Nanoscale III-V CMOS J. A. del Alamo Microsystems Technology Laboratories Massachusetts Institute of Technology SEMI Advanced Semiconductor Manufacturing Conference Saratoga Springs, NY; May 16-19, 2016 Acknowledgements: Students and collaborators: D. Antoniadis, J. Lin, W. Lu, A. Vardi, X. Zhao Sponsors: Applied Materials, DTRA, KIST, Lam Research, Northrop Grumman, NSF, Samsung Labs at MIT: MTL, EBL
Contents 1. Motivation: Moore s Law and MOSFET scaling 2. Planar InGaAs MOSFETs 3. InGaAs FinFETs 4. Nanowire InGaAs MOSFETs 5. InGaSb p-type MOSFETs 6. Conclusions 2
1. Moore s Law at 50: the end in sight? 3
Moore s Law Moore s Law = exponential increase in transistor density Intel microprocessors 4
Moore s Law How far can Si support Moore s Law?? 5
Transistor scaling Voltage scaling Performance suffers Supply voltage: Transistor current density: Intel microprocessors Intel microprocessors Transistor performance saturated in recent years 6
Chip Price vs. Chip Cost Chip area price: Chip area cost: Intel microprocessors Holt, ISSCC 2016 Increasing chip cost might bring the end to Moore s Law 7
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Moore s Law: it s all about MOSFET scaling 1. New device structures: Enhanced gate control improved scalability 9
Moore s Law: it s all about MOSFET scaling 2. New materials: n-channel: Si Strained Si SiGe InGaAs p-channel: Si Strained Si SiGe Ge InGaSb Future CMOS might involve: two different channel materials with two different relaxed lattice constants! del Alamo, Nature 2011 (updated) 10
III-V electronics in your pocket! 11
2. Self-aligned Planar InGaAs MOSFETs dry-etched recess selective MOCVD W Mo Lin, IEDM 2012, 2013, 2014 Lee, EDL 2014; Huang, IEDM 2014 implanted Si + selective epi reacted NiInAs Sun, IEDM 2013, 2014 Chang, IEDM 2013 12
Self-aligned Planar InGaAs MOSFETs @ MIT W Mo Recess-gate process: CMOS-compatible Refractory ohmic contacts (W/Mo) Extensive use of RIE Lin, IEDM 2012, 2013, 2014 13
Fabrication process Mo/W ohmic contact + SiO 2 hardmask SF 6, CF 4 anisotropic RIE Resist CF 4 :O 2 isotropic RIE SiO 2 W/Mo n + InGaAs/InP InGaAs/InAs InAlAs -Si InP Waldron, IEDM 2007 Cl 2 :N 2 anisotropic RIE Digital etch Finished device O 2 plasma H 2 SO 4 Pad Mo HfO 2 Lin, EDL 2014 Ohmic contact first, gate last Precise control of vertical (~1 nm), lateral (~5 nm) dimensions MOS interface exposed late in process 14
Mo Nanoscale Contacts Mo on n + -In 0.53 Ga 0.47 As: R c ~ 40 Ω.μm for L c ~ 20 nm Need low c and m Mo best contact system Average c = 0.69. m 2 Lu, EDL 2014 15
L g =20 nm InGaAs MOSFET I d (ma/ m) 1.0 L g =20 nm 0.8 0.6 0.4 0.2 R on =224 m V gs -V t = 0.5 V 0.4 V 0.0 0.0 0.1 0.2 0.3 0.4 0.5 V ds (V) Lin, IEDM 2013 L g = 20 nm, L access = 15 nm MOSFET tightest III-V MOSFET made at the time 16
Highest performance InGaAs MOSFET Channel: In 0.7 Ga 0.3 As/InAs/In 0.7 Ga 0.3 As Gate oxide: HfO 2 (2.5 nm, EOT~ 0.5 nm) 3.45 ms/ m L g =70 nm: Record g m,max = 3.45 ms/ m at V ds = 0.5 V R on = 190 m Lin, EDL 2016 17
Benchmarking: g m in MOSFETs vs. HEMTs g m of InGaAs MOSFETs vs. HEMTs (any V DD, any L g ): MIT MOSFETs del Alamo, J-EDS 2016 InGaAs MOSFETs now superior to InGaAs HEMTs No sign of stalling more progress ahead! 18
Excess OFF-state current Transistor fails to turn off: I d (A/ m) 10-5 L g =500 nm 10-7 10-9 10-11 V ds V ds =0.3~0.7 V step=50 mv -0.6-0.4-0.2 0.0 V gs (V) OFF-state current enhanced with V ds Band-to-Band Tunneling (BTBT) or Gate-Induced Drain Leakage (GIDL) Lin, IEDM 2013 19
