Quantum-size effects in sub-10 nm fin width InGaAs finfets

Transcription

1 Quantum-size effects in sub-10 nm fin width InGaAs finfets Alon Vardi, Xin Zhao, and Jesús A. del Alamo Microsystems Technology Laboratories, MIT December 9, 2015 Sponsors: DTRA NSF (E3S STC) Northrop Grumman

2 Outline Motivation Process Technology Electrical characteristics Modeling Conclusions 2

3 InGaAs planar Quantum-Well MOSFETs MIT MOSFETs InGaAs channel High-K oxide del Alamo, CSICS 2015 InGaAs planar MOSFET performance matches that of High Electron Mobility Transistors (HEMT) 3

4 InGaAs planar Quantum-Well MOSFETs - short-channel effects S min (mv/dec) nm t c =12 nm t c V ds =0.5 V L g (µm) DIBL (mv/v) nm t c =12 nm t c L g (µm) Lin, IEDM 2014 Short-channel effects limit scaling to L g ~40 nm 3D transistors required for further scaling 4

5 InGaAs finfets W F ~30 nm W F ~50 nm Thathachary, VLSI 2015 Waldron, VLSI 2014 W F ~50 nm Radosavljevic,IEDM 2011 Kim, IEDM 2013 Kim, TED 2014 III-V finfets improve short-channel effects Most InGaAs finfets demonstrations feature =30-50 nm 5

6 V T variation with Si InGaAs Increased sensitivity of V T to W F in InGaAs Si In 0.53 Ga 0.47 As x [nm] W F x [nm] W F Nidhi, DRC 2012 m* e (Si)/m* e (InGaAs) >7 Quantum effects ΔV T (InGaAs) Goal of this work: experimental verification Need InGaAs finfet with <10 nm 6

7 Key technologies nanostructure definition Dry etch BCl 3 /SiCl 4 /Ar RIE of InGaAs nanostructures with smooth, vertical sidewalls and high aspect ratio (>10) As etched 40 nm 7

8 Key technologies nanostructure definition Digital etch (DE) Digital etch (DE): self-limiting O 2 plasma oxidation + H 2 SO 4 oxide removal As etched 5 cycles DE 40 nm 30 nm Shrinks fin width by 2 nm per cycle Unchanged shape Reduced roughness Lin, EDL

9 Key technologies nanostructure definition Dry etch + Digital etch 20 nm 15 nm 240 nm Zhao, EDL 2014 Stand alone nano structures down to 15 nm 9

10 Key technologies nanostructure definition sidewall slope Etching time 90 nm ~ nm 20 nm 20 nm 30nm Etching depth impacts sidewall slope at top 50 nm For H f > 150 nm, upper 50 nm sidewalls become vertical 10

11 Sidewall finfet G D Thick Top Gate Oxide S G Vardi, DRC 2014 = InGaAs Typical device consists of 100 fins, L g =3 µm 11

12 Sidewall finfet - process flow 50 nm thick, n-ingaas N D =10 18 cm -3 HSQ Gate dielectric + Mo InAlAs buffer on SI-InP Fin Patterning + Digital etch Gate stack G D S G Gate Patterning Contacts + Pads 12

13 Sub-10 nm fin-width InGaAs finfets =7 nm, L g =3 μm MOSFET 50 nm thick InGaAs channel N D =10 18 cm -3 L g =3 μm Oxide: Al 2 O 3 /HfO 2 (EOT~3 nm) SW ~ 90 o 5 nm SW ~ 80 o 7 nm 50 nm 50 nm I D [na/fin] I D [A/fin] =7 nm (SW ~ 90 o ) V GS =0.6 V V DS =7 nm 0.1 V DS =500 mv V GS 13

14 I D [A/fin] V GS 0.4 Impact of on subthreshold characteristics =35 5 SW90 V DS =50 mv I D [A/fin] =35 nm V GS SW80 V DS =50 mv V T -0.4 V T SW W F [nm] -0.8 SW W F [nm] V T defined at 5 na/fin Strong sensitivity of V T to <10 nm for SW90 14

15 Low-temperature measurements V T I D [A/fin] =7 nm V GS RT RT SW90 90K 90K V DS =50 mv W F [nm] V T as T D it impact Rigid ΔV T >0 Strong sensitivity of V T to for SW90 maintained RT SW80 90K W F [nm] 15

