North American Molecular Beam Epitaxy Conference (NAMBE),8-11-2009
Improved Regrowth of Self-AlignedImproved Regrowth of Self Aligned Ohmic Contacts for III-V FETs
Mark A. Wisteyy
Now at University of Notre [email protected]
A.K. Baraskar, U. Singisetti, G.J. Burek, M.J.W. Rodwell, A.C. Gossard
P. McIntyre, B. Shin, E. KimStanford University
M.J.W. Rodwell, A.C. GossardUniversity of California Santa Barbara
Stanford University
Funding: SRC
Outline: Regrown III-V FET Contacts
•Motivation for Self-Aligned Regrowthg
•Facets, Gaps, Arsenic Flux and MEEMEE
•MOSFET Results•Conclusion
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Motivation for Regrowth: Scalable III-V FETs
Classic III-V FET (details vary):
GateGapSource Drain
Large Area Contacts
• Advantages
ChannelBottom BarrierInAlAs Barrier
Top Barrier or Oxide
Low
Large Rc
Implant: straggle
gof III-V’s
• Disadvantages of III-V’s
InAlAs BarrierLow doping
III-V FET with Self-Aligned Regrowth:
Implant: straggle,short channel effects
Hi h b i
Gate
High Velocity ChannelSmall Raccess
Small RcSelf-aligned, no gaps
High barrier
ChannelIn(Ga)P Etch Stop
Bottom Barrier
High-kn+ Regrowth
Small RcHigh mobility
access regionsUltrathin 5nm doping layer
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High doping: 1013 cm-2
avoids source exhaustion 2D injection avoids source starvation
Dopants active as-grown
MBE Regrowth: Bad at any Temperature?200nm Gap
• Low growth temperature (<400°C):–Smooth in far field GateGate
p
Smooth in far field–Gap near gate (“shadowing”)–No contact to channel (bad) Source-Drain
RegrowthSource-Drain
RegrowthRegrowthRegrowth
Metals
SiO2
Metals
Channelhigh-k GateGate
• High growth temperature (>490°C):
Source-DrainRegrowth
Source-DrainRegrowth
–Selective/preferential epi on InGaAs–No gaps near gate
–Rough far field
4Wistey, NAMBE 2009 SEMs: Uttam Singisetti
RegrowthRegrowth
Regrowth: 50nm InGaAs:Si, 5nm InAs:Si. Si=8E19/cm3, 20nm Mo, V/III=35, 0.5 µm/hr.
Rough far field –High resistance
490C460C
High Temperature MEE: Smooth & No Gaps
490C460C
Gap
560C540C 560C
SiO2 dummy gate
540C Smooth regrowth
SiO2 dummy gate
gateNo gaps, but faceting next
to gates
5Wistey, NAMBE 2009 Note faceting: surface kinetics, not shadowing.In=9.7E-8, Ga=5.1E-8 Torr
Shadowing and Facet CompetitionShen & Nishinaga, JCG 1995
Fast surface diffusion = slow facet
growth
Slow diffusion = rapid facet growth
O2
[100]
growth
SiO
Fast surface
• Shen JCG 1995 says:Increased As favors [111] growth
[100]
Slow diffusion =fast growth
Fast surface diffusion =
slow facet growth
SiO
2
[100]
Wistey NAMBE 2009 6
Good fill next to gate.
• But gap persists
Gate Changes Local Kinetics
1. Excess In & Ga d ’t ti k t SiO
2. Local i h t
4. Low-angle planes grow
don’t stick to SiO2
[100]
enrichment of III/V ratio
g p ginsteadsidew
SiO2 or SiNx
[100]all
3. Increased surface mobility
Gate
Diff i f G III’ f t
Wistey NAMBE 2009 7
• Diffusion of Group III’s away from gate
Change of Faceting by Arsenic Flux
• InGaAs layers with increasing As fluxes, separated by InAlAs.
Increasing As fluxInAlAs
markers InGaAs
SiO2WCr 1x10-6
2x10-65x10-6
W
0.5x10-6
(Torr)
• Lowest arsenic flux → “rising tide fill”
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• No gaps near gate or SiO2/SiNx• Tunable facet competition
Growth conditions: MEE, 540*C, Ga+In BEP=1.5x10-7 Torr, InAlAs 500-540°C MBE.
Control of Facets by Arsenic Flux
• InGaAs:Si layers with increasing As F ti
InAlAs
• InGaAs:Si layers with increasing As fluxes, separated by InAlAs.
[100]O2
Faceting
Increasing As flux
InAlAsmarkers
InGaAs
SiO
SiO2WCr 1x10-6
2x10-65x10-6
[100]O2
ConformalW
0.5x10-6
(Torr)
SiO
• Lowest arsenic flux → “rising tide fill” [100]iO
2
Filling
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• No gaps near gate or SiO2/SiNx• Tunable facet competition
Growth conditions: MEE, 540*C, Ga+In BEP=1.5x10-7 Torr, InAlAs 500-540°C MBE.
S
Low-As Regrowth of InGaAs and InAs
InGaAs InAs
InAsth
InGaAs regrowth (top view)
regrowth
(top view)
• Low As flux good for InAs too. • InAs native defects are donors.
Bhargava et al , APL 1997
R d f d l ti
• No faceting near gate• Smooth far-field too
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4.7 nm Al203, 5×1012 cm-2 pulse dopingIn=9.7E-8, Ga=5.1E-8 Torr
SEMs: Uttam Singisetti
• Reduces surface depletion.
InAs Source-Drain Access Resistance4.7 nm Al203, InAs S/D E-FET.
740 Ω-µm
• Upper limit: Rs,max = Rd,max = 370 Ω−μm.• Intrinsic gmi = 0.53 mS/⎧m
1/R 3 3 S/ ( li it d )• gm << 1/Rs ~ 3.3 mS/μm (source-limited case)
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Ohmic contacts no longer limit MOSFET performance.
Conclusions
• Reducing As flux improves filling near gate• Self-aligned regrowth: a roadmap for scalable III-V FETs–Provides III-V’s with a salicide equivalent
I G A d l d I A t t• InGaAs and relaxed InAs regrown contacts–Not limited by source resistance @ 1 mA/µmResults comparable to other III V FETs but now–Results comparable to other III-V FETs... but now scalable
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Acknowledgements
• Rodwell & Gossard Groups (UCSB): Uttam Singisetti, Greg Burek, Ashish Baraskar, Vibhor Jain...
• McIntyre Group (Stanford): Eunji Kim Byungha Shin• McIntyre Group (Stanford): Eunji Kim, Byungha Shin, Paul McIntyre
• Stemmer Group (UCSB): Joël Cagnon, Susanne StStemmer
• Palmstrøm Group (UCSB): Erdem Arkun, Chris Palmstrøm
• SRC/GRC funding• UCSB Nanofab: Brian Thibeault, NSF
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