

Vds=0.5 V

tc ↓

tc=12 nm

3 nm

4

InGaAs finFETs

Radosavljevic ,IEDM 2011 Kim, IEDM 2013

• III-V finFETs improve short-channel effects• Most InGaAs finFETs demonstrations feature Wf=30-50 nm

Kim, TED 2014

Thathachary, VLSI 2015 Waldron, VLSI 2014

WF~30 nm

WF~50 nm

WF~50 nm

5

VT variation with Wf

• m*e(Si)/m*e(InGaAs) >7 Quantum effects ↑ ΔVT(InGaAs) ↑• Goal of this work: experimental verification• Need InGaAs finFET with Wf<10 nm

Nidhi, DRC 2012

Increased sensitivity of VT to WF in InGaAs

In0.53Ga0.47As

Si

x [nm] x [nm]WF WF

Si InGaAs

6

Key technologies – nanostructure definition –Dry etch

• BCl3/SiCl4/Ar RIE of InGaAs nanostructures with smooth, vertical sidewalls and high aspect ratio (>10)

40 nm

As etched

7

40 nm 30 nm

• Digital etch (DE): self-limiting O2 plasma oxidation + H2SO4 oxide removal

As etched 5 cycles DE

• Shrinks fin width by 2 nm per cycle• Unchanged shape• Reduced roughness

Key technologies – nanostructure definition –Digital etch (DE)

Lin, EDL 2014

8

Key technologies – nanostructure definitionDry etch + Digital etch

20 nm

Zhao, EDL 2014

15 nm

240 nm

Stand alone nano structures down to 15 nm

9

• Etching depth impacts sidewall slope at top 50 nm• For Hf > 150 nm, upper 50 nm sidewalls become vertical

Key technologies – nanostructure definition –sidewall slope

30nm

20 nm

20 nm

220 nm

~800

90 nm

Etching time

10

Thick Top Gate OxideG

GS

D

• Typical device consists of 100 fins, Lg=3 µm

Wf=

InGaAs

Sidewall finFET

Vardi, DRC 2014

11

HSQ

Gate dielectric + Mo

Gate Patterning

Fin Patterning + Digital etchInAlAs bufferon SI-InP

50 nm thick, n-InGaAsND=1018 cm-3

Contacts + Pads

Sidewall finFET - process flow

Gate stack

G

GS

D

12

0 0.1 0.2 0.3 0.40

20

40

60

80

100

120

VDS [V]

I D [n

A/fin

]

Wf=7 nm

Sub-10 nm fin-width InGaAs finFETsWf=7 nm, Lg=3 μm MOSFET

(SW ~ 90o)• 50 nm thick InGaAs channel • ND=1018 cm-3

• Lg=3 μm• Oxide: Al2O3/HfO2 (EOT~3 nm)

SW ~ 90o SW ~ 80o

-0.25 0 0.25 0.5 0.7510-1310-1210-1110-1010-910-810-710-6

VGS [V]

I D [A

/fin]

Wf=7 nm

50

VDS=500 mV

VGS=0.6 V

0.5

0.1 0.3 0.2

0.4

5 nm7 nm

50 nm 50 nm

13

-1 -0.5 0 0.5 110-1310-1210-1110-1010-910-810-710-610-5

VGS [V]

I D [A

/fin]

-1 -0.5 0 0.5 110-1310-1210-1110-1010-910-810-710-610-5

VGS [V]

I D [A

/fin]

0 5 10 15 20 25 30 35

-0.8

-0.4

0.0

0.4

V T [V]

WF [nm]

Impact of Wfon subthreshold characteristics

0 5 10 15 20 25 30 35

-0.8

-0.4

0.0

0.4

V T [V]

WF [nm]• VT defined at 5 nA/fin• Strong sensitivity of VT to Wf <10 nm for SW90

SW90VDS=50 mV

5

5

Wf=35 Wf=35 nm

SW90 SW80

SW80VDS=50 mV

Wf Wf

14

-0.25 0 0.25 0.5 0.7510-1510-1410-1310-1210-1110-1010-910-810-7

VGS [V]

I D [A

/fin]

