[PPT] - InGaSb p-Channel Self-Aligned FinFETs with 10 nm Fin-Width Using PowerPoint Presentation

SLIDE 1

InGaSb p-Channel Self-Aligned FinFETs with 10 nm Fin-Width Using Sb-Compatible Digital Etch

W. Lu1, I. P. Roh2, D.-M. Geum2, S.-H. Kim2, J. D. Song2, L. Kong1,

and J. A. del Alamo1

1Microsystems Technology Laboratories, MIT 2Korea Institute of Science and Technology

December 5, 2017 Sponsors:

DTRA KIST Lam Research SRC

SLIDE 2

Outline

Motivation
Key technology: III-Sb-compatible digital etch
InGaSb p-channel FinFET fabrication
Electrical characteristics
Conclusions

2

SLIDE 3

3

Properties of III-Sb:

High µn
High µp
Strong strain effect
Eg engineering
Applications in

photonics, etc.

InSb GaSb

[Miki, 1975] [Kawashima and Kataoka, JJAP 1979] [del Alamo, Nature, 2011]

Electron mobility Hole mobility in QW-FETs

A Case for III-Sb

SLIDE 4

4

III-Sb Transistor Research

InGaAs (IEEE)

SLIDE 5

5

III-Sb Transistor Research

Gu, IEDM 2011 Vardi, EDL 2016 Zhou, VLSI 2016 Waldron, VLSI 2016 Vardi, IEDM 2015 Zota, IEDM 2016 Zhao, IEDM 2013

InGaAs (IEEE)

SLIDE 6

6

III-Sb Transistor Research

III-Sb transistors (All publications) InGaAs (IEEE)

SLIDE 7

7

III-Sb Transistor Research

InSb QW p-FET Radosavljevic, IEDM ’08 InGaSb p-MOSFET Nainani, IEDM ’10 InGaSb p-SOI Nishi, VLSI ’15 InGaSb p-FinFET Lu, IEDM ’15 InAs/GaSb TFET Memišević, EDL ’16 InAs/AlSb/GaSb HEMT

B. Bennett, JVST ’00

InAs/GaSb CMOS Goh, IEDM ’15

III-Sb transistors (All publications) InGaAs (IEEE)

SLIDE 8

8

Digital etch: key of sub-10 nm InGaAs transistors

Challenges: III-Sb Digital Etch

D = 8 nm WF = 5 nm D = 5 nm

[Vardi, IEDM 2017] [Lu, EDL, 2017]

SLIDE 9

9

Wf limited by EBL and RIE

Challenges: III-Sb Digital Etch

XSEM of InGaSb FinFET

[Lu, IEDM, 2015]

SLIDE 10

10

XSEM of InGaSb FinFET Wf = 30 nm, Lg = 100 nm

Wf limited by EBL and RIE
Suffers from large off current

Challenges: III-Sb Digital Etch

0.8
0.4

0.0 100 200 300

ID (µA/µm) VDS (V)

VGS = 0.5 V to -3.5 V

[Lu, IEDM, 2015]

SLIDE 11

11

GaSb MOSCAPs

Previous research: HCl cleans GaSb surface

HCl Digital Etch on III-Sb

As-Is HCl

[Nainani, JAP 2011]

SLIDE 12

12

HCl Digital Etch on III-Sb

3
2
1

1 1x10

1

1x10

2

1x10

3

after HCl

ID (µA/µm) VGS (V)

Vds= -1.05 V

[Lu, IEDM, 2015]

FinFETs: only mild improvement of off current

[Nainani, JAP 2011]

GaSb MOSCAPs

Previous research: HCl cleans GaSb surface

As-Is HCl

SLIDE 13

13

1% HCl 30s After RIE

HCl etches the InGaSb sidewall

Issue with HCl Digital Etch

SLIDE 14

14

1% HCl 30s After RIE

HCl etches the InGaSb sidewall

Issue with HCl Digital Etch

DI water 2 min

Water-based HCl problematic for III-Sb DE

SLIDE 15

15

Self-limiting process
No damage on the sidewall

20 nm

10% HCl:IPA 2 min After RIE

Alcohol-based Digital Etch

20 nm

[Lu, EDL, 2017]

SLIDE 16

16

D = 20 nm D = 20 nm

Alcohol-based Digital Etch

2 4 6 20 40 60

VNW Radius (nm) Digital Etch Cycles

First digital etch on III-Sb: HCl:IPA + O2 plasma 10 nm

SLIDE 17

17

Etch rate ↓ after multiple DE cycles

D = 20 nm D = 20 nm

Alcohol-based Digital Etch

2 4 6 20 40 60 0.6 nm/cycle

VNW Radius (nm) Digital Etch Cycles

2 nm/cycle

First digital etch on III-Sb: HCl:IPA + O2 plasma

SLIDE 18

18

r (III-Sb) ↓ after 3 cycles
r (III-As) >> r (III-Sb)

InGaSb InAs HSQ 25 nm No DE 10 cycles r = 0.2 nm/cycle 16 nm 19 nm 3 cycles r = 1 nm/cycle

Alcohol-based Digital Etch

AlGaSb

SLIDE 19

Oxidation of GaSb:

In air:

‒Ga2O3, Sb2O3

19

Sb-compatible Digital Etch

[Liu, JVST B. 2002]

SLIDE 20

Oxidation of GaSb:

In air:

‒Ga2O3, Sb2O3

In strong oxidation agents:

‒Ga2O3, Sb2O3, Sb2O5 (insoluble in aqueous acid/alkali)

20

DE = oxidation + dissolution, both critical for III-Sb!

