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

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

Contents • Motivation • Digital etch in III-V’s • III-As (InGaAs) • III-Sb (InGaSb) • InGaAs vertical nanowire MOSFETs • Conclusions 2

Motivation – Why III-Vs? del Alamo, Nature 2011 • Exceptional carrier transport properties • Rich band structure engineering 3

Motivation – why vertical nanowire? Top-down L c L spacer L g Lam Research Leverage existing dry etch infrastructure 1 nm Vertical NW FET: Iutzi 2012  uncouples footprint scaling Advanced epitaxial growth technology 4

VNW RIE & digital etch – 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 After RIE 2 cycles 5 cycles 10 cycles • Radial etch rate = 1 nm/cycle Zhao, IEDM 2013 Lu, EDL 2017 • Can reach sub-20 nm NW diameter • Aspect ratio > 10 5 Smooth sidewalls •

Digital Etch – Problem I 8 nm InGaAs VNWs after 7 DE cycles: 10% HCl in DI water Yield = 0% Water-based acid is problem: Broken NW’s Surface tension (mN/m): • Water: 72 • Methanol: 22 • IPA: 23 Lu, EDL 2017 Difficult to reach 10 nm VNW diameter due to breakage 6

Alcohol-based Digital Etch - InGaAs 8 nm InGaAs VNWs after 7 DE cycles: 10% HCl in IPA 10% HCl in DI water Yield = 97% Yield = 0% Broken NW’s Alochol-based DE enables D < 10 nm 7

Radial Etch Rate Arsenide in 2.0 M H 2 SO 4 :methanol Arsenide in 0.1 M HCl:IPA 20 20 Final NW Radius (nm) 1.0 nm/cycle Final NW Radius (nm) 1.2 nm/cycle 15 15 10 10 r init = 17 nm r init = 17 nm r init = 16 nm r init = 16 nm 5 5 r init = 15 nm r init = 15 nm r init = 14 nm r init = 14 nm 0 0 0 2 4 6 8 10 0 2 4 6 8 10 Digital Etch Cycles Digital Etch Cycles About same etch rate as water-based DE  oxidation step • sets etch rate Etch rate in H 2 SO 4 :methanol > HCl:IPA  different surface • conditioning? 8

D = 5 nm VNW 10% H 2 SO 4 in methanol Lu, EDL 2017 First demonstration of D=5 nm diameter InGaAs VNW ( Aspect Ratio > 40) 9

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% H 2 SO 4 in methanol 10

Close-packed VNW arrays 10% HCl in IPA D=10 nm, pitch=80 nm, 100% yield 11

Role of Rinsing • H 2 SO 4 :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 12

Digital Etch – Problem II III-Sb very reactive: unable to perform digital etch on III-Sb 1% HCl:H 2 O 30 s Dip in DI water for 2 min InAs InGaSb AlGaSb Lu, EDL 2017 Lu, IEDM 2015 • Conventional HCl treatment damages III-Sb vertical sidewalls • Aqueous solution not suitable for vertical III-Sb 13

Alcohol-based Digital Etch – InGaSb RIE (BCl 3 /N 2 ) 10% HCl:IPA 2 min 20 nm 20 nm Alcohol-based HCl treatment does not damage III-Sb sidewall 14

Alcohol-based Digital Etch – InGaSb 10 nm InGaSb fin Antimonide in 0.1 M HCl:IPA 60 after 5 cycles DE in HCl:IPA Final NW Radius (nm) 40 20 r init = 52 nm r init = 42 nm 1.0 nm/cycle r init = 32 nm r init = 21 nm 0 0 2 4 6 Digital Etch Cycles First demonstration of InGaSb DE with radial etch rate = 1.0 nm/cycle 15

InGaAs VNW MOSFETs MIT pursuing top-down approach for VNW fabrication Starting heterostructure: n + InGaAs, 70 nm i InGaAs, 80 nm n + InGaAs, 300 nm n + : 6 × 10 19 cm -3 Si doping • 5 DE cycles in H 2 SO 4 :methanol • Al 2 O 3 = 2 nm (EOT = 1 nm) • W gate, Mo ohmic contacts • D = 20 – 40 nm 16

InGaAs VNW MOSFETs – Process flow Starting VNW mask EBL SOG spacer dep VNW digital etch heterostructure & etch-back ALD Al 2 O 3 & W sputter Ohmic contacts SOG dep & etch-back SOG dep & etch- back Al 2 O 3 wet etch W dry etch 17

InGaAs VNW MOSFETs - Characteristics Single VNW devices 200 MIT 2013 V DS = 0.05 V 180 D = 40 nm D = 20 nm -6 10 160 L G = 80 nm V DS = 0.5 V Single NW S lin [mV/dec] -7 140 10 70 mV/dec I D (A/ µ m) 120 -8 10 This work 100 -9 10 80 -10 10 60 -0.4 -0.2 0.0 0.2 0.4 0.6 0 5 10 15 20 25 30 V GS (V) L g / λ eff • Minimum S lin = 70 mV/dec for D = 40 nm D it ≈ 3.9∙10 12 eV -1 cm -2 • 18

Conclusions • 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 19