Sub-10 nm Diameter InGaAs Vertical Nanowire MOSFETs X. Zhao, C. - - PowerPoint PPT Presentation

Sub-10 nm Diameter InGaAs Vertical Nanowire MOSFETs

• X. Zhao, C. Heidelberger, E. A. Fitzgerald, W. Lu, A. Vardi,

and J. A. del Alamo

Microsystems Technology Laboratories, Massachusetts Institute of Technology

Outline

• Motivation
• Process technology
• Device electrical characteristics
• Conclusions

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Vertical NW MOSFETs: ultimate scalable transistor

Lc Lg

Vertical NW MOSFET:  uncouples footprint scaling from Lg, Lspacer, and Lc scaling

Lc Lg

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State-of-the-art VNW MOSFETs: Si/Ge

• D = 18 nm devices demonstrated

20 40 60 80 100 200 400 600 800 1000 1200 1400

gm,pk (µS/µm) Si/Ge (1-1.2 V) Diameter (nm)

Peak gm of Si and Ge VNW MOSFETs (Vds = 1-1.2 V )

* Normalization by the total circumference

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State-of-the-art VNW MOSFETs: InGaAs

• InGaAs competitive with Si

20 40 60 80 100 200 400 600 800 1000 1200 1400

gm,pk (µS/µm) Si/Ge (1-1.2 V) InGaAs (0.5 V) Diameter (nm)

Peak gm of InGaAs (VDS=0.5 V), Si and Ge VNW MOSFETs

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State-of-the-art VNW MOSFETs: InGaAs

• InGaAs competitive with Si
• Need to demonstrate VNW MOSFETs with D<10 nm

20 40 60 80 100 200 400 600 800 1000 1200 1400

gm,pk (µS/µm) Si/Ge (1-1.2 V) InGaAs (0.5 V) Diameter (nm)

Target: D = 7 nm (Yakimets TED 2015) III-V TFET

Peak gm of InGaAs (VDS=0.5 V), Si and Ge VNW MOSFETs

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III-V VNW MOSFET process flow @ MIT

Adhesion layer HSQ n+ Starting substrate InGaAs i n+ n+ i n+ Sputtered W ALD-Al2O3 1st SOG 2nd SOG

Mo/Ti/Au

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Key enabling technologies:

• RIE = BCl3/SiCl4/Ar chemistry
• Radial etch rate=1 nm/cycle
• Sub-20 nm NW diameter
• Aspect ratio > 10
• Smooth sidewalls

RIE + 5 cycles DE

Zhao, IEDM 2013 Zhao, EDL 2014 Zhao, IEDM 2014

InGaAs vertical nanowires @ MIT

• Digital Etch (DE) =

self-limiting O2 plasma oxidation + H2SO4 or HCl oxide removal

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Challenge for sub-10 nm VNW: mechanical stability

8 nm InGaAs VNWs: Yield = 0%

Broken NW

Difficult to reach 10 nm VNW diameter due to breakage Water-based acid is problem: Surface tension (mN/m):

• Water: 72
• Methanol: 22
• IPA: 23

Solution: alcohol-based digital etch?

Lu, EDL 2017

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Alcohol-Based Digital Etch

10% HCl in IPA Yield = 97% 10% HCl in DI water Yield = 0%

Alcohol-based DE enables D < 10 nm

Broken NW

Radial etch rate: 1.0 nm/cycle Radial etch rate: 1.0 nm/cycle 8 nm InGaAs VNWs after 7 DE cycles:

Lu, EDL 2017

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D=5.5 nm VNW arrays

90% yield 10% H2SO4 in methanol

• H2SO4:methanol yields 90% at D=6 nm!
• Viscosity matters: methanol (0.54 cP) vs. IPA (2.0 cP)

Lu, EDL 2017

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Toward sub-10 nm InGaAs VNW MOSFETs

New element: H2SO4:methanol DE

Starting heterostructure:

n+ InGaAs, 55 nm i InGaAs, 80 nm n+ In0.7Ga0.3As: 6 nm n+ InGaAs, 300 nm n+ InAs: 2 nm n+ InGaAs: 11 nm

