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 2

Vertical NW MOSFETs: ultimate scalable transistor L c L g L g L c Vertical NW MOSFET:  uncouples footprint scaling from L g , L spacer , and L c scaling 3

State-of-the-art VNW MOSFETs: Si/Ge Peak g m of Si and Ge VNW MOSFETs (V ds = 1-1.2 V ) 1400 Si/Ge (1-1.2 V) * Normalization 1200 by the total circumference g m,pk ( µ S/ µ m) 1000 800 600 400 200 0 0 20 40 60 80 100 Diameter (nm) • D = 18 nm devices demonstrated 4

State-of-the-art VNW MOSFETs: InGaAs Peak g m of InGaAs (V DS =0.5 V), Si and Ge VNW MOSFETs 1400 Si/Ge (1-1.2 V) 1200 InGaAs (0.5 V) g m,pk ( µ S/ µ m) 1000 800 600 400 200 0 0 20 40 60 80 100 Diameter (nm) • InGaAs competitive with Si 5

State-of-the-art VNW MOSFETs: InGaAs Peak g m of InGaAs (V DS =0.5 V), Si and Ge VNW MOSFETs Target: D = 7 nm (Yakimets TED 2015) 1400 Si/Ge (1-1.2 V) 1200 InGaAs (0.5 V) g m,pk ( µ S/ µ m) 1000 800 600 400 200 0 0 20 40 60 80 100 III-V TFET Diameter (nm) • InGaAs competitive with Si • Need to demonstrate VNW MOSFETs with D<10 nm 6

III-V VNW MOSFET process flow @ MIT Sputtered W Starting substrate ALD-Al 2 O 3 n+ InGaAs i n+ Adhesion 1 st SOG HSQ layer n+ i n+ 2 nd SOG Mo/Ti/Au 7

InGaAs vertical nanowires @ MIT Key enabling technologies: • RIE = BCl 3 /SiCl 4 /Ar chemistry • Digital Etch (DE) = self-limiting O 2 plasma oxidation + H 2 SO 4 or HCl oxide removal RIE + 5 cycles DE • Radial etch rate=1 nm/cycle • Sub-20 nm NW diameter • Aspect ratio > 10 • Smooth sidewalls Zhao, IEDM 2013 Zhao, EDL 2014 Zhao, IEDM 2014 8

Challenge for sub-10 nm VNW: mechanical stability Lu, EDL 2017 Difficult to reach 10 nm VNW diameter due to breakage 8 nm InGaAs VNWs: Yield = 0% Water-based acid is problem: Surface tension (mN/m): Broken NW • Water: 72 • Methanol: 22 • IPA: 23 Solution: alcohol-based digital etch? 9

Alcohol-Based Digital Etch 8 nm InGaAs VNWs after 7 DE cycles: Lu, EDL 2017 10% HCl in DI water 10% HCl in IPA Yield = 0% Yield = 97% Broken NW Radial etch rate: 1.0 nm/cycle Radial etch rate: 1.0 nm/cycle Alcohol-based DE enables D < 10 nm 10

D=5.5 nm VNW arrays 10% H 2 SO 4 in methanol Lu, EDL 2017 90% yield • H 2 SO 4 :methanol yields 90% at D=6 nm! • Viscosity matters: methanol (0.54 cP) vs. IPA (2.0 cP) 11

Toward sub-10 nm InGaAs VNW MOSFETs Starting heterostructure: n+ InGaAs: 11 nm n+ InAs: 2 nm n+ In 0.7 Ga 0.3 As: 6 nm n+ InGaAs, 55 nm i InGaAs, 80 nm n+ InGaAs, 300 nm D = 40, 30, 18, 15, 11, 7 nm No. of wires = 1 L ch = 80 nm EOT = 1.25 nm New element: H 2 SO 4 :methanol DE 12