Wf=7 nm

Low-temperature measurements

0 5 10 15 20 25 30 35-1.0-0.8-0.6-0.4-0.20.00.20.40.6

V T [V]

WF [nm]

SW90

0 5 10 15 20 25 30 35-1.0-0.8-0.6-0.4-0.20.00.20.40.6

V T [V]

WF [nm]

SW80

• Dit impact ↓• Rigid ΔVT>0• Strong sensitivity of VT to Wf for

SW90 maintained

RT 90K

as T↓

VDS=50 mV

RTRT

90K90K

15

-0.5 0.0 0.5 1.0

0.0

0.2

0.4

0.6

0.8

Wf=13 nm

Cg/C

ox

VGS [V]

7

T=90K

-0.5 0.0 0.5 1.00

500

1000

1500Wf=13 nm

11 nm

9 nm7 nm

µ [c

m2 /V

sec]

VGS [V]

-0.5 0.0 0.5 1.010-12

10-11

10-10

10-9

10-8

10-7

10-6

Wf=13 nm7

7I D [A

/fin]

VGS [V]-0.5 0.0 0.5 1.0

101

102

103

104

105

106

107

108

Wf=13 nm

n fin [c

m-1]

VGS [V]

Subthreshold carrier concentration at 90K

• CV+IV μ(VGS)• Use μmax to transfer subthreshold characteristics to nfin

VTn definition

16

0 5 10 15 20 25 30 35-0.4

-0.2

0.0

0.2

0.4V Tn

[V]

WF [nm]

T=90K

Impact of Wf on VT

Strong sensitivity of VT toWf for SW~90o MOSFETs

VTn at constant nfin=5·105 cm-1

SW80 SW90

VTn sensitivity to Wf persists 17

0 10 20 30 40-0.5

-0.4

-0.3

-0.2

-0.1

0

Wf [nm]

V T-Vfb

[V]

Classic VT – Wf dependence

Wfn

2

0 1 1 12 2

f oxT fb

ox s

WVV Vt

εε

− = − + −

00 2

s D

ox

q NVC

ε ε≡

Threshold:

Wfw>Wfn

Vtw<Vtn Vtn

W W’

ND=1018 cm-3

• Wf↑ |VT –Vfb| ↑ 18

Quantum VT – Wf dependence

subband

• Quantum confinement creates subbands CB Min↑• For constant ND EF ↑• Positive shift to VT as Wf↓

Wfn

VtC

Wfn

VtQ

Classic Quantum

19

0 10 20 30 40-0.6

-0.4

-0.2

0

0.2

0.4

Wf [nm]

V Tn [V

]

Impact of Wf on VT

Poisson-Schrodinger simulations (Nextnano):

• ΔVT>0 due to quantum confinement for Wf<10 nm

• Larger ΔVT in SW90 due to greater quantum confinement

SW=90o

SW=80o

Wf = 4nm

Classic

QuantumSW90SW80

T=90 K

20

Impact of Wf on VT

Comparison of simulation and experiments:

Good agreement after rigid VT shift

0 5 10 15 20 25 30 35-0.4

-0.2

0.0

0.2

0.4V Tn

[V]

Wf [nm]

T=90KSW90

SW80

P-S simulation

21

Impact of sidewall slope

Wf= 4 nm

Wf

0 5 10 15 20 25 30 35-0.4

-0.2

0.0

0.2

0.4

SW90 SW80

V Tn [V

]

Wf [nm]

VT vs. Wf match for both sidewall slopes

Wf=Wf + 4 nm

T= 90 K

22

0 10 20 30 40

-0.4

-0.2

0

0.2

0.4

Wf [nm]

V Tn [V

]

Impact of Wf on VT: effect of doping

• Reduced doping (inv. mode) reduced VT variation• Strong quantum ΔVT for Wf<10 nm regime

ND=1018 cm-3

1017 1016

Quantum

Classic

23

0 5 10 15 20 25 30 350.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

V Tn [V

]

Wf [nm]

Impact of Wf on VT: comparison with Si

Self-consistent P-S simulations:

VT of InGaAs finFETs with Wf<10 nm: • ~4x more sensitive to Wf than Si!• due to quantum effects

ND=1016 cm-3

*em ↑

InGaAs

Si

Conclusions• InGaAs finFETs with Wf<10 nm demonstrated

experimentally

• Observation of quantum size effects in sub-10 nm fins

• Implication for manufacturing control in future nm-scale InGaAs finFETs

25

Thank you !