D = 40, 30, 18, 15, 11, 7 nm

• No. of wires = 1

Lch = 80 nm EOT = 1.25 nm

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D = 15 nm Mo-contacted device

Single nanowire MOSFET:

• D = 15 nm & Lch= 80 nm
• Slin= 69 mV/dec
• 2.5 nm Al2O3 (EOT = 1.25 nm)
• 300 oC N2 RTA, 1 min

0.0 0.1 0.2 0.3 0.4 0.5 50 100 150 200 Vgs= 0 V to 0.6 V in 0.1 V step

Ron= 5500 Ω⋅µm

Mo contact D = 15 nm 300

• C N2 RTA

Vds (V)

Id (µA/µm)

• 0.2

0.0 0.2 0.4 0.6 10

• 10

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• 9

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• 8

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• 7

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• 6

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• 5

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• 4

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• 3

Mo contact D = 15 nm 300

• C N2 RTA

Slin = 69 mV/dec Ssat = 76 mV/dec DIBL = 67 mV/dec Vds=0.5 V

Vgs(V) Id (A/µm)

Vds=0.05 V

• 0.2
• 0.1

0.0 0.1 0.2 0.3 0.4 100 200 300 400 500 Vds= 0.5 V gm,pk = 460 µS/µm Mo contact D = 15 nm 300

• C N2 RTA

Vgs(V) gm (µS/µm)

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Diameter scaling of Mo devices

5 10 15 20 25 30 35 40 1000 2000 3000 4000 5000 6000 Ron(Ω⋅µm) D (nm) 5 10 15 20 25 30 35 40 100 150 200 250 300 350 Ioff = 100 nA/µm & Vdd= 0.5 V Ion(µA/µm) D (nm) 5 10 15 20 25 30 35 40 400 800 1200 1600 2000 Vds= 0.5 V D (nm) gm,pk(µS/µm)

• Narrowest working device has D = 15 nm
• Ron skyrockets with D ↓

5 10 15 20 25 30 35 40 65 70 75 80 85 90 Vds= 0.05 V Slin(mV/dec) D (nm)

* Mean values

• f 3 individual

devices

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Challenge for sub-10 nm VNW: top contact

InGaAs Depletion region ? D = 30 nm D = 7 nm Mo “Fully depleted” “Partially depleted” D = 30 nm D = 7 nm

Solution: alloyed contacts?

Lee IEDM 2013

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Ni contacted D = 7 nm MOSFET

• 0.2

0.0 0.2 0.4 0.6 10

• 9

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• 8

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• 7

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• 6

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• 5

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• 4

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• 3

Before FGA Vds=0.5 V Ni contact D = 7 nm Vgs(V) Id (A/µm)

• 0.2

0.0 0.2 0.4 0.6 200 600 1000 1400 1800 Before FGA Vds=0.5 V Vgs(V) gm (µS/µm) Ni contact D = 7 nm 0.0 0.1 0.2 0.3 0.4 0.5 100 200 300 400 500 600 700 800 Ni contact D = 7 nm Vgs= 0 V to 0.8 V in 0.1 V step Vds(V) Id(µA/µm) Before RTA

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Ni contacted D = 7 nm MOSFET

Single nanowire MOSFET:

• D = 7 nm & Lch= 80 nm
• 2.5 nm Al2O3 (EOT = 1.25 nm)
• 200 oC FGA, 1 min
• Ion = 350 μA/μm @ VDD= 0.5 V &

Ioff = 100 nA/μm

0.0 0.1 0.2 0.3 0.4 0.5 100 200 300 400 500 600 700 800 Id (µA/µm)

Vgs= 0 V to 0.8 V in 0.1 V step Ron= 1100 Ω⋅µm

Ni contact D = 7 nm 200

• C FGA

Vds (V)