III-Sb-compatible Digital Etch

[Liu, JVST B. 2002]

SLIDE 21

Survey of digital etch combinations:

21

Best results: RT O2 atmosphere + HCl:IPA

III-Sb-compatible Digital Etch

SLIDE 22

O2 oxidation + HCl:IPA, IPA rinsing

22

r (III-As) = r (III-Sb)

25 nm No DE 9 nm 4 cycles r = 2 nm/cycle 17 nm 2 cycles r = 2 nm/cycle

III-Sb-compatible Digital Etch

InGaSb InAs HSQ AlGaSb

SLIDE 23

23

Channel μp = 1175 cm2/V∙s
Buffer/channel resistivity ~ 109

InGaSb FinFETs

Heterostructure (MBE at KIST) Composite cap

1.1% strain

Hc = 23 nm Graded buffer TEM

20 nm

23 nm InGaSb 6 nm InAlSb p+ cap AlGaSb

SLIDE 24

24

Ni Ohmic contact
SiO2 spacer
Gate recess (dry + wet)
Fin RIE
Digital etch
Al2O3/Al Gate stack
Via + metal

InGaSb FinFET Process

HSQ InGaSb Al2O3/Al

SLIDE 25

25

Rc = 22 Ω∙μm  4x reduction of Rc from 2015 FinFETs

Ohmic Contacts

Ni contacts, 350 °C RTA, 3 min

100 200 300 400 10

1

10

2

10

3

10

4

Ni W

Rc (Ω⋅µm) RTA Temp (°C)

Mo

Ni [MIT '15]

[Guo, EDL, 2015]

5 10 15 20 1 2 3 4 Na = 1⋅10

19 cm

3

Rc = 93 Ω⋅µm

RTotal⋅W (Ω⋅µm) Ld (µm)

Na = 3⋅10

19 cm

3

Rc = 22 Ω⋅µm ×10

4

SLIDE 26

26

High-quality simultaneous InAs and GaSb etching

Fin Etch

BCl3/Ar/SiCl4 3:11:0.4, 250°C This work BCl3/N2 13.5:5.5, 250°C [Lu, IEDM 2015]

50 nm InAs GaSb

SLIDE 27

Finished devices

27

3.5 nm Al2O3 gate dielectric
Final FGA anneal at 150 °C for 3 min

InGaSb FinFET Process

SLIDE 28

28

Narrowest Wf = 10 nm
Fin AR = 2.3

InGaSb FinFET Process

50 nm 84° HSQ InGaSb Al2O3 AlGaSb 10 nm 10 nm 3.5 nm 23 nm

SLIDE 29

29

S ~ 260 mV/dec
gm,max= 160 μS/μm
Single fin device: current fluctuations

Electrical Characteristics

1.0
0.8
0.6
0.4
0.2

0.0 50 100 150 200

ID (µA/µm) VDS (V)

VGS = -1 V to 1 V in 0.4 V step

0.5

0.0 0.5 10

1

10 10

1

10

2

VDS = -0.5 V VDS = -50 mV

ID (µA/µm) VGS (V)

Smin = 260 mV/dec

1.0
0.5

0.0 0.5 1.0 50 100 150 200 VDS = -50 mV VDS = -0.5 V

gm (µS/µm) VGS (V)

Wf = 10 nm, Lg = 20 nm, Nf = 1

SLIDE 30

30

Electrical Characteristics

1.0
0.8
0.6
0.4
0.2

0.0 1 2 3 4

ID (µA/µm) VDS (V)

VGS = -1 V to 1 V in 0.4 V step

0.5

0.0 0.5 10

3

10

2

10

1

10 VDS = -0.5 V VDS = -50 mV

ID (µA/µm) VGS (V)

Smin = 290 mV/dec

Wf = 10 nm, Lg = 1 μm, Nf = 100

SLIDE 31

31

Electrical Characteristics

1.0
0.8
0.6
0.4
0.2

0.0 1 2 3 4

ID (µA/µm) VDS (V)

VGS = -1 V to 1 V in 0.4 V step

Wf = 10 nm, Lg = 1 μm, Nf = 100 Significant improvement over 1st gen FinFETs

1.0
0.8
0.6
0.4
0.2

0.0 4 8 12

ID (µA/µm) VDS (V)