16 Subthreshold carrier concentration at 90K C g /C ox I D [A/fin] T=90K =13 nm V GS =13 nm 7 µ [cm 2 /Vsec] V GS 7 n fin [cm -1 ] =13 nm 11 nm 9 nm 7 nm V GS =13 nm V GS CV+IV μ(v GS ) Use μ max to transfer subthreshold characteristics to n fin 7 V Tn definition 16

17 0.4 Impact of on V T V Tn at constant n fin = cm T=90K V Tn 0.0 SW80 SW90 Strong sensitivity of V T to for SW~90 o MOSFETs W F [nm] V Tn sensitivity to persists 17

18 Classic V T dependence V T 2 V 0 1 Wf ε ox Vfb = tox ε s W W Threshold: V T -V fb V qεεn 0 s 0 2 Cox D N D =10 18 cm [nm] V tw <V tn V tn w >n n V T V fb 18

19 Quantum V T dependence Classic Quantum subband V tc V tq n n Quantum confinement creates subbands CB Min For constant N D E F Positive shift to V T as 19

20 Impact of on V T Poisson-Schrodinger simulations (Nextnano): SW=90 o SW90 SW80 Quantum T=90 K SW=80 o V Tn Classic = 4nm [nm] ΔV T >0 due to quantum confinement for <10 nm Larger ΔV T in SW90 due to greater quantum confinement 20

21 Impact of on V T Comparison of simulation and experiments: SW90 T=90K V Tn SW80 P-S simulation [nm] Good agreement after rigid V T shift 21

22 Impact of sidewall slope = 4 nm T= 90 K = + 4 nm V Tn SW90 SW [nm] V T vs. match for both sidewall slopes 22

23 Impact of on V T : effect of doping Quantum V Tn Classic N D =10 18 cm [nm] Reduced doping (inv. mode) reduced V T variation Strong quantum ΔV T for <10 nm regime 23

24 Self-consistent P-S simulations: V Tn Impact of on V T : comparison with Si Si InGaAs * me [nm] V T of InGaAs finfets with <10 nm: ~4x more sensitive to than Si! due to quantum effects N D =10 16 cm -3

25 Conclusions InGaAs finfets with <10 nm demonstrated experimentally Observation of quantum size effects in sub- 10 nm fins Implication for manufacturing control in future nm-scale InGaAs finfets 25

26 Thank you! 26

27 n f [cm -1 ] Al 2 O 3, 4 cyc DE, FGA =70 nm Mid gap branch =10 nm V GS Sidewall D it profile 60 mv/dec Ideal Measured n f [cm -1 ] Fitting with μ max extracted via CV+IV E-E v [ev] U-shape D it profile provides excellent agreement with measurements for the entire range. At the flat minima D it level of 3x10 12 cm -2 ev -1 D it [10 12 cm -2 ev -1 ] 10 1 CB branch Mid gap branch Ec 1.0 CB branch =37 nm =12 nm Measurement Simulation: U-shape D it V GS Vardi, DRC

28 Low-temperature measurements V T I D [A/fin] =7 nm V GS RT SW90 90K V DS =50 mv W F [nm] V T as T D it impact Rigid ΔV T >0 Strong sensitivity of V T to W F for SW90 maintained SW W F [nm] 28

29 Subthreshold carrier concentration at 90K C g /C ox I D [A/fin] T=90K =13 nm 7 nm µ [cm 2 /Vsec] V GS 13 nm V GS 7 nm n fin [cm -1 ] =13 nm 11 nm 9 nm 7 nm V GS 13 nm 7 nm V GS V Tn definition CV+IV μ(v GS ) Use μ max to transfer subthreshold characteristics to n fin 29

30 Effect of D it on V T -W F dependence V Tn T=90K No D it D it =3 [10 12 cm -2 ev -1 ] D it [10 12 cm -2 ev -1 ] 1 T 0.5 Ec E-E v [ev] [nm] 30

31 SW80 - different W F 7 nm 19 nm 31

32 SW90 - different W F 12 nm 7 nm 5 nm 32

33 Sub T carrier concentration ( ) W kt qvgs VT qvds ID = De CT exp 1 exp L q nkt nkt I 2 ( ) W kt qvgs VT qvds = µ C exp 1 exp L q nkt nkt D e T W kt I = µ QV V L q (, ) D e GS DS (, V ) QV I L D GS DS = W µ e kt For long channel at small V DS, the channel charge (source side) is: ( ) D QV GS e q I L q = W µ kt 33

34 Sub-bands spectrum SW90, WF=8 (1D) 1 Subband energy [ev] SW80, WF=4 (2D) Subband energy [ev] Subband energy [ev] V GS SW80 eigs are lower with smaller dispassion (larger density of states) 34