D = 15 nm Mo-contacted device 500 V ds = 0.5 V -3 10 V ds =0.5 V Mo contact g m,pk = 460 µ S/ µ m D = 15 nm 400 -4 10 Mo contact o C N 2 RTA 300 D = 15 nm g m ( µ S/ µ m ) -5 10 300 o C N 2 RTA 300 V ds =0.05 V I d ( A/ µ m ) -6 10 200 -7 10 S lin = 69 mV/dec 100 -8 10 S sat = 76 mV/dec 0 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 -9 DIBL = 67 mV/dec 10 V gs (V) 200 V gs = 0 V to 0.6 V in 0.1 V step -10 10 R on = 5500 Ω ⋅ µ m -0.2 0.0 0.2 0.4 0.6 V gs (V) Mo contact 150 D = 15 nm I d (µ A/ µ m) Single nanowire MOSFET: o C N 2 RTA 300 100 • D = 15 nm & L ch = 80 nm • S lin = 69 mV/dec 50 • 2.5 nm Al 2 O 3 (EOT = 1.25 nm) 0 • 300 o C N 2 RTA, 1 min 0.0 0.1 0.2 0.3 0.4 0.5 13 V ds (V)

Diameter scaling of Mo devices 2000 V ds = 0.5 V 6000 * Mean values of 3 individual 1600 5000 g m,pk ( µ S/ µ m) devices R on ( Ω⋅µ m) 4000 1200 3000 800 2000 1000 400 5 10 15 20 25 30 35 40 5 10 15 20 25 30 35 40 D (nm) 350 D (nm) 90 I off = 100 nA/ µ m & V dd = 0.5 V V ds = 0.05 V 300 85 S lin (mV/dec) I on ( µ A/ µ m) 250 80 200 75 150 70 100 65 5 10 15 20 25 30 35 40 5 10 15 20 25 30 35 40 D (nm) D (nm) • Narrowest working device has D = 15 nm • R on skyrockets with D ↓ 14

Challenge for sub-10 nm VNW: top contact D = 7 nm D = 30 nm D = 7 nm D = 30 nm Mo InGaAs Depletion region ? “Partially “Fully depleted” depleted” Lee IEDM 2013 Solution: alloyed contacts? 15

Ni contacted D = 7 nm MOSFET -3 10 Ni contact Ni contact D = 7 nm 1800 D = 7 nm -4 10 1400 -5 g m ( µ S/ µ m ) 10 I d ( A/ µ m ) 1000 -6 10 600 -7 10 200 Before FGA V ds =0.5 V -8 10 Before FGA V ds =0.5 V -0.2 0.0 0.2 0.4 0.6 -9 10 V gs (V) 800 Ni contact -0.2 0.0 0.2 0.4 0.6 D = 7 nm 700 V gs (V) V gs = 0 V to 0.8 V in 0.1 V step 600 I d ( µ A/ µ m) 500 400 300 200 100 Before RTA 0 16 0.0 0.1 0.2 0.3 0.4 0.5 V ds (V)

Ni contacted D = 7 nm MOSFET -3 V ds =0.5 V 10 Ni contact V ds =0.5 V 1800 D = 7 nm g m,pk = 1700 µ S/ µ m -4 10 Ni contact 1400 o C FGA 200 D = 7 nm -5 g m ( µ S/ µ m ) 10 V ds =0.05 V o C FGA I d ( A/ µ m ) 200 1000 -6 10 S lin /S sat = 85/90 mV/dec 600 -7 10 DIBL = 222 mV/dec 200 Before FGA V ds =0.5 V -8 10 V ds =0.5 V -0.2 0.0 0.2 0.4 0.6 Before FGA -9 10 V gs (V) 800 V gs = 0 V to 0.8 V in 0.1 V step -0.2 0.0 0.2 0.4 0.6 R on = 1100 Ω ⋅ µ m 700 V gs (V) Single nanowire MOSFET: 600 Ni contact D = 7 nm I d (µ A/ µ m) 500 • D = 7 nm & L ch = 80 nm o C FGA 200 400 • 2.5 nm Al 2 O 3 (EOT = 1.25 nm) 300 • 200 o C FGA, 1 min 200 100 • I on = 350 μ A/ μ m @ V DD = 0.5 V & 0 I off = 100 nA/ μ m 17 0.0 0.1 0.2 0.3 0.4 0.5 V ds (V)