Wf = 30 nm, Lg = 1 μm

[Lu, IEDM, 2015]

SLIDE 32

32

Lg ↓  gm↑ Wf ↓  gm ↓

gm Scaling

100 1000 100 200 300

Wf = 26 nm Wf = 18 nm Wf = 14 nm Wf = 10 nm

gm (µS/µm) Lg (nm) Wf ↓

SLIDE 33

33

ON Resistance

20 40 60 80 100 120 2 4 6 8 10

RSD

Ron (kΩ⋅µm) Lg (nm)

Wf = 26 → 10 nm Rf

SLIDE 34

34

ON Resistance

10 100 1 10 100

Rf (kΩ/฀) Wf (nm)

1

20 40 60 80 100 120 2 4 6 8 10

RSD

Ron (kΩ⋅µm) Lg (nm)

Wf = 26 → 10 nm Rf

SLIDE 35

35

Rf and RSD ~ 1/Wf

ON Resistance

10 100 1 10 100

Rf (kΩ/฀) Wf (nm)

1

10 100 0.1 1 10

1

RSD (kΩ⋅µm) Wf (nm)

20 40 60 80 100 120 2 4 6 8 10

RSD

Ron (kΩ⋅µm) Lg (nm)

Wf = 26 → 10 nm Rf

SLIDE 36

36

Wf ↓  better VT roll-up

VT Scaling

10 100 1000 0.0 0.4 0.8 1.2

Wf = 26 nm Wf = 18 nm Wf = 14 nm Wf = 10 nm

VT (V) Lg (nm)

Wf ↓

SLIDE 37

37

1 DE cycle significantly improves off current

Off-state Current

Wf = 20 nm, Lg = 1 µm

1.0
0.5

0.0 0.5 1.0 10

2

10

1

10 10

1

10

2

1 DE cycle

ID (µA/µm) VGS (V)

0 DE cycle

SLIDE 38

38

Off-state Current

1.0
0.5

0.0 0.5 1.0 10

2

10

1

10 10

1

10

2

4 DE cycle 1 DE cycle

ID (µA/µm) VGS (V)

0 DE cycle

Wf = 20 nm, Lg = 1 µm

Device degrades after multiple DE cycles

SLIDE 39

39

Buffer is damaged after multiple DE cycles

Off-state Current

1.0
0.5

0.0 0.5 1.0 10

2

10

1

10 10

1

10

2

4 DE cycle 1 DE cycle

ID (µA/µm) VGS (V)

0 DE cycle

3 cycles of DE InGaSb AlGaSb

Wf = 20 nm, Lg = 1 µm

SLIDE 40

40

Buffer is damaged after multiple DE cycles
AlGaSb is very reactive

Exposure in air after fin etch

Off-state Current

1.0
0.5

0.0 0.5 1.0 10

2

10

1

10 10

1

10

2

4 DE cycle 1 DE cycle

ID (µA/µm) VGS (V)

0 DE cycle

3 cycles of DE InGaSb AlGaSb

Wf = 20 nm, Lg = 1 µm

SLIDE 41

41

0.6
0.4
0.2

0.0 0.2 0.4 0.6 10

3

10

2

10

1

10 10

1

ID (µA/µm) VGS (V)

Off-state Current

Lg = 1 µm Wf = 100  14 nm

HSQ InGaSb AlGaSb

SLIDE 42

42

0.6
0.4
0.2

0.0 0.2 0.4 0.6 10

3

10

2

10

1

10 10

1

ID (µA/µm) VGS (V)

No InGaSb channel

Off-state Current

Lg = 1 µm Wf = 100  14 nm Buffer leakage contributes substantially to off current

AlGaSb HSQ InGaSb AlGaSb

SLIDE 43

43

Record gm = 268 μS/μm at Wf = 46 nm

Benchmark

Normalized by conducting width

50 100 150 200 100 200 300

gm (µS/µm) Wf (nm)

This work

MIT CSW ’17 MIT IEDM ’15

FinFETs Planar

SLIDE 44

44

Benchmark

Normalized by conducting width Normalized by Wf

Planar FinFETs This work

50 100 150 200 200 400 600 800

ddd ddd

gm/Wf (µS/µm) Wf (nm)

If normalized by footprint, gm = 704 μS/μm at Wf = 10 nm

50 100 150 200 100 200 300

gm (µS/µm) Wf (nm)

This work

MIT CSW ’17 MIT IEDM ’15

FinFETs Planar

SLIDE 45

Studied sidewall cleaning of InGaSb FinFETs

‒ III-Sb-compatible digital etch ‒ Etching rate = 2 nm/cycle ‒ Mitigation of surface leakage

Demonstrated most scaled InGaSb p-channel FinFETs

‒ Minimum Wf = 10 nm ‒ Record device performance ‒ Improved subthreshold performance

Face challenge: to improve turn-off characteristics

45