Excess OFF-state current I d (A/ m) 10-4 10-5 10-6 10-7 10-8 T=200 K V ds =0.7 V L g =80 nm 120 nm 280 nm 500 nm -0.6-0.4-0.2 0.0 V gs -V t (V) Lin, EDL 2014 Lin, TED 2015 L g OFF-state current additional bipolar gain effect due to floating body I d (A/ m) I d (A/ m) 10-5 L g =500 nm 10-7 10-9 10-11 10-5 w/ W/ BTBT+BJT w/o W/O BTBT+BJT L g =500 nm 10-7 10-9 10-11 V ds V ds =0.3~0.7 V step=50 mv -0.6-0.4-0.2 0.0 V gs (V) Simulations V ds =0.3~0.7 V step=50 mv -0.4-0.2 0.0 0.2 V gs (V) 20
Planar MOSFET scaling limit Scaling of linear subthreshold swing del Alamo, J-EDS 2016 ideal scaling λ =electrostatic scaling length Nearly ideal electrostatic scaling behavior At limit of scaling around L g ~50 nm 21
3. InGaAs FinFETs Intel Si Trigate MOSFETs 22
Bottom-up InGaAs FinFETs Aspect-Ratio Trapping Fiorenza, ECST 2010 Si Epi-grown fin inside trench Waldron, VLSI Tech 2014 23
Top-down InGaAs FinFETs Radosavljevic, IEDM 2010 dry-etched fins 60 nm Kim, IEDM 2013 24
InGaAs FinFETs: g m g m per width of gate periphery Kim, IEDM 2013 Natarajan, IEDM 2014 Oxland, EDL 2016 g m [ms/ m] 2.0 1.5 1.0 0.5 Si FinFETs 5.3 4.3 0.8 0.66 0.57 0.23 0.6 InGaAs FinFETs 0.63 0.0 0 20 40 60 W f [nm] 1 0.18 channel aspect ratio Narrowest InGaAs FinFET fin: W f =25 nm Best fin aspect ratio of InGaAs FinFET: 1 g m much lower than planar InGaAs MOSFETs Radosavljevic, IEDM 2011 Thathachary, VLSI 2015 25
InGaAs FinFETs @ MIT Key enabling technologies: BCl 3 /SiCl 4 /Ar RIE + digital etch Sub-10 nm fin width Aspect ratio > 20 Vertical sidewalls Vardi, DRC 2014, EDL 2015, IEDM 2015 26
InGaAs Double-Gate MOSFET Vardi, VLSI 2016 CMOS compatible process Mo contact-first process Fin mask left in place double-gate MOSFET 27
InGaAs Double-Gate MOSFET L g =30 nm, W f =17 nm, H c =40 nm (AR=2.3): I d [ma/ m] 1.0 L g =30 nm V GS =0.75 V W 0.8 f =17 nm 0.6 V GS =0.25 V 0.4 0.2-0.5 V 0.0 0.0 0.2 0.4 0.6 0.8 1.0 V DS [V] I d [A m] 1E-3 V DS =500 mv 1E-4 50 mv 1E-5 S sat =140 mv/dec 1E-6 DIBL=220 mv/v 1E-7 L g =30 nm W f =17 nm 1E-8-0.6-0.4-0.2 0.0 0.2 0.4 0.6 V GS [V] g m =1.12 ms/µm R on =230 Ω.µm S sat =140 mv/dec Vardi, VLSI 2016 28
InGaAs FinFETs: g m benchmarking g m per width of gate periphery g m [ms/ m] 2.0 1.5 1.0 0.5 Si FinFETs 5.3 4.3 MIT InGaAs FinFETs 3.3 5.7 1.8 2.3 0.8 0.66 0.57 0.23 0.6 InGaAs FinFETs 0.63 0.0 0 20 40 60 W f [nm] 1 0.18 First InGaAs FinFETs with W f <10 nm First InGaAs FinFETs with channel aspect ratio >1 29
InGaAs FinFETs: g m benchmarking Figure-of-merit for density: g m per fin width g m /W f [ms/ m] 20 15 10 5 5.3 MIT InGaAs FinFETs 5.7 Si FinFETs 4.3 3.3 2.31.8 0.8 InGaAs FinFETs 0.66 0.23 0.57 0.6 0.63 0 0 20 40 60 W f [nm] 1 0.18 Improved by 50% over earlier InGaAs FinFETs Still far below Si FinFETs poor sidewall charge control 30
InGaAs FinFETs: electrostatics Linear subthreshold swing scaling: del Alamo, J-EDS 2016 ideal scaling λ c =electrostatic scaling length Close to ideal scaling reveals good quality sidewalls 31
Impact of fin width on V T InGaAs doped-channel FinFETs: 50 nm thick, N D ~10 18 cm -3 Oxide: Al 2 O 3 /HfO 2 (EOT~3 nm) Strong V T sensitivity for W f < 10 nm; much worse than Si Due to quantum effects Vardi, IEDM 2015 32
4. Nanowire InGaAs MOSFETs Waldron, EDL 2014 Tanaka, APEX 2010 Persson, EDL 2012 Tomioka, Nature 2012 Nanowire MOSFET: ultimate scalable transistor Vertical NW: uncouples footprint scaling from L g and L c scaling 33
InGaAs Vertical Nanowires on Si by direct growth Au seed InAs NWs on Si by SAE Vapor-Solid-Liquid (VLS) Technique Selective-Area Epitaxy Riel, MRS Bull 2014 Björk, JCG 2012 34