Output characteristics vs. D D = 7 nm D = 15 nm D = 30 nm 800 800 800 V gs = 0 V to 0.8 V in 0.1 V step V gs = 0 V to 0.8 V in 0.1 V step V gs = 0 V to 0.8 V in 0.1 V step 700 700 700 600 600 600 I d (µ A/ µ m) I d (µ A/ µ m) 500 500 I d (µ A/ µ m) 500 Ni 400 400 400 300 300 300 200 200 200 100 100 100 0 0 0 0.0 0.1 0.2 0.3 0.4 0.5 0.0 0.1 0.2 0.3 0.4 0.5 0.0 0.1 0.2 0.3 0.4 0.5 V ds (V) V ds (V) V ds (V) 800 V gs = 0 V to 0.8 V in 0.1 V step 800 800 V gs = 0 V to 0.7 V in 0.1 V step V gs = 0 V to 0.6 V in 0.1 V step 700 700 700 600 600 600 I d ( µ A/ µ m) I d (µ A/ µ m) 500 500 I d (µ A/ µ m) 500 Mo 400 400 400 300 300 300 200 200 200 100 100 100 0 0 0 0.0 0.1 0.2 0.3 0.4 0.5 0.0 0.1 0.2 0.3 0.4 0.5 0.0 0.1 0.2 0.3 0.4 0.5 V ds (V) V ds (V) V ds (V) Better current situation at D = 15 nm devices 18

Diameter scaling of Ni vs Mo devices 2000 V ds = 0.5 V * Mean values 6000 of 3 individual 5000 1600 devices g m,pk ( µ S/ µ m) R on ( Ω⋅µ m) 4000 1200 Mo Ni 3000 2000 800 Mo Ni 1000 400 5 10 15 20 25 30 35 40 5 10 15 20 25 30 35 40 D (nm) D (nm) 350 90 I off = 100 nA/ µ m & V dd = 0.5 V V ds = 0.05 V 300 85 S lin (mV/dec) I on ( µ A/ µ m) 250 Ni 80 Ni 200 Mo 75 150 70 Mo 100 65 5 10 15 20 25 30 35 40 5 10 15 20 25 30 35 40 D (nm) D (nm) Excellent g m & I on scaling with D for Ni devices 19

Benchmarking Persson EDL 2010 2000 Tomioka IEDM 2011 Tomioka Nature 2012 This work - Ni Persson DRC 2012 Berg IEDM 2015 1600 Kilpi VLSI 2017 Ramesh VLSI 2016, 0.4 V g m,pk ( µ S/ µ m ) Zhao IEDM 2013 1200 This work - Mo This work - Ni This work - Mo 800 400 V ds =0.5 V 0 60 110 160 210 260 S sat (mV/dec) High performance and good electrostatics 20

Benchmarking Si/Ge, 1-1.2 V 2000 InGaAs Target: D = 7 nm This work - Mo This work - Ni This work - Ni 1600 g m,pk ( µ S/ µ m) 1200 800 This work - Mo 400 0 5 10 15 20 25 30 35 40 Diameter (nm) • First sub-10 nm diameter VNW transistor of any kind • Record performance 21

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 22

Appendix 23

Ni contact for sub-10 nm InGaAs VNW MOSFETs Starting heterostructure: n+ InGaAs: 11 nm n+ InAs: 2 nm n+ In 0.7 Ga 0.3 As: 6 nm n+ InGaAs, 55 nm i InGaAs, 80 nm n+ InGaAs, 300 nm D = 40, 30, 18, 15, 11, 7 nm No. of wires = 1 L ch = 80 nm EOT = 1.25 nm New elements: H 2 SO 4 :methanol DE + Ni alloyed contact 24

Effect of RTA 1000 560 V ds = 0.5 V Ni, 30 Ni, 30 Ni, 30 Mo, 30 Mo, 30 Mo, 30 5 5x10 800 460 V ds = 0.05 V S lin (mV/dec) g m,pk ( µ S/ µ m) R on ( Ω⋅µ m) 600 360 4 5x10 400 260 3 5x10 200 160 2 0 60 5x10 No RTA 250 C 300 C 350 C No RTA 250 C 300 C 350 C No RTA 250 C 300 C 350 C T (K) T (K) T (K) 250 I off = 100 nA/ µ m Ni, 30 Mo, 30 & V dd = 0.5 V • Performance for Ni devices ↓ then 200 I on ( µ A/ µ m) ↑ with ↑ T 150 100 • Refractory metal Mo contact → 50 thermal stability 0 No RTA 250 C 300 C 350 C T (K) 25