• 0.2

0.0 0.2 0.4 0.6 10

• 9

10

• 8

10

• 7

10

• 6

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• 5

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• 4

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• 3

Before FGA 200

• C FGA

Vds=0.5 V Ni contact D = 7 nm Slin/Ssat = 85/90 mV/dec DIBL = 222 mV/dec Vds=0.5 V Vgs(V) Id (A/µm) Vds=0.05 V

• 0.2

0.0 0.2 0.4 0.6 200 600 1000 1400 1800 Before FGA Vds=0.5 V Vgs(V) gm (µS/µm) Vds=0.5 V gm,pk = 1700 µS/µm Ni contact D = 7 nm 200

• C FGA

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Output characteristics vs. D

Better current situation at D = 15 nm devices

0.0 0.1 0.2 0.3 0.4 0.5 100 200 300 400 500 600 700 800 Id (µA/µm)

Vgs= 0 V to 0.8 V in 0.1 V step

Vds (V) 0.0 0.1 0.2 0.3 0.4 0.5 100 200 300 400 500 600 700 800 Vds(V) Vgs= 0 V to 0.6 V in 0.1 V step Id (µA/µm) 0.0 0.1 0.2 0.3 0.4 0.5 100 200 300 400 500 600 700 800 Vgs= 0 V to 0.7 V in 0.1 V step Id (µA/µm) Vds (V)

0.0 0.1 0.2 0.3 0.4 0.5 100 200 300 400 500 600 700 800 Vgs= 0 V to 0.8 V in 0.1 V step Vds(V) Id(µA/µm)

0.0 0.1 0.2 0.3 0.4 0.5 100 200 300 400 500 600 700 800

Vgs= 0 V to 0.8 V in 0.1 V step

Id (µA/µm) Vds(V) 0.0 0.1 0.2 0.3 0.4 0.5 100 200 300 400 500 600 700 800 Vds(V)

Vgs= 0 V to 0.8 V in 0.1 V step

Id (µA/µm)

Mo Ni D = 7 nm D = 15 nm D = 30 nm

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Diameter scaling of Ni vs Mo devices

5 10 15 20 25 30 35 40 1000 2000 3000 4000 5000 6000 Ron(Ω⋅µm) D (nm) Ni Mo 5 10 15 20 25 30 35 40 100 150 200 250 300 350 Ioff = 100 nA/µm & Vdd= 0.5 V Ion(µA/µm) D (nm) Ni Mo 5 10 15 20 25 30 35 40 400 800 1200 1600 2000 Mo Vds= 0.5 V D (nm) gm,pk(µS/µm) Ni 5 10 15 20 25 30 35 40 65 70 75 80 85 90 Vds= 0.05 V Slin(mV/dec) D (nm) Ni Mo

Excellent gm & Ion scaling with D for Ni devices

* Mean values

• f 3 individual

devices

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Benchmarking

High performance and good electrostatics

60 110 160 210 260 400 800 1200 1600 2000 This work - Mo Vds=0.5 V

Ssat (mV/dec)

gm,pk (µS/µm)

Persson EDL 2010 Tomioka IEDM 2011 Tomioka Nature 2012 Persson DRC 2012 Berg IEDM 2015 Kilpi VLSI 2017 Ramesh VLSI 2016, 0.4 V Zhao IEDM 2013 This work - Mo This work - Ni

This work - Ni

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Benchmarking

• First sub-10 nm diameter VNW transistor of any kind
• Record performance

5 10 15 20 25 30 35 40 400 800 1200 1600 2000 Target: D = 7 nm This work - Mo gm,pk (µS/µm)

Si/Ge, 1-1.2 V InGaAs This work - Mo This work - Ni

Diameter (nm) This work - Ni

Conclusions

• First sub-10 nm diameter VNW transistors of any kind in

any material system

• Key technologies: alcohol based DE + Ni alloyed contact
• Record performance demonstrated
• Top contact: key challenge for VNW MOSFET technology

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Appendix

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Ni contact for sub-10 nm InGaAs VNW MOSFETs

