Towards Sub-10 nm Diameter III-V VNW Transistors Wenjie Lu, Xin - - PowerPoint PPT Presentation

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Towards Sub-10 nm Diameter III-V VNW Transistors Wenjie Lu, Xin Zhao, Jess A. del Alamo Massachusetts Institute of Technology wenjie@mit.edu Task/Theme: 2655.001 Contents Motivation Digital etch in III-Vs III-As (InGaAs)

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SLIDE 1

Towards Sub-10 nm Diameter III-V VNW Transistors

Wenjie Lu, Xin Zhao, Jesús A. del Alamo

Massachusetts Institute of Technology wenjie@mit.edu

Task/Theme: 2655.001

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SLIDE 2

2

  • Motivation
  • Digital etch in III-V’s
  • III-As (InGaAs)
  • III-Sb (InGaSb)
  • InGaAs vertical nanowire MOSFETs
  • Conclusions

Contents

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SLIDE 3

3

Motivation – Why III-Vs?

del Alamo, Nature 2011

  • Exceptional carrier transport properties
  • Rich band structure engineering
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SLIDE 4

4

Motivation – why vertical nanowire?

Lc Lg Lspacer Vertical NW FET:  uncouples footprint scaling Top-down

1 nm

Iutzi 2012 Lam Research

Leverage existing dry etch infrastructure Advanced epitaxial growth technology

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SLIDE 5

5

VNW RIE & digital etch – key enabling technologies

  • RIE = BCl3/SiCl4/Ar chemistry
  • Digital Etch (DE) =

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

  • Radial etch rate = 1 nm/cycle
  • Can reach sub-20 nm NW diameter
  • Aspect ratio > 10
  • Smooth sidewalls

Zhao, IEDM 2013 Lu, EDL 2017

After RIE 2 cycles 5 cycles 10 cycles

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SLIDE 6

6

Digital Etch – Problem I

Surface tension (mN/m):

  • Water: 72
  • Methanol: 22
  • IPA: 23

Broken NW’s

Water-based acid is problem: Difficult to reach 10 nm VNW diameter due to breakage

Lu, EDL 2017

8 nm InGaAs VNWs after 7 DE cycles:

10% HCl in DI water Yield = 0%

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SLIDE 7

7

Alcohol-based Digital Etch - InGaAs

8 nm InGaAs VNWs after 7 DE cycles:

Broken NW’s

Alochol-based DE enables D < 10 nm

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

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SLIDE 8

8

Radial Etch Rate

  • About same etch rate as water-based DE  oxidation step

sets etch rate

  • Etch rate in H2SO4:methanol > HCl:IPA  different surface

conditioning?

2 4 6 8 10 5 10 15 20 rinit = 17 nm rinit = 16 nm rinit = 15 nm rinit = 14 nm

Final NW Radius (nm) Digital Etch Cycles 1.0 nm/cycle Arsenide in 0.1 M HCl:IPA

2 4 6 8 10 5 10 15 20

Arsenide in 2.0 M H2SO4:methanol 1.2 nm/cycle

rinit = 17 nm rinit = 16 nm rinit = 15 nm rinit = 14 nm

Final NW Radius (nm) Digital Etch Cycles

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SLIDE 9

9

D = 5 nm VNW

First demonstration of D=5 nm diameter InGaAs VNW

(Aspect Ratio > 40)

10% H2SO4 in methanol Lu, EDL 2017

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SLIDE 10

10

D = 5.5 nm VNW Arrays D= D=5. 5.5 nm nm VN VNW arrays s with 9 90% 0% y yiel eld

10% H2SO4 in methanol

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SLIDE 11

11

Close-packed VNW arrays

D=10 nm, pitch=80 nm, 100% yield

10% HCl in IPA

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SLIDE 12

12

Role of Rinsing

  • H2SO4:methanol yields 90% at D=6 nm!
  • Viscosity matters: methanol (0.54 cP) vs. IPA (2.0 cP)
  • Rinse in alcohol improves DE yield at D=12 nm but not below  oxide removal is

most aggressive step

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SLIDE 13

13

Digital Etch – Problem II

III-Sb very reactive: unable to perform digital etch on III-Sb

  • Conventional HCl treatment damages III-Sb vertical sidewalls
  • Aqueous solution not suitable for vertical III-Sb

Lu, EDL 2017

Dip in DI water for 2 min 1% HCl:H2O 30 s Lu, IEDM 2015

InAs InGaSb AlGaSb

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SLIDE 14

14

Alcohol-based Digital Etch – InGaSb

Alcohol-based HCl treatment does not damage III-Sb sidewall

10% HCl:IPA 2 min RIE (BCl3/N2) 20 nm 20 nm

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SLIDE 15

15

Alcohol-based Digital Etch – InGaSb

First demonstration of InGaSb DE with radial etch rate = 1.0 nm/cycle

10 nm InGaSb fin after 5 cycles DE in HCl:IPA

2 4 6 20 40 60

Antimonide in 0.1 M HCl:IPA 1.0 nm/cycle

rinit = 52 nm rinit = 42 nm rinit = 32 nm rinit = 21 nm

Final NW Radius (nm) Digital Etch Cycles

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SLIDE 16

16

InGaAs VNW MOSFETs

  • 5 DE cycles in H2SO4:methanol
  • Al2O3 = 2 nm (EOT = 1 nm)
  • W gate, Mo ohmic contacts
  • D = 20 – 40 nm

n+ InGaAs, 70 nm i InGaAs, 80 nm n+ InGaAs, 300 nm

Starting heterostructure: n+: 6×1019 cm-3 Si doping

MIT pursuing top-down approach for VNW fabrication

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SLIDE 17

17

InGaAs VNW MOSFETs – Process flow

Starting heterostructure VNW mask EBL SOG spacer dep & etch-back VNW digital etch ALD Al2O3 & W sputter SOG dep & etch- back W dry etch SOG dep & etch-back Al2O3 wet etch Ohmic contacts

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SLIDE 18

18

InGaAs VNW MOSFETs - Characteristics

  • Minimum Slin = 70 mV/dec for D = 40 nm
  • Dit ≈ 3.9∙1012 eV-1cm-2
  • 0.4
  • 0.2

0.0 0.2 0.4 0.6 10

  • 10

10

  • 9

10

  • 8

10

  • 7

10

  • 6

VDS = 0.5 V

D = 40 nm D = 20 nm LG = 80 nm Single NW

ID (A/µm) VGS (V) VDS = 0.05 V

70 mV/dec

Single VNW devices

5 10 15 20 25 30 60 80 100 120 140 160 180 200

This work

Lg/λ

eff

Slin [mV/dec]

MIT 2013

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SLIDE 19

19

  • Novel digital etch scheme using alcohol-based

etchants:

  • High mechanical yield at sub-10 nm diameter
  • Record VNW with D = 5 nm and AR > 40
  • First demonstration of DE on InGaSb
  • InGaAs VNW MOSFETs fabricated using alcohol-

based DE with excellent subthreshold characteristics

Conclusions