InGaAs VNW-MOSFETs fabricated via top-down approach @ MIT Starting heterostructure: n + InGaAs, 70 nm i InGaAs, 80 nm n + InGaAs, 300 nm n + : 6 10 19 cm 3 Si doping Top-down approach: flexible and manufacturable Zhao, IEDM 2013 35
Key enabling technologies: RIE + digital etch RIE = BCl 3 /SiCl 4 /Ar chemistry Digital Etch (DE) = self-limiting O 2 plasma oxidation + H 2 SO 4 oxide removal RIE + 5 cycles DE Sub-20 nm NW diameter DE shrinks NW diameter by 2 nm per cycle Aspect ratio > 10 Smooth sidewalls Zhao, EDL 2014 36
Optimized RIE + Digital Etch 15 nm 240 nm Zhao, EDL 2014 Sub-20 nm resolution Aspect ratio = 16, vertical sidewall Smooth sidewall and surface 37
Tomioka, Nature 2012 Persson, DRC 2012 Process flow 38
NW-MOSFET I-V characteristics: D=40 nm I d A/ m) 350 V gs =-0.2 V to 0.7 V in 0.1 V step 300 Bottom electrode as the source (BES) 250 200 150 100 50 0 0.0 0.1 0.2 0.3 0.4 0.5 V ds (V) Single nanowire MOSFET: L ch = 80 nm 3 nm Al 2 O 3 (EOT = 1.5 nm) g m,pk =620 μs/μm @ V DS =0.5 V R on =895 Ω.μm Zhao, EDL 2016 (submitted) g m,pk ( S/ m) I d (A/ m) 700 600 500 400 300 200 100 V gs (V) V ds=0.5 V 10-4 10-5 10-6 10-7 10-8 10-9 V ds =0.5 V 0-0.4-0.2 0.0 0.2 0.4 V ds =0.05 V S=98 mv/dec, V ds =0.05 V S=110 mv/dec, V ds =0.5 V DIBL = 177 mv/v -0.4-0.2 0.0 0.2 0.4 V gs (V) 39
This work Zhao, 2016 (submitted) Best bottom up devices Berg, IEDM 2015 Vertical InGaAs NW-MOSFETs Benchmark g m,pk ( S/ m) 1400 1200 1000 800 600 400 200 0 V ds =0.5 V Tanaka, APEX 2010 Tomioka, IEDM 2011 Tomioka, Nature 2012 Persson, DRC 2012 Persson, EDL 2010 Zhao, IEDM 2013 Berg, IEDM 2015 This work 200 400 600 S sat (mv/dec) Top down approach as good as bottom up approach 40
InGaAs VNW MOSFETs: electrostatics Linear subthreshold swing scaling: del Alamo, J-EDS 2016 ideal scaling λ c =electrostatic scaling length Close to ideal scaling reveals good quality sidewalls 41
5. InGaSb p type MOSFETs Planar InGaSb MOSFET demonstrations: Nainani, IEDM 2010 Takei, Nano Lett. 2012 42
InGaSb p type FinFETs at MIT Key enabling technology: BCl 3 /N 2 RIE [digital etch under development] 20 nm fins, 20 nm spacing Lu, IEDM 2015 15 nm fins, AR>13 Smallest W f = 15 nm Aspect ratio >10 Fin angle > 85 Dense fin patterns 43
Si-compatible contacts to p + -InAs Ni/Ti/Pt/Al on p + -InAs (circular TLMs): Lu, IEDM 2015 Record ρ c : 3.5x10-8 Ω.cm 2 at 400 o C 44
InGaSb FinFETs Fin mask left in place double-gate MOSFET Channel: 10 nm In 0.27 Ga 0.73 Sb Gate oxide: 4 nm Al 2 O 3 (EOT=1.8 nm) Gate: 45 nm Mo Lu, IEDM 2015 45
InGaSb FinFETs Lu, IEDM 2015 W f = 30 100 nm L g = 0.1 1 μm N f = 70 46
InGaSb FinFET I-V characteristics L g = 100 nm, W f = 30 nm (AR=0.33) Normalized by conducting gate periphery Lu, IEDM 2015 High current Poor turn-off 47
Peak g m at T=290K: g m benchmarking Lu, IEDM 2015 g m ( S/ m) 100 This work (FinFET) In 0.27 Ga 0.73 Sb Planar MOSFETs Yuan, 2013 [7] Nainani, 2010 [8] Chu, 2014 [11] Xu, 2011 [12] Nagaiah, 2011 [13] GaSb GaSb In 0.36 Ga 0.64 Sb 10 0.01 0.1 1 10 100 L g ( m) In 0.35 Ga 0.65 Sb In 0.2 Ga 0.8 Sb First InGaSb FinFET Peak g m approaches best InGaSb planar MOSFETs 48
Conclusions 1. Great recent progress on planar, fin and nanowire III-V MOSFETs 2. Planar and multigate InGaAs MOSFETs exhibit nearly ideal electrostatic scaling behavior 3. Device performance still lacking for multigate designs 4. P-type InGaSb MOSFETs promising 49
A lot of work ahead but exciting future for III-V electronics 50