New elements: H2SO4:methanol DE + Ni alloyed contact

Starting heterostructure:

n+ InGaAs, 55 nm i InGaAs, 80 nm n+ In0.7Ga0.3As: 6 nm n+ InGaAs, 300 nm n+ InAs: 2 nm n+ InGaAs: 11 nm

D = 40, 30, 18, 15, 11, 7 nm

• No. of wires = 1

Lch = 80 nm EOT = 1.25 nm

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No RTA 250 C 300 C 350 C 60 160 260 360 460 560 Slin(mV/dec) Vds= 0.05 V T (K)

Ni, 30 Mo, 30

No RTA 250 C 300 C 350 C 200 400 600 800 1000 Vds= 0.5 V

gm,pk(µS/µm)

T (K)

Ni, 30 Mo, 30

No RTA 250 C 300 C 350 C 50 100 150 200 250 Ioff = 100 nA/µm & Vdd= 0.5 V

Ion(µA/µm)

T (K)

Ni, 30 Mo, 30

No RTA 250 C 300 C 350 C 5x10

2

5x10

3

5x10

4

5x10

5

Ron(Ω⋅µm)

T (K)

Ni, 30 Mo, 30

Effect of RTA

• Performance for Ni devices ↓ then

↑ with ↑ T

• Refractory metal Mo contact →

thermal stability

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D = 30 nm Mo-contacted device

Single nanowire MOSFET:

• D = 30 nm & Lch= 80 nm
• 2.5 nm Al2O3 (EOT = 1.25 nm)
• 300 oC N2 RTA, 1 min
• Slin= 66 mV/dec
• 0.2

0.0 0.2 0.4 0.6 10

• 10

10

• 9

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• 8

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• 7

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• 6

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• 5

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• 4

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• 3

Mo contact D = 30 nm 300

• C RTA

Slin = 66 mV/dec Ssat = 85 mV/dec DIBL = 67 mV/dec Vds=0.5 V

Vgs(V) Id (A/µm)

Vds=0.05 V

0.0 0.1 0.2 0.3 0.4 0.5 50 100 150 200 250 300 350 Mo contact D = 30 nm 300

• C RTA

Vgs= 0 V to 0.7 V in 0.1 V step Ron= 1358 Ω⋅µm

Id (µA/µm) Vds (V)

• 0.2

0.0 0.2 0.4 100 200 300 400 500 600 700 Mo contact D = 30 nm 300

• C RTA

Vds=0.5 V gm,pk = 600 µS/µm

Vgs(V) gm (µS/µm)

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Diameter scaling: electrostatics

• DIBL degradation likely due to top contact
• Narrowest working device is 15 nm for Mo

5 10 15 20 25 30 35 40 65 70 75 80 85 90 Vds= 0.05 V Slin(mV/dec) D (nm)

5 10 15 20 25 30 35 40 80 120 160 200 240 280 Ni, 200 C FGA Mo, 300 C RTA DIBL (mV/V) D (nm) 5 10 15 20 25 30 35 40

• 0.05

0.00 0.05 0.10 0.15 0.20 0.25 Vds= 0.05 V & IVt = 1 µA/µm Vt (V) D (nm)

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Diameter scaling: performance

5 10 15 20 25 30 35 40 1000 2000 3000 4000 5000 6000 Ron(Ω⋅µm) D (nm) 5 10 15 20 25 30 35 40 100 150 200 250 300 350 Ioff = 100 nA/µm & Vdd= 0.5 V Ion(µA/µm) D (nm) 5 10 15 20 25 30 35 40 400 800 1200 1600 2000 Vds= 0.5 V D (nm) gm,pk(µS/µm) Ni, 200 C FGA Mo, 300 C RTA

Excellent gm & Ion scaling with D for Ni devices

Acknowledgement

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• NSF E3S, Lam Research and SRC for funding
• Fabrication facility at MIT labs: MTL, SEBL
• MIT colleagues: W. Chern, T. Yu, L. Xia, D. Antoniadis, J. Hoyt
• E3S colleagues: E. Yablonovitch, M. Wu, M. Eggleston, A.

Lakhani