26

Sidewall Dit profile

-1.0 -0.5 0.0 0.5 1.0101

102

103

104

105

106

107

108

Wf=37 nm

Wf=12 nm

Measurement Simulation: U-shape Dit

n f [cm

-1]

VGS [V]-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0

10-6

10-4

10-2

100

102

104

106

108

Ideal Measured

Wf=70 nm

Wf=10 nm

n f [cm

-1]

VGS [V]

60 mv/dec

• Fitting with μmax extracted via CV+IV• U-shape Dit profile provides excellent agreement with

measurements for the entire Wf range.• At the flat minima – Dit level of 3x1012 cm-2eV-1

Al2O3, 4 cyc DE, FGA

0.5 Ec 1.01

10

Dit [

1012

cm-2eV

-1]

E-Ev [eV]

Vardi, DRC 2014

Mid gap branch

CBbranch

CBbranch

Mid gap branch

27

-0.25 0 0.25 0.5 0.7510-1510-1410-1310-1210-1110-1010-910-810-7

VGS [V]

I D [A

/fin]

Wf=7 nm

Low-temperature measurements

0 5 10 15 20 25 30 35-1.0-0.8-0.6-0.4-0.20.00.20.40.6

V T [V]

WF [nm]

SW90

0 5 10 15 20 25 30 35-1.0-0.8-0.6-0.4-0.20.00.20.40.6

V T [V]

WF [nm]

SW80

• Dit impact ↓• Rigid ΔVT>0• Strong sensitivity of VT to WF for

SW90 maintained

RT 90K

as T↓

VDS=50 mV

28

-0.5 0.0 0.5 1.0

0.0

0.2

0.4

0.6

0.8

Wf=13 nm

Cg/C

ox

VGS [V]

7 nm

T=90K

-0.5 0.0 0.5 1.00

500

1000

1500Wf=13 nm

11 nm

9 nm7 nm

µ [c

m2 /V

sec]

VGS [V]

-0.5 0.0 0.5 1.010-12

10-11

10-10

10-9

10-8

10-7

10-6

13 nm7 nm

7 nmI D [A

/fin]

VGS [V]

-0.5 0.0 0.5 1.0101

102

103

104

105

106

107

108

13 nm

n fin [c

m-1]

VGS [V]

Subthreshold carrier concentration at 90K

• CV+IV μ(VGS)• Use μmax to transfer subthreshold characteristics to nfin

VTn definition

29

Effect of Dit on VT-WF dependence

0 5 10 15 20 25 30 35-0.4

-0.2

0.0

0.2

0.4 No Dit

Dit=3 [1012cm-2eV-1]

V Tn [V

]

Wf [nm]

T=90K0.5 Ec 1.0

1

10

Dit [

1012

cm-2eV

-1]

E-Ev [eV]

T↓

30

19 nm7 nm

SW80 - different WF

31

12 nm7 nm 5 nm

SW90 - different WF

32

Sub T carrier concentration

( )exp 1 expGS T DSD e T

q V V qVW kTI D CL q nkT nkT

− = − −

( )2

exp 1 expGS T DSD e T

q V V qVW kTI CL q nkT nkTµ

− = − −

( )

( )

,

,

D e GS DS

DGS DS

e

W kTI Q V VL q

I L qQ V VW kT

µ

µ

=

→ =

( ) DGS

e

I L qQ VW kTµ

=

For long channel at small VDS, the channel charge (source side) is:

33

-0.35

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

0

Subband e

nerg

y [e

V]

-2 -1.5 -1 -0.5 0 0.5 1V

GS [V]

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Subband e

nerg

y [e

V]

SW90, WF=8 (1D)

SW80, WF=4 (2D)

SW80 eigs are lower with smaller dispassion (larger density of states)

-0.33

-0.32

-0.31

-0.3

-0.29

-0.28

-0.27

-0.26

Subband e

nerg

y [e

V]

Sub-bands